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A Comprehensive manual

Prepared By: Jyothi Prasanth ( 29.11.2008)

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1. Power Aluminium is a power intensive industry. The electrolysis process used to produce aluminium requires large quantities of electrical power. When the cost of producing one tonne of primary aluminium is broken down almost one third is devoted to electrical power. The DC power required depends on the total number of cells or pots installed & the potline DC current. For meeting this huge power requirement most aluminium smelters are equipped with their own Captive Power Plants. Balco Plant II is also powered by its own captive power plant CPP-II with a capacity of 540MW. The main load is Potline 408 MW for 288 pots & 320 KA & the auxiliary load is 20MW. The excess power generated is exported to CSEB grid through 220 KV tie lines connected to CSEB grid through MRSDS in Plant I. Potlines require DC for the reduction process and AC for all other auxiliary requirements. The entire power transmission, rectification & distribution of Balco consist of the following main sections : Uninterrupted supply of power is required for the electrolysis process of alumina. A power failure for more than 1 hour can never be afforded as the temperature of aluminium metal in pots decreases resulting in freezing of aluminium and it takes about 3 days to restart the electrolysis process.

Pic . Balco Power Network( above)

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1.1 CPP-II CPP-II is a Coal based thermal power plant. It consists of 4 generators of 135 MW rated capacity each, making a total of 540 MW. The power generated is fed to the 220 KV bus from where it is further distributed to different areas. CPPII is built by EPC Contractor M/s SEPCO ( Shandong Electric Power Company),China. The salient features of the power plant are : Primary Fuel : Non-Coking Coal Start up Fuel : LDO/HFO Water Source : 3600m3/hr water is pumped in from Hasdeo reservoir Pulverizing system : Cold Primary Air System with Ball mills Steam Turbine : Double cylinder, Impulse, Condensing & Nozzle & throttle goverened

turbine. Turbo Generator : Air Cooled direct coupled generator, Static Excitation Detailed information of Balco’s power generation process is given in CPP-II manual.

CPP-II : 4*135 MW

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1.2 220 KV Switchyard Balco has a 220 KV switchyard with a 2 Bus Configuration. It has one main & one standby bus. The switchyard comprises of 16 Bays ie. 2 bays for Utility Transformers, 2 bays for station Transformers, 5 Bays for Rectiformers, 4 Bays for 4 Generator Transformers,2 Bays for Tie Lines from MRSDS, 1 Bay for Bus Coupler .

Pic: 220 KV Switchyard ( Balco Plant II)

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The Switchyard has 2 Bus configuration and both buses are coupled through Bus Coupler. Provision is there to connect the above equipment like Utility Transformers, Station Transformers, Rectiformers, Generator Transformers and Tie Lines to either of the 220 KV Bus through Bus Isolators. Each Bay comprises switchyard equipment like SF6 Circuit Breaker, CT, Isolators etc. Power is received from CPP2 ( 4X135 MW ). Bulk of the Power is consumed in Potline ( 408 MW ) and remaining Power is consumed for Auxiliaries like Carbon Plant , Air Compressors and Cast House ( 19 MW) and Power Plant Auxiliaries ( 17 MW ). Around 90 MW Power is exported to MRSDS when all the 4 units of CPP2 are in operation. When 3 units are in operation, around 40 MW Power is imported from MRSDS. Pic: Block diagram showing power flow

220 KV BUS

RECTIFIER UNITS

ST G GENERATOR UT UTILITY TRANSFORMERRT RECTIFIER TRANSFORMER

STATION TRANSFORMER

320 KA DC TO POTLINE 11KV Area Substations

GAP POT ROOM Compressor FTP1&2 Wire rod mill

LINE-2

UT-1 UT-2 RT-1 RT-2 RT-3 RT-4 RT-5

CPP-2 MRSDS

G-1 G-2 G-3 G-4 ST-1 ST-2 LINE-1

GAP, BAKE OVEN, RODDING

Pot MCC11,21,22

Air Compressor,Cast House, Pot Overhaul Shop,Pot MCC12

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1.3 DC Rectiformers The function of rectiformer units is to Convert the AC power generated into DC for feeding the potline to carry out reduction process. Balco has 5 units of 87.5 KA rectiformer system. The rectifomers continuously feeds a current of 320-325 KA to the potline. Each Rectiformer has a Regulating Transformer of 137 MVA, 230 KV/ 66 KV , a Rectifier Transformer of 2 windings, Y Winding of 67.58 MVA , 66 KV / 1103.3 v & D winding of 67.58 MVA, 66 KV / 1092 V & Diode Rectifier for converting AC Power into DC & associated cooling systems. Control is through Tap Changers provided on 66 KV Side of Regulating Transformer. Each Rectiformer is capable of supplying 87.5 KA , 1300 V DC. At present all the Rectiformers are in operation supplying 64 KA each to the Potline. When one Rectiformer is taken for maintenance, each Rectiformer shall supply 80 KA to give 320 KA to Potline .The no. of Pots & the Pot Voltage ( 4.2 V per Pot normally ) determines the Potline Voltage and at present Potline is operating at 1250 Volts.

1. Regulating transformer : The main function of regulating transformer is to regulate the potline voltage depending on the number of pots connected in series and other factors like anode effect, voltage shaking etc.

2. Rectifier Transformer : This is used for generating a 12 pulse system for the three phase bridge rectifier which converts ac to dc.

3. Diode rectifier : Our system consist of a three phase , 12 pulse bridge rectifier for ac to dc conversion. The 12 pulse system ensures a pure DC wave at the output.

4. Cooling System : This system consist of transformer cooling system & rectifier cooling system. Oil forced water forced cooling is used for transformers & for diodes DM water is the primary coolant & raw water is the secondary coolant.

Fig : DC Current flow in a pot

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1.4 Area Substations The central power distribution centre for providing power supply to all plant auxiliaries is a 11 KV system. The Utility transformer steps down the 200 KV from Bus to 11 KV . This 11 KV Central Distribution centre is located in rectifier control Room. From here the auxiliary power is supplied to Air compressor, carbon, pot room , FTP & wire rod mill substations. The two main area substations are :

5. Air Compressor Station : From here power is supplied to Compressor HT Motors, Compressor Station transformer, pot MCC-12, cash house & pot overhaul shop.

6. Carbon Substation : From this 11 KV substation power is distributed to GAP, GAP-HTM, Bake Oven , Rodding & Rodding Induction Furnaces .

11 KV / 415 V Transformers are located in various locations like GAP, Anode Rodding, Bake Oven , Compressor House, Cast House, Pot Rooms – 11,12,21 & 22 , Pot Overhaul Shop ,wire rod mill etc and these Transformers are connected to the Main Switchyard Sub Station through 11 KV unearthed Cables. In GAP & Compressor House, a full fledged 11 KV Distribution Panel is provided feeding loads like Ball Mill and Air Compressor Motors. FTP Substations have 11 / 6.6 KV transformers for feeding 6.6 KV Power to 6.6 KV FTP ID Fan Motors. All other locations have 2 nos 11 KV Feeders to feed 2 Nos 11 KV / 415 V Transformers. The entire power transmission & distribution network, compressed air network, fire line network, process & drinking water network is taken care by the rectifier & utilities department of Plant II.

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Rectifier & Utilities As mentioned earlier, the main function of this section is to provide uninterrupted supply of power to potline & plant auxiliaries, compressed air to potline & carbon, and process & drinking water to the whole plant. Utilities section ensures the uninterrupted supply of cooling water to rectiformers , compressed air to potline, carbon & cast house and also looks after the steam pipeline network in plant II and fire fighting water circulation system of the whole plant. The four major subdivisions are:

1. 220 KV Switchyard 2. DC rectiformers 3. Area substations 4. Utilities

A detailed explanation of these subdivisions , their functions & equipments are mentioned below. 1. 220 KV Switchyard Switchyard Comprises of 16 Bays. which contains isolators, circuit breakers(CB), Capacitive Voltage Transformers (CVT), Current Transformers(CT), lightening arrestors (LA) in addition to the main equipment. 1.1 Bay 2, 3 : Utility Transformer-1, 2 These bays contain transformer, circuit breaker, Current transformer, Capacitive Voltage Transformer, Lightning arrestor, isolators etc. 1.1.1 Transformer : Utility Transformer is a 50 MVA transformers which steps down 220 KV from the bus to 11 KV. This 11KV is then used for further power distribution downstream.

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Pic.220 KV Power Distribution Network( Single line diagram)

Pic: Power Transformer

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1.1.2 Circuit Breaker Circuit Breakers are mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal conditions such as those of short circuit. It is a premium against damage of the equipment. It is the only automatic moving equipment in the transmission system. It is a slave of relay. Two contacts called electrode remains closed under normal operating conditions. When fault occurs on any part of the system, the trip coil of the circuit breaker get energized and contacts are separated. An arc is struck when contacts are separated. The current is thus able to continue. Thus the main duty of a circuit breaker is to estinguish the arc within the shortest possible time. The arc provides the low resistance path to the current and the current in the circuit remains uninterrupted.

Fig. Operation of CB

Classification of CBs – On principle of current interruption

• SF6 (puffer, self blast)

– Present day CBs for medium voltage and high voltage. – Uses SF6 gas as a interrupting media and insulation media – Meets almost all technical requirements

Fault Occurs

Relay • Senses • Contact

Closes

Circuit Breaker • Trip Coil Energises • Operating Mechanism

Starts • Contacts Separate • Arcing between Contacts • Arc Extinguishes • CB Fully Opens

Faulted Part Gets Isolated

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• Vacuum – Uses vacuum as interruption media – Used mainly for medium voltages – Offers good electrical life

• Bulk oil, • Minimum oil, • Air break, • Air Blast CB

– On class of voltage

• Medium voltage

– From above 1 kV up to 52 kV class voltage – Generally used indoors – Housed in a cubicle – Outdoor is also getting popular in India

• High voltage – From 72.5 kV up to 300 kV – short line fault requirement for this voltage and above

• Extra High voltage – Above 300 kV – Switching Impulse withstand requirement - Additional

– Type of installation

• Indoor, outdoor etc. – Application

• Railway, Generator CB, Line CB, Transformer CB, Reactor CB, furnace CB, Bus coupler, etc.

– Type of mechanism • Pneumatic, spring, Hydraulic, Hydro-mechanical, spring-

pneumatic, solenoid, motor

• Spring Charged – Spring charged using motor to store energy and transferred through

mechanical links – Spring can be helical, spiral (clock), etc

• Pneumatic – Energy stored by compressing air in a receiver. – Energy transmitted pneumatically and motion created using cylinder

piston arrangement • Hydraulic, Hydro - mechanical

– Energy stored either in compressed air or springs – Energy transmitted hydraulically and motion created using cylinder piston

arrangement

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• Puffer In these breakers the continuous gas pressure can be kept at low enough levels, 0.5-0.7 Mpa (abs), to permit operations under most climatic conditions, without risk of liquefaction. The pressure difference and resulting gas flow required for interruption are obtained by compression of gas, by operating mechanism, in direct connection with opening of the contacts.

• Auto-Puffer (Self-Blast) In self-blast breakers the gas blast that is required is mainly obtained by use of energy from the arc itself. The arc heats the gas in a compression volume, and the resulting differential pressure leads to the gas flow used for interruption. The operating mechanism can be kept smaller and simpler than for corresponding puffer breakers.

Extinguishing Position 220KV switchyard is installed with SF6 Circuit breakers. Mainly two types of SF6 Breakers are used . They are Individually operated & gang operated circuit breakers. In individually operated breakers, there is a separate operating mechanism for all the three phases whereas in a gang operated circuit breaker there is only one single operating mechanism for all the three phases. Gang operated circuit breakers are used in Generator

Closed PositionSmall Current

SC Current

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Transformer & station transformer bays. All other bays contain individually operated Circuit breakers. SF6 Circuit breakers make full use of excellent arc quenching & electrical insulating characteristics of SF6 gas. In this breaker the gas flow puffed by a puffer cylinder extinguishes the arc. The pneumatic operating mechanism which is operated by air pressure for opening & spring force for closing is very simple & reliable. These breakers are of single pressure type, operating on puffer principle wherein the gas flow on to the arcing zone is generated by puffer cylinder & piston. Some main features of this breaker are : - Superior interrupting capability -Low operation noise -Simple construction & Compact size -Easy installation, inspection & maintenance -High Safety

SF6 Circuit Breaker S.No Property Specifications

1 Type 200-SFM-40A

2 Rated Voltage 245 KV

3 Rated Insulation Level 1050 KVp

4 Rated Frequency 50 Hz

5 Rated Normal Current 3150 A

6 Rated SC making Current 100 KA

7 Rated Break time 60 ms ( 3 Cycles)

8 Rated Short time current 40 KA for 3 Sec

9 Operating Sequence O-0.3S-CO-3min-CO

10 Rated TRV 364 KVp

11 Operating Mechanism Spring Closing, Pneumatic tripping

12 Operating Pressure(air) 15.0 Kg/Cm2

13 SF6 gas pressure 6.0 Kg/Cm2 at 20oC

14 Applicable standard IEC-56

15 Opening Time 30 ms

16 Closing Time 100 ms

17 Pole Discrepancy 3.3 ms ( between poles)

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A typical single pole of the breaker consist of interrupting unit, Supporting unit & mechanism housing. Operating mechanism is connected to pole unit through linkages. The electrical control units are mounted in central phase or a separate free standing marshelling box. Compressed air is required for opening of the breaker. It is stored in 3 interconnected air receivers of 70L capacity each which act as local source of compressed air for the operating mechanism. This system is provided with motor compressor unit. To ensure safety of the breaker operation two types of pressure switches have been incorporated. -Temperature Compensated gas pressure switch which cuts off the trip coil circuit and closing coil circuit in case SF6 gas pressure goes below the specified range due to leakage. The operating pressure is corrected to ambient temperature. -Air pressure Switch Properties of SF6 Gas SF6 gas in a pure state is inert, exhibits exceptional thermal stability and has excellent arc quenching properties as well as exceptional high insulating properties. It is one of the most stable compounds, nonflammable, nontoxic & odorless. SF6 remains gas without liquidification down to -30oC at the maximum pressure of the puffer type breakers. The density of gas is about five times that of air & heat dissipation in it is also much more than in air. At atmospheric pressure, the dielectric strength is about 2.4 times that of air. 1.1.3 Capacitive Voltage Transformers ( CVT )

Capacitive Voltage Transformers are used for Voltage measurement just like potential transformers. At high system voltages the cost of conventional potential transformer is high, due to prohibitive cost of insulation. In CVT, it is possible to obtain voltage from capacitor divider as the insulation is inherent in its design at no extra cost. Further economy can be obtained by using capacitor divider as a coupling capacitor for Power Line Carrier Communication.

Functions of CVT

• Measure Voltage • Measure Power • Isolation between High Voltage & Low Voltage. • Inputs to Relay/Protection systems • PLCC (Power line Carrier Communication)

The CVT has the following inherent advantages : – Since the primary insulation is made up of capacitors elements connected

in series, the surge withstand capability of a CVT is very good. It acts a surge suppressor.

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– The Ferroresonance is controllable in a CVT because the same happens between the capacitor part and the electromagnetic unit of the CVT which are known values.

– Since it is packed and shipped in parts, handling , erection and assembly of the same at site is convenient.

In case of CVT’s and PT’s, all the secondary windings are wound on a common secondary core. Hence, the load connected on any winding, affects the accuracy of the other. The requirement of the standard is that the accuracy should be guaranteed for the total connected burden on all windings put together. For the total burden, the burden of open delta windings may not be considered as they are not continuous loads. Whenever we are unable to meet the accuracy with the total combined load, we specify the maximum simultaneous burden upto which the accuracy of the metering class is guaranteed. Transient performance is the response of secondary of a CVT in relation to transient (sudden) changes in primary voltages. Since high speed protective relays operate usually within one cycle, it is essential that a CVT should have good transient response, i.e. it should reach its steady state value within 10 milliseconds after a step change in the input.

Various situations causing transients in CVT are – Energizing and de-energizing of the line – Short circuit on the primary terminals

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– Rapid reclosure within a few seconds – Releasing of a secondary short circuit – Ferro-resonance

The transients produce non power frequency superimposed oscillations on the secondary side. The transient oscillations can be damped rapidly by using suitable damping device like ferroresonance protection circuit. A practical CVT consists of tuning inductance and wound PT each having iron core, and capacitance. Whenever a capacitor and non-linear inductor are connected in series, there is a danger of non-linear energy interchanges at sub-harmonic frequencies. This causes large overvoltage in the circuit. To avoid ferroresonance the operating flux of iron parts is kept at 1/2 to 1/3rd of the saturation flux density. Alternately a special provision for damping the oscillations is provided.

Capacitive Voltage Transformer (CVT)

S.No Property Specifications 1 Rated Primary Voltage 220KV/√3 2 Secondary Voltage 110V/√3 ( Wdg-I,Wdg-II) 3 No. Of windings 2 4 Type CVE 245/1050/50 5 Standard Applicable IS:31565 (1992), IS 9348 6 Rated Frequency 50 Hz 7 Rated Voltage Ur (KV) 245KV rms ( line to line)

8 Rated Voltage Factor 1.2 Continuous/1.5 for 30 Secs

9 Equivalent Capacitance 4400 PF+ 10%-5% 10 Accuracy Class 1( Metering), 3P ( Protection)

11 VA Burden 100 VA (wdg-1), 100VA (wdg-2)

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1.2/50 micro-second impulse withstand voltage (KVp) 1050 KVp

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One minute dry & wet power frequency withstand voltage 460 KVrms

14 Total Creepage distance 6125 mm

15 Standard to which oil conforms generally IS : 335(1993)

16 Temp. rise over an ambient temp at 50oC 45oC

In Power Line Carrier Communication (PLCC), Coupling Capacitor (CC) is used as coupling device between power line and carrier accessories to allow high frequency (40-500KHz.) carrier signals into/out of carrier accessories (Line Matching Unit (LMU), Drain coil and etc.).Some times, the capacitor part in CVT is used as CC in PLCC. When CVT is used as CC the terminal HF will be connected to carrier accessories (carrier coupling unit) instead of grounding it.

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1.1.4 Current Transformer Current Transformer is an instrument transformer in which the secondary current, in normal conditions of use, is substantially proportional to the primary current and differs in phase from it by an angle which is approximately zero for appropriate direction of connections. A CT Provides

– Inputs to measuring and protection devices – Galvanic Isolation

The CGL make current transformers used in 220 KV Switchyard have the electromagnetic system accommodated in the transformer head. Primary current carrying system through the head endows the transformer with high dynamic & thermal stability. The secondary windings are insulated & located inside the head. External insulation is ensured by an outdoor porcelain insulator. The insulation system is fully encapsulated & hermetically sealed. Active Component The secondary windings are of insulated copper wire uniformly distributed over the circumference of the core. Each layer of winding is perfectly insulated from the other using good quality insulating material. The ring type cores with secondary windings are accommodated in a cavity free aluminium alloy casting. The secondary leads are taken out through a condenser bushing and porcelain to the bottom housing. The entire active part is impregnated with oil. Transformer Head The transformer head accommodates the primary winding with the externally accessible primary reconnections & metal bellow made of stainless steel as expansion element for the temperature dependent oil volume changes. Then oil level & operating mode can be checked by means of a readable bellows position indicator located at the top of the CT and can be easily read at any time. The hermetical sealing ensures that the insulating characteristics of the dielectric system are maintained during operation Insulator The insulator is made of vitrified electro porcelain and is cemented to the flanges with Portland cement. Bottom Housing

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The transformer bottom housing is used to take out the secondary leads for external connections. The terminal box os fixed to the bottom housing. The rating plate is permanently fixed on terminal box cover. The transformer bottom housing also accommodates the grounding pads, oil drain screw, lifting holes and mounting holes. A detachable blind plate is provided for cable lead-in.

Main parts of CT

• Primary Conductor • Carries the current through the CT • Can be made of Copper or Aluminum

• Primary Insulation • The heart / Most important part of the CT • Isolation between the high voltage and low voltage • The life of the CT depends on the quality of primary insulation • Is the same irrespective of customer specification

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• Quartz in IMB CTs

• Reduces the quantity of oil

• Provides mechanical strength for the conductors • Improves the quality of oil by absorbing moisture • Being a bad conductor of heat, it does not allow rapid heating /

cooling of the CT. It hence eliminates the possibility of gas generation due to rapid cooling of CT

• Nitrogen gas / Metal Bellow

• To compensate for the volumetric changes in oil due to temperature variations

Three types of cores are provided in a CT

> Metering Core • VA burden, Accuracy, Instrument Security Factor • VA Burden is Burden consumed by the Meters, Burden of

the lead wires • Accuracy Class- 1.0, 0.5 or 0.2 (Tariff Metering) • Instrument Safety factor decides the max. current that will

flow through the meters connected to the secondary > Protection Core

• VA burden, Accuracy class, Accuracy Limit Factor (e.g. 5P20, 10 P 20)

• VA Burden is Burden consumed by the connected relays, Burden of the lead wires

• Accuracy Class - 5P or 10P • Accuracy Limit Factor (ALF) is the maximum value of

current upto which the accuracy class is guaranteed •

> PS Class • Knee point Voltage, Magnetizing current, Resistance of

secondary • Knee Point Voltage is the maximum voltage that the CT

secondary will develop before going into saturation. This is specified by the protection personnel based on the relay used and the system parameters

• Magnetising current is the magnetizing current that the core will draw and its value is measured at a specific percentage of Vk (specified by client). The value generally depends on the relay used and the sensitivity of the protection system. This is decided by the protection system engineer

• Secondary resistance is an important parameter because it is used to calculate the value of Vk.

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CURRENT TRANSFORMER

S.No Property Specifications

1 Type Outdoor ,oil filled self cooled, single phase bar wound primary

2 Impulse withstand voltage(kVp) 1050

3 One min. power frequency withstand voltage(KV rms) 460

4 Rated short time current for three sec(KA) 40

5 Dynamic peak withstand current rating(KA p) 100

6 Standard IEC publication 185 / IS:2705-1992

7 Voltage rating(nominal/maximum) 220KV/245KV

8 system neutral earthing Effectively earthed

9 CT ratio as per SLD

10 No. of cores 5 cores

11 class of insulation A

12 Temp. -rise over ambient of 50 deg C oil a top of housing (measured by thermometer) 35 deg C

13 winding(measured by increase in resistance method) 45 deg C

14 Accuracy class 0.5 for metering and PS for protective relaying

15 Oil level gauge & pressure relieving devices: Provided for all CTs

16 Installation Outdoor

17 Burden As per requirement, considering 15% spare for future additions

18 Min creepage distance 31 mm/KV

19 Mounting Steel structures 1.1.5 Lightning Arrester (Surge Arrester) Surge arrester is a device designated to protect electrical apparatus from high transient voltage and to limit the duration and frequently and amplitude of follow-current. The term “surge arrester” includes any external series gap which is essential for the proper functioning of the device as installed for service, regardless of whether or not it is supplied as an integral part of device.

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At present the following types of surge arresters are used: 1. Gapped silicon-carbide surge arresters called valve type or conventional gapped arresters. These consists of silicon carbide discs in series with gap units. 2. Zinc-oxide gapless arresters called ZnO arresters or metal-oxide arresters. These are gapless and consist of zinc-oxide discs in series. ZnO arresters have superior V/I characteristic and higher energy absorption level. They are preferred for EHV and HVDC installations

Fig. Surge Arrester Surge arresters are the primary protection against different types of overvoltages (atmospheric or switching). Surge Arresters are usually connected between phase and ground in distribution system; near the terminals of large medium voltage rotating machines and in HV, EHV, HVDC sub-stations to protect the apparatus insulation from lightning surges and switching surges. The active elements (blocks) of surge arresters are manufactured using a highly non-linear ceramic resistor material composed of the most part of ZnO mixed with other metal oxide. The resistor blocks in the surge arrester offers low resistance to high voltage surge to ground. Surge Arrester discharges current impulse surge to earth and dissipates energy in the form of heat. After discharging the impulse wave to earth, the resistor blocks in the surge arrester offers a very high resistance to the normal power frequency voltage and acts as open circuit.

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Fig. Construction of Surge Arrester

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Fig. Location of surge arrestors in a power system

Fig. Arrester protective characteristic. Arrester protective characteristic is the combination of its residual voltages for different current impulses. For good protection, the arrester characteristic should lie well below the equipment insulation withstand characteristic at all points

Bus Bar Isolator

Circuit Breaker

Earthing switch

P.T. C.T. Overhead

Line

lightning Arrester

lightning Arrester

Transformer

| | | | | | | | | | | | | |

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Circuit Breaker Bus Insulator

Line Insulator

Surge Arrester

kV

1200 --- 1100 --- 1000 --- 900 --- 800 --- 700 --- 600 --- 500 --- 400 --- 300 ---

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1.1.6 Isolators ( Disconnectors)

Isolator is a mechanical switching device which provides, in the open position, an isolating distance in accordance with the specified requirements - IEC 50(441-14-05). It is appropriate for switching small currents, between the terminals, when no significant change in voltage occurs. Equipped with either one, two or no earth switches.

Fig. Isolators

• Isolators are used to isolate a part or complete network for

maintenance or long shutdown. They are also used for switching small currents during transfer/changeover in the system.

• For maintenance and operational safety it is also used for earthing the system through earth switch.

Most isolators are also provided with earth switches.

Earthing Switch is necessary to earth the conducting parts before maintenance and also to provide deliberate short-current while testing. There can be three types of Earthing switches .Manually operated, automatic high speed Earthing Switch, protective Earthing Switch for Earthing the installation.

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Fig. Isolator Parts

There are several versions of Earthing Switches for following applications 1 - Maintenance Earthing Switches. These are single pole or three pole units; manually operating mechanism with a provision of filling motor mechanism. 2 - High Speed Earthing Switches. These are operated by spring energy. Spring is charged by motor-mechanism

For earthing isolated sections of Switchgear for protection of personal during maintenance and over-hauls or erection, the maintenance Earthing Switches are employed. For earthing higher capacitances (cables, overhead line etc.) high speed earthing Switch are employed. Depending on the substation scheme, the Bus-Bars may be earthed either by maintenance or high-speed Earthing Switches.

To check whether a point to be earthed really is dead, the Earthing Switch can be equipped with a capacitive tap for connecting a voltage test unit. This additional safety device reduces the risk of closing onto a live conductor.

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ISOLATORS

S.No Property Specifications

1 Type

Outdoor duty, centre post, rotating blade moving in horizontal plane, double end brake ,gang operated.

2 Earth switch earth switch, single break gang operated with contact blade moving in vertical plane

3 Pole : 3 pole

4 System Voltage :

Nominal 220KV

Rated 245 KV

5 Lightning impulse withstand

Between phase to phase (kv) 1200 KVp

Between phase to ground (kv) 1050 KVp rms

6 Power frequency withstand voltage (min.)

Between phase to phase (kv) 530 KV rms

Between phase to ground (kv) 460 KV

7 Rated Current

continuous rating at 50 deg C ambient as per SLD

short time rating 40 KA for 3 sec.

peak short time current 100 kA

8 Minimum creepage distance 31 mm per KV.

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Phase to phase spacing for corona & RIV(mm) 4500

10 Operating mechanism Motor operated/ manual with reversible starter

11 Earth switch hand operated

12 Control voltage 220 V DC,+10%, -20%

13 Auxillary supply 240 V ac, +/- 10% ,1-phase

14 Auxillary supply for motor AC 415 V, +/- 10%, 3-phase, 50 hz

15 Auxillary contacts on each isolator

10 NO + 10 NC per pole, 8 make before break on each pole for CT switching

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16 Auxillary contacts on each earthing switch 6NO + 6 NC

17 Rating of auxillary contacts 10 A at 220 V DC each

18 Breaking capacity of auxillary contacts 2A DC with time constant not less than 20 ms

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support insulator cantillever strength(minimun) 600 kg

20 Sandards IEC-129/IS: 1818, IS-9921-1985

21 terminations suitable for overhead ACSR conductors

22 Installations outdoor

23 operating time 12 sec or less 1.1.7 Siprotec Relays

The SIPROTEC® 4 family is an innovative product series of numerical protective and control devices with open communication interfaces for remote control and remote parameter settings, ergonomically designed user interface and highly flexible functionality. The devices utilize numerical measuring techniques. Completely numerical signal processing offers high measurement accuracy and long-term consistency as well as the reliable handling of harmonics and transients. Digital filter techniques and dynamic stabilization of measured values endure the highest degree of security in determining the protective responses. Device errors are recognized and indicated rapidly by integrated self-monitoring routines. Failure of protection during a network fault is therefore almost entirely excluded. We can choose devices with separate protective and process control functions, or select a solution that implements both requirements on the field level.

SIPROTEC® 4 devices completely fulfil the requirements of modern communication technology. They dispose of interfaces that allow for integration into higher-level control centres comfortable parameter settings and operation via an on-site PC or via a modem connection. SIPROTEC® 4 devices support the widespread, internationally accepted open communication standards _ PROFIBUS FMS, _ PROFIBUS DP, _ IEC 60870-5-103, _ DNP3.0 Level 2 and _ MODBUS ASCII/RTU

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In the above sample configuration the data transmitted from the field devices in the monitoring direction can be processed in the station control device SICAM® SC, displayed at the operator monitoring and control station SICAM® WinCC and passed via the remote control interface to the higher-level control center. In the command direction equally flexible processing is possible, that is switching operations can be initiated both from the network control center as well as from the monitoring and control unit of the station control system. Operator Interface SIPROTEC® device can be operated via • The operator control panel on the front of the device or • The DIGSI® 4 user interface of PC which is connected on-site to the operator

interface of the device or via modem and service interface. Operator control panels The operator control panel of the SIPROTEC® 4 devices, which is ergonomically designed and easy to read, allows on-site control operations to be carried out, individual device parameter settings to be effected and all the information required for

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operations to be displayed. The operator control panels of the devices contain either a graphical or a 4-line display, depending on the specific device type

. Figure SIPROTEC® 4 devices, operator control panel

DIGSI® 4 DIGSI® 4 is used to set parameters and operate the SIPROTEC® devices via PC. DIGSI® 4 uses the Window technique common for PC applications for the operator guidance.

1.2 Bay-3 Bus Coupler Bus coupler joins main & standby buses thereby maintaining the generation load balance. Generally the bus coupler is in ON Condition. 1.3 Bays-4,6,14,16- Generator Transformer Through these 4 bays total power generated in CPP-2 is fed to 220KV switchyard.

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1.4 Bays 5,13-Station Transformer Station transformer feeds the station loads of CPP-2 like cooling tower, compressor, boiler etc. It also provides power to all the generators for black start. 1.5 Bays 8,9,10,11,12- Rectiformers The five rectiformer units are the main load of the generators. They consume around 410 MW of the total generated power. 1.6 Bays 16,17 -220KV Tie lines to MRSDS Power Export/Import to CSEB Grid is done through these tie lines. 2. DC Rectiformers As mentioned earlier, the function of rectiformer units is to Convert the AC power generated into DC for feeding the potline to carry out reduction process. Balco has 5 units of 87.5 KA rectiformer system. The rectifomers continuously feeds a current of 320-325 KA to the potline. Each rectiformer units consist of a regulating transformer, a rectifier transformer, a diode rectifier cubicle & associated cooling systems. Each unit is capable of delivering a maximum of 87.5 KA . As the total potline current requirement is 320 ± 5 KA, the total current will be shared by the five units as 320/5= 64±5 KA. Any one unit can be taken out for maintenance by increasing the current of the remaining four units. The entire rectiformer system with regulating transformer, rectifier transformer, diode rectifier, cooling system , PSR and all other auxiliaries is supplied by M/s ABB.

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Fig. Block diagram of a rectiformer unit.

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2.1 Regulating Transformer In this stage 220KV is stepped down at 69 KV through STAR-STAR Transformer. Here 25 KV DELTA tertiary winding is provided to supply to APFC bank.

The regulating transformer is provided with a Multi Range OLTC.( On Load Tap Changer).OLTC has got a total of 107 taps for operation. The rectifier control system will perform current regulation by stepping the regulating transformer's on-load tap changer upwards or downwards depending on the voltage target value. This will allow an automated rectifier system operation with best possible power factor. A built-in hysteresis mechanism in the control system will avoid excessive switching within the allowed time frame. There will be 106 steps in the OLTC concerned.

Rated Power (in MVA)

Rated Voltage (in V)

Input 137.2 220000 – 5%+10% Output 137.2 66000 Tertiary 40MVAR 25000

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Regulating trafo is a star-star transformer with a Delta tertiary winding. This 25KV tertiary winding is connected to the Capacitior banks. The regulating transformer is fitted with an On Load Tap Changer ( OLTC) with 107 taps for potline voltage regulation. OLTC is connected to the secondary winding of regulating transformer.

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Name plate details of regulating transformer

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Fig. Regulating Transformer Cooling system

36

2.2 Rectifier Transformer Before rectification, voltage is stepped down once more and fed to 3 phase DIODE-BRIDGE for DC power. The rectifier transformer has got two primary & two secondary windings. This vector group arrangement is done to obtain a 12 pulse output and to produce a minimum ripple DC Output. Rectifier transformer phase shifts

Unit DETFO ser.no.

rel. Phase shift

basic vector group

absolute phase angle

LV phase sequence

1 180148 0° D d0 0° u-v-w 2 180149 +6° D d0 6° u-v-w 3 180150 +12° D d0 12° u-v-w 4 180151 -12° D d0 348° u-w-v 5 180152 -6° D d0 354° u-w-v

Unit DETFO ser.no.

rel. Phase shift

basic vector group

absolute phase angle

LV phase sequence

1 180148 0° D y11 330° u-v-w 2 180149 +6° D y11 336° u-v-w 3 180150 +12° D y11 342° u-v-w 4 180151 -12° D y1 18° u-w-v 5 180152 -6° D y1 24° u-w-v

upper tier, delta

lower tier, star

Vector Group

• To obtain 12 pulse from each rectibloc • Minimum ripple DC output.

Figure below shows the phase shift of all units to produce a 12 * 5 =60 pulse system.

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Unit 1 (180148) : Connection D/d0 D/y11 Unit 2 (180149): Connection D/d0 + 6° D/y11 +6° Unit 3 (180150): Connection D/d0 + 12° D/y11 +12° Unit 4 (180151): Connection D/d0 – 12° D/y1 –12° Unit 5 (180152): Connection D/d0 –6° D/y1 –6°

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Fig. Internal View of Rectifier Transformer

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Name plate details of rectifier transformer

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Protections for Regulating & rectifier Transformers Internal Protection:

1.Buccholz relay 2.PRV 3.OTI/WTI External Protection 1.Over-curreent 2.Earth Fault

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3.Over-voltage 4.Over frequency and under frequency 5.Inrush and harmonic restraint 6.Oil level and temperature 7. Differential protection, Directional feature 8.LBB (Local Breaker Backup) 2.3 Diode Rectifier

• Final DC power is obtained in this stage. • 3 Phase,12 pulse diode bridge rectifier • Total 144 diodes/unit. • Four divisions of 36 diodes each. • Voltage control is taken care by Transductor.

The liquid cooled diode rectifier, type RectiBloc® is constructed of extruded aluminum profiles, welded to form a self-supporting frame. Diodes and fuses are mounted on specially designed, water-cooled current conductor aluminum profiles where the contact area of the semiconductors is nickel-plated. The disc-type silicon diodes are liquid cooled on both sides. The cooling medium is de-ionized water. A high-speed current limiting fuse is provided for each diode unit for selective isolation in case of a failure. Each fuse is fitted with a micro-switch and a striker pin for easy identification of the faulty element. A suitable rated and fused capacitor circuit is connected in parallel to the rectifier as a protection against over-voltage. The rectifier is equipped with arc resistant phase barriers eliminating the risk of a phase-to-phase flashover.. The fuse assembly is liquid cooled on both sides. The rectifier is protected against hole-storage effect surges and over voltage disturbances coming from the network by a specially designed over- voltage protection circuit. Protections for Diodes :

• Snubber-circuit and fuses for o/v • Diode fail • Reverse current relay • High temperature • Open-circuit protection • Fire Protection

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Fig. Diode arrangement inside cubicle

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2.4 Transductor Transductor is the controlling tool. Whenever Potline voltage varies it tries to maintain load current constant. It has two segments, viz. Star control and Delta control. If any variation in voltage(anode effect) beyond certain limit then it issues tap up/down command to Regulating Transformer. The Potline voltage fluctuates due to a phenomenon called Anode Effect. This is the phenomenon occuring in potline where normal steady state voltage shoots up by rise in resistance inside the pot. There are two current in Tranductor. They are Bias current which is fixed and opposes the main flux and Control Current which favours the main flux. Control current varies along with main flux. When Bias current opposes, the main flux weakens , hence a voltage drop of 40-50V DC occurs in transductor. This is stored in transductor and released at the time of anode effect. There are 12 transductors in one trafo as shown below.

2.5 Control Philosophy

• To supply dc power to potline we need to operate the parallel rectifier system either in MASTER/MASTER or MASTER/MMI.

• We use PSR-2 technology with FUPLA-2 Software.

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• Fast, Modular and Multi-processor control system with efficient peripheral devices

• Multi level control:LCP-URCP-MMI. • AUTO/MANUAL Tap changer

2.5.1 Control / Metering

All signals coming from the rectifier equipment, process sensors, and push buttons will be processed at PHSC (Programmable High Speed Controller) to perform current regulation, rectifier equipment control and alarm/event indication.

2.5.2 Protection Special current limiting Semiconductor fuses connected in series with the semiconductor elements will ensure protection against internal short circuits by isolating a faulty element. Protection relays will be installed in the local control cubicle. The protective relays will release the primary breaker in case of a serious fault. Additionally Backup protection unit in local control cubicle will ensure that primary breaker will trip in case of major trip fault even in unlikely case of PHSC failure.

2.5.3 Regulation Range of Operation System should be suitable for operation from 0 kA to 87.5 kA with all pots connected using OLTC and transductor control. Constant Current Regulation Each rectifier unit will feature constant current regulation of ± 1% accuracy of rated current. The total pot line current regulation under group mode should be 0.1% (Based on set point). The actual value of unit current, measured by the Current Transformers mounted on primary of rectifier transformer will be compared with a preset (set point) value. In group mode the total current is measured by a 0 – 350 KA DCCT.

On-Load Tap Changer

The rectifier control system will perform current regulation by stepping the regulating transformer's on-load tap changer upwards or downwards depending on the voltage target value. This will allow an automated rectifier system operation with best possible power factor. A built-in hysteresis mechanism in the control system will avoid excessive switching within the allowed time frame. There will be 106 steps in the OLTC concerned.

Transductor Control

Transductor control will provide smooth control of DC voltage between two OLTC positions. The Transductor will be designed for operating voltage 50V DC ( designed

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for 65 V DC ) for offering smooth control of the Current and having an overlapping Voltage of 15 V, so that it avoids spurious changing of taps.

2.6 SCADA System at Common Control Room.

SCADA system is for control and monitoring of the five rectifier bays of the potline. This includes the critical parameters and status signals of transformers and rectifiers (only for the five rectifier bays) ,control actions like opening/closing of Breakers and isolators, Starting & stopping of Fans and pumps.

SPIDER Micro SCADA system for Unit 1 till Unit 5 consists of a redundant SCADA server, one operator work station , One Laser Jet Printer and a dot matrix Printer. The Monitor of these PCs will be of Compaq 18.2" TFT 2 tone Flat panel Monitor.

Each SCADA server shall communicate with LCP (Local Control Panel) and MCP (Master Control Panel) using one Multiport Card, which will have 8 ports each for communication. It shall collect data from LCPs and MCP using RS232 connectivity. Operator workstations will be used for monitoring & controlling of required parameter. SCADA server and Operator Workstation will be communicating with each other using Ethernet LAN.

Micro SCADA combines a user-friendly and consistent operator technique with the capacity for extensive information processing, advanced calculation and reporting and varied automatic functions. Full Graphic features built into the powerful Human Machine Interface (HMI) provides the operator all the required flexibility to monitor and control the external process.

HMI supports functions such as control and supervision of equipment, object tagging, alarm and event reports, measurement and reports presentation etc.

Communication

For this project, SCADA Servers shall interface with LCP and MCP units of Unit 1 & 2, Unit 3 & 4 , Unit 5 using RS 232 interface via a fall back switch. The fall back switch ensures bumpless transfer of data from the primary to secondary server, in the unlikely failure of the primary server. The protocol used for communication is ANSI X3.28 full duplex.

The data collected from each Unit shall be transferred directly to SCADA Servers as well as to Master Control Panel. The communication media between the Local Control Panel and SCADA Server is Fibre Optic via a fiber optic converter. Similarly

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the communication between the Local Control Panel & Master control Panel is through fiber optic cable with a fiber optic converter on either side. The same data from the Master Control Panel shall be communicated to SCADA server using RS485 connectivity. This link will behave as a redundant link between LCPs and SCADA.

‘

Fig. Overview of Rectifier Micro SCADA 2.7 LCP,MCP & URCP 2.7.1 LCP ( Local Control Panel) There is one LCP per Rectifier. The local control Panel is equipped with all necessary apparatus, completely wired and factory tested for local rectifier control, metering and protection. The system is optimized for control tasks on the process control level and includes all necessary functions like

• Signal input/output • Signal processing • Signal transfer to and from peripheral devices and/or to supervisory or

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• Parallel systems • Service functions • Auxiliary functions

GA of Local Control Panel 2.7.2 MCP ( Master Control Panel) We have 1 No. Master Control Panel (MCP) for group control of 5 Nos. Rectifier systems feeding to potline. The Panel is equipped with PHSC that receives potline current signals from DCCT (LKP350). Potline set point can be set through the ARCnet control panel mounted on the front of the MCP. MCP is also equipped with individual ARCnet control panels for units through which individual rectifiers can be controlled and monitored. All the common potline functions like open circuit protection, emergency trip etc. is executed at the MCP. It displays potline parameters like voltage and current.

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Fig. GA of Master Control Panel 2.7.3 URCP ( Unit Remote Control Panel) These panels are located in common control room. They are also used for individual unit operation . 2.8 Cooling System The Cooling system which is skid mounted consists of the following:

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1) Pump 02 Nos., Centrifugal Pumps (1 working + 1 standby) are used for pumping De-ionized water in the closed loop through the system and the rectifier. Change over of the pumps are done manually by operating the isolation valves. 2) Plate Heat Exchangers This is used for cooling the De-ionized water from the rectifier which is then re-circulated back to the rectifier. Cooling/Raw water is used as the cooling medium. 3) Expansion Tank with Level Indicator This is connected to the De-ionized water on the bypass line and is used to make up for any losses due to leakages in the system. It also serves the purpose of maintaining a constant pressure in the closed DI water circuit. The overhead tank supported by means of angular supports is provided with a visual level indicator, level switches and necessary drain, overflow & filling connections. 4) De-ioniser Cartridge Based on the indication of the conductivity level from the digital conductivity meter, the de-ionsier cartridge is taken in line for maintaining the conductivity level in the De-ionized water below 50 micro-siemens/cm. This is done by opening the isolation valve upstream of the cartridge and allowing flow of the De-ionized water through the cartridge. Once the desired conductivity level is achieved, it is again isolated from the system. 5) Variable Area Rotameter This is mounted on the bypass line on the De-ionized water circuit and is used to indicate the flow rate in this circuit. 6) Flow Transmitter This is mounted on the main line of the De-ionized water circuit primarily to indicate and also provide a signal for the pump trip through the process indicator cum controller. 7) Control Panel A cubicle type control panel is provided to accommodate the push button starters for the motors, process-indicating controller, digital conductivity meter, temperature controller along with necessary spare terminals. The process indicating controller accepts the signal from the flow monitor which is mounted on the De-ionized line for pump trip. In addition to this, it also indicates the DI water flow rate. The digital temperature controller accepts the signal from the RTDs mounted on the DI water outlet for alarm and pump trip.

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8) Electrical Junction Box All electrical components mounted on the Rectifier cooling system are wired to this box. Further connections are taken to Electrical control panel/for remote operations. 9) Series of online accessories such as valves, pressure gauge, drain and vent connections and cocks are also provided. For more details, please refer piping layout drawing and the literature for the components

Specifications - Rectiformer: DM water Pump S.no Pump Make Capacity Head Sr.no Model RPM

1 Pump#1 Johnson pump

45 M3/Hr

50 mts

P211109010 CCR 50 – 200

2900

2 Pump#2 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

3 Pump#3 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

4 Pump#4 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

5 Pump#5 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

6 Pump#6 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

7 Pump#7 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

8 Pump#8 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

9 Pump#9 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

10 Pump#10 Johnson pump

45 M3/Hr

50 mts

CCR 50 – 200

2900

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Fig. GA Drawing of rectifier cooling system.

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2.9 Common Trip Panel (CTP) All critical common protections like Reverse current, Emergency trip from pot room etc are brought to common trip panel through hard-wired logic. In case this panel detects fault, trip command will be given directly to all the 5 LCP ‘s to trip the 220kV breakers. This ensures that even during the worst case of controller not initiating a trip command, the breaker is getting tripped 2.10 Common DC Metering Panel This is mounted near totalising dc bus bar and used for generating signals for dc voltage metering in Master Control Panel.

2.11 AC/DC DB Panel AC/DC distribution panel used for distributing different feeders to rectifier system. The following are the incoming/outgoing feeders to AC/DC DB: • 2 x 415V, 3ph, 4 wire, 50Hz supply (incoming) Out going feeders are as under • 3ph 415V, 50Hz supply : One feeder each to Regulating Trafo cooling, OLTC

Rectifier Trafo cooling, Rectifier cooling and dc isolator

• 1 ph 415 V, 50Hz supply : One feeder to Pre-mag panel supply 1ph 230V, 50Hz supply : One feeder each to dc isolator, rectifier cubicle, and

rectifier control Panel. 220Vdc supply (incoming) Outgoing feeders are as under: • One feeder each to Regulating Trafo, Rectifier trafo, Rectifier control panel, rectifier

cooling system, pre-mag panel, rectifier panel 2.12 Common AC/DC DB. Common AC/DC distribution panel used for distributing different feeders to common panels like Master Control panel, common trip panel, SCADA 2.13 DC Isolator 100 kA DC isolators of type, which is required to be welded directly to Aluminium dc bus bars at both ends are installed in all units. As dc isolators absorb dimensional variations due to expansions additional flexible joints are not required. DC isolators are of motor operated type.

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2.14 DC Current Measuring System Pot line DC-Current Measurement The potline current is measured by LEM make DCCT (LKP 350) Metering system. DC current is measured using ‘closed loop’ Hall effect principle. LEM's general mounting recommendations are followed during installation. The signal from the measuring head will be connected to an isolation transducer/ amplifier. The transducers will be located near the LEM. The output signal is used for potline current regulation, protection and metering. Technical Details of DC CT : Manufacturer/Supplier : LEM DYN Type : LKP 350 Maximum bus current : 350 kA Accuracy class : 0.1% Installation : loose supply, Output : 200mA per kA or 1mV per kA

Unit DC-Current Measurement

Measuring unit AC current on the primary side of the rectifier transformer will derive unit dc current. The measured ac current value is processed and unit dc current is calculated in the PHSC system. Accuracy class: 1.0% 2.15 Capacitor Banks ( APFC Units)

• Improves the Power Factor in the Network • Reduces the Network Losses • Counteracts Voltage Drops and Improves Voltage Stability

We have 87.5*5KA,1300V Rectifier Station, which is fed by 5 regulating transformers of 137.5MVA each. These transformers feed rectifier transformers which have 12 pulse rectification but are arranged in such a way that the complete system work as 60 pulse. Due to such high pulse rectification, harmonics are much lesser. This mode of operation has been termed as balanced mode of operation. The whole system is designed to work with any of the four out of the total five groups giving the same rated output on the DC side. In this case individual current of transformer increases as well as the percentage of harmonic contents. This operation is termed as unbalanced node of operation. The plant can work on this mode for much longer period if required. There is a third mode of operation in which currents are same as in unbalanced mode of operation but the harmonic contents are quite high as it works like a 12 pulse rectifier. This is termed as worst case operation mode which is for a short duration only.

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Regulating transformers have been provided with tertiary winding of 25KV on which power factor correction capacitors are to be provided to improve the power factor of rectifier system. The purpose of capacitors is to primarily improve the power factor to ensure that it does not resonate with any of the dominant harmonics present in the system. 2.5.1 Requirement of capacitor Banks The reactive power required for improving the power factor of the system to 0.95 is calculated as given below : D.C Load of 87.5 KA, 1300V System = 113.75MW A.C Load considering 99.77% efficiency = 114.00 MW Capacitor required to improve the power factor from existing 0.87 to 0.95 = MW load( Tan cos-10.87- Tan cos-10.95) = 27.136 MVAR Total requirement is split into two equal banks, hence the rating of one bank at 25KV works out to 13.57 MVAR Capacitors are provided with series reactors to avoid resonance & magnification of current at higher harmonics. Therefore, series reactors tuned to 4.7 harmonic order is provided. Tuning being closer to 5th harmonic, the bank will be absorbing bulk of fifth harmonics and at the same time the combinations of series reactors and capacitirs become inductive for all harmonice i.e 5th and higher order, therefore, eliminating any possibility of resonance at higher harmonics. Capacitors are rated at 28.8 KV to take care of overvoltage due to series reactors, the flow of harmonic current and system voltage variations. 2.5.2 Overvoltages on capacitors & adequacy of rated voltage of capacitors Capacitor banks are subjected to overvoltages on account of the following :

a.) Overvoltage due to series reactor b.) Overvoltage due to harmonic current in capacitors c.) Overvoltage due to system voltage variation.

There are three sets of harmonic values. One for balance mode of operation, second for unbalance mode of operation and third for worst condition of operation. These harmonics generated in rectifier system gets distributed between source & capacitor banks. Some harmonics may also flow to other connected loads like aux load etc but the values of these harmonics are very small due to higher impedance of the load and due to the fact that these are inductive loads and they offer still higher impedance to higher harmonics. Hence, these loads are ignored.

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Fig. 25 KV Capacitor banks The Specification of our capacitor bank are :

• 30 MVAR per bank. • Two sub-units per bank • 48 capacitors/unit • 3 inductors/unit • Rating of Inductor:2.17 ohm @ 50 Hz.

Protections for APFC Units :

• Over voltage • Under-voltage • Over current • Earth-fault • Sensitive E/F

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3. Area Substations 3.1 11 KV Central Distribution 11 KV central distribution is the central power distribution centre for all auxiliary loads. This is locate in Switchyard & rectifier common control room. In this system there are 2 11KV incomers from Utility transformer & one 11 KV buscoupler.

Fig. 11 KV Central Distribution Panels 3.2 Self Use Two Nos. of Self use transformers are connected to two feeders of 11 KV central distribution. These trafos are 11/0.415 KV. The 415V LT distribution supply is used for self use as well as for AC Control Supply to Switchyard & Rectifiers.

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3.3 Air Compressor Substation This is one of the two main area substations (11KV). This provides power to Air Compressor HT Motors (11KV), Cast House Transformers, Pot MCC-12 Trafos and Pot Overhaul shop. This substation is located in Compressor house. The main equipments installed in all substations are transformers, Siprotec relays, Air Circuit breakers in LT side, Vacuum Circuit Breakers etc.

Fig. Air Compressor Substation distribution panels 3.3.1 Vacuum Circuit Breakers

► Vacuum is used as an arc quenching medium. ► Have greatest insulating strength. ► 10-7 to 10-5 pressure is to be maintained. ► Used in 11KV panel in control room of grid station.

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Vacuum Circuit breakers are used for low voltage applications. The making & breaking of the breaker contacts are done inside a vacuum chamber. Both closing & opening operations of VCB are through spring mechanism. The breaker is also provided with spring charging motor.

Fig. Side View of Switchgear Cubicle

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Fig. Withdrawable truck with CB

The circuit breaker compartment contains a withdrawable truck with Vacuum circuit breaker or Bus PT Truck. The breaker terminals are fitted with contact arms .The withdrawable truck can be transferred between the service & test posit ions behind closed doors using a hand crank. Service Position (Connected Position) The position of a Withdrawable Truck in which it is fully connected for its intended function. In this position of the truck, the contact arms of the circuit breaker are connected to the busbars as well as to the outgoing cables via the fixed mounted isolating

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contacts in the cubicle. The truck is locked against withdrawing. The low voltage circuit is connected through the low voltage plug & socket connect ion . Test Position The position of withdrawable truck in which an isolating distance or segregation is established in the main circuit & in which control circuits are connected. In the test posit ion, the truck with the breaker is withdrawn so far between busbars & outgoing cables That there is isolating distance . The truck is locked against moving. The low voltage circuit is connected through low voltage plug connection . The circuit breaker can be switched for testing & all functions. Disconnected Position (Isolated Position ) The position of withdrawable truck in which an isolating distance or segregation is established in the circuits of the withdrawable truck, the truck remaining mechanically attached to the enclosure. In this position the truck is withdrawn as in test position but the LV plug is disconnected. In the test & disconnected posit ion the contact arms & their mating contacts are separated by metallic shutters. Removed Position The position of withdrawable truck when it is outside the panel and electrically & mechanically separated from it . Ramps are provided at the front bottom of the panel to withdraw the truck out of the panel smoothly. Drive Mechanism of the truck is attached to the cubicle frame using Rod Lever. The Earthing strip at the bottom of the breaker compartment , along with the spring loaded pin provided at the bottom of the circuit breaker truck ensures the earthing of the truck in all the positions.

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Fig. Rear view of the Truck Advantages of VCB

► Compact, reliable and have longer life. ► No fire hazards. ► No generation of gas during and after operation. ► Can interrupt any fault current. ► No noise is produced while operating. ► Require less power for control operation

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3.3.2Air Compressor Motors Air Compressor station is installed with 6 Nos of 3 Phase Squirrel Cage induction motors. They are 11 KV motors getting supply from compressor HT substation. Induction motors are classified into two types : • Squirrel Cage Induction Motor – Normal applications – Pumps & Fans • Slip Ring Induction Motor – used for starting against heavy Loads ie. Where

Starting Torque required is very high – Crushers, Mills, Heavy Cranes Air Compressor motors are 3 Phase Squirrel cage induction motors. Factors affecting Size of Induction motor • Depends on Speed & Output Co efficient • Higher the Speed, lesser the size & Cost • Higher output coefficient , Lower the size & Cost ie. Higher specific Magnetic & Electric Loadings , lower the size & Cost . Diameter & Length affects size For fixed poles, L/D = 1.5 to 2 ( less cost ) – High Voltage M/c L/D = 1 to 1.25 ( good Power Factor ) L/D = 1.5 ( Good Efficiency ) L/D = 1 ( overall good Design) L – Large ; M – Medium ; S - Small Methods of Starting Induction Motor Direct On Line Starter

• Star Delta Starter • Auto Transformer Starter • Soft Starters • Variable Frequency Drives

Delta & Star Connections Delta Connection : Vph = VL Iph = IL / sqrt 3 ; or IL = sqrt 3 * Iph

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Star Connection : Vph = VL / sqrt 3 Iph = IL To reduce starting Line Currents, Motors are started in Star and run in Delta ( Line current is sqrt 3 times higher in delta) DOL Starter • Widely used in Industries. • Comprises Fuse, Bimetal Overload Relay, Power Contactor. • Fuse – Protection against Short Circuit • Bimetal overload Relay – Protection against Thermal overloads • Contactor – For switching off & Switching On Protections for HT Motors Motor Protection Relay Protection against Overloads Protection against Earth Fault Protection against stalling or Locked Rotor Protection against Prolonged Starting Protection against Short Circuit Protection against no. of Starts ( Hot / Cold Starts) Over Temperature Protection: Bearing Temperature Detectors – 70 deg C Alarm & 80 deg C Trip Winding Temperature Protection – RTD’s Depends on Class of Insulation . For Class F Insulation motors, Alarm -110 deg C & Trip – 120 deg C

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HT Motor-Air Compressor (6 Nos)

S.No Property Specifications

1 Duty Continuous

2 Frame No. 12A7717-2

3 KW 1210

4 Stator Voltage 11000 Volts

5 Stator current 74 Amps

RPM

6 RPM: 2985

Phase: 3

7 Hertz: 50

Motor standard: IS:325

8 Ambient temperature: 50 degC

9 Deg. of prot. IP55

10 Connection: Star

11 Driving end bearing, sleeve dia: 100mm

12 Non-driving end bearing, sleeve dia: 100mm

13 Insulation class: F

14 Rotor type: squirrel cage

15 Year: 2004

16 Weight: 7100Kg

17 Rating of each heater: 240 volts, 800 watts

18 Oil flow: 2.5 Dl

19 Oil pressure: 0.2 bar 3.3.3Air Compressor Station Transformer Air Compressor station transformer is used for providing supply to all aux. loads of air compressor like , circulating water system, CMC panels, cooling towers, secondary air compressors, drier panels etc. There are two 11/0.415KV transformers in air compressor house.

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Air Compressor Station Transformer (2 Nos)

S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP

3 PF Voltage HV :28 KVrms LV : 3 KVrms

4 Taps 5 (OCTC)

5 Cooling ONAN

6 Rating 1250 KVA

7 Voltage HV : 11 KV

8 LV : 0.433 KV

9 Current HV : 65.61 A

LV : 1666.72 A

10 Phase HV : 3 Phase

LV : 3 Phase

11 Rated Frequency 50 Hz

12 Impedance Voltage 4.91 % , 4.86% (T-1)

13 WTI CT 1670/5A, CL-5 20VA

14 Neutral CT 2000/5A, CL-5P10,20VA

15

Guaranteed max. temp rise Over an ambient of 50oC 40/50oC (oil/Winding)

16 Serial No. JN 7656/4, JN 7656/3 (tr-1)

17 Diag. of Connetion No 3RD 7656/a

18 Core & wdg. Weight 1900 Kgs

19 Weight of oil 670 Kgs

20 oil Quantity 750 Litres

21 Total Weight 4270 Kgs

22 Year of Mfg 2004

23 Customer Ref.No 45253961 (01.03.04)

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Transformers : Most of the transformers installed in various area substations are supplied by Voltamp. Some of the main fittings and accessories of these transformers are : Off-Circuit Switch The transformer is normally fitted with an off circuit tap changing switch to obtain required voltage ratio. It can be hand operated by a switch handle mounted either on tankl cover or on the tank side. The locking devices is fitted to the handle to lock in any lock position. The switch mechanism is such that it can be locked only when it is located in its proper position and not in any intermediate position. The transformers must be isolated from all the live lines, before operating the switch. Operating the switch when transformer is energized, will damage the switch contacts due to severe arcing between the contacts and may damage transformer winding. When the switch handle is provided on the side wall, it is necessary that Switch handle assembly is dismantled before untanking. Off-Circuit Ratio Changing Links Sometimes links are provided inside the transformer tank to obtain required voltage ratio. Links are required to be loosened and fixed in new required position as given in name plate. Links are accessible from the inspection cover. In case of conservator units, oil level has to be lowered below the inspection cover before unbolting inspection cover. On-Loading Tap Changer The on-load tap changer is an optional fitting. The on-load tap changers are provided with local manual control, local electrical control and remote electrical control. The automatic voltage regulation can also be provided as an optional fitting. The tappings are located on high voltage winding. Earthing Terminals The core laminations assembly is connected to core clamping frame which is in turn connected to the tank. Two earthing terminals are provided on the transformer tank. The earthing terminals should be connected to the earthing. Lifting Lugs Two/Four lifting lugs of adequate capacity are provided on tank sides/top cover to lift fully assembled transformer filled with oil. All lugs are designed for simultaneous use and must be used accordingly. Two/Four lifting lugs are provided for untaking the core and windings of larger capacity transformers. All heavy fittings are also provided with individual lifting lugs.

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Valves Every transformer is provided with drain cum filter valve at bottom of the tank, and filter valve at top of the tank. Valves are fitted with plugs/blanking plates to stop oil coming out. Mainly two types of valves are provided: i. Wheel Valves ii. Butterfly valves The wheel valves are used either with female screw threads or with flanges. These are of gun-metals/cast iron type. Generally, one Isolating Valve also known as shut off valve is provided for transformer upto 2000 KVA between conservator and buchholz relay. The Butterfly type cast-steel valves with the machined flanges are used at points of connection between tank and detachable radiators. Bushings 1.Oil Communicating Type Transformers windings are connected to the external circuit through terminal bushings. The bushings are installed on the cover or, on side walls of the transformer tank. The lower end of the bushing protrudes into the tank and both their ends are provided with suitable fasteners to connect the line leads inside the transformers and external conductors outside it. The shape and size of the bushings depend on the voltage class, type of current. Electrical performance of these bushings conform to I.S. 2099 & I.S. 7421 Dimensional details and associated parts generally conform to IS-3 upto 36 KV class. Bushings of 1000Volts are of two piece constructions without arcing horns, whereas all other bushings are of single piece porcelain type. Assembly and dismantling of single tank cover is required to be removed for necessary access to the inner (lower) end of the bushings. These bushings are not detached at the time of transportation. 2. Condenser Bushings Generally, condenser bushings are used for 72.5 KV and above. These bushings contain their own oil and are sealed to retain the same. Whenever these bushings are mounted on bushing pockets or raised truncated portions, air vent pipes are provided for carrying away air or gases from these pockets to Buchholz relay during service typical assembly . These bushings are detached from the transformers and dispatched separately, they are packed as per manufacturers instructions. The draw through type lead is coiled and kept temporarily below the bushing blanking plate. The equipment required for mounting the bushings are (i) rope slings (ii) flexible steel wire approx 2mm in dia, of suitable length. Cable Boxes Cable boxes are designed for receiving and protecting cable ends. Insulating paper is most hygroscopic and all paper insulated cable ends must be protected by suitable insulating Compound .These cable boxes are provided with brass wiping glands and are

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designed with Clearance inside the box suitable for compound filling. The cable box in such case must be Filled with compound. Cable boxes for PVC or XLPE cables are designed with air clearance and hence these boxes are not required to be filled with compound. Cable boxes of 3.6 KV and above are provided with detachable gland plates. Earthing terminals are also provided on these cable boxes for earthing the armouring of individual cable. When cable boxes are provided with disconnecting chambers they permit removal of Transformers for servicing without disturbing cable terminations. Bus-Duct/Trunkings Some users prefer connections to load by means of Bus-Duct. Bus duct is supplied by some other agency. However, we provide suitable flanges. trunkings around transformer bushings for receiving the busduct. Marshalling Box The transformer is provided with certain fittings directly mounted on the transformer at various locations. These fittings are having electrical contacts or terminals which are required to be connected to the protection schemes to give alarm/annunciation under abnormal conditions and if further required to disconnect the transformer form mains. In order to facilitate connections of all such devices to the protective scheme, the cable form all such contacts are wired upto a weather proof terminal box. This box called Marshalling Box, is also used for housing Oil Temperature Indicator (OTI) and Winding temperature Indicator (WTI). The Marshalling box is made of sheet Metal and is provided with glass window for observing OTI & WTI. It has hinged door with locking facility to prevent unauthorized access. The capillaries from OTI &WTI come out from the bottom of the Marshalling box through suitably recessed gland plate thus preventing ingress of dust. I t has detachable gland plate with glands through which cables enter and leave. It has a rain shed provided on top to prevent rain falling directly over it. All these provisions make Marshalling Box a Weather-proof enclosure. Buchholz Relay Buchholz relay is a very sensitive, gas and oil operated apparatus which detects formation of gas or development of sudden pressure inside the oil filled transformer. It is connected to protection circuits to give an early audible alarm of gas collection and to disconnect the transformer from supply in case of severe fault inside the transformer. The basic function of the relay, is to initiate an electrical signal in the protection circuit when : a. Gas is accumulated in the relay, as result of incipient fault.

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b. Surge of oil is developed on account of sudden increase in pressure inside the transformer due to sever fault. c. Oil level in the relay is reduced below the minimum level. Buchholz relay operates in the following manner: The relay comprises a housing containing two pivoted buckets/Floats counter balanced by dead weights. Each bucket assembly carries a mercury switch. The relay is fitted in the oil connection between conservator and tank. Due to gas collection, the oil level inside the relay drops and the upper bucket moves down. This tilts the mercury switch brining fluid mercury in such a position that it bridge the normally open (NO) contacts. Other probable reasons for dropping of level in the relay are: a. Leakage of oil from main tank, conservator or relay itself. b. Collection of air in the relay which is trapped earlier in the tank and in the winding. The lower bucket operates similar to upper bucket when level in the relay drops further. However important function of this relay is to disconnect transformer from circuit under sudden development of pressure inside the transformer doe to severe internal fault In such cases, gas generation is rapid and displaced oil surges through the relay impinging on the baffle plates causing lower bucket to tilt and close the Normally Open (NO) contact of the mercury switch carried by it. Upper bucket contacts are connected to audible alarm-‘A’- circuit and lower bucket contacts-‘T’- are connected to trip circuit. The relay is mounted in position with associates piping and Isolating valves at works. In larger transformers, the buchholz relay assembly is dismantled and sent separately. When Test Lever is provided, it is sent in ‘Test’ position to prevent damage in transit. To ensure successful operation of the relay the pipe work on either side of the relay is set inclined to horizontally by 3-50. MOUNT RELAY SUCH THAT ARROW DIRECTION POINTS TOWARDS CONSERVATIOR Radiators The function of radiators is to limit the temperature of oil and winding by dissipating heat that is generate due to the losses within the transformer while in the service. The number of sections per radiator and the number of radiators per transformer will depend upon the losses and permissible temperature rise. Distribution Transformers are normally provided with radiators welded to tank. Owing to transport limitation and possible transit damages, power transformers are provided with detachable radiator with radiator valves .

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Each radiator consists of number of “Section” made from pressed CRCA Sheets forming channels for oil flow. These “Sections” are welded to Header Pipes at Top and Bottom. Detachable radiators are provided with M.S. Flanges at Top and Bottom. Flanged radiators are fitted with Air Release Plug, Drain Plug and Lifting Lug. Bracing Straps, made from M.S. Flat are provided on radiator to prevent vibration of section. Radiators are cleaned internally to remove scales and a coat of varnish is applied. External surface cleaned off all rust and one coat of Red-Oxide primer is applied which is followed by final painting. Silica Gel Breather Whenever there is a change in the ambient temperature or in the load of an oil immersed transformer there is a change in oil temperature , & hence in the volume of oil. Increase in oil volume, causes the air above the oil level in the conservator to be pushed out and decrease causes air to be drawn in. Thus the transformer “Breathes”. When air is breathed in , there is a possibility of moisture and dust from atmosphere to be sucked in. These contaminants deteriorate the insulation properties of oil. Hence, Silica Gel Breather is provided which arrests moisture and dust from the air drawn in. A Typical- Silica Gel Breather has following main components: 1. A Casing 2. Silica Gel Crystal 3. An oil Seal at the lower end of casing The casing has a window at the upper part for observation of the color of the Gel crystals. It has flange connection at the top for the connecting the breather to the breather pipe. The lower part of the casing has at its lower end an oil seal arrangement, a window for observation of oil level and an oil filling hole with gasket and plug. Due to the chemical affinity possessed by Silica Gel Crystals, they absorb moisture from the air drawn in. The color of silica gel is blue when dry and turns pink when it is saturated with moisture. The color of crystal can be observed from the outside of the casing. Oil seal assembly at the lower end of the casing consists of little quantity of oil with an inverted cup partly dipped in the oil and a tube fixed at the center of the cup. The oil acts as a coarse filter and removes the dust from the outside air when it is passes through oil. Magnetic Oil Level Gauge (MOG) This is a dial type oil level indicating device provided on larger transformers with conservator at relatively high levels from the ground. In large transformers conventional glass oil level indicators are difficult to observe due to their heights and color change/dust accumulation on the glass. Further, the low oil contacts provided on the MOG can be used for automatic alarm when the oil level in the conservator falls to a low level.

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This protection feature and clear visibility justify the cost of MOG on a bigger transformer. It consists of two compartments: a. The oil side compartment which fixed on the opening in the conservator. b. The pointer side compartment. These compartments are sealed against leakage of oil by a metallic diaphragm. On the oil side compartment, there is a bevel gear wheel and it is positioned near the diaphragm. Movement of the float due to rise and fall of oil level in the conservator results into circular motion of the driving magnet. A follower magnet is positioned in the pointer side compartment near the diaphragm. This magnet has its poles face to face poles of driving magnet from the oil side compartment coupling them magnetically. The movement of float is, therefore, transferred through the diaphragm, eliminating direct oil light mechanical coupling. At the other end of the axis of the driven magnet an indicating pointer is fitted. The dial is calibrated to show the oil level in the conservator. The dial and the pointer area housed behind the front glass. The dial has three position marked. The follower magnet has also a cam fitted on it which operates a mercury switch. When this magnet is at a position corresponding to low oil level the mercury switch closes the Normal Open (NO) contacts. These contacts are normally wired to give audible alarm. The contacts are brought to terminal box at the lower end of the dial, for external connection. Oil Temperature Indicator (OTI) Oil Temperature Indicator (OTI) is generally provided on all transformers except for very small ratings. The direct reading pointer arrangement in this instrument greatly facilitates observation of working temperature of oil. It also helps, if need be, in deciding the permissible overloads in accordance with I.S. 6600-1972. guide for loading of oil immersed transformers. A Typical-Oil temperature indicator consists of a Bourdon tube with a pointer arrangement mounted in a case comprising of a reading dial and a glass cover. There is a temperature sensing bulb which communicates to the Bourdon tube through the armoured capillary. The oil temperature indicator is provided with two pointers and associated contacts for protection of transformers. Both the pointers are independently adjustable and can be set to desired temperature. Setting of these pointers at required temperatures can be done from outside through the knob by using special keys. The OTI is generally housed and wired upto terminal strip in the Marshalling box having a glass window on the door for observation. The length of capillary does not influence the accuracy of measurement and extra length of capillary tubing must not be cut, as it would be break communication between bulb and Bourdon tube.

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If the oil temperature increases beyond set limit due to overload or inadvertent closure of radiator valves or insufficient air draft, the indicating pointer touches the present alarm pointer and actuates the alarm contact. The alarm contacts, when duly wired give an alarm. If the alarm is not attended and there is a further increase of temperature, the trip contacts which are wired to the trip circuit will operate and isolate the transformer form mains. Winding Temperature Indicator (WTI) A winding temperature indicator (WTI) is an optional fitting and is provided when ordered. It is set to read Hot Spot Temperature (HST).A typical WTI arrangement comprises of the following: (a) WTI instrument having a temperature sensing bulb and a capillary similar to OTI. In addition it is provided with a heater coil around its operating bellow. (b) A current transformer mounted on one of the transformer leads, sensing load current. The bulb of the instrument is placed in an oil filled pocket located on the top cover of the transformer similar to OTI pocket. The Heater Coil is fed by the W.T.I.C.T. Thus the Temperature indicated by WTI accounts for Temperature of Top Oil and Winding Gradient ( Temperature Rise of winding over surrounding oil) which is dependent on load Current. And is adjusted to read HST = [Top oil Temp.] + 1.1 x Gradient The Heater Coil is provided with an adjustable resistive shunt in parallel which allows the instrument to be adapted for a range of winding Gradients. The adjustable shunt by-passes certain amount of current (ISH) from the C.T. Secondary Current (IS). Thus Heater Coil current IH = IS - ISH

For the particular transformer, the shunt is adjusted at factory for the applicable Winding Gradient. WTI also has Alarm & Trip Contacts. For Fan Cooled Transformers auxiliary contacts of WTI are used for Fan switching. Repeater OTI & WTI Instruments Repeater OTI & WTI instruments are Optional Fittings and are provided when ordered. They enable readings being taken in control room also. They are generally provided in the RTCC Panel, when it is a part of contact. They are available in one of the following types: a.Simple Analog Repeater b. 4-20mA. d.c. Analog Repeater c. 4-20mA. d.c. Digital Repeater d. 4-20mA. d.c. Digital Repeater plus signal for SCADA They all require the Local Instrument to be provided with a precision potentiometer.

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In cases (b), (c), & (d), they also require Auxiliary Devices like Power Supply Unit, Resistance to Current Converter (RCXT) and/or Current to Current Converter (CCXT) etc. They are housed in a UNIT BOX mount on the transformer. OTI & WTI Instruments Operated By Resistance Temperature Detectors (RTDs) Temperature sensing can alternatively be done by Resistance Temperatures Detectors (RTDs). Thus OTI & WTI can be operated by RTDs. When, so ordered, they are provided accordingly. In this case also Power Supply Unit and RCXT Unit will be required and they are provided in the Unit Box. Thermosyphon Filter: Thermosyphons Thermosyphon Filter is devices which continuously improve the quality of oil in the transformer tank. It is an optional fitting and is provided when ordered. It is a container having perforated trays filled with Activated Alumina. It is fitted to the transformer tank similar to a radiator with provision of isolating valves, air release plug, drain valve etc. Due to the convection current set up in oil, oil flows continuously over the exposed surface of Activated Alumina (i.e. the adsorbent material) and in the process, contaminants like moisture, organic acids etc. generated due to ageing of insulation, get collected in the adsorbent material and thus improve the quality of oil. Periodic recharging of adsorbent material is necessary. Flexible Separator Also known as ‘Diaphragm Conservator’ or ‘Rubber Diaphragm’. It is an optional fitting and is provided when ordered. The ‘Flexible Separator’ is sealed, nonporous flexible bag of a highly resistant fabric, coated externally to resist transformer oil and internally to resist external atmosphere. It is fitted inside the conservator such that variations in oil volume due to variations of temperature are taken up by the Flexible Bag. Oil in conservator is sealed from the outside atmosphere by the mounting flanged to which the Flexible Bag is attached. Thus the atmospheric moisture and gases cannot contaminate the oil inside the conservator. Oil Level Transmitter: When oil in conservator is to be remotely monitored Oil level transmitter is to be provided. It is an optional fitting and is provided when ordered. Transmitter System comprises of: i. Stainless Steel Rod which goes inside the conservator tank. ii. Transducer which gives electrical signal dependent on the oil level. iii. Power Supply/V-I Module which provides 4-20mA signal from the transducer output.

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On Load Tap Changer (OLTC): OLTC is an optional device and is provided when ordered. Tapings are located on High Voltage Winding of the transformer. One type of OLTC is fitted external to transformer main tank . In the other type, contacts mounted on insulated cylinder are immersed in the transformer main tank. In both the types, Drive Mechanism (DM) is contained in a separate box. Different arrangements are used to effect tap changing . They are:

a. Linear: Commonly used arrangement when no of tap positions is moderate. b. Coarse/Fine: By means of a changer over contacts, the Coarse tap winding is

included in or excluded from the circuit. Thus two voltages (i.e. tap positions) are obtained for one position of moveable arm.

c. Reverse/Forward: By Means of a changer-over contact, the taping winding is connected in Forward (Adding) or Reverse (i.e. Subtracting) direction w.r.t. main winding. Thus two voltages (i.e. tap positions) are obtained for one position of movable arm. Arrangement (b) & (c) used when no. of tap positions is large. OLTC is generally operated electrically through a Remote Tap Control Cubicle (RTCC) located in Control Room. A electrical control is also provided in the DM, along with a selector switch for Local or Remote Control. For emergency manual operation, an operating Handle is provided. When Automatic Voltage Regulating (AVR) Relay is ordered and a Voltage Transformer (V.T.) is wired on the transformer output side, the output voltage is compared in the AVR Relay with the settable reference voltage and difference used to give command to OLTC so as to reduce the difference. Thus the output voltage is automatically controlled to the preset value. A Line Drop Compensator (LDC) is included in the AVR when specially ordered R&X of the cable, connecting transformer to load, are to be set by means of adjustable knobs In such a case; voltage at the end of the cable and not a transformer terminals, is controlled. Direction of Power Flow is an important consideration in OLTC. Only some types are suitable for Full Power Flow in –terms of current and no. of operations in the reverse direction. These details are given in the plate fitted to OLTC. Pre-Commissioning Tests Prior to energizing the transformer, several pre-commissioning tests are done. The objective of these tests is to confirm that the transformer has not suffered damage during transit and also to check any inadvertent slips in the factory tests, or supply.

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1.Ratio Test

Ratio between all the three corresponding H.V. & L.V. phases is to be measured on all taps. It is desirable to do this test by a Ratio-meter. But if it is not available, a simple test of measuring voltages can also serve the purpose. Referring to R&D plate, find out which terminals of H.V. & L.V. correspond to one phase e.g. for a vector Group of Dyn-11, H.V. Terminals 1U, 1V & L.V. terminals 2U, 2N correspond to U phase. Apply single phase, 415V or 240V, AC., 50Hz to H.V. side and measure voltage on the L.V. side. Measure this voltage on all taps and note them. Repeat for the other two phases. These observations should indicate a consistent trend of variation in line with the details given in R&D Plates. Numerical values should approximately check with the voltage ratio. 2. Vector Group Check Test: Connect terminals 1U, 2U together. Apply 3-Phase, 415V, 50Hz. AC. To H.V. terminals 1U, 1V, 1W. Measure voltages between terminals 1V-2V, 1V-2W & 1W-2V, 1W-2W (suitable other voltages if required). Check that the measured voltages confirm the relative position of H.V. & L.V. vector group. For vector group DYn-11, the method is illustrated below.

H.V. & L.V. vectors are shown independently positions for DYn-11. For the condition 1U & 2U connected together, L.V. Vectors are redrawn .With this configuration, Voltages 1V-2V & 1V-2W will equal while 1W-2V will be greater than 1W-2W. The method can be extended to any other Vector Group.

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3. Magnetizing Current Test: Apply 415 volts, 2-Phase, AC to the H.V. terminals, keeping the L.V. terminals open and tapping switch in the normal position. Measure the 3 line currents, if possible simultaneously, otherwise one after the other. Because the 3-Phases of the magnetic circuit of the core not similar, the 3 line currents will be approximately equal & V phase current around 80% of either on them. If H.V. is delta connected, V & W phase currents will be approximately equal and U phase current around 110%. In case of Power Transformers, such a test is done, some times, along with routine tests at the manufacturer works. When done at site and results compared with the factory test confirms that there are no transit damages to the core and windings 4. Magnetic Balance Test:

This is simple test to detect shorted turns in a winding. Its principle is that shorted turns oppose establishment of flux in that limb because of the current that circulates through the shorted turns. Apply single phase, 415V or 220V AC to such H.V. line terminals which would energizes U phase (Outer limb). Use an averaging instrument like a Multimeter. Measure the voltage induced in the V phase (Center limb) and W phase (other outer limb). Measure also the current drawn by the energized phase. In case the H.V. voltage is 66KV and above, the current drawn may be very small. In that case L.V. would, generally, be 11KV or more. This test can, then, be carried out on L.V. Side . Center limb being nearer to the energized limb, more flux passes through it and less flux in the outer limb. The division is around 70-30% & hence the measured voltage will be having approx this proportion. Next, energize W phase and measure the other two voltages as before. Results should be similar to previous ones. Then energize V phase (Center limb). As both the outer limbs are symmetrically located w.r.t. center limb, flux will divide equally between them. Hence the voltages measured on outer phases will be approx. equal. Also, for reasons explained earlier, currents drawn when outer phases are excited, will be equal that center phase will be less (approx. 70%). Thus these observation will confirm the healthiness of the windings. In case one of the phase has shorted turns, it will draw a comparatively large current when it is energized. When other phases are energized, flux and hence voltage in the shorted phase will be significantly reduced. Hence all three observations will indicate the shorted phase. When the Magnetic Balance Test indicates a shorted phase, commissioning cannot be undertaken. 5. Measurement of Insulation Resistance: Measure Insulation Resistance (IR) between windings, and between windings and earth with a 2500/1000 V Megger, preferably motor driven, otherwise hand-driven. Before measuring I.R., thoroughly clean all the bushings with clean cotton cloth. If required

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using Carbon Tetrachloride. Also there should be no external connections to the transformer terminals. Check and adjust if required, the infinity setting of the Megger. Lead wires from the Megger to the transformer should run independently and be permanently clamped. They should not have any joints. It is known that IR readings continuous to increase initially and for comparison purpose, reading is to be taken at 1 min of energizing. It is also known that IR value is dependent on temperature. Hence temperature at the time of measurement should be noted. Compare the IR values measured, with the Factory result keeping in view the temperature at the time of measurement. Note Also measure and note the IR values of power the cables. 6. Short-Circuit Test: For the HV side voltage and the % impedance, it would be possible to calculate the current which would flow in the HV side, with 415 V applied to it, while keeping LV side shorted. If the 415 V source can feed that current, a short circuit test can be carried out. This test would confirm proper contact engagement at all tap positions. Apply 3 phase, 415 V, 50 Hz to HV side, keeping LV side shorted. Measure the 3 line current at all tap positions. If the switch is an OFF-CIRCUIT switch, supply has to be disconnected before charging tap. A Consistent trend indicates healthiness. If short-circuit test is not possible due to limitation of source, carry out one tap changing operation over the entire range increasing as well as decreasing. Check the other modes of OLTC operation . 7.Parallel Operation: Sometimes the transformer to be commissioned is required to run in parallel with an existing transformer. In this case, the following condition must be fulfilled by the incoming transformer: 1. Its voltage ratio is same as the existing transformer on all tappings. 2. Its % Impedance is +- 1% of value of existing transformer. Due to difference in % impedance, when one transformer reaches its rated load, the other would share less than its rated load. As a result, the combination can supply load less than the sum of the two KVAs. 3. Rated KVAs of the two transformers to be connected in parallel should not differ by more than 1:3 as otherwise only marginal increase will be obtained in the capacity of the combination. 4. Vector group is compatible. If the vector groups of the two are such that terminals to be paralleled have a phase difference then they cannot be connected in parallel. Hence only certain Vector Groups are compatible with each other. If possible, one should check zero voltage between the corresponding phases to be paralleled.

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3.3.4 Air Circuit Breakers Air circuit breakers are commonly used in electrical distribution systems. A typical air circuit breaker comprises a component for connecting an electrical power source to electrical power consumer called a load. The component is referred to as a main contact assembly. A main contact is typically either opened, interrupting a path for power to travel from the source to the load, or closed, providing a path for power to travel from the source to the load. In a low voltage air circuit breaker, the movable contact is mounted on a contact arm that is pivoted to open the contacts by a spring powered operating mechanism triggered by a trip unit responsive to an overcurrent condition in the protected circuit. In many air circuit breakers, the mechanism for controlling the compression springs comprises a configuration of mechanical linkages between a latching shaft and an actuation device. The actuation device may be manually or electrically operated. An air circuit breaker is divided into a fixed type fixedly installed between power source and a load and a drawer type in which a breaker is movable so as to be separated from power source and a load in order to facilitate maintenance and secure stability. We have Siemens make 3WL Series of air circuit breakers installed in all he LT distribution panels. SENTRON 3WL air circuit breakers offer a very flexible applicability and integrated communication capability. With only three sizes, the SENTRON 3WL air circuit breakers cover a power range from 630 A to 6300 A. Featuring a 3- or 4-pole design, they are suitable for applications up to 1000 V. All models are characterized by identical design – in fixed-mounted as well as withdrawable version – identical operation and identical comprehensive accessories.

Fig. Siemens Air Circuit Breakers

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Applications

• As incoming-feeder, distribution, coupler and outgoing-feeder circuit breaker in electrical systems.

• For the switching and protection of motors, capacitors, generators, transformers,

busbars and cables

• Devices in AC version are available as circuit breaker and non-automatic circuit breaker. Devices in DC version are available as non automatic circuit breaker.

SENTRON 3WL Air Circuit Breakers - Parts

1 Guide frame 2 Main connection front, flange, horizontal, vertical 3 Position signaling switch 4 Grounding contact, leading 5 Shutter

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6 COM15 PROFIBUS module or COM16 MODBUS module 7 External Cubicle Bus modules 8 Closing solenoid, auxiliary release 9 Auxiliary conductor plug-in system 10 Auxiliary switch block 11 Door sealing frame 12 Locking set base plate 13 Transparent panel, function insert 14 EMERGENCY-STOP pushbutton, key operation 15 Motorized operating mechanism 16 Switching cycle counter 17 Breaker status sensor (BSS) 18 Protective device with device carrier, overcurrent release (ETU) 19 Remote reset solenoid 20 Breaker data adapter (BDA) 21 Four-line display 22 Ground-fault protection module 23 Rated current module 24 Measuring function module 25 Circuit breaker 3.4 Carbon Area Substation This is the second main 11 KV substation. This substation provides supply to GAP, Bake Oven, Rodding substations.

Fig. Carbon Substation Distribution Panels

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3.4.1 GAP GAP has got a total of 7 transformers. 3 for GAP machines, 3 for HTM & one for ball mill 6.6 KV Motor. In the LT side, GAP & HTM trafos have 2 LT Incomers & 2 Bus couplers.

GAP Station Transformer (3 Nos)

S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP LV : ---

3 PF Voltage HV :28 KVrms LV : 3 KVrms

4 Taps 7 (OCTC)

5 Cooling ONAN

6 Rating 2000 KVA

7 Voltage HV : 11 KV

LV : 0.433 KV

8 Current HV : 104.97 A

LV : 2665.75 A

9 Phase HV : 3 Phase

LV : 3 Phase

10 Rated Frequency 50 Hz

11 WTI CT 2670/5A, CL-5 20VA

12 Neutral CT 3000/1A, CL-5P10,15VA

13 Serial No. JN 7654/3, JN 7654/2 (tr-2), JN 7654/1 (tr-1)

14 Diag. of Connetion No 3RD 7654/6

15 Core & wdg. Weight 2400 Kgs

16 Weight of oil 930 Kgs

17 oil Quantity 1040 Litres

18 Total Weight 6330 Kgs

19 Year of Mfg 2004

20 Make Voltamp Baroda

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3.4.2 HTM For HTM ,there are 3 HT Incomers in GAP substation & 2 LT Incomers & 2 Buscouplers in LT Substation.

GAP HTM Transformer (3 Nos)

S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP LV : ---

3 PF Voltage HV :28 KVrms LV : 3 KVrms

4 Taps 7 (OCTC)

5 Cooling ONAN

6 Rating 2000 KVA

7 Voltage HV : 11 KV

LV : 0.433 KV

8 Current HV : 104.97 A

LV : 2665.75 A

9 Phase HV : 3 Phase

LV : 3 Phase

10 Rated Frequency 50 Hz

11 WTI CT 2670/5A, CL-5 20VA

12 Neutral CT 3000/1A, CL-5P10,15VA

13 Impedance Voltage 6.34%(T-1),6.32% (T-2),4.31%(T-3)

14 Serial No. JN 7654/4, JN 7654/5 (tr-2), JN 7654/6 (tr-3)

15 Diag. of Connetion No 3RD 7654/6

16 Core & wdg. Weight 2400 Kgs

17 Weight of oil 930 Kgs

18 oil Quantity 1040 Litres

19 Total Weight 6330 Kgs

20 Year of Mfg 2004

21 Make Voltamp Baroda

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3.4.3 Ball Mill This is a 11/6.6 KV Trafo which feeds the ball mill 6.6KV Motor. Both 11KV & 6.6 KV feeders are located in GAP Substation.

GAP Ball mill Transformer (1 No)

S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP LV : 60 KVp

3 PF Voltage HV :28 KVrms LV : 20 KVrms

4 Taps 7 (OCTC)

5 Cooling ONAN

6 Rating 1250 KVA

7 Voltage HV : 11000 V

LV : 6900V

8 Current HV : 65.608 A

LV : 104.592A

9 Phase HV : 3 Phase

LV : 3 Phase

10 Rated Frequency 50 Hz

11 WTI CT 105/5A, CL-5 20VA

12 Neutral CT 75/1A, CL-5P10,15VA

13 Impedance Voltage 5.07%

14 Serial No. JN 7655/1

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Guaranteed max. temp rise Over an ambient of 50oC 40/50oC (oil/Winding)

16 Diag. of Connetion No 3RD 7655/c

17 Core & wdg. Weight 2100 Kgs

18 Weight of oil 780 Kgs

19 oil Quantity 875 Litres

20 Total Weight 4880 Kgs

21 Year of Mfg 2004

22 Customer's Ref.No. 45254000 Dtd 1.03.2004

23 Make Voltamp Baroda

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3.5 Bake Oven Bake Oven has got 2 substations namely Bake Oven-1 Substation & Bake Oven-2 substation.In both Bake Oven-1 & 2 substations, there are 2 HT incomers & 2 LT Incomers with a bus coupler.

Bake Oven Transformer (4 Nos)

S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP LV : ---

3 Make Voltamp, Baroda

4 PF Voltage HV :28 KVp LV :3 KVp

5 Cooling ONAN

6 Rating 2000 KVA

7 No load Voltage HV : 11000 Volts

LV : 433 Volts

8 Current HV : 104.97 A

LV : 2666.75 A

9 Phase HV : 3 Phase

LV : 3 Phase

10 Rated Frequency 50 Hz

11 Neutral CT Core-1 3000/5A, CL-5P10, 20VA

Core-2 3000/1A, CLPS Vk ≥400V at RCT≤10 Ohm,Imag≤30mA at Vk/4

12 WTI CT 2670/5A, CL-5, 20VA

13

Guaranteed max. temp rise Over an ambient of 50oC

40/50oC (oil/Winding)

14 Serial No. JN 7657/4(bo1t1)JN 7657/6(bo1t2), JN 7657/5, JN7657/3

15 Core & wdg. Weight 2400 Kgs

16 Weight of oil 925 Kgs

17 oil Quantity 1035 Litres

18 Total Weight 5925 Kgs

19 Year of Mfg 2004

20 Impedance Voltage 6.11%,6.25%,6.15%,6.09%

21 Customer Ref.No 452544000 Dtd (1.03.2004)

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3.6 Rodding 3.6.1 Rooding Station Trafo Rodding substation is similar to bake oven with 2 HT Incomers , 2 LT incomers & one bus coupler.

Rodding Transformer (2 Nos) S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP LV : ---

3 Make Voltamp, Baroda

4 PF Voltage HV :28 KVp LV :3 KVp

5 Cooling ONAN

6 Rating 2000 KVA

7 No load Voltage HV : 11000 Volts

LV : 433 Volts

8 Current HV : 104.97 A

LV : 2666.75 A

9 Phase HV : 3 Phase

LV : 3 Phase

10 Rated Frequency 50 Hz

11 Neutral CT Core-1 3000/5A, CL-5P10, 20VA

Core-2 3000/1A, CLPS Vk ≥400V at RCT≤10 Ohm,Imag≤30mA at Vk/4

12 WTI CT 2670/5A, CL-5, 20VA

13

Guaranteed max. temp rise Over an ambient of 50oC

40/50oC (oil/Winding)

14 Serial No. JN 7657/2 (T1),JN 7657/1(T2)

15 Core & wdg. Weight 2400 Kgs

16 Weight of oil 925 Kgs

17 oil Quantity 1035 Litres

18 Total Weight 5925 Kgs

19 Year of Mfg 2004

20 Impedance Voltage 6.29%(T-1), 6.20% (T-2)

21 Customer Ref.No 452544000 Dtd (1.03.2004)

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3.6.2 Induction Furnace In addition to Rodding main substation, there is also an induction furnace substation in Rodding. This has got 3 Induction furnace trafos, whose HT is located in GAP substation & LT near Trafo. These trafos are exclusively for the 4 Nos. Of Induction Furnaces.

Rodding Induction Furnace Transformer (3 Nos)

S.No Property Specifications

1 Insulation Level HV : 75 KVP LV : ---

HV : 28 KVrms LV : 3 KVrms

2 Vector Group Dyn11

3 Cooling ONAN

4 Rating 1440 KVA

5 No load Voltage HV : 11000 Volts

LV : 5750 Volts

6 Current HV : 75.5 A

LV : 1445.88 A

7 Phase HV : 3 Phase

LV : 3 Phase

8 Rated Frequency 50 Hz

9 Impedance Voltage 6.56%(T3),6.58%(T2),6.54%(T1)

10 Phase Displacement 30

11 Ref Standard IS 2026

12

Guaranteed max. temp rise Over an ambient of 50oC 35/45oC (oil/Winding)

13 Serial No. 2412(T3),2411 (T2),2413(T1)

14 Core & wdg. Weight 3075 Kgs

15 Weight of oil 1000 Kgs

16 oil Quantity 1125 Litres

17 Total Weight 5800 Kgs

18 Year of Mfg 2004

19 Make Transformers & Rectifiers India ( Ahmedabad)

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3.7 Rectifier Pump House In RPH, the substation has got 2 HT incomers , 2 LT Incomers & one bus coupler on the LT side. The RPH cooling pumps are also installed with Variable Frequency Drives.

RPH Transformer (2 Nos)

S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP LV : ---

3 PF Voltage HV :28 KVrms LV : 3 KVrms

4 Taps 5 (OCTC)

5 Cooling ONAN

6 Rating 1600 KVA

7 Voltage HV : 11 KV

8 LV : 0.413 KV

9 Current HV : 83.98 A

10 LV : 2133.4 A

11 Phase HV : 3 Phase

12 LV : 3 Phase

13 Max. Ambient temp

50oC

14 Max. Temp rise oil/wdg 40/50oC

15 Rated Frequency 50 Hz

16 Impedance Voltage 5.03% (T-1), 5.001% (T-2)

17 Make Voltamp Baroda

18 Sl.No 7653/9, 7653/8

19 Neutral CT 2500/5 A, CL 5P10 20VA

20 Daigram 3RD-7653/a

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3.8 Pot MCC’s There are a total of 4 MCC’s in Pot Room as given below. The substation is similar to RPH substation. This substation provides power supply to DSL,Cranes and other auxiliary equipments of pot room. 3.8.1 MCC11 : Supplies auxiliary power to section 1,2 3.8.2 MCC12 : Supplies auxiliary power to section 3,4 3.8.3 MCC21 : Supplies auxiliary power to section 7,8 3.8.4 MCC22 : Supplies auxiliary power to section 5,6

Pot MCC Transformer (8 Nos)

S.No Property Specifications

1 Vector Group Dyn11

2 Impulse Voltage HV : 75 KVP LV : ---

3 PF Voltage HV :28 KVrms LV : 3 KVrms

4 Taps 5 (OCTC)

5 Cooling ONAN

6 Rating 1600 KVA

7 Voltage HV : 11 KV

8 LV : 0.413 KV

9 Current HV : 83.98 A

10 LV : 2133.4 A

11 Phase HV : 3 Phase

12 LV : 3 Phase

13 Max. Ambient temp

50oC

14 Max. Temp rise oil/wdg 40/50oC

15 Rated Frequency 50 Hz

16 Impedance Voltage 4.85% (11-T-1) , 5.01 % (11-T-2)

17 Make Voltamp Baroda

18 Sl.No 765315 ( Trafo-1 MCC-11), 7653/7 (Trafo-2 MCC-11)

19 Neutral CT 2500/5 A, CL 5P10 20VA

20 Daig 3RD-7653/a

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3.9 FTP There are a total of 4 FTP’s for potroom. FTP Substation ½ Provides supply to both FTP-1 & FTP-2. Similarly FTP substation ¾ provides supply to FTP-3,4. In both FTP’s there 2 HT incomers(11KV), and two 6.6 KV incomers along with a bus coupler. All the FTP HT motors are getting supply from this substation. 3.9.1 Trafos

FTP Transformer (4 Nos)

S.No Property Specifications

1 Vector Group Dd0

2 Impulse Voltage HV : 75 KVP LV : 60 KVP

3 PF Voltage HV :28 KVrms LV :20 KVrms

4 Taps 21 (OLTC)

5 Cooling ONAN ONAF

6 Rating 6000 KVA 7500KVA

7 Voltage HV : 11000 Volts

LV : 6900 Volts

8 Current HV : 314.92 A HV : 393.65 A

LV : 502.04 A LV : 627.55 A

9 Phase HV : 3 Phase

LV : 3 Phase

10 Rated nominal system Voltage

11 KV ± 10 %

11 Rated Insulation Voltage

12 KV

12 Rated Frequency 50 Hz ± 3 %

13 Earthing system Unearthed

14 WTI CT 630/1A, CL-5, 20VA

15 Impedance Voltage 7.8/9.75 (%), 7.67/9.59 , 7.70/9.63 , 7.92/9.9

16 Guaranteed max. temp rise Over an ambient of 50oC 35/45oC (oil/Winding)

17 Serial No. JN 8216/1, JN 8216/2, JN 8216/3, JN 8216/4

90

18 Diagram,. of Connetion No 3RD-8216/0

19 Core & wdg. Weight 10300 Kgs

20 Weight of oil 4865 Kgs

21 oil Quantity 5465 Litres

22 Total Weight 20365 Kgs

23 Transport Wt. 17400 Kgs

24 Year of Mfg 2004

25 Customer Ref.No 915917 3.9.2 HT Motors FTP has a total of 16 nos. of 6.6KV motors installed, 4 in each FTP. These motors are used for running their ID fans.

91

Data sheet for High voltage Squirrel Cage induction motor

ELECTRICAL DESIGN DATA 1 Motor tag no.

2 Voltage (KV) 6.6 +/- 10% Phase 3 Frequency(Hz) 50 HZ+/- %3

3 System Fault level (KA)

350 MVA Symmetrical

4 Method of starting DOL 5 Phase 3 Connection Star No. of terminals

6 Design Ambient temp.(c )

500 C Temp. rise (0 C) 700 C

7 Cable size(mm2)

3C x 185 sq. mm Type XLPE

8 Enclosure type IP55 Cooling CACA 9 Insulation class F Qty. 16 Nos.

Technical particulars from motor manufacturer 10 Manufacturer Alstom Limited, Kolkata 11 KW Rating 575 KW No. of Poles 6 12 Frame designation DC450U1120 Mounting Horizontal Foot ( B3) 13 Full load speed (rpm) 990 rpm Full load Torque (mkg) 568

14 Starting torque as % of full load torque 110 % FLT

15 Full load current(A) 62 Amps.

16 Starting current at 100% Voltage(A) 550 % FLC

17 Break down or pull out torque% 250 % FLT

18 Rotation viewed from coupling end 8 Nos. CW & 8 Nos. CCW

19 Starting time at 80%V : 28 Secs. Starting time at 100%V : 15 Secs.

20

Time (Te) for increased safety motors at 100% Voltage (secs.) Not Applicable

21

Locked rotor with stand time cold/hot at 80% V(sec) : At 100% V ( Sec) : 40 / 30

22 WK2 of motor (kgm2 ) (GD2) 150

23 Power factor at 100% load 0.86

24 Efficiency at 100% load 95.2%

25 Space heater watts/volts 220 Volts, 1 Ph., 50 Hz / 2 x 170 Watts

26 Bearing type /no. DE

Anti-Friction / NU226 + 6226C3 Bearing type /no. NDE

Anti-Friction / NU226

27 Type of Lubrication Grease 28 Weight of motor (kg) 6500 Kg. 39 Canopy Not Required

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3.10 Cast House Cast house substation is similar to RPH substation.

Cast House Transformer (2 No)

S.No Property Specifications

1 Impulse Voltage HV : 75 KVP LV : ---

2 PF Voltage HV :28 KVrms LV :3 KVrms

3 Cooling ONAN

4 Rating 1250 KVA

5 No load Voltage HV : 11000 Volts

LV : 433 Volts

6 Current HV : 65.61 A

LV : 1666.72 A

7 Phase HV : 3 Phase

LV : 3 Phase

8 Rated Frequency 50 Hz

9 Neutral CT 2000/5A, CL-5P10, 20VA

10 WTI CT 1670/5A, CL-5, 20VA

11 Ref ISS 2026

12

Guaranteed max. temp rise Over an ambient of 50oC 40/50oC (oil/Winding)

13 Serial No. JN 7656/5, JN 7656/4

14 Diag. of Connetion No 3RD-7656-1/a

15 Core & wdg. Weight 1900 Kgs

16 Weight of oil 670 Kgs

17 oil Quantity 750 Litres

18 Total Weight 4270 Kgs

19 Year of Mfg 2004

20 Impedance Voltage 4.89%

21 Customer Ref.No 45253961 Dtd (1.03.2004)

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3.11 Wire Rod Mill This substation provides supply to two nos of wire rod mills.

Wire Rod Mill Transformer (2 No)

S.No Property Specifications 1 Vector Group Dyn11

2 Insulation Level HV : 75 AC LV : ---

3 Cooling ONAN

4 Rating 2500 KVA

5 No load Voltage HV : 11000 Volts

LV : 433 Volts

6 Current HV : 131.2 A

LV : 3333.4 A

7 Phase HV : 3 Phase

LV : 3 Phase

8 Rated Frequency 50 Hz

9 WTI CT 3333/1.75A, CL-5, 10VA

10

Guaranteed max. temp rise Over an ambient of 50oC

45/50oC (oil/Winding)

11 Serial No. TWRA-3051 D6826/D6827 (T1)

12 Core & wdg. Weight 2660 Kgs

13 Weight of oil 1140 Kgs

14 oil Quantity 1310 Litres

15 Total Weight 7110Kgs

16 Year of Mfg 2006

17 % Impedance Voltage HV/LV 6.49/6.27(T-1)

18 Customer Ref.No BITCO/06-07/10 Dtd 28.08.06

19 Make Areva T&D India Ltd

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3.12 Pot Overhaul Shop There is one HT & LT incomer in pot overhaul shop. The HT incomer is getting supply from Air Compressor house.

Pot Overhaul Shop Transformer (1 No)

S.No Property Specifications

1 Impulse Voltage HV : 75 KVP LV : ---

2 PF Voltage HV :28 KVrms LV :3 KVrms

3 Cooling ONAN

4 Rating 1250 KVA

5 No load Voltage HV : 11000 Volts

LV : 433 Volts

6 Current HV : 65.61 A

LV : 1666.72 A

7 Phase HV : 3 Phase

LV : 3 Phase

8 Rated Frequency 50 Hz

9 Neutral CT 2000/5A, CL-5P10, 20VA

10 WTI CT 1670/5A, CL-5, 20VA

11 Ref ISS 2026

12

Guaranteed max. temp rise Over an ambient of 50oC 40/50oC (oil/Winding)

13 Serial No. JN 7656/2

14 Diag. of Connetion No 3RD-7656/a

15 Core & wdg. Weight 1900 Kgs

16 Weight of oil 670 Kgs

17 oil Quantity 750 Litres

18 Total Weight 4270 Kgs

19 Year of Mfg 2004

20 Customer Ref.No 45253961 Dtd (1.03.2004)

95

3.13 Plant Illumination System Lighting is an essential service in all the industries. The power consumption by the industrial lighting varies between 2 to 10% of the total power depending on the type of industry. Basic Terms in Lighting System and Features Lamps Lamp is equipment, which produces light. The most commonly used lamps are described briefly as follows: • Incandescent lamps: Incandescent lamps produce light by means of a filament heated to incandescence by the flow of electric current through it. The principal parts of an incandescent lamp, also known as GLS (General Lighting Service) lamp include the filament, the bulb, the fill gas and the cap. • Reflector lamps: Reflector lamps are basically incandescent, provided with a high quality internal mirror, which follows exactly the parabolic shape of the lamp. The reflector is resistant to corrosion, thus making the lamp maintenance free and output efficient. • Gas discharge lamps: The light from a gas discharge lamp is produced by the excitation of gas contained in either a tubular or elliptical outer bulb. The most commonly used discharge lamps are as follows: • Fluorescent tube lamps (FTL) • Compact Fluorescent Lamps (CFL) • Mercury Vapour Lamps • Sodium Vapour Lamps • Metal Halide Lamps Luminaire Luminaire is a device that distributes, filters or transforms the light emitted from one or more lamps. The luminaire includes, all the parts necessary for fixing and protecting the lamps, except the lamps themselves. In some cases, luminaires also include the necessary circuit auxiliaries, together with the means for connecting them to the electric supply. The basic physical principles used in optical luminaire are reflection, absorption, transmission and refraction.

96

Control Gear The gears used in the lighting equipment are as follows: • Ballast: A current limiting device, to counter negative resistance characteristics of any discharge lamps. In case of fluorescent lamps, it aids the initial voltage build-up, required for starting. • Ignitors: These are used for starting high intensity Metal Halide and Sodium vapour lamps. Illuminance This is the quotient of the illuminous flux incident on an element of the surface at a point of surface containing the point, by the area of that element. The lighting level produced by a lighting installation is usually qualified by the illuminance produced on a specified plane. In most cases, this plane is the major plane of the tasks in the interior and is commonly called the working plane. The illuminance provided by an installation affects both the performance of the tasks and the appearance of the space. Lux (lx) This is the illuminance produced by a luminous flux of one lumen, uniformly distributed over a surface area of one square metre. One lux is equal to one lumen per square meter. Luminous Efficacy (lm/W) This is the ratio of luminous flux emitted by a lamp to the power consumed by the lamp. It is a reflection of efficiency of energy conversion from electricity to light form. Colour Rendering Index (RI) Is a measure of the degree to which the colours of surfaces illuminated by a given light source confirm to those of the same surfaces under a reference illuminent; suitable allowance having Figure below shows the various types of lamps available along with their features.

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Table : Various types of lamps with their features

Table below gives the recommended illuminance range for different tasks and activities for chemical sector. Petroleum, Chemical and Petrochemical works Exterior walkways, platforms, stairs and ladders 30–50–100 Exterior pump and valve areas 50–100–150 Pump and compressor houses 100–150–200 Process plant with remote contro l 30–50–100 Process plant requiring occasional manual intervention 50–100–150 Permanently occupied work stations in process plant 150–200–300 Control rooms for process plant 200–300–500 Pharmaceuticals Manufacturer and Fine chemicals manufacturer Pharmaceutical manufacturer Grinding, granulating, mixing, drying, tableting, 300–500–750 sterilising, washing, preparation of solutions, filling, capping, wrapping, hardening Fine chemical manufacturers Exterior walkways, platforms, stairs and ladders 30–50–100 Process plant 50–100–150 Fine chemical finishing 300–500–750 Inspection 300–500–750 Soap manufacture

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General area 200–300–500 Automatic processes 100–200–300 Control panels 200–300–500 Machines 200–300–500 Paint works General 200–300–500 Automatic processes 150–200–300 Control panels 200–300–500 Special batch mixing 500–750–1000 Colour matching 750–100–1500 Plant Street Lighting : Throughout plant II 250W HPSV lamps are used for street lighting. These lights are all controlled through timers for efficient utilization of energy. High pressure sodium vapour (HPSV) lamps offer more efficacy. But the colour rendering property of HPSV is very low. Hence, it is recommended to install HPSV lamps for applications such street lighting, yard lighting, etc where colour rendering index is not critical. There are 9 FPB’s or Feeder Panel Boards in various locations of plant II which provides supply to all lighting loads. They are as shown below : FPB Location FPB-1 Pot Room Substation –MCC-21 FPB-2 Pot Room Substation- MCC 22 FPB-3 Pot Room Substation- MCC-11 FPB-4 Pot Room Substation- MCC-12 FPB-5 Air Compressor Substation FPB-6 Self Use substation FPB-7 GAP Substation FPB-8 Baking Substation FPB-9 Baking Substation

99

5. UILITIES- Air Compressor House & Rectifier Cooling Tower. 5.1 Air Compressors

Air Compressors are used for generation of compressed air required in potroom, alumina handling, cast house & Carbon areas.

Compressors are broadly classified as Positive displacement compressor and Dynamic compressor. Positive displacement Compressors increase the pressure of the gas by reducing the volume. Positive displacement compressors are further classified as :

i. Reciprocating Compressors and ii. Rotary Compressors

. Dynamic compressors increase the air velocity, which is then converted to increased pressure at the outlet. Dynamic compressors are basically centrifugal compressors and are further classified as radial and axial flow types. The flow and pressure requirements of a given application determine the suitability of a particular type of compressor.

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5.1.1 Positive Displacement Compressors

i. Reciprocating Compressors

Reciprocating compressors are the most widely used type for air compression. They are characterized by a flow output that remains nearly constant over a range of discharge pressures. Also, the compressor capacity is directly proportional to the speed. The output, however, is a pulsating one. Reciprocating compressors are available in many configurations, the four most widely used of which are horizontal, vertical, horizontal balance-opposed and tandem. Vertical type reciprocating compressors are used in the capacity range of 50 – 150 cfm. Horizontal balance opposed compressors are used in the capacity range of 200 – 5000 cfm. in multi-stage design and upto 10,000 cfm in single stage designs. Reciprocating compressors are also available in variety of types: • Lubricated and non-lubricated • Single or multiple cylinder • Water or air-cooled. • Single or multi stage In the case of lubricated machines, oil has to be separated from the discharge air. Non-lubricated compressors are especially useful for providing air for instrumentation and for processes which require oil free discharge. However non-lubricated machines have higher specific power consumption (kW/cfm) as compared to lubricated types. Single cylinder machines are generally air-cooled, while multi-cylinder machines are generally water cooled, although multi-stage air-cooled types are available for machines up to 100

101

kW. Water-cooled systems are more energy efficient than air-cooled systems. Two stage machines are used for high pressures and are characterized by lower discharge temperature (140 to 160°C) compared to single-stage machines (205 to 240°C). In some cases, multi-stage machines may have a lower specific power consumption compared to single stage machines operating over the same total pressure differential. Multi-stage machines generally have higher investment costs, particularly for applications with high discharge pressure (above 7 bar) and low capacities (less than 25 cfm). Multi staging has other benefits, such as reduced pressure differential across cylinders, which reduces the load and stress on compressor components such as valves and piston rings. ii Rotary Compressors Rotary compressors have rotors in place of pistons and give a continuous, pulsation free discharge air. They are directly coupled to the prime mover and require lower starting torque as compared to reciprocating machine. They operate at high speed and generally provide higher throughput than reciprocating compressors. Also they require smaller foundations, vibrate less, and have a lower number of parts - which means less failure rate. Among rotary compressor, the Roots blower (also called as lobe compressor) and screw compressors are among the most widely used. The roots blower is essentially a low-pressure blower and is limited to a discharge pressure of 1 bar in single-stage design and up to 2.2 bar in two stage design. The most common rotary air compressor is the single stage helical or spiral lube oil flooded screw air compressor. These compressors consist of two rotors, within a casing where the rotors compress the air internally. There are no valves. These units are basically oil cooled (with air cooled or water cooled oil coolers) where the oil seals the internal clearances. Since the cooling takes place right inside the compressor, the working parts never experience extreme operating temperatures. The oil has to be separated from discharge air. Because of the simple design and few wearing parts, rotary screw air compressors are easy to maintain, to operate and install. The oil free rotary screw air compressor uses specially designed air ends to compress air without oil in the compression chamber producing true oil free air. These compressors are available as air cooled or water cooled types and provide the same flexibility as oil flooded rotary compressors. T here is a wide range of availability in configuration and in pressure and capacity. Dry types deliver oil-free air and are available in sizes up to 20,000 cfm and pressure upto 15 bar. Lubricated types are available in sizes ranging from 100 to 1000 cfm, with discharge pressure up to 10 bar. 5.1.2 Dynamic Compressors Dynamic compressors are mainly centrifugal compressors and operate on similar principles to centrifugal pump. These compressors have appreciably different characteristics as compared to reciprocating machines. A small change in compression ratio produces a marked change in compressor output and efficiency. Centrifugal machines are better suited for applications requiring very high capacities, typically above 12,000 cfm. The centrifugal air compressor depends on transfer of energy from a rotating impeller to the air. The rotor accomplishes this by changing the momentum and pressure of the air. This momentum is converted to useful pressure by slowing the air down in a stationary diffuser. The centrifugal air compressor is an oil free compressor by design. The oil-lubricated running gear is separated from the air by shaft seals and atmospheric

102

vents. The centrifugal is a continuous duty compressor, with few moving parts, and is particularly suited to high volume applications, especially where oil free air is required. A single-stage centrifugal machine can provide the same capacity as a multi-stage reciprocating compressor. Machines with either axial or radial flow impellers are available. Axial flow compressors are suitable for higher compression ratios and are generally more efficient than radial compressors. Axial compressors typically are multi-stage machines, while radial machines are usually single-stage designs. 5.1.3 Capacity of a Compressor

Capacity of a compressor is the full rated volume of flow of gas compressed and delivered at conditions of total temperature, total pressure, and composition prevailing at the compressor inlet. It sometimes means actual flow rate, rather than rated volume of flow. This also termed as Free Air Delivery (FAD) i.e. air at atmospheric conditions at any specific location. Because the altitude, barometer, and temperature may vary at different localities and at different times, it follows that this term does not mean air under identical or standard conditions.

5.1.4 Compressed Air System Components Compressed air systems consist of following major components: Intake air filters, inter-stage coolers, after coolers, air dryers, moisture drain traps, receivers, piping network, filters, regulators and lubricators. • Intake Air Filters: Prevent dust from entering compressor; Dust causes sticking valves, scoured cylinders, excessive wear etc. • Inter-stage Coolers: Reduce the temperature of the air before it enters the next stage to reduce the work of compression and increase efficiency. They are normally water cooled. • After Coolers: The objective is to remove the moisture in the air by reducing the temperature in a water-cooled heat exchanger. • Air-dryers: The remaining traces of moisture after after-cooler are removed using air dryers, as air for instrument and pneumatic equipment has to be relatively free of any moisture. The moisture is removed by using adsorbents like silica gel /activated carbon, or refrigerant dryers, or heat of compression dryers. • Moisture Drain Traps: Moisture drain traps are used for removal of moisture in the compressed air. These traps resemble steam traps. Various types of traps used are manual drain cocks, timer based / automatic drain valves etc. • Receivers: Air receivers are provided as storage and smoothening pulsating air output - reducing pressure variations from the compressor

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Fig. A typical Compressed air system & its components.

Cooling Water Circuit Most of the industrial compressors are water-cooled, wherein the heat of compression is removed by circulating cold water to cylinder heads, inter-coolers and after-coolers. The resulting warm water is cooled in a cooling tower and circulated back to compressors. The compressed air system performance depends upon the effectiveness of inter-coolers, after coolers, which in turn are dependent on cooling water flow and temperature. Further, inadequate cooling water treatment can lead to increase, for example, in total dissolved solids (TDS), which in turn can lead to scale formation in heat exchangers. The scales, not only act as insulators reducing the heat transfer, but also increases the pressure drop in the cooling water pumping system.

Pic. Typical Centac Air Compressor

104

Pic. Front View of Centac Air Compressor

105

106

I. Compressor Air End

• Simple Design - 3 Moving Parts

107

– Rotor assembly each stage – Bullgear

• Efficient Air Flow Passages • Compact Design • Low Pressure drop thru coolers • High Efficiency Separators • Eliminates Compressor Hot Areas

Air End Components

1. Impeller

• 15-5 pH stainless steel • Backward leaning vanes for peak performance • Excellent throttling range for constant pressure control • Polygon attachment for reduced stress concentrations • High pressure capabilities for conservative operations 2. Rotor Assembly • 15 - 5 pH stainless steel • Impeller, pinion shaft, and thrust collar • Reverse threaded rotor bolt • Helical gearing for thrust loading • Components balanced in two plane • Complete assembly balanced as a whole

108

3. Diffuser

• Converts Velocity energy to Pressure energy • 40% of compression work • One piece Stainless Steel

– 2ACII and below – 2CV uses a ring and plate design

• Eliminated Pinned on vanes • Directs flow thru casing

109

4. Air Seal

• Non-contacting carbon ring type - full floating • Unsurpassed seal life • Single piece construction (not complicated or split) • Less than 1% air leakage as compared to other designs which leak 3 - 5% • Guaranteed 100% oil free air under all operation conditions

StagePressure

Diffuser

Inlet Air

AirSeal

Impeller

OilSeal OilSeal

VentToAtmos.

Seal Air Injection (12-15 Psig)

Oil Pressure(Approx. 25 Psig)

Pinion Plain

110

5.Bearing

• Fixed Tilted Pad Oil Film Bearings:

– For radial loads – Hydrodynamic bearing running on film of oil – Long life (2 to 3 times as long as an

antifriction type) – Medium Speed Application – Quiet Operation – Modest Tolerance for Contaminants – Hydrodynamic - Virtually Unlimited Life – Good Load Carrying Capability – No moving parts – Best field diagnostics

Tapered Land/Pocket Type Oil Film Bearing

– For thrust loads – Hydrodynamic bearing on film of oil – Single piece construction requiring no yearly inspection

111

6. Air Cooler

• Air through the tubes, water across the shell • Internally finned tubes for increased surface area • Square pitch design for easy cleaning • Low approach temperatures for peak performance • Low pressure drops for highest efficiency • Multi-pass counter flow for highest cooling efficiency • Integral cooler for most compact design • Low inherit noise level • Lower water flow requirements • Heresite coating available • CuNi cooler tubes available • Low air velocity thru separator 7. Air Cooler External

• Water-in-tube, air-in-shell design external to compressor casing • Complies with ASME, TEMA C, and

API 672

112

• 5/8” O.D., 18 BWG, Admiralty tubes with Aluminum plate fins • 0.002 hr-ft2-°C/Btu water-side fouling design standard • Carbon steel shells, channels and tubesheets • Removable bonnets (on both ends) • Bundles can be rodded in place • Removable tube bundles • Tubes and tubesheets available in

various materials • Aluminium plate fins • Phenolic coating • Larger tube diameters • TEMA “R” or “B” design

II Base Plate & Driver

III Lube Oil system Components

113

Fig. Lubricating System Components & their locations

Reservoir Heater Pump suction Screen

Compresso

HT

M

PS

RESERVOIR HEATER

OIL RESERVOIR DEMISTER

PUMP SUCTION SCREEN

MOP CHECK VALVE

PLOP

PLOP CHECK VALVE

MOP OIL COOLER THERMOSTATIC VALVE

OIL FILTER

SYSTEM PRESSURE ADJUSTMENT VALVE

114

Demisyter MOP Check Valve

115

P LOP

PLOP Check Valve MOP

Oil Cooler Thermostatic Valve

116

Oil Filter Pressure Relief Valve

IV Control Systems

117

CMC Hardware • Base Control Module (BCM) • Operator User Interface (OUI) • Universal Communication Module (UCM) • Service Tool (Lap Top Computer)

5.2 Compressor Cooling Tower CMC Hardware - BCM Standards • Can Link Two BCM’s in a One Panel • Temperature Rating

– Operating: 0 to 70 deg C – Storage: -30 to 80 deg C

• Vibration: MIL Standard 810E • Electrical Interference: 20 volts / m • UL, CSA, and TUV Code Certified CMC Hardware - BCM Features • 23 Analog Inputs • 2 Dedicated Analog Outputs • 16 Digital Inputs • 16 Digital Outputs • Programmable Names

Base Control Module

Digital Inputs

AnalogOutputs

FloatingAnalogInputs

GroundedAnalogInputs

Speed Sensor Current Transformer

Digital(Discrete)Outputs

IRBUS Data Link

24 VoltInput

Power

118

CMC Hardware - OUI Features • 240 x 128 Pixel Graphic Display • 12-Button Keypad • NEMA 4/4X Rated • Ultraviolet (UV) Resistant Overlay • Windows Look and Feel • Password Protected • Sunlight Readable • Dual Language and Units • 16 Event Log

CENTAC Microcontroller

1/2

SETTINGSINFO

MotorCurrent

SystemPressure

PressureSetpoint

105.3

105.0

173.4

Loaded

InletValve

BypassValve

95

0

RemoteLoad Selected

22JUL96 12:00:00

SYSTEM

1/4

SYSTEM SETTINGSINFO

Loaded RemoteLoad Selected

START LOAD UNLOAD

RESET

HORN SILENCE

CONTRAST

LEFT

UP

RIGHT

DOWN

ENTER

STOP

119

CMC Hardware - UCM

• IRBUS Protocol • MODBUS (RS422/485) • Modem Ready • Multiple Cards

Top View

RS232 ActivityIndicator

RS422 ActivityIndicator

RS485 ActivityIndicator

IRBUS Address Switch

Unused Switch (Must be set to 0)

OptionalEquipment

24 VDC PowerRS485

RS485

CENTAC Microcontroller

Base Control Module(BCM) #2

Base Control Module(BCM) #1

Universal CommunicationsModule (UCM)

RS-232

24 Volt Power Supply120/240 VAC

Power

120

V Instrument Systems

Instruments are required for : • Protection • Compressor control • Monitoring • Trending • Troubleshooting

The following are the instruments used in air compressor system • RTD • Pressure transmitters • Vibration transmitters • Pressure and level switches • Gauges

RTD’s

• Resistance Temperature Detector • Monitors temperature:

– Oil supply – Air temperature – Motor stator and bearings

• 4-20 mA output from transmitter • Alarm and Trip values in CMC

Thermocouples

• Used for similar applications as RTD’s • Dissimilar metals joined at measurement point • 4-20 mA output from transmitter • Used in higher temperature applications • Used in special applications

Pressure Transmitters

• Variable capacitance detector • 4-20 mA output from transmitter

121

• Monitors pressure: – Oil supply – Air pressure

• Alarm and Trip values in CMC

Vibration Transmitters

• Used on pinions, bullgears and motors to measure relative movement • Monitors vibration of shafts:

– Y Plain radial position – X Plain radial position – Axial position (Z)

• Alarm and Trip values in CMC Vibration systems

• Tuned system for specific needs • Eddy current vibration probe • Vibration extension cable • Vibration transmitter for CMC • 4-20 mA output from transmitter • Optional vibration proximitor for special applications

Fig. Vibration Probe

122

Switches • Digital signal used for indication • Monitors different applications:

– Seal air pressure – Filter differential pressure(Optional) – Level (condensate or oil) (Optional)

• Digital On/Off signal • Alarm or Trip indication in CMC

Gauges

• Temperature • Pressure • Differential Pressure:

– Oil filter – Inlet filter

• Level for oil reservoir

Fig. Temp Gauges Pressure Gauge VI Control Valves

Fig. Gate Valve

123

Fig. Globe Valve Fig. Butterfly Valve

Fig. Ball valve

VALVE BODY

DISC/BALL/PLUG

SEAT

BONNETT BEARINGS

SHAFT or STEM

124

Valve Types Used

• BUTTERFLY • BALL • GLOBE

• BUTTERFLY • Inlet

• All machines not equipped with IGVs • Swing thru design

• Bypass • Standard on all CI except high pressure, CII above 2ACII except

for high pressure, all CH and X-Flo

• BALL (Segmented) – Bypass Valve – Standard on all CV machines 2CV and smaller – Segmented w/o Q-trim – Segmented w/ Q-trim

VII Water Systems and Condensate Systems Types of removal systems

• Carbon steel traps • Electronic/Solenoid

Operated traps • V-Notch drain valves

125

VIII Air Filters

Function of air filters is to remove particles and contaminants from the air. This is to avoid :

– Corrosion of internal components – Build up – Quality of discharge air

• Remote mtd.

126

• 2 stage filtration process • Uses two elements • 1st element removes particles to

10 microns (cleanable synthetic element) • 2nd element removes particles to

2 microns • Std ANSI flange connections

Fig. Typical Suction Piping

Fig. Bypass Piping

D is c h a rg e d e f le c to r

R o o f l in e

D ra in

A lt . s id e w a ll d is c h a rg e

S ile n c e r

H a n g e r ( ty p )

B y p a s s v a lv e

L o n g ra d iu s e lb o w

M in im u m8 p ip ed ia m e te rs

Inlet filter

Roof line

Work platform

p

p 0.3 psi (2.1 kPa[a])Max

8 ft. (2.4 M) min.

Pipe hangars

Removabletransition piece

Entire pipe to benon-corroding material

Inlet air temp

Long radius elbow

Low point drain

Inlet valve

Minimum of 4pipe diameters

127

Fig. Discharge Piping

5.2 Cooling Towers( Circulating Water Systems) Cooling towers are a very important part of many chemical plants. The primary task of a cooling tower is to reject heat into the atmosphere. They represent a relatively inexpensive and dependable means of removing low-grade heat from cooling water. The make-up water source is used to replenish water lost to evaporation. Hot water from heat exchangers is sent to the cooling tower. The water exits the cooling tower and is sent back to the exchangers or to other units for further cooling. Cooling Tower Types Cooling towers fall into two main categories : Natural draft and Mechanical draft. Natural draft towers use very large concrete chimneys to introduce air through the media. Due to the large size of these towers, they are generally used for water flow rates above 45,000 m3/hr. These types of towers are used only by utility power stations. Mechanical draft towers utilize large fans to force or suck air through circulated water. The water falls downward over fill surfaces, which help increase the contact time between the water and the air - this helps maximise heat transfer between the two. Cooling rates of Mechanical draft towers depend upon their fan diameter and speed of operation.

Located a m inim umof 3 pipe diam etersfrom check valve

Block valve

Pipe hanger

Low point drain

Long radius elbow

M aintenance flange

D ischarge pressure

Discharge tem perature

Safety valve

check valve

CA tap in. To be located a m inimum of 10 pipe diameters from check valve in non-turbulent flow area.

Compressorm ounted

Non-rusting control air line.Connects to control panel at connection marked ‘CA’

128

Mechanical draft towers Mechanical draft towers are available in the following airflow arrangements: 1. Counter flows induced draft. 2. Counter flow forced draft. 3. Cross flow induced draft. In the counter flow induced draft design, hot water enters at the top, while the air is introduced at the bottom and exits at the top. Both forced and induced draft fans are used. In cross flow induced draft towers, the water enters at the top and passes over the fill. The air, however, is introduced at the side either on one side (single-flow tower) or opposite sides (double-flow tower). An induced draft fan draws the air across the wetted fill and expels it through the top of the structure. Mechanical draft towers are available in a large range of capacities. Normal capacities range from approximately 10 tons, 2.5 m3/hr flow to several thousand tons and m3/hr. Towers can be either factory built or field erected - for example concrete towers are only field erected. Many towers are constructed so that they can be grouped together to achieve the desired capacity. Thus, many cooling towers are assemblies of two or more individual cooling towers or "cells." The number of cells they have, e.g., an eight-cell tower, often refers to such towers. Multiple-cell towers can be lineal, square, or round depending upon the shape of the individual cells and whether the air inlets are located on the sides or bottoms of the cells. Components of Cooling Tower The basic components of an evaporative tower are: Frame and casing, fill, cold water basin, drift eliminators, air inlet, louvers, nozzles and fans. Frame and casing: Most towers have structural frames that support the exterior enclosures (casings), motors, fans, and other components. With some smaller designs, such as some glass fiber units, the casing may essentially be the frame.

129

Fill: Most towers employ fills (made of plastic or wood) to facilitate heat transfer by maximizing water and air contact. Fill can either be splash or film type.With splash fill, water falls over successive layers of horizontal splash bars, continuously breaking into smaller droplets, while also wetting the fill surface. Plastic splash fill promotes better heat transfer than the wood splash fill. Film fill consists of thin, closely spaced plastic surfaces over which the water spreads, forming a thin film in contact with the air. These surfaces may be flat, corrugated, honeycombed, or other patterns. The film type of fill is the more efficient and provides same heat transfer in a smaller volume than the splash fill. Cold water basin: The cold water basin, located at or near the bottom of the tower, receives the cooled water that flows down through the tower and fill. The basin usually has a sump or low point for the cold water discharge connection. In many tower designs, the cold water basin is beneath the entire fill.

In some forced draft counter flow design, however, the water at the bottom of the fill is channeled to a perimeter trough that functions as the cold water basin. Propeller fans are mounted beneath the fill to blow the air up through the tower. With this design, the tower is mounted on legs, providing easy access to the fans and their motors.

Drift eliminators: These capture water droplets entrapped in the air stream that otherwise would be lost to the atmosphere.

Air inlet: This is the point of entry for the air entering a tower. The inlet may take up an entire side of a tower–cross flow design– or be located low on the side or the bottom of counter flow designs. Louvers: Generally, cross-flow towers have inlet louvers. The purpose of louvers is to equalize air flow into the fill and retain the water within the tower. Many counter flow tower designs do not require louvers. Nozzles: These provide the water sprays to wet the fill. Uniform water distribution at the top of the fill is essential to achieve proper wetting of the entire fill surface. Nozzles can either be fixed in place and have either round or square spray patterns or can be part of a rotating assembly as found in some circular cross-section towers. Fans: Both axial (propeller type) and centrifugal fans are used in towers. Generally, propeller fans are used in induced draft towers and both propeller and centrifugal fans are found in forced draft towers. Depending upon their size, propeller fans can either be fixed or variable pitch. A fan having non-automatic adjustable pitch blades permits the same fan to be used over a wide range of kW with the fan adjusted to deliver the desired air flow at the lowest power consumption. Automatic variable pitch blades can vary air flow in response to changing load conditions.

130

Tower Materials In the early days of cooling tower manufacture, towers were constructed primarily of wood. Wooden components included the frame, casing, louvers, fill, and often the cold water basin. If the basin was not of wood, it likely was of concrete. Today, tower manufacturers fabricate towers and tower components from a variety of materials. Often several materials are used to enhance corrosion resistance, reduce maintenance, and promote reliability and long service life. Galvanized steel, various grades of stainless steel, glass fiber, and concrete are widely used in tower construction as well as aluminum and various types of plastics for some components. Wood towers are still available, but they have glass fiber rather than wood panels (casing) over the wood framework. The

131

inlet air louvers may be glass fiber, the fill may be plastic, and the cold water basin may be steel. Larger towers sometimes are made of concrete. Many towers–casings and basins–are constructed of galvanized steel or, where a corrosive atmosphere is a problem, stainless steel. Sometimes a galvanized tower has a stainless steel basin. Glass fiber is also widely used for cooling tower casings and basins, giving long life and protection from the harmful effects of many chemicals. Plastics are widely used for fill, including PVC, polypropylene, and other polymers. Treated wood splash fill is still specified for wood towers, but plastic splash fill is also widely used when water conditions mandate the use of splash fill. Film fill, because it offers greater heat transfer efficiency, is the fill of choice for applications where the circulating water is generally free of debris that could plug the fill passageways. Plastics also find wide use as nozzle materials. Many nozzles are being made of PVC, ABS, polypropylene, and glass-filled nylon. Aluminum, glass fiber, and hot-dipped galvanized steel are commonly used fan materials. Centrifugal fans are often fabricated from galvanized steel. Propeller fans are fabricated from galvanized, aluminum, or moulded glass fiber reinforced plastic.

Pumps: S.no Pump Make Capacity

m3/hr Head Sr.no Model RPM coupling

1 Cold well pump#1

Kirloskar 475 40 1.746E+09 UP200/38 1450 290phi-pinbush

Cold well pump#2

Kirloskar 475 40 1.746E+09 UP200/38 1450 290phi-pinbush

Cold well pump#3

Kirloskar 475 40 1.746E+09 UP200/38 1450 290phi-pinbush

Cold well pump#4

Kirloskar 475 40 1.746E+09 UP200/38 1450 290phi-pinbush

2 Hot well pump#1

Kirloskar 475 23 1.746E+09 UP250/30 1450 SW 276

Hot well pump#2

Kirloskar 475 23 1.746E+09 UP250/30 1450 SW 276

Hot well pump#3

Kirloskar 475 23 1.746E+09 UP250/30 1450 SW 276

Hot well pump#4

Kirloskar 475 23 1.746E+09 UP250/30 1450 SW 276

3 Sump pump

132

Motors: S.No

Motor Make Power KW

Volt Sl No Frame size

Model RPM Drive end

bearing

Non drive end

bearing

Max amps

1 Cold well Motor#1

ALSTOM 75 415 2.456E+09

D280S 3 phase SQ Ind

1480

6317 6314 128

Cold well Motor#2

ALSTOM 75 415 2.456E+09

D280S 3 phase SQ Ind

1480

6317 6314 128

Cold well Motor#3

ALSTOM 75 415 2.456E+09

D280S 3 phase SQ Ind

1480

6317 6314 128

Cold well Motor#4

ALSTOM 75 415 2.456E+09

D280S 3 phase SQ Ind

1480

6317 6314 128

2 Hot well Motor#1

ALSTOM 45 415 2.456E+10

D225M 3 phase SQ Ind

1475

6313 6313 78

Hot well Motor#2

ALSTOM 45 415 2.456E+10

D225M 3 phase SQ Ind

1475

6313 6313 78

Hot well Motor#3

ALSTOM 45 415 2.456E+10

D225M 3 phase SQ Ind

1475

6313 6313 78

Hot well Motor#4

ALSTOM 45 415 2.456E+10

D225M 3 phase SQ Ind

1475

6313 6313 78

5.3 Rectifier Cooling Tower

Pumps: S.no Pump Make Capacity m3/hr Head Sr.no Model RPM

1 Cold well pump#1 Kirloskar 750 65 1737904041 SCT200/48 1450 Cold well pump#2 Kirloskar 750 65 1737904040 SCT200/48 1450 Cold well pump#3 Kirloskar 750 65 1737904042 SCT200/48 1450 2 Hot well pump#1 Kirloskar 750 18 1737504008 SCT250/30 1450 Hot well pump#2 Kirloskar 750 18 1737504009 SCT250/30 1450 Hot well pump#3 Kirloskar 750 18 1737504010 SCT250/30 1450 3 Filter feed pump # 1 Kirloskar 200 42 1745804194 UP 100/38 1450 Filter feed pump # 2 Kirloskar 200 42 1745804195 UP 100/38 14504 Sump pump

133

Motors:

S.no Motor Make Power KW

Voltage Sl no Frame size

Model Speed RPM

Max amps

1 Cold well Motor#1

ALSTOM 185 415

D315 L 3 phase SQ

1485 315

Cold well Motor#2

ALSTOM 185 415

24561860010

D315 L 3 phase SQ

1485 315

Cold well Motor#3

ALSTOM 185 415

D315 L 3 phase SQ

1485 315

2 Hot well Motor#1 ALSTOM 55 415

24560180042

D250M 3 phase SQ

1470 96

Hot well Motor#2 ALSTOM 55 415

24560180038

D250M 3 phase SQ

1470 96

Hot well Motor#3 ALSTOM 55 415

24560180040

D250M 3 phase SQ

1470 96

Filter feed pump

motor #1 ALSTOM 37 415

24560160051

D225 F 3 phase SQ

1470 65

Filter feed pump motor #2

ALSTOM 37 415

24560160045

D225 F 3 phase

SQ

1470 65

3 Sump pump motor

4 Cooling tower

motor #1 Paharpur 22 415

180 L 3 phase Ind.

1460 40

Cooling tower motor #2

Paharpur 22 415

180 L 3 phase Ind.

1460 40

Cooling tower motor #3

Paharpur

22 415

180 L 3 phase Ind. 1460 40

5

Softener agitator motor

Siemens 0.75 415 80

3 phase Ind. 1415 1.8

134

5.4 Fire Fighting System The main purpose of Fire fighting system is to provide water for Fire protection which is a statutory requirement.

Fire Pump house Pumps & Motors S.no. Name of Euipment Pump details Motor Details

1 Jockey Pump #4 S.no. 44804542/2 S.no.158114 Make - Mather & Platt Make - ABB Cap. - 10.8 m3/hr Hp / KW - 20 / 15 Head - 88 MWC 2 Jockey Pump #5 S.no.44804542/1 S.no.158113 Make - Mather & Platt Make - ABB Cap. - 10.8 m3/hr Hp / KW - 20 / 15 Head - 88 MWC 3 Jockey Pump #3 S.no.43106515/7 S.no.24567940033 Make - Mather & Platt Make - ABB

135

Cap. - 10.8 m3/hr Hp / KW - 20 / 15 Head - 88 MWC 4 Main Pump #1 S.no.44804541/2 S.no. 155324

Make - Mather & Platt Make - ABB Cap. - 171 m3/hr Hp / KW - 100 / 75 Head - 88 MWC

5 Main Pump #2 S.no.44804541/1 S.no. 155323 Make - Mather & Platt Make - ABB Cap. - 171 m3/hr Hp / KW - 100 / 75 Head - 88 MWC 6 Diesel Pump #1 S.no.44804540/1 S.no.14320450032 Make - Mather & Platt Make - ABB Cap. - 171 m3/hr Hp / KW - 100 / 75 Head - 88 MWC 7 Diesel Pump #2 S.no.13106137/1 S.no.12050650043

Make - Mather & Platt Make - ABB Cap. - 171 m3/hr Hp / KW - 100 / 75 Head - 88 MWC

8 Main Pump #3 S.no.957678/M 1 S.no 24560270029 Make ; Mather & Platt Make - ABB Head - 88 MWC Hp / KW - 110 / 150 Cap. 273 m3/hr

5.5 Perssurising Pump House( Process & Drinking Water system) The main purpose is to provide water for process & domestic consumption.

Pumps: S.no Pump Make Capacity Head Sr.no Model RPM

1 Transfer pump#1

Kirloskar brothers

200 m3/Hr

44 mts

1783104050 CPHM 125/40

1450

2 Transfer pump#2

Kirloskar brothers

201 m3/Hr

45 mts

1783104048 CPHM 125/40

1450

3 Transfer pump#3

Kirloskar brothers

202 m3/Hr

46 mts

1783104043 CPHM 125/40

1450

4 Transfer pump#4

Kirloskar brothers

203 m3/Hr

47 mts

1783104047 CPHM 125/40

1450

5 Sump pump Kirloskar brothers

136

Motors: S.no Motor Make Power

KW Voltage Sr No Frame

size Model Speed

RPM Max amps

1 Transfer pp Motor#1

Alstom 37 415 24560160047 D 225 S 3 phase SQ Ind

1450 65 A

2 Transfer pp Motor#2

Alstom 37 415 24560160048 D 225 S 3 phase SQ Ind

1450 66 A

3 Transfer pp Motor#3

Alstom 37 415 24560160049 D 225 S 3 phase SQ Ind

1450 67 A

4 Transfer pp Motor#4

Alstom 37 415 24560160053 D 225 S 3 phase SQ Ind

1450 68 A