report bqps ii- saad janjua

Saad Janjua

Internship Report- BQPS II

By

Saad Janjua

Preface

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Bin Qasim Power Plant 2 (BQPS II) is a Combined Cycle Power Plant which houses 3 Gas Turbines and 1 Steam Turbine. The total generation capacity of the plant is 560 MW, where each of the GTs contribute 130.8MW, whereas the ST contributes 190 MW. The plant site boasts an efficiency of 45 percent, and uses Natural Gas procured from SSGC, as its fuel. Harbin Electric, China, was responsible for BQPS II Plant Engineering Procurement and Commission (EPC).

A scaled map of the Plant Site:

ADMINISTRATION

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Administration of the plant site is divided into three main departments. The workings of each department are as follows:

ElectricalElectrical Department deals with, and not limited to the Generators, Transformers, Switchgears, Gas Insulated Substation (GIS), DCS and the PLC System installed at the plant site.

MechanicalAt BQPS II, the maintenance of all sorts of machinery including ST and GT falls under the domain of the Mechanical Department.

Instruments and Control The regulatory control and measurement of the power, gas

and water flow of the plant is basically the domain of I&C

Department at BQPS II. This includes but is not restricted to

PEECC, DCS control, Unit Data Highway (UDH), Plant Data

Highway (PDH) PLCs, and vibration, heat and other Measuring valves and instruments.

Installations at the Plant Site

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NG Compressors and Switchgear:

Three NG Compressors are installed at the plant site, but only 2 are in working order, as only 2 NG Compressors fulfill the demand of the plant site. NG Compressors compress incoming gas at 3Bars to 28 Bars as per requirement of the GTs. The NG switchgear consists of breakers and supply for the motors and pumps present for the efficient operation of NG compressors. NG compressor parameters are all controlled by Allan Bradley PLC. It includes pumps for the circulation of CCCW, ACW, lube oil pumps, filters and the NG compressor starting motor. A UPS is also present to supply power only to the PLCs.

The starting motor of the NG compressor is an MV motor having the rated power 8.5MW and rated current around 850A. The motors contain soft starters to control the starting current and keep it at a low value. The soft starter operates only for 40 seconds and then it is disconnected once the motor attains speed. The compressor rotates at 10000 rpm.

Gas Turbines:

Power Plant at BQPS II comprises of 3 GTs. All of the GTs have been installed adjacent to each other and have the following characteristics:

GE 9E 3 bearing machine GE Mark VI E control

GT Generator:

Type: GE 9A5 TEWAC Specs:

2 poles, 3 phase, 50Hz 163500 KVA / 130.8MW Armature Amps: 6293A

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Armature Volts: 15000V +/-5VAC Field Amps: 969A Field Exciter Volts: 375V Rated Speed: 3000 rpm Direction of Rotation from Exciter end: Clockwise Lagging Power Factor: 0.8 Leading Power Factor: 0.93 Site Elevation: 5m Water Cooled (in 35-out 40) Production at Y Configuration

Generator Excitation System:

EX 2100 Output: 81VDC, 10.3A Brushless

Vibration Measuring Equipment:

Proximity probes Flux Probe Velocity Vibration Probes

Factors affecting GT performance:

Ambient Temperature Fuel Heating Value Humidity

Compressor Protection:

Inlet Guide Vanes Inlet Bleed Valves

GT Auxiliaries

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Power Electrical and Electronic Circuit Centre (PEECC):

Every GT has its own PEECC installed. PEECC is responsible for controlling the auxiliaries associated with the GTs.

Installed Systems in PEECC:

Bentley Nevada vibration Protection Backup DC batteries for auxiliary lube oil motors Ex 2100 GE Mark VI E Normal Incoming (400V) Stand-by Incoming Motor Control Space Heater Control Isolator Transformer Coupling Circuit Breaker Essential Breaking DC Panel Emergency Motor Power Inverter DC Battery Charger

Main and Auxiliary Transformers:

The main transformer for each GTG is rated at 170MVA 15KV/220KV (ONAF). The transformer houses a shell type winding. The transformers are manufactured

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by TBEA, China. CTs and PTs are connected to it for instrumentation and protection purposes.

The electrical protections for the transformers include overcurrent, earth fault, differential protection and winding temperature protection. The mechanical protections included are backhauls relay and pressure relief valve (PRV). Bushings are present for the connections of the transformer.

For the voltage regulation of the transformer there is an ON-LTC (On-Load Tap Changer) attached to the HV side of the transformer. The LTC is always attached to the HV side because the current at the HV side is less it is easier to change the taps. Secondly the HV windings are done over the LV windings on one limb, so it is easier to change turn ratio from the HV windings.

The auxiliary transformer is air cooled and steps down the generated 15kV to 6.6kV to provide power to auxiliaries and unit PCs and common PCs. The rating of the transformer is 30MVA. Three auxiliary transformers 15KV/6.6KV are installed on-site, one for each GT.

GT GE G60 Protection System

GE G60 is the protection system being used for each of the 3 GTs at plant site. For General Electric Generators, rating more than 100 MW, G60 is the standard protection system. At BQPS II, the first parameter of this protection system

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includes a GCB (Generator Circuit Breaker) manufactured by ABB which is controlled by numeric relays for protection of the generator. Numeric relays are microprocessor based relays, programmed according to the desired parameters. Numeric Relays are more reliable and responsive as compared to electromechanical relays. Each GT is installed with many protection parameters such as the ones mentioned below.

Differential Protection:

For a GT, differential protection is used to identify any internal (stator) fault of a generator. There are two CTs connected in the GLAC and GNAC compartments, on each phase, to feed the relay. The relay works on the difference between the two currents. Any difference of current causes the relay to operate. Therefore the relay is programmed to operate on a Differential Current vs Restraining Current curve, which inherently depends on the ratio error and the phase angle error of the CTs. This curve consists of two slopes, one for the internal faults of the generator and the other for any external faults.

Under-voltage Protection:

The Under-voltage protection in a GT, is used to protect the generator when voltage produced falls below a certain value. Under-voltage can be caused when a heavy load is added to the system. When the voltage falls it can damage the machines operating on low voltages, because the current in the generator winding increases. This protection kicks in at 0.9 times the rated voltage (15KV).The Under-voltage fault is detected by a definite time overcurrent relay.

Over-voltage Protection:

Over-voltage protection is triggered when a heavy load is removed from the system or as a result of regulator failure which cause the voltage produced to increase. This causes the internal flux of the generator to increase, which results in

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core heat up, and produces core losses. The setting for overvoltage protection is around 1.1 times the rated value.

Over-frequency Protection:

Over-frequency protection is triggered when a heavy load is removed from the system. This removal causes the internal flux of the generator, and the produced voltage value to drop. The alarm triggering value for Over-frequency protection is 52.5Hz.

Under-frequency Protection:

Under-frequency condition can be triggered when a heavy load is added to the system. It can cause the internal flux of the generator to increase, as a result of which, the core may heat up and core losses might increase. Generally, the Under-frequency and Over-frequency protections are collectively called abnormal frequency protection.

Volts/Hz relay:

This is a backup protection for the abnormal voltage and frequency protections. If somehow, they fail to operate, Volts/Hz relay can operate and trip the breaker.

Phase Unbalance:

Phase unbalance protection may be triggered when unequal loads are connected to each phase. This can cause the production of negative sequence currents in the armature windings. As a result, the frequency of the generator may be disturbed, thus phase unbalance protection should be tripped.

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Reverse Power Protection:

It is important that when the turbine output is very low and it starts drawing power from the system and starts acting as a motor, it should be tripped. This phenomenon of generator acting as a motor is known as motoring. It acts as an induction motor. This phenomenon can also be caused when the generator is energized at low speeds. For protection against reverse power, reverse power relays are used.

Reverse power relay will operate whenever the generator is tripped or turned off. The setting for the reverse power relay for low forward power is 0.05% of the rated power which is operated by the relay 32L (NEMA code). The setting for low reverse power is -0.08% of the rated power which is operated by the relay 32R.

Over-Excitation Protection:

When current in the field winding is increased the excitation increases beyond limit. It causes the flux to increase and the core to heat up and increase the core losses. Maximum excitation limit system is used to control the excitation and keep it under limit. This protection can also be triggered by loss of potential transformer signal to voltage regulator.

Loss of Excitation:

When there is a loss of excitation in the field windings, Reactive Power is absorbed from the system to make up for less excitation. As a result of that, major system shutdown may occur. Loss of synchronism can also occur, thus causing damage to the generator. As there is a sudden and significant change in the reactive power consumption, this fault may be detected by loss of excitation relay.

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Black Start Condition:

When the plant site completely shuts down in case of emergency, with no gas supply, and a ‘dead’ national grid, the following black start conditions apply.

1 Emergency Diesel Generator of 1.2MW for emergency loads such as Lube Oil Motor for ST

800Ah battery Bank for ST and plant auxiliaries

Heat Recovery Steam Generator (HRSG)

3 horizontal HRSGs have been installed at the plant site, one for each GT. The function of HRSG is to recover the heat of the GTG exhaust gas. HRSG utilizes this heat to convert the input DeMin water into steam, which in turn rotates the steam Turbine. The HRSG system contains two HP feed pumps (6.6KV). One of the two pumps is the main pump and the other is standby. These are the pumps which take hot water from condenser, and pump it into HP drums. Two LP feed pumps and two lube oil pumps are also present which have redundancy too. These motors are three phase LV motors. A diverter damper skid connects the GT exhaust gas system to HRSG. Diverter Damper is hydraulically controlled. A sealing fan is used to seal the GT exhaust gas flow into either direction. HRSG

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Boiler being used is of CICI # 703, manufactured in China. The steam collected from all HRSGs is then collectively sent to the ST.

The Steam Turbine and Generator

The steam turbine facility is installed behind the CCR. It includes the ST and its generator.

ST Generator:

Power Rating: 190MW Rated Voltage: 25.75 KV Rated Current: 8000A Hydrogen Cooled

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Rotation Speed: 3000 rpm

STG Cooling:

The auxiliary system for the generators include hydrogen cooling, water cooling, seal oil system and lube oil system. A generator has mainly four important parts, stator core, stator winding, rotor core and rotor winding. The stator winding is cooled by the demineralized water produced in the water treatment plant. It has the conductivity of almost 0.125S/cm. The cooling of rotor core, rotor winding and stator core is done by Hydrogen gas coming from the hydrogen plant. The hydrogen gas is present between the rotor and the stator winding.

It is important that the bearings of the generators have proper lubrication and for that purpose, lube oil is used which is circulated by pumps. A sealing oil system is also maintained to trap the hydrogen gas in the generator. The pressure of oil is greater than the pressure of hydrogen to keep it inside. There are four CCCW hydrogen coolers for the cooling of hydrogen too.

Excitation System:

The exciter for the steam turbine generator is UNITROL-5000 and it provides the rated current of 1100A and a rated voltage of 230V. The static exciter consists of a generator as well as thyristor banks. An FCB (Field Circuit Breaker) is used to trip the circuit for excitation. The excitation transformer is a 2500kVA transformer and provides AC to thyristor banks. This AC voltage is then converted to DC. A control mechanism is used which is to control the magnitude of field current. On gaining load, a voltage drop occurs, as a result of which, additional current is needed for the exciter to produce more terminal voltage. This is the reason why thyristors and not diodes are used to control the average voltage and current.

Protection Systems for STG:

The protection system for ST generator is similar to that of GT generator. ABB protection system, RET-650 and/or REG-650 for transformers and generators

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respectively. The exciter has a crowbar circuit for protection too. It trips when fault occurs in the stator. It grounds all the flux present on the body of the rotor so that the generator doesn’t act like a motor.

EH Pressure Low Trip Lube Oil Pressure Low Trip Condenser Value Low Trip Over speed of TSI Trip Axial Displacement Trip Rotor Vibration Trip Turbine Differential Expansion Trip Generator Fault Trip HP Casing Temperature Differential Trip Over Speed of DEH Trip Loss of Power DEH Trip Exhaust Temperature High Trip Manual Trip Bearing Temperature and Return Oil Trip

Maintenance

Power Systems at BQPS II, like any other plant, require constant monitoring and maintenance. Maintenance forms a significant portion of the daily chores of the on-site workforce. Mentioned below are the basics of maintenance practice used at BQPS II.

Plant Maintenance Types:

Preventive MaintenanceThis type of maintenance takes place at scheduled intervals.

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Corrective MaintenanceThis type of maintenance is undertaken after an error occurs at the plant site. This is also known as Breakdown maintenance.Causes:

Errors in Synchronizing Under/Over frequency operation Lightning surges Faults i.e. short circuits Single phase or out of phase operation Unbalanced load Overload Over/Under voltage Loss of field

Predictive MaintenanceThe engineering staff plans predictive maintenance by using measurement tools to get an early diagnosis of a possible error in the system.

Operating Maintenance

CoolersAccumulation of sludge may start to vary difference in input/output cooling water temps. Continually decreasing efficiency indicates that cleaning needs to be done.

Air Filters:Dirty air filters raise working temp of machine, also accumulate dirty air. Examine filters once a week to avoid physical damage.

Shaft Grounding Brush:

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Check shaft to ground voltage atleast once a week. Brushes must not be allowed to wear beyond a certain limit.

Excitation:Normally exciter components require little or no maintenance. Equipment should be kept dry and clean.

Inspection of Generator Parts

Armature Core:Should be inspected for hot spots or damaged punchings. The inside of a generator should be checked for evidence of oil which indicates oil leakage past the oil detectors.

Armature Windings:Checked for leakage oil and over-heating.

Water Usage at Plant Site

Water Intake Facility:

Water Intake facility includes basic filtering of seawater and pumping it to the rest of the plant. The electrical pumping of water takes place through certain LV and MV motors. At the sea water intake, there are two ACW (Auxiliary Cooling Water) pumps and three STCW (Steam Turbine Cooling Water) which are all MV pumps. The ACW pumps are rated at 670kW each, whereas the STCW pumps are rated at 2.5MW pumps each. The STCW Pumps carry the cooling water to condensers. These pumps have journal bearing to take care of the radial movement

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and thrust bearings to take of the axial movement. These pumps also have inbuilt lube oil system and cooling system for lubrication and cooling.

Sodium Hypochlorite (NaOCl) Manufacturing Plant:

Sodium Hypochlorite is by its nature, an antimicrobial agent, which suppresses/kills microbial growth. NaOCl is produced by the process of electrolysis. In this plant, water is passed electrolyzed in six different electrolysis chambers. In each chamber, water is electrocuted at 55KA, 24V to produce NaOCl. Transformers are used to step down 6.6KV to 235V. This voltage is then converted to 23V DC using thyristor banks (water cooled) in the Rectifier Chamber. NaOCl is added to all the water which is pumped from the water intake facility to inhibit the growth of organic matter, which might later block the water ducts being used for cooling or other purposes.

Water Treatment Plant:

Water Treatment Plant is an integral part of the CCPP. It produces Demineralized (DeMin) Water which has two essential functions; Firstly, being converted to steam to drive Steam Turbine, and secondly as cooling water for NG Compressor lube oil and the ST Generator Stator Windings. Sea water has a conductivity of 55-60K micro Siemens, and a turbidity of 35NTU, whereas, DeMin water has a requirements of conductivity less than 10 micro Siemens, and turbidity less than 0.1 NTU. Question arises as to how this significant change in water’s properties is brought about. Shown below is a schematic of the process involved in making demineralized water from sea water.

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Installed Switchgear at BQPS II

6.6kV Switchgear:

The 6.6kV switchgear is placed in the CCR building. It controls the supply for all the MV motors. It contains 3 bus bars which can be coupled using bus couplers.

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The supply comes from UAT (Unit Auxiliary Transformer) through three buses. It supplies power to various areas of the plant as mentioned below. The circuit breakers used are VCBs (Vacuum Circuit Breakers), manufactured by Schneider.

6.6KV Loads:

Black Start Diesel Generator 2 VFDs (Hiconics) 12 Transformers (6.6KV/400V) 27 motors NaOCl Plant Transformers (6.6KV/235V)

400V Switchgear and ATS:

The 400V switchgear is also known as the common PC which contains the transformers which step down 6.6kV coming from the UAT to 400V. It contains the supply system and breakers for all the LV motors and other auxiliaries which are operated at this voltage. This switchgear is present in the CCR so the feedback from all the breakers goes to the CCR and is remotely operated. There are two 400KV bus bars which are also coupled together.

ATS (Auto Transfer Switch) is a system incorporated at the plant site which provides support for LV and MV supply. In case of any tripping, the ATS distributes load on other online transformers evenly ATS panels are present in the net relay room in CCR. TS is an integral feature of the plant and any improper operation of the ATS can result into problems in the auxiliaries present on the plant site.

Gas Insulated System (GIS)

The GIS houses Bus bars and extend for a length of 1 km from the GIS. An underground cable (XLPE) is used to carry the supply from the transformers to the GIS. The bus bar scheme used for carrying the supply for transmission is single bus double breaker type. This scheme is economical as well as reliable as compared to single bus single breaker scheme. It includes breakers, isolators, earth

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switches, CTs and PTs which are all gas insulated. The gas used for insulation is SF6 which is a common practice at 220kV systems.

The advantage of using SF6 over vacuum is that it reduces the size of the substation and less space is needed for isolation of equipment. The incoming lines in the GIS are from the transformers of GT and ST transformers. The outgoing lines are KCR-I, KCR-II, Short Line 1 and Short Line 2. The short lines are the lines which are coupled the plant BQPS-1. A bus coupler is used for switching from one bus to the other whenever needed.

The GIS also includes a control room and also houses the protection systems. The protection system present in the control room sends signal to the protection system

of the GIS control room and as a result of that communication takes place between both the systems. This is how the line breaker is going to be tripped. The only breaker for the ST generator is the line breaker which should trip in any fault situation. A DC system is present to supply power to the control system. Wattmeters are also present to calculate the energy utilized.

Map of GT connected to the Bus Bar at GIS.

Central Control Room (CCR)

Central Control Room houses all the HMI. It centralizes all the communication on the plant site. The

CCR has 8 display panels which display all the numbers (data) from every corner of the plant,

(DCS) and provides read and control options all under one roof. All the alarms that generate in the

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machinery installed at the plant show at CCR. CCR also coordinates all the work permits and

tagging system for maintenance related work at the plant. 6.6KV switchgear is also housed in the

building where CCR is present.

THE END

report bqps ii- saad janjua

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