SUMMER TARNING REPORT ON

UTTAR PRADESH POWER

TRANSMISSION CORPORATION

LIMETED

Prepared By: Rajesh Kumar

Roll No. 0829021033

ABES INSTITUTE OF TECHNOLOGY

ACKNOWLEDGEMENT

I am extremely thankful & indebted to the numerous UPPTCL Engineers, who provided vital

information about the functioning of their respective departments thus helping me to gain an

overall idea about the working of organization. I am highly thankful for the support & guidance of

each of them.

I am highly indebted to my project guide, Mr. Rajiv Chaun(A.E.), Mr.Satya Prakash(J.E.), Mr. P.K.

Mishra (A.E.-T&C) for giving me his valuable time and helping me to grasp the various concepts

of switchyard equipments and their control instruments and their testing.

Last but not the least, I would like to thank my parents & all my

fellow trainees who have been a constant source of encouragement & inspiration during my studies

& have always provided me support in every walk of life.

Rajesh Kumar

ABES INSTITUTE OF TECHNOLOGY

CONTENT

What is an Electrical Substation?

Energy growth in UP

Grid map of UP

Introduction: about substation

Overview of substation

Single line digram of substation

Brief description :

Power transformer

Isolators

Circuit breaker

Lightning arrestor

Current transformer

Capacitor voltage transformer

Wave trap

Protective relays

Shunt reactor for bus voltage

Capacitor bank

Clearance at glance

Power line communication & SCADA system

Other definitions

Appendix

References

What is an Electrical Substation

“Electric Power is generated in Power Stations and transmitted to various cities and towns. During

transmissions, there are power (energy) loss and the whole subject of Transmission and

Distribution...

An electrical substation is a subsidiary station of an electricity generation, transmission and

distribution system where voltage is transformed from high to low or the reverse using

transformers. Electric power may flow through several substations between generating plant

and consumer, and may be changed in voltage in several steps. The word substation comes

from the days before the distribution system became a grid. The first substations were

connected to only one power station where the generator was housed, and were subsidiaries

of that power station. Elements of a substation Substations generally have switching,

protection and control equipment and one or more transformers.

In a large substation, circuit breakers are used to interrupt any short-circuits or overload currents

that may occur on the network. Smaller distribution stations may use reclose circuit breakers or

fuses for protection of distribution circuits. Substations do not usually have generators, although a

power plant may have a substation nearby. Other devices such as power factor correction capacitors

and voltage regulators may also be located at a substation.

Substations may be on the surface in fenced enclosures, underground, or located in special- purpose

buildings. High-rise buildings may have several indoor substations. Indoor substations are usually

found in urban areas to reduce the noise from the transformers, for reasons of appearance, or to

protect switchgear from extreme climate or pollution conditions.

Where a substation has a metallic fence, it must be properly grounded (UK: earthed) to protect

people from high voltages that may occur during a fault in the network. Earth faults at a substation

can cause a ground potential rise. Currents flowing in the Earth's surface during a fault can cause

metal objects to have a significantly different voltage than the ground under a person's feet; this

touch potential presents a hazard of electrocution.

Transmission substation:

A transmission substation connects two or more transmission lines. The simplest case is where all

transmission lines have the same voltage. In such cases, the substation contains high-voltage switches that allow lines to be connected or isolated for fault clearance or maintenance. A transmission station may have transformers to convert between two transmission voltages, voltage control devices such as capacitors, reactors or static VAr compensator and equipment

such as phase shifting transformers to control power flow between two adjacent power systems. Transmission substations can range from simple to complex. A small "switching station" may be little more than a bus plus some circuit breakers. The largest transmission substations can cover a

large area (several acres/hectares) with multiple voltage levels, many circuit breakers and a large

amount of protection and control equipment (voltage and current transformers, relays and SCADA systems).

Distribution substation:

A distribution substation in Scarborough, Ontario, Canada disguised as a house, complete with a

driveway, front walk and a mown lawn and shrubs in the front yard. A warning notice can be

clearly seen on the "front door". A distribution substation transfers power from the transmission

system to the distribution system of an area.

It is uneconomical to directly connect electricity consumers to the high-voltage main transmission

network, unless they use large amounts of power, so the distribution station reduces voltage to a

value suitable for local distribution. The input for a distribution substation is typically at least two

transmission or sub transmission lines. Input voltage may be, for example, 115 kV, or whatever is

common in the area. The output is a number of feeders. Distribution voltages are typically medium

voltage, between 2.4 and 33 kV depending on the size of the area served and the practices of the

local utility.

GENERATING SUBSTATION:-

A substation that has a step-up transformer increases the voltage while decreasing the current,

while a step-down transformer decreases the voltage while increasing the current for domestic and

commercial distribution. The word substation comes from the days before the distribution system

became a grid. The first substations were connected to only one power station, where the generators

were housed, and were subsidiaries of that power station.

Early electrical substations required manual switching or adjustment of equipment, and manual

collection of data for load, energy consumption, and abnormal events. As the complexity of

distribution networks grew, it became economically necessary to automate supervision and control

of substations from a centrally attended point, to allow overall coordination in case of emegencies

and to reduce operating costs. Early efforts to remote control substations used dedicated

communication wires, often run along side power circuits.

Energy growth in UP:

Grid map of UP:

Introduction: about substation

400 kv Agra substation is one important substation of UPGCL & UPPTCL. It is one of the largest

power grids in the state of UP and the north India. It is situated at 13 mile stone NH 39( Aligarh

agra Road) The construction of this substation completed during 1994-98 by CGL(Crompten

Grives Limted).The area of this substation is about 66 acre.

The whole substation is divided in Three parts:

1. 400kv switchyard

2. 220kv switchyard

3. 132kv switchyard

For 400kv &220kv, 132kv switchyard a common control room is used Crompton Greaves Limited

(CG), an Indian Multinational with manufacturing bases in 8 countries, have signed the contract on

5th March’2010 with Uttar Pradesh Power Transmission Corporation Ltd for construction of

765/400 kV Substation at Agra, in Uttar Pradesh. The value of contract is Rs 302 Corers . A

765/400 kV substation is the highest grade system voltage for transmission in India. UPPTCL is

first state utility to enter into 765 kV arena. The scope of the project includes Design, Engineering,

Manufacture, Supply, Erection, Testing and Commissioning of 8 Bays of 765 kV & 2 Bays of

400kV, along with 3No. of 315 MVA (Single Phase) 400 kV Power Transformers and 2 No.of 31.5

MVAR .The project is expected to be commissioned in July 2011. The project is of strategic

importance for entry into market of 765 kV Substations global y and widens up the horizon for the

entire product range of CGL

Approximate Cost :- 59 Cr.(OECF) 11.89 Cr.(Taj Trapezium)

9.71 Cr.(Mission Management)

Construction Period :- 4year(OECF)

1 year(TT)

Date of Energisation :- 220 kv switchyard:10 July 1998

:- 400kv switchyard: 3 Nov. 1998

:- 132kv switchyard:16 Jan. 1998

Overview of substation

As we said earlier the whole substation is divided in three parts:132kv site ,400 kv &220kv site.

The civil work is completing by L&T Company. Other part of project Design, Engineering,

Manufacture, Supply, Erection, Testing and Commissioning of Bays wil complete by CGL.

In 400/220kv switchyard following outdoor instrument used:

Two 165MVA 220/132kv autotransformer

Three 315MVA 400/220kv autotransformer

Two 31.5MVAR shunt reactor

15 lighting tower

SF6 circuit breaker

Capacitor voltage transformer(CVT)

Current transformer(CT)

In switchyard one room for mulsi fire system and one for generator system is also present. In 400kv

switchyard fol owing lines are present for incoming and outgoing power:

400 kv Incoming

PGCIL I

PGCIL II

MURAD NAGAR

UNNAO

220kv Outgoing

Agra I

Agra II

Trans Yamuna Nagar

132kv Outgoing

Foundry nagar

Sadabad

Taj

Etmadpur

Shamsabad

One 400kv transfer bus control bus coupler.

Two 100MVA 220/132 KV auto transformer manufactured from BHEL.

Three 315 MVA 400/220 KV auto transformer manufactured from

BHEL,ALSTHOM,SIEMENS

Two 31.5 MVAR shunt reactor manufactured from BHEL.

Circuit breaker from CGL.

Isolators from S&S.

Current transformer by SCT

CVT

Wave trap

Lighting arrester

Surge capacitor

Capacitor Bank

Bus Coupler

Marshalling box

Conservator and Breather

Substation Fuse

Relay

Brief Description

Of all

Outdoor Equipment

Power transformer:

Various types of transformers have been provided at 220& 400 KV Substation from UPPTCL.

Capacity and voltage ratio wise 100 MVA , 315MVA & 160 MVA and 220/132/11 kV. 400/220

kV, These transformers are of TELK, BHEL, ALSTHOM,SIMENCE C & G, Hitachi and Bharat

Bijlee make and have most of the features common except few accessories which may be different.

In this substation al transformers made by BHEL.

These transformers have fol owing main components:

MAIN CORE & WINDING.

BUSHING :-

backelised with paper wound capacitor have been provided. Innermost of the capacitor layer is

electrically connected to the tube and outermost to the mounting flange on insulating body. The

central tube insulating body and mounting flange are oil fil ed assembled. High dielectric Strength

oil is fil ed between central tube and insulating body. Oil level indicators are provided on the

bushing. Condenser type bushings with insulating body and central conducting tube-

(b) 132 kV Medium voltage bushing:

These bushing are also of condenser type and are of similar construction as in the case of 220 kV

bushing in 200 MVA transformers. In 40 & 20 MVA transformers 132 kV bushings are also of oil

fil ed type in which oil is fil ed up when the transformer tank is topped up. Necessary air vent

screws are provided on top of the bushings for release of trapped air at the top of oil fitting.

(c) 66 kV. 33 kV. & 11 kV. Bushings:

These are oil fil ed bushing and simpler in construction.

3. TAP CHANGER:

The transformers have been provided with on load tap changer, which consists of diverter switch

instal ed in an oil compartment separated from transformer oil and the tap selector mounted below

it. The tap changer is attached to the transformer cover by means of tap changer head, which also

serves for connecting the driving shaft and the oil conservator.

4. PROTECTIVE RELAYS:

General y there are two protective buchholz relays, one for main transformer tank and other for tap

changer. In 40MVA GEC transformers oil surge relay has also been provided in tap changer.

5. PRESSURE RELIEF VALVE:

40 MVA GEC make transformers have been provided with pressure relief valve which operates in

case of sudden pressure formation in side the transformer.

6. COOLING SYSTEM :

100 MVA transformers have been provided with cooling bank instal ed on separate

structures. These cooling banks have provided with to groups of fans and 2 nos. pumps. These fans

and pumps automatical y operate, depending upon the settings of winding temperature Indicator.

The fol owing electrical protection have been provided on the transformers :-

Differential Protection

Restricted Earth Fault

Winding temp high

Oil temp high

Pressure relief valve

Oil surge relay

Over current relay

The transformers that are used in Agra substation have following specification:

Specification of 100 MVA 220/132/11 KV 3-Φ auto transformer:

Types of cooling

Rating of H.V. & I.V.(MVA)

Rating of L.V. (MVA)

Line current H.V.(Amps)

ONAN

60

18

157.4

ONAF

80

24

209.9

OFAF

100

30

262.4

Line current I.V. (Amps) 262.4 349.9

437.4

Line current L.V. (Amps) 944.8 1259.7

1574.6

No load voltage H.V. 220kv

No load voltage I.V. 132kv

No load voltage L.V. 11kv

Temp. Rise winding ˚C 55 55

60

Temp. rise oil ˚C 50

Phase 3

Frequency 50Hz

Specification of 315 MVA 400/220 KV 3- Φ auto transformer:

Types of cooling ONAN ONAF

OFAF

Rating of H.V. & I.V.(MVA)

Rating of L.V. (MVA)

Line current H.V.(Amps)

Line current I.V. (Amps)

189

105

272.76

495.96

252

105

363.68

661.28

315

105

454.6

826.6

Line current I.V. (Amps) 262.4 349.9 437.4

Line current L.V. (Amps) 944.8 1259.7 1574.6

No load voltage H.V. 220kv

No load voltage I.V. 132kv

No load voltage L.V. 11kv

Temp. Rise winding ˚C 55 55

ISOLATOR

This type of construction has three insulator stacks per pole. The two one each side is fixed and one

at the center is rotating type. The central insulator stack can swing about its vertical axis through

about 900C. The fixed contacts are provided on the top of each of the insulator stacks on the side.

The contact bar is fixed horizontally on the central insulator stack. In closed position, the contact

shaft connects the two fixed contacts. While opening, the central stack rotates through 900C, an

contact shaft swings horizontal y giving adouble The isolators are mounted on a

galvanized rol ed steel frame. The three poles are interlocked by means of steel shaft. A common

operating mechanism is provided for al the three poles. One pole\ of a triple pole isolator is closed

position.

This type of construction has three insulator stacks per pole. The two one each side is fixed and one

at the center is rotating type. The central insulator stack can swing about its vertical axis through

about 900C. The fixed contacts are provided on the top of each of the insulator stacks on the side.

The contact bar is fixed horizontally on the central insulator stack. In closed position, th contact

shaft connects the two fixed contacts. While opening, the central stack rotates through 900C,

Pantograph isolator:

il ustrates the construction of a typical pantograph isolator. While closing, the linkages of

pantograph are brought nearer by rotating the insulator column. In closed position the upper two

arms of the pantograph close on the overhead station bus bar giving a grip.

The current is carried by the upper bus bar to the lower bus bar through the conducting arms of the

pantograph. While opening, the rotating insulator column is rotated about its axis. Thereby the

pantograph blades break. col apse in vertical plane and vertical isolation is obtained between the

line terminal a

pantograph upper terminal. Pantograph isolators cover less floor area. Each pole can be located at a

suitable point and the

three poles need not be in one line, can be located in a line at desired angle with the bus axis.

Isolator with earth switches (ES):

The instrument current transformer (CT) steps down the current of a circuit to a lower value and is

used in the same types of equipment as a potential transformer. This is done by constructing the

secondary coil consisting of many turns of wire, around the primary coil,

which contains only a few turns of wire. In this manner, measurements of high values of current

can be obtained. A current transformer should always be short-circuited when not connected to an

external load. Because the magnetic circuit of a current transformer is designed for low

magnetizing current when under load, this large increase in magnetizing current wil build up a

large flux in the magnetic circuit and cause the transformer to act as a step-up transformer,

inducing an excessively high voltage in the secondary when under no load.

The main use of using the earth switch (E/S) is to ground the extra voltage which may dangerous

for any of the instrument in the substation.

Circuit breaker:

A circuit breaker is an automatical y-operated electrical switch designed to protect an electrical

circuit from damage caused by overload or short circuit. Its basic function is to detect a fault

condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse,

which operates once and then has to be replaced, a circuit breaker can be reset (either manual y or

automatically) to resume normal operation. Circuit breakers are made in varying sizes, from\ smal

devices that protect an individual household appliance up to large switchgear designed to protect

high voltage circuits feeding an entire city. Once a fault is detected, contacts within the circuit

breaker must open to interrupt the circuit; some mechanically-stored energy (using something such

as springs or compressed air) contained within the breaker is used to separate the contacts, although

some of the energy required may be obtained from the fault current itself. Smal circuit breakers

may be manual y operated; larger units have solenoids to trip the mechanism, and electric motors to

restore energy to the springs.

The circuit breaker contacts must carry the load current without excessive heating, and must als

withstand the heat of the arc produced when interrupting the circuit. Contacts are made of coppe or

copper al oys, silver al oys, and other materials. When a current is interrupted, an arc is generated.

This arc must be contained, cooled, and extinguished in a control ed way, so that the gap between

the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum,

air, insulating gas or oil as the medium in which the arc forms. Different techniques are used to

extinguish the arc including:

Lengthening of the arc

Intensive cooling (in jet chambers)

Division into partial arcs

Zero point quenching (Contacts open at the zero current time crossing of the AC waveform,

effectively breaking no load current at the time of opening. The zero crossing occures a twice the

line frequency i.e. 100 times per second for 50Hz ac and 120 times per second for 60Hz ac )

Connecting capacitors in paral el with contacts in DC circuitsFinally, once the fault condition has

been cleared, the contacts must again be closed to restore power to the interrupted circuit.

Types of circuit breaker:

Many different classifications of circuit breakers can be made, based on their features such as

voltage class, construction type, interrupting type, and structural features. Electrical power

transmission networks are protected and control ed by high-voltage breakers. The definition of high

voltage varies but in power transmission work is usual y thought to be 72.5 kV or higher, according

to a recent definition by the International Electrotechnical Commission(IEC).

High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays

operated through current transformers. In substations the protection relay scheme can be complex,

protecting equipment and busses from various types of overload or ground/earth fault. High-voltage

breakers are broadly classified by the medium used to extinguish the arc.

Bulk oil

Minimum oil

Air blast

Vacuum

SF6

In unnao substation only SF6 circuit breaker is used. The breaker uses SF6 (Sulpher Hexa fluoride)

gas for arc extinction purpose. This gas has excel ent current interrupting and insulating properties,

chemical y, it is one of the most stable compound in the pure state and under normal condition it is

physical y inert, non-flammable, non toxic and odorless and there is no danger te personnel and fire

hazard. It's density is about. 5 times that of air insulating strength is about 2-3 times that of air and

exceeds that of oil at 3 Kg/Cm pressure.

SF6 breaker cal ed as maintenance free breaker, has simple construction with few moving parts:

The fission products created during breaking and not ful y recombined are, either precipitated as

metal ic fluoride or absorbed by a static filter which also absorbs the residual moisture. Since no

gas is exhausted from the breaker and very little compressed air is required for operation, noise

during the operation is also very Jess.

Since SF6 gas is inert and stable at normal temperature, contacts do not settler from oxidization or

other chemical reactions, whereas in air or oil type breakers oxidation of contacts would cause high

temperature rise. SF6 gas circuit breakers, designed to conform to the same standards as air or oil

breakers, but in operation it is possible to get better service even at higher fault levels.

Sulphur hexafluoride gas is prepared by burning coarsely crushed rol sulphur in the fluorine gas, in

a steel box, provided with staggered horizontal shelves, each bearing about 4 kg of sulphur. The

steel box is made gas tight. The gas thus obtained contains other fluorides such as S2F10, SF4 and

must be purified further SF6 gas general y supplier by chemical firms. The cost of gas is low if

During the arcing period SF6 gas is blown axial y along the arc. The gas removes the heat from the

arc by axial convection and radial dissipation. As a result, the arc diameter reduces during the

decreasing mode of the current wave. The diameter becomes smal during the current zero and the

arc is extinguished. Due to its electro negativity, and low arc time constant, the SF6 gas regains its

dielectric strength rapidly after the current zero, the rate of rise of dielectric strength is very high

and the time constant is very smal .

Gas circuit breaker: high voltage side

\

Type 220-SFM-20B

Voltage rating: 220kv

Rated lightening impulse withstand voltage: 1050 kVp

Rated short circuit breaker current: 40 kV

Rated operating pressure: 16.5 kg/ cm2g

First pole to clear factor 1.3

Rated duration of short circuit current is 40 kA for 30 sec.

Rated ling charging breaker breaking current 125 Amp

Rated voltage 245 kV

Rated frequency 50 Hz

Rated normal current 1600 Amp

Rated closing voltage: 220 V dc

Rated opening voltage 220 V dc

Main parts:

(a) Power circuit

(b) Control circuit

Gas circuit breaker: low voltage side

\Type 120-SFM-32A

Voltage rating: 220kv

Rated lightening impulse withstand voltage: 650 kVp

Rated short circuit breaker current: 31.5 kV

Rated operating pressure: 15.5 kg/ cm2g

Lightning arrester:

High Voltage Power System experiences overvoltages that arise due to natural lightning or the

inevitable switching operations. Under these overvoltage conditions, the insulation of the power

system equipment are subjected to electrical stress which may lead to catastrophic failure.

Broadly, three types of overvoltages occur in power systems: (i) temporary over-voltages,(ii)

switching overvoltages and(iii) lightning overvoltages.

The duration of these overvoltages vary in the ranges of microseconds to sec depending upon the

type and nature of overvoltages. Hence, the power system cal s for overvoltage protective devices

to ensure the reliability.

Conventional y, the overvoltage protection is

obtained by the use of lightning / surge arresters .

Under normal operating voltages, the impedance

of lightning arrester, placed in parallel to the

equipment to be protected, is very high and al ow

the equipment to perform its respective function.

Whenever the overvoltage appears across the

terminals, the impedance of the arrester

col apses in such a way that the power system

equipment would not experience the overvoltage.

As soon as the overvoltage disappears, the arrester recovers its impedance back. Thus the

arrester protects the equipment from overvoltages.

The technology of lightning arresters has undergone major transitions during this century. In the

early part of the century, spark gaps were used to suppress these overvoltages. The silicon

carbide gapped arresters replaced the spark gaps in 1930 and reigned supreme til 1970. During

the mid 1970s, zinc oxide (ZnO) gapless arresters, possessing superior protection characteristics,

replaced the silicon carbide gapped arresters. Usage of ZnO arresters have increased the

reliability of power systems many fold.

Current transformer:

Current Transformers (CT’s) are instrument transformers that are used to

supply a reduced value

of current to meters, protective relays, and other instruments. CT’s

provide isolation from the high voltage primary, permit grounding of the

secondary for safety, and step-down the magnitude of the measured

current to a value that can be safely handled by the instruments.

TECHNICAL SPECIFICATION FOR CURRENT TRANSFORMERS

1.0 GENERAL

1.1 This specification covers manufacture, test, & supply of LT Current

transformers ofclass 0.5 accuracy.

1.2 The CTs shal be suitable for metering purpose.

2.0 TYPE:

2.1 The CTs shal be of ring type or window type (bar type or bus-bar

type CT’s shal not be

accepted).

2.2 The secondary leads shal be terminated with Tinned Cooper rose

contact terminals with

arrangements for sealing purposes.

2.3 Polarity (both for primary and second leads) shal be marked.

2.4 The CTs shal be varnished, fiberglass tape insulated or cast resin, air-

cooled type. Only super

enameled electrolytic grade copper wires shal be used.

2.5 The CTs shal conform to IS 2705:Part-I & II/IEC:185 with latest

amendments. Wave Trap

3.0 TECHNICAL DETAILS:

3.1 Technical details shal be as given below:

1. Class of Accuracy 0.5

2. Rated Burden 5.00VA

3. Power Frequency Withstand 3KV

Voltage Current Transformer

4. Highest System Voltage 433V

5. Nominal System Voltage 400V

6. Frequency 50hz

40AT Vk/2 PS

REF

1CT 1U1 500/1

1CT 1V1 1CT

1W1

1CT 2U1 500/1

1CT 2V1

1CT 2W1 1CT 3U1 2000/1 1CT 3V1 1CT3W1

2CT 3U1 2000/1

2CT 3V1 2CT 3W1 3CT 3U1 2000/1

3CT 3V1 3CT 3W1

-

-

-

-

30VA

300

300

600

300

-

40AT Vk/2 PS

40AT Vk/2 PS

30AT Vk/2 PS

40AT Vk/2 PS

- 1.0

5

5

5

5

5

REF

REF

Differenti

al

Spare

Metering

WCT

1U2

198/3.0 1.7VA

-2.5

-

-

5

-

WTT+RT

D

Capacitor voltage transformer:

In high and extra high voltage transmission systems, capacitor voltage transformers (CVTs) are used

to provide potential outputs to metering instruments and protective relays. In addition, when

equipped with carrier accessories, CVTs can be used for power line carrier (PLC) coupling. A

capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra high

voltage signals and provide low voltage signals either for measurement or to operate a protective

relay.

In its most basic form the device consists of three parts: two capacitors across which the voltage

signal is split, an inductive element used to tune the device to the supply frequency and a transformer

used to isolate and further step-down the voltage for the

instrumentation or protective relay. The device has at least four terminals, a high-voltage terminal

for connection to the high voltage signal, a ground terminal and at least one set of secondary

terminals for connection to the instrumentation or protective relay. CVTs are typical y single-phase

devices used for measuring voltages in excess of one hundred kilovolts where the use of voltage

transformers would be uneconomical. In practice the first capacitor, C1, is often replaced by a

stack of capacitors connected in series. This results in a large voltage drop across the stack of

capacitors that replaced the first capacitor and a comparatively smal voltage drop across the

second capacitor, C2, and hence the secondary terminals.

INSULATING SYSTEMS:

The external insulation is provided by the porcelain housing and coordinated with the capacitor

stack, consisting of virtual y identical elements so that the axial voltage distribution from the line

terminal to ground is essential y uniform. The capacitor elements have a mixed dielectric material

consisting of alternating layers of polypropylene film and Kraft paper. The Kraft paper layers serve

as a wicking agent to ensure homogenous synthetic oil impregnation. The electromagnetic unit

(EMU) is housed in an oil-fil ed tank at the base of the capacitor stack. Mineral oil is employed as

the insulating medium instead of air because of its superior insulating and heat transfer properties.

The use of an oil-fil ed base tank removes the need for space heaters in the secondary terminal

box as this area is warmed by heat transfer from the insulating oil. This results in a more reliable

and cost effective design.

INSULATING OIL:

We use insulating oils with excel ent dielectric strength, aging, and gas absorbing properties. The

synthetic oil used for the capacitor units possesses superior gas absorption properties resulting in

exceptional y low partial discharge with high inception/extinction voltage ratings. The oil used for

CAPACITOR STACK:

The capacitor stack is a voltage divider which provides a reduced voltage at the intermediate

voltage bushing for a given voltage applied at the primary terminal. The capacitor stack is a multi-

capacitor-unit assembly. Each unit is housed in an individual insulator. A cast aluminum

cover is on top of the upper capacitor assembly and is fitted with an aluminum terminal. An

adapter for mounting a line trap on top of the CVT can be

1 - Primary terminal

provided with an optional (and removable) HV terminal. 2 - Cast aluminum bellow housing

The capacitor units are mechanical y coupled together by 3 - Stainless steel expansion

bellow means of stainless steel hardware passing through the

4 - Compression spring

5 - Insulated voltage connection

6 - Capacitor elements

7 - Insulator (porcelain or

composite)

8 - Voltage divider tap connection

9 - Cast-epoxy bushing

10 - HF terminal connection

11 - Ferro-resonance suppression

device

12 - Secondary terminals

13 - Oil level sight-glass

14 - Aluminum terminal box

15 - Intermediate transformer

16 - Oil/air block

17 - Oil sampling device

18 - Compensating reactor

19 - Aluminum cover plate

corrosion resistant cast aluminum housing. The mechanical

connection also establishes the electrical connection between

capacitor units. This facilitates field assembly of the CVT

.

1. High Voltage terminal

2. Compensation reactor 3. Intermediate voltage transformer

4. Ground terminal 5. Ferro-resonance suppression

device 6. Damping resistor

7. Carrier (HF) terminal (optional) 8. Overvoltage protective device

9. Secondary terminals 10. Link, to be opened for test

Purposes

;

Wave trap:-

Line trap also is known as Wave trap. What it does is trapping the high frequency communication signals sent on the line from the remote substation and diverting them to the telecom/teleportation panel in the substation control room (through coupling capacito andLMU). This is relevant in Power Line Carrier Communication (PLCC) systems for communication among various substations without dependence on the telecom company network. The signals are primarily teleportation signals and in addition, voice and data communication signals. The Line trap offers high impedance to the high frequency communication signals thus obstructs the flow of these signals in to the substation busbars. If there were not to be there, then signal loss is more and communication wil be ineffective/probably impossible.

Protective relays: Protective relaying is one of the several features of power system design. Every part of the power system is protected. The protective relaying is used to give an alarm or to cause prompt removal of any element of power system from service when hat element behave abnormal y. The relays are compact and self contained devices which can sense abnormal conditions. Whenever abnormal condition occur , the relays contacts get closed. This in turn closes the trip circuit of a circuit breaker. For switchyard protections fol owing type relays are used: 1. Overcurrent relay 2. Earth fault relay 3. REF relay 4. Differential relay 5. Directional relay 6. Over flux relay 7. Buchoolz relay 8. IDMT relay Buchholz relay: In the field of electric power distribution and transmission, a Buchholz relay, also cal ed a gas relay or a sudden pressure relay, is a safety device mounted on some oil-fil ed power transformers and reactors, equipped with an external overhead oil reservoir cal ed a conservator. The Buchholz Relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment. The relay has two different detection modes. On a slow accumulation of gas, due perhaps to slight overload, gas produced by decomposition of insulating oil accumulates in the top of the relay and forces the oil level down. A float switch in the relay is used to initiate an alarm signal that also serves to detect slow oil leaks. If an arc forms, gas accumulation is rapid, and oil flows rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the path of the moving oil. This switch normal y wil operate a circuit breaker to isolate the apparatus before the fault causes additional damage. Buchholz relays have a test port to al ow the accumulated gas to be withdrawn for testing.

IDMT relay: The IDMT relay work on the induction principle, where an aluminum or copper disc rotates between the poles of electromagnet and damping magnet. The fluxes induce eddy current in the disc which interact and produce rotational torque. The disc rotates to a point where it operates a pair of contact that breaks the circuit and removes the fault condition. Shunt reactor for bus voltage: In EHV substations, it is a common practice to use breaker switched bus reactors to maintain the bus voltage within permissible limits under varying load conditions. With the development of

Control ed Shunt Reactor (CSR) which is a thyristor control ed high impedance transformer, a stable bus voltage can be maintained by providing variable reactive power based on the bus voltage deviations due to the load variations. The high impedance transformer which is also known as reactor transformer (RT) can be made to any size without any limitation unlike gapped core shunt reactors. As a single CSR of large capacity can be realized with suitable control mechanism, this approach proves to be technically superior and economical compared to the existing practice of breaker switched bus reactors. A CSR with a detailed control system is modeled along with a typical EHV system in PSCAD/EMTDC environment. The study includes the effectiveness of filters introduced in the tertiary of the reactor transformer in controlling the harmonics generated during partial conduction of thyristors. The transient and steady state performance of the CSR system for varying system conditions is studied and the same is compared with the conventional practice. The paper presents and discusses the results of the study. Keywords: High impedance transformer, shunt reactor, reactive power, compensation, EHV systems, voltage control, thyristors. Shunt reactors which are meant to be used for control ing the bus voltage of sub station are known as bus reactors. These are always connected through a circuit breaker and switched on or off, based on the voltage variations. In large switching substations, it is not uncommon to find multiple bus reactors when the total reactor capacity required is large. Due to limited standard ratings of gapped core shunt reactors, it is necessary to provide in multiples of standard ratings along with associated bay equipment and space for accommodating the same. The CSR mentioned above is based on a high impedance transformer known as Reactor Transformer (RT) with a provision to control from the secondary side through thyristor valves. As RT of any large capacity can be realized as a single three phase unit or three single phase units, it is possible to provide variable reactive power support by control ing the firing angle of the thyristor valves. This continuously variable CSR as bus reactor offers fol owing Advantages. 1. Continuously variable reactive power based on the voltage variation. 2. Fast Response to dynamic conditions like load throw off 3. Reduced losses with optimized reactive power support. 4. Better economy in terms of substation space and auxiliary equipment. Shunt capacitor bank: Shunt capacitor banks are used to improve the quality of the electrical supply and the efficient operation of the power system. Studies show that a flat voltage profile on the system can significantly reduce line losses. Shunt capacitor banks are relatively inexpensive and can be easily instal ed anywhere on the network. Shunt capacitor banks (SCB) are mainly instal ed to provide capacitive reactive compensation/ Power factor correction. The use of SCBs has increased because they are relatively inexpensive, easy and quick to instal and can be deployed virtual y anywhere in the network. Its instal ation has other beneficial effects on the system such as: improvement of the voltage at the load, better voltage regulation (if they were adequately designed), reduction of losses and reduction or postponement of investments in transmission. The main disadvantage of SCB is that its reactive power output is proportional to the square of the voltage and consequently when the voltage is low and the system need them most, they are the least efficient.

\

Various clearances required to be maintained as per Indian Electricity Rules and Code o practice etc.

during construction of a transmission line are given at appropriate places in various chapters.

However, for convenience, the various clearances required to be maintained in the construction of a

transmission line at a glance are given in the fol owing table:

TABLE

SI.

No.

1.

Particulars

Live Metal Clearance

(a) Suspension Towers

(b) Tension towers

Unit

s

mm

mm

Clearance required to be maintained for

132 KV 220 KV

1525(0°- 25° swing) 2130 (0° - 20°)

1075(25° - 45° swing) 1675 (20° -50")

1525 2130

400 KV

2600 (V - string)

2600

2.

3.

4.

5.

6.

7.

8.

9.

10.

Ground Clearance

Mid Span Clearance

Phase to Phase

Clearance

Maximum Shielding

Angle

PowerLine

Crossing Clearance

between Lines

Clearance Between lines

and Tramway Crossing

Clearance from Railway^

Track

Prescribed Corridor for

Forest clearance etc.

Minimum Clearances

from Trees

m

in

mm

30°

m

m

m

m

m

6.1

6.1

3900

30°

3.05 (from other lines

of 11 KV to 132KV)

3.05

14.60

27.60

4.0

7.0

8.5

5130

30°

4.58 (from other

lines of 11 KV to 220 KV)

3.05

15.40

35.00

4.6

8.84

9.0

7000

20°

6.10 (front other lines

of 11-KV to 400KV)

3.05

17.90

52.00

5.5

11. Clearance over Rivers from HFL

(i) Non Navigable River

m

6.1

7.00

8.84

(ii) Navigable River

12. Clearances from Buildings

m To be maintained in relation to tallest mast in consolation with

navigation authorities

Power line communication & SCADA system of UPPTCL:

Uttar Pradesh Power Transmission Corporation Ltd. (UPPTCL) has a very large network of hig

voltage transmission lines in whole UP (about 24,000Km). Transmission lines transfer power from

power houses to substations and from one substation to many other substations or vice versa. Power is

generated at low Voltage (of the order of 3.3KV to 25KV) and is stepped-up to high voltage (765KV,

400KV, 220KV & 132KV) for evacuating power into the grid network through

transmission lines.

Transmission of Data

Figure 1: Transmission of Data from substation/Power house to subLDC

Current Transformers (CTs) and Potential Transformers (PTs), instal ed on transmission lines, provide

inputs to transducers of SIC (Supervisory Interface & Control) & RTU (Remote Terminal Unit) panel.

Circuit breakers & isolators' status are extended up to SIC panel. If for such extension extra potential

free contacts are not available in the Control Panels, Contact Multiplying Relays (CMRs) are used to

provide potential free contacts. The output of RTU is connected to the communication equipment,

through Modem. In between substation & subLDC, a communication link has been shown. Telephone

exchanges are connected with the communication equipment. Such communication links can be of

any type. UPPTCL has got its own three different type of communication systems, i.e. PLCC (Power

Line Carrier Communication), microwave and fibre-

optic. PLCC system is more prevalent in UPPTCL. Modem output at receive side is connected

with the CFE (Communication End Frame). Its output is connected with data takes over. Each

RTU is automatical y pol ed by Server of subLDC to obtain each data of repeats at least once in 10

sec and is stored in the database of subLDC. This data is processed in database formats and is

retrieved for different applications. These formats or graphics are displayed or printed as per

requirement. At subLDC, System Control Officers use this data to monitor and analyze position of

the grid.

.

Below in Figure 2, main equipment from subLDC to SLDC, Lucknow has been shown in a very

simple form.

A systematical y combined/processed data of al RTUs, in server of subLDC, is transmitted t SLDC

Lucknow. This data in the form of 64Kb/s signal is sent through multiple paths/channels.Presently

four channels are used. For this purpose 'Routers' are used. Routers basical y work asmodem but is has

multiple paths for LAN, WAN or internet, etc. In UPPTCL, for transmission of data, from subLDC to

SLDC, only wideband communication system (microwave or fibre-optic links) is being used. In

SLDC, data from al other subLDCs is also received simultaneously and are processed for different

purposes and applications. From Inter-Control Centre Communications Protocol (ICCP) Servers of

SLDC, complete data of al subLDCs is sent to NRLDC, New Delhi through wideband

communication system. This way communication plays a major role in grid management.

Communication for Power System

Fol owing are mainly three inter-related areas of functions in UPPTCL for management of power

system:

A) Telecommunication

B) SCADA- Supervisory Control and Data Acquisition System.

C) EMS- Energy Management System

A) TELECOMMUNICATION

There are three different types of telecommunication systems in UPPTCL i.e.

Microwave Communication System,

Fibre-optic Communication System,

PLCC-Power Line Carrier Communication.

Voice Frequency (VF) channels of al these systems have been integrated/interconnected to make a

hybrid communication system. Microwave & Fibre Optic are multi-channels communication systems

and are also cal ed 'Wideband communication system'. PLCC is single channel

communication system.

SCADA SYSTEM

In SCADA system measured values, i.e. analogue (measured value) data (MW, MVAR, V, Hz

Transformer tap position), and Open/Closed status information, i.e. digital data (Circuit

Breakers/Isolators position i.e. on/off status), are transmitted through telecommunication channels to

respective sub-LDCs. For this purpose Remote Terminal Units (RTUs) at 400KV, 220KV and few

important 132KV sub-stations have been instal ed. System values & status information below 132 KV

have not been picked up for data transmission, except for 33KV Bus isolator position and LV side of

generators. Secondary side of Current Transformers (CT) and Potential Transformer (PT) are

connected with 'Transducers'. The output of transducers is available in dc current form (in the range of

4mA to 20mA). Analogue to digital converter converts this current into binary pulses. Different inputs

are interleaved in a sequential form and are fed into the CPU of the RTU. The output of RTU,

containing information in the form of digital pulses, is sent to subLDC through communication links.

Depending upon the type of communication link, the output of RTU is connected, directly or through

Modem, with the communication equipment. At subLDC end, data received from RTU is fed into the

data servers. In general, a SCADA system consists of a database, displays and supporting

programmes. In UPPTCL, subLDCs use al major functional areas of SCADA except the 'Supervisory

Control/Command' function. The brief overview of majo 'functional areas' of SCADA system is as

below:

1. Communications - Sub-LDC's computer communicates with al RTU stations under its control,

through a communication system. RTU pol ing, message formatting, polynomial checking and

message retransmission on failure are the activities of 'Communications' functional area.

2. Data Processing - After receipt of data through communication system it is processed. Data process

function has three sub-functions i.e. (i) Measurements, (ii) Counters and (ii ) Indications.

'Measurements' retrieved from a RTU are converted to engineering units and linearised, if necessary.

The measurement are then placed in database and are checked against various limits which if

exceeded generate high or low limit alarms. The system has been set-up to col ect 'Counters' at regular

intervals: typical y 5 or 10 minutes. At the end of the hour the units is transferred into appropriate

hour slot in a 24- hour archive/history.

'Indications' are associated with status changes and protection. For those statuses that are not classified

as 'alarms', logs the change on the appropriate printer and also enter it into a cyclic event list. For

those statuses, which are defined as an 'alarms' and the indication goes into alarm, an entry is made

into the appropriate alarm list, as wel as in the event list and an audible alarm is generated in the sub-

LDC.

3. Alarm/Event Logging - The alarm and event logging facilities are used by SCADA data processing

system. Alarms are grouped into different categories and are given different priorities. Quality codes

are assigned to the recently received data for any 'limit violation' and 'status changes'. Alarms are

acknowledged from single line diagram (or alarm lists) on display terminal in LDCs.

4. Manual Entry - There is a provision of manual entry of measured values, counters and indications

for the important sub-station/powerhouse, which are uncovered by an RTU or some problem is going

on in its RTU, equipment, communication path, etc.

5. Averaging of Measured Values - As an option, the SCADA system supports averaging of al

analogue measurements. Typical y, the averaging of measured values over a period of 15 minutes is

stored to provide 24 hours trend.

6. Historical Data Recording (HDR) - The HDR, i.e. 'archive', subsystem maintains a history of

selected system parameters over a period of time. These are sampled at a pre-selected interval and are

placed in historical database. At the end of the day, the data is saved for later analysis and for report

generation.

7. Interactive Database Generation - Facilities have been provided in such a way that an off- line copy

of the SCADA database can be modified al owing the addition of new RTUs, pickup points and

communication channels.

8. Supervisory Control/Remote Command - This function enables the issue of 'remote control'

commands to the sub-station/powerhouse equipment e.g. circuit breaker trip command. Though, there

is provision of this function in this system, yet it is not used in U.P. As such, related/associated

equipment have not been ordered.

9. Fail-over - A 'Fail-over' subsystem is also provided to secure and maintain a database of devices

and their backups. The state of the device is maintained indicating whether it is 'on- line' or 'failed'.

There is a 'backup' system, which maintains database on a backup computer and the system is

duplicated.

SLDC Lucknow has a large and active 'Mimic Board' in its Control room. This mimic board displays

single line diagram of intra State transmission system i.e. grid network of 400KV, 220KV and

important 132KV sub-stations, transmission lines, thermal & hydro powerhouses. Outgoing feeders,

shown in the mimic board, have 'achieve' (LED display) colored indications, of three different colors,

to show the range of power flow at any moment i.e. 'Normal', 'Nominal' or 'Maximum' of its line

capacity. UPPTCL's transmission network is expanding rapidly and thereby number of RTUs is also

increasing. For new substations and lines, displays in active and passive forms are required to be made

in the Mimic diagram. But, Mimic Board has a limitation that it cannot incorporate/add large volume

of displays for substations/power houses/transmission lines in 'active' form due to space constraint and

congestion. Due to this Mimic Board is going to be supplemented with a Video Projection System

(VPS) at SLDC, Lucknow in near future. Also in SLDC & subLDCs, displays of single line diagrams

of RTU sub-stations/power house are viewed on VDUs of large size (21").

Other definitions and terms:

What is OLTC in a transformer:

Onload Tap Changer (OLTC) is used with higher capacity transformers where HT side voltage

variation is frequent and a nearly constant LT is required. OLTC is fitted with the transformer itself.

Multiple tappings from HV windings are brought to the OLTC chamber and conacted to fixed

contacts. Moving contacts rotates with the help of rotating mechanism having a spindle. This spindle

can be rotated manual y as wel as electrically with a motor. Motor is connected in such a way that it

can rotate in both the directions so as to rotate the OLTC contacts in clockwise and anticlock-wise

direction. Two push buttons are fitted on the LCP (local control panel) to rotate the motor and hence

the OLTC contacts in clockwise and anti- clockwise direction. This movement of contacts thus

controls the output LV voltage of the transformer. So rotating of OLTC contacts with spindle or push

buttons in this way is a manuall process. In case this process of rotating the OLTC contacts and hence

control ing the LV side voltage is to be done automatical y then a RTCC (Remote Tap Changer

Control er) is instal ed with the transformer HT Panel. The RTCC sends signals to LCP and LCP in

turn rotates the motor as per the signals received from the the RTCC.

Interposing CT:

Transformer differential relays compare the phase and magnitude of the current entering one winding

of the transformer with that leaving via the other winding(s). Any difference in Phase or magnitude

between the measured quantities wil cause current to flow through the operate winding of the relay. If

this current exceeds the relay setting, tripping of the Transformer circuit breakers wil be initiated. To

enable a comparison to be made, the differential scheme should be arranged so that the relay wil see

rated current when the ful load current flows in the protected circuit. In order to achieve this, the line

current transformers must be matched to the normal ful load current of the transformer. Where this is

not the case it is necessary to use an auxiliary interposing current transformer to Provide amplitude

correction. The connection of the line CTs should compensate for any phase shift arising across the

transformer. Alternatively the necessary phase correction may also be provided by the use of an

interposing CT.

Local backup protection:

The primary objective of back-up protection is to open all sources of generation to an uncleared fault

on the system. To accomplish this objective, an adequate back-up protective system must meet the

following functional requirements:

1. It must recognize the existence of all faults which occur within its prescribed zone of protection.

2. It must detect the failure of the primary protection to clear any fault as planned.

3. In clearing the fault from the system, it must

a. Initiate the tripping of the minimum number of circuit breakers.

b. Operate fast enough (consistent with coordination requirements) to maintain system

stability, prevent excessive equipment damage, and maintain a prescribed degree of service

continuity.

Insulators:

Table for insulators string: Line voltage

132 KV 220KV 400KV

Corona ring:

Single suspension

9 14

Single tension

10 16

Double

suspension 2*9 2*14 2*21

Double tension

2*10 2*16 2*21

A corona ring, also cal ed anti-corona ring, is a toroid of (typical y) conductive material located in

the vicinity of a terminal of a high voltage device. It is electrical y insulated. Stacks of more spaced

rings are often used. The role of the corona ring is to distribute the electric field gradient and lower

its maximum values below the corona threshold, preventing the corona discharge.

Corona rings are typical y instal ed on very high voltage power line insulators. Manufacturers

suggest a corona ring on the line end of the insulator for above 230 kV and on both ends for above

500 kV. Corona rings prolong lifetime of insulator surfaces by suppressing the effects of corona

Discharge

. Appendix

A. Protection diagram .1

C.Terminal on tank cover of transformer