Summer_Training_HTPP-libre (1).pdf

8/11/2019 Summer_Training_HTPP-libre (1).pdf

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Summer Training

REPORTHarduaganj Thermal Power Plant

Uttar Pradesh Rajya Vidyut Utpadan

Nagar Limited (UPRVUNL)

1

st

July 2013 1

st

August 2013

Ali Shazan Gulrez

B-Tech (Electrical) II Year

Aligarh Muslim University

Verified By: Checked By:


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Harduaganj Thermal Power Plant

UNIT 1 to 4 & 6 DeletedUNIT 5 60 MW

UNIT: 7(R&M) 120 MWExtension (UNIT: 8 &9) 2 x 250 MW

Proposed 1 x 660 MW

Harduaganj Thermal Power Plant, Kasimpur


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Contents

S.No Topic Page No.

1 Thermal Power Plant: An Overview 42 Electrical System Layout 53 System Components 5

3.1 Switchyard 53.2 Isolator 63.3 Circuit Breaker 63.4 Generator 73.5 Generator Transformer 7

3.6 Neutral Grounding Transformer 73.7 Station Transformer 73.8 Unit Auxiliary Transformer 83.9 Switchgear 8

3.10 Double Bus System with Transfer Bus 83.11 Bays 93.12 Instrument Transformers 9

4 Electrical Protection System 104.1 Fuse 104.2 Relays 104.3 Circuit Breakers 10

4.4 Lightning Arrestor 104.5 Isolators 105 Generator Protection 11

5.1 Class A Trip 115.2 Class B Trip 115.3 Class C Trip 115.4 Differential Protection 125.5 Earth Fault Protection 125.6 Negative Phase Sequence 125.7 Over Voltage Protection 12

5.8 Backup Impedance 125.9 Reverse Power Protection 13

5.10 Low Forward Power Protection 135.11 Pole Splitting Protection 135.12 Over-Current Protection 135.13 Under Frequency Protection 135.14 Generator Relay Protection Panels 145.15 GRP 8A 145.16 GRP 8B 145.17 GRP 8C 145.18 BCU Panel 14


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6 Transformer Protection 156.1 Buchholz Protection 156.2 PRV Protection 156.3 OSR Protection 156.4 Temperature Protection 157 Ratings 16

7.1 Generator Rating 167.2 Generator Transformer Rating 17

7.3 Station Transformer Rating 177.4 Unit Auxiliary Transformer Rating 18


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(1) Thermal Power Plant: An Overview

In a coal based power plant coal is transported from coal mines to the power plant by

railway in wagons. Coal is unloaded from the wagons to a moving underground

conveyor belt. This coal from the mines is of no uniform size. So it is taken to the

Crusher house and crushed to a size of 20mm. It is then stored in coal bunkers. Raw

coal from the raw coal bunker is supplied to the Coal Mills by a Raw Coal Feeder.

The Coal Mills or pulverizer pulverizes the coal to 200 mesh size. The powdered coal

from the coal mills is carried to the boiler in coal pipes by high pressure hot air. The

pulverized coal air mixture is burnt in the boiler in the combustion zone. The boiler is

a water tube boiler hanging from the top. Water is converted to steam in the boiler

and steam is separated from water in the boiler Drum. The saturated steam from the

boiler drum is taken to the Low Temperature Superheater, Platen Superheater and

Final Superheater respectively for superheating. The superheated steam from the

final superheater is taken to the High Pressure Steam Turbine (HPT). In the HPT thesteam pressure is utilized to rotate the turbine and the resultant is rotational energy.

From the HPT the out coming steam is taken to the Reheater in the boiler to

increase its temperature as the steam becomes wet at the HPT outlet. After

reheating this steam is taken to the Intermediate Pressure Turbine (IPT) and then to

the Low Pressure Turbine (LPT). The outlet of the LPT is sent to the condenser for

condensing back to water by a cooling water system. This condensed water is

collected in the Hotwell and is again sent to the boiler in a closed cycle. The

rotational energy imparted to the turbine by high pressure steam is converted to

electrical energy in the Generator.


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(2) Electrical System Layout

(3) System Components

3.1 Switchyard

A switchyard is essentially a hub for electrical power sources. For instance, a

switchyard will exist at a generating station to coordinate the exchange of

power between the generators and the transmission lines in the area. A

switchyard will also exist when high voltage lines need to be converted to

lower voltage for distribution to consumers.

The function of electrical switch yard is to delivered the generated power from

power plant at desired voltage level to the nearest grid. or In Another way we

can say Simply switching the received power supply from various generatingstations to various locations with respect to their requirement. Therefore a

switchyard will contain; current carrying conductors, grounding wires and


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switches, transformers, disconnects,isolators, remotely controlled arc snuffing

breakers, metering devices, etc.

Switchyard of Harduaganj Thermal Power Plant 220KV/132KV

3.2 Isolator

Isolators are used in electrical substations to allow isolation of apparatus

such ascircuit breakers andtransformers, and transmission lines, formaintenance. Often the isolation switch is not intended for normal control of

the circuit and is used only for isolation.

3.3 Circuit Breakers

A circuit breaker is an automatically operatedelectricalswitch designed to

protect anelectrical circuit from damage caused byoverload orshort circuit.

Its basic function is to detect a fault condition and interrupt current flow. Unlike

afuse,which operates once and then must be replaced, a circuit breaker canbe reset (either manually or automatically) to resume normal operation. Circuit

breakers are made in varying sizes, from small devices that protect an
http://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Overcurrenthttp://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Fuse_(electrical)http://en.wikipedia.org/wiki/Fuse_(electrical)http://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Overcurrenthttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Circuit_breaker


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individual household appliance up to largeswitchgear designed to protect

high-voltage circuits feeding an entire city.

3.4 Generator

The Generator is 250MW, 16.5KV, 10KA hydrogen cooled generator. The

generator operate typically at 3000 rpm. When Generator is in operating

Condition a part of Power delivered is diverted to run the auxiliaries which is

about 8-10% of total power developed. It produces power at 0.85 power

factor.

3.5 Generator Transformer (16.5KV/220KV)

This is a type of Power Transformer of 315 MVA where the LV winding isconnected to the generator through the bus duct and HV winding to the

transmission system. In addition to the features of Power Transformer, our

Generator Transformer is designed to withstand over voltage caused by

sudden load throw off from the generator. It is built as a single or three phase

unit and located in power stations.

3.6 Neutral Grounding Transformer (NGT)

Neutral grounding transformers are used to derive a neutral-to-earthconnection for systems that do not otherwise have one.The transformerprimary terminals (wye side) are connected to the power system, and itsneutral is connected to earth, perhaps through a controlled impedance. Noother load is connected to the delta of the transformer.These transformersprovide a high impedance to normal currents (positive & negative sequence),but allow ground fault currents (zero sequence) to flow, thereby allowingprotective devices to operate if a ground fault occurs.

3.7 Station Transformer

This transformer 220KV/6.6KV 50MVA is used in sub stations to transfer theincoming voltage to the next voltage level. It can be system or autotransformer with two/three windings. In general it is equipped with On load tapchangers and are connected to transmission grids by bushings and cables.The system/auto transformer is built in core form. HV/LV windings aregalvanically separated for system transformer while they are Auto connectedfor auto transformer.
http://en.wikipedia.org/wiki/Switchgearhttp://en.wikipedia.org/wiki/Switchgear


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3.8 Unit Auxiliary Transformer UAT

The Unit Auxiliary Transformer is the Power Transformer that provides power

to the auxiliary equipment of a power generating station during its normal

operation. This transformer is connected directly to the generator out-put by atap-off of the isolated phase bus duct and thus becomes cheapest source of

power to the generating station. It is generally a three-winding transformer i.e.

one primary and two separate secondary windings. Primary winding of UAT is

equal to the main generator voltage rating. The secondary windings can have

same or different voltages. In power plant at Harduaganj it is rated as

16.5KV/6.6KV 31.5MVA.

3.9 Switchgear

In an electric power system, switchgear is the combination of electrical

disconnect switches, fuses or circuit breakers used to control, protect and

isolate electrical equipment. Switchgear is used both to de-energize

equipment to allow work to be done and to clearfaults downstream. This type

of equipment is important because it is directly linked to the reliability of the

electricity supply. It is rated as 6.6KV and 0.4KV switchgear in the Power plant

Switchgear of Harduaganj Thermal Power Plant

3.10 Double Bus System with Transfer Bus

In double bus bar system two identical bus bars are used in such a way that

any outgoing or incoming feeder can be taken from any of the bus.Actually
http://en.wikipedia.org/wiki/Electric_power_systemhttp://en.wikipedia.org/wiki/Fuse_%28electrical%29http://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Fault_%28power_engineering%29http://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Fault_%28power_engineering%29http://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Fuse_%28electrical%29http://en.wikipedia.org/wiki/Electric_power_system


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every feeder is connected to both of the buses in parallel through individual

isolator. By closing any of the isolators one can put the feeder to associated

bus. Both of the buses are energized and total feeders are divided into two

groups, one group is fed from one bus and other from other bus. But any

feeder at any time can be transferred from one bus to other. If necessary thetransfer bus can be energized by main bus power by closing the transfer bus

coupler isolators and then breaker. Then the power in transfer bus can directly

be fed to the feeder line by closing the bypass isolator.

3.11 Bays

In switchyard electrical bays usually consists of Circuit Breakers , earth

switches, Instrument transformers and protection equipments. A substation

comprise of number of bays connected to busbars.

A Bay has following equipments

1. Line isolator with e/s and bus isolator

2. Lightning arrestor

3. Potential transformer

4. Current transformer

5. Circuit Breaker and

6. Carrier communication equipments

The following are the type of Bays1. Incoming feeder bay

2. Outgoing feeder bay and

3. Transformer bay

3.12 Instrument Transformers

Potential Transformer: Potential transformers (PT) (also called voltage

transformers (VT)) are a parallel connected type of instrument transformer.

They are designed to present negligible load to the supply being measured

and have an accurate voltage ratio and phase relationship to enable accurate

secondary connected metering.

Current transformer: A current transformer also isolates the measuring

instruments from what may be very high voltage in the monitored circuit.

Current transformers are commonly used in metering and protective

relays in theelectrical power industry
http://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Electrical_power_industryhttp://en.wikipedia.org/wiki/Electrical_power_industryhttp://en.wikipedia.org/wiki/Electrical_power_industryhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relay


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(4) Electrical Protection System

4.1 Fuse

It is a type of low resistanceresistor that acts as asacrificial device to provide

overcurrent protection, of either the load or source circuit. Its essential

component is a metal wire or strip that melts when too much current flows,

which interrupts thecircuit in which it is connected. Short circuit,overloading,

mismatched loads or device failure are the prime reasons for excessive

current.

4.2 Relays

A relay is anelectrically operatedswitch.Many relays use anelectromagnet to

operate a switching mechanism mechanically, but other operating principles

are also used. Relays are used where it is necessary to control a circuit by a

low-power signal (with complete electrical isolation between control and

controlled circuits), or where several circuits must be controlled by one signal.

The first relays were used in long distance telegraph circuits, repeating the

signal coming in from one circuit and re-transmitting it to another. Relays were

used extensively in telephone exchanges and early computers to perform

logical operations.

4.3 Circuit Breakers

They are used to isolate the faulty circuits, and are capable of carrying these

fault currents until the fault currents are totally cleared. Circuit Breakers are

the main isolating devices and which can be said to directly protect the

system.

4.4 Lightning Arrestor

It is a device used in electric power system to protect the insulation and

conductors from the damaging effect of lightning. It has a high voltage terminal

and a ground terminal.When a lightning surge travels along the line to

arrester, current from the surge is diverted to the earth.

4.5 Isolators

Isolators are used in electrical substations to allow isolation of apparatus such

ascircuit breakers andtransformers,and transmission lines, for maintenance.

Often the isolation switch is not intended for normal control of the circuit and is

used only for isolation
https://en.wikipedia.org/wiki/Resistorhttps://en.wikipedia.org/wiki/Sacrificial_devicehttps://en.wikipedia.org/wiki/Overcurrenthttps://en.wikipedia.org/wiki/Electrical_networkhttps://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Electrichttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Circuit_breakerhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electrichttps://en.wikipedia.org/wiki/Short_circuithttps://en.wikipedia.org/wiki/Electrical_networkhttps://en.wikipedia.org/wiki/Overcurrenthttps://en.wikipedia.org/wiki/Sacrificial_devicehttps://en.wikipedia.org/wiki/Resistor


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(5) Generator Protection

5.1 Class A Trip:

This is applied to those protections which operate for severe electrical faults within

the machine or associated equipments (Generator Differential,Overall

Differential,Stator E/F,GT/UAT REF,Rotor E/F,Back up Impedance or Overcurrentprotection). It is used only in emergencies where continuation in service ,for any

length of time, is not permitted.

5.2 Class B Trip:

This is applied to such of those protections for which electrical isolation of the

generator can be delayed without any significant damage to the machine, in this

mode, the turbine is tripped immediately, but tripping of GT/UAT/Field circuit breakers

is interlocked through a low forward power relay, thereby delaying electrical isolation

until the power output of the generator has been substantially reduced. This avoids

over speeding of generator.

5.3 Class C Trip:

The Turbine-Generator (TG) unit is isolated from the grid by opening the transmission

lines, and allowed to continue service with station load. This is applied to those

protections, which operate for conditions external to the Generators and its

associated equipments. This enables quick restoration by re-synchronizing the

machine with the systems


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5.4 Differential Protection

87GT : GENERATOR+UT+ GT OVERALL PROTECTION

87G : GENERATOR PROTECTION (EXCLUSIVE)

87HV : GENERATOR TRANSFORMER HV WINDING

87UAT: UNIT TRANSFORMER PROTECTION

5.5 Earth Fault Protection

64G2: PROTECTION OF GENERATOR STATOR WINDING

64UAT: UNIT TRANSFORMER LV WINDING E/F PROTECTION

51NGT BACK-UP EARTH FAULT RELAY FOR GT

64G1: 100% PROTECTION OF GENERATOR STATOR WINDING

95G: STATOR PHASE INTER-TURN PROTECTION

5.6 Negative Phase Sequence Protection

Connected on Generator Phase side CTs.

Provided to prevent rotor Over heating in case of Unbalanced loading. Relay has Inverse Current Vs timecharacteristics with two stages

Voltage induced in the rotor at double frequency.

5.7 Over-Voltage Protection

Overvoltage may be caused by the following contingencies:

Defective operation of AVR.

Operation under manual control with AVR out of service.

Sudden loss of load (due to line tripping).

5.8 Backup Impedance Protection

Employed for the protection of the Generator against the uncleared system

line to line faults.

Relay has Reach setting and time delay setting

Relay reach Setting for trip is decided based on System conditions;

Reach should be limited and time to be more than the highest line backup

protection time setting.


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5.9 Reverse Power Protection

This protection acts under the following conditions of operation:

Turbine tripped and reverse power detected for 2 seconds

Reverse Power detected for 15 seconds.

5.10 Low Forward Power Protection

This protection acts under the following conditions of operation:

Turbine tripped and reverse power detected for 2 seconds

Reverse Power detected for 15 seconds.

5.11 Pole Slipping Protection

During system disturbance, Generator rotor oscillates with consequent

variation of Voltage, Current and Power factor. This leads to variation in speed

of rotor from synchronous speed leading to slip of Pole pitch.

Causes:

System Faults(delayed uncleared faults)

Power Swings

Weak field conditions

Effects:

Causes rotor oscillations with cyclic variation in voltage, current,

active/reactive power.

5.12 Over-Current Protection

It is usual to provide overcurrent relays of IDMT pattern to generators as ageneral back up feature. These are in no way related to the thermal

characteristics of the generator and are intended to operate only under fault

conditions.

5.13 Under frequency Protection

Results due to overloading of the generator beyond the corrective limits of

governor. This protection is employed for the system disturbances such as

tripping of multiple units of power stations.


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5.14 Generator Relay Protection Panels

There are 4 nos. of Generator Relay Protection Panel comprising the following

relays having the integrated functions of the Generator Protection.

1. GRP 8A

2. GRP 8B

3. GRP 8C

4. BCU(Bay Control Unit) Panel

5.15 GRP 8A

It comprises the following relays:

Overall Differential relay

GT Overhang Differential Relay Generator Relay- 1(GR-1): It incorporates Generator Back up Impedance

protection,Negative Phase sequence,Overvoltage,Field Failure, Undervoltage,

Low Forward Power,Reverse Power,Stator 95% E/f Protection,

Underfrequency / Overfrequency,Overfluxing,Generator Overload Protection)

5.16 GRP 8B

UAT Differential Relay

GT Overcurrent/Earth Fault Relay Generator Relay -2(GR-2): It incorporates Generator Back up Impedance

protection,Negative Phase sequence,Overvoltage,Pole Slipping,Field

Failure,Undervoltage,Low Forward Power,Reverse Power,100% Stator E/f

,Underfrequency/Overfrequency,Overfluxing,Generator Overload Protection,

Dead Machine Protection,Rotor E/F,Generator Differential Protection

5.17 GRP 8C

UAT Overcurrent/Earth fault Relay

Energy Meter-Main

Energy MeterCheck

5.18 BCU Panel

BCU relays serve the function of controlling the remote operation(opening/closing) of

the isolators in the 220 kV Switchyard.


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(6) Transformer Protection

6.1 Buchholz Protection

A gas operated protection with capability of detecting and warning early about an

incipient fault. Most useful for winding inter turn faults.

6.2 PRV Protection

The relay detects a sudden rise in pressure and it is used to evacuate any over

pressure due to extreme heating, to avoid explosion of the transformer tank.

6.3 OSR Protection

The relay detects the rate of change of pressure

6.4 Temperature Protection

OTI Alarm/Trip : 90/100 deg

WTI Alarm/Trip : 95/105 deg


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(7) Ratings

7.1 Generator Rating:

Stator:

Active Power 250000kW

Power Factor 0.85(lagging)

Volt Ampere 294100kVA

Generated Voltage 16.5kV

Current 10291A

Rotor:

DC voltage 299VCurrent 2497A

R.P.M 3000

Frequency 50

Connection YY

Coolant Hydrogen

Insulation Class F

PM Generator (Pilot Exciter)

Active Power 35kW

Voltage 220V

R.P.M 3000

Coolant Air

Connection YYYY

YYYY

Volt Ampere 35kVA

Current 105A

Phase 3Power Factor 1

Frequency 400

BRUSHLESS EXCITER

Active Power 1350kW

Excitation Voltage 106(DC)

R.P.M 3000

Insulation Class F

Excitation Current 36.5A

Coolant Air


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Voltage 420V

Current 3200A

7.2 Generator Transformer rating:

Type of cooling OFAF

Rated Power HV-315000kVALV-315000kVA

Rated voltage at HV-230kVno load LV-16.5kV

Rated Line current HV-760.72ALV-11022.14A

Maximum temperature Oil-50oCrise Winding-55oC

Phase 3

Frequency 50 Hz

7.3 Station Transformer Rating:

Type of cooling ONAN/ONAF

Rated Power HV - 30000kVA 50000kVALV1-15000kVA 25000kVALV2-15000kVA 25000kVA

Rated voltage at HV -220kV 220kVno load LV1- 6.9kV 6.9kV

LV2- 6.9kV 6.9kV

Rated Line current HV - 78.73A 131.22ALV1-1255.11A 2091.85ALV2-1255.11A 2091.85A


Phase 3

Frequency 50Hz


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7.4 Unit Auxiliary Transformer Rating:

Type of cooling ONAN/ONAF

Rated Power HV - 30000kVA 50000kVALV1-15000kVA 25000kVALV2-15000kVA 25000kVA

Rated voltage at HV -220kV 220kVno load LV1- 6.9kV 6.9kV

LV2- 6.9kV 6.9kV

Rated Line current HV - 78.73A 131.22A

LV1-1255.11A 2091.85ALV2-1255.11A 2091.85A


Phase 3

Frequency 50Hz


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