generator operation and protection

7/13/2019 Generator Operation and Protection

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GENERATOR OPERATION, PROTECTION

& PROTECTION SYSTEMIOCL, PARADIP REFINERY


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Topics covered

Generator details

Checks during normal operation

Different capability curves of generator

Control & Monitoring Architecture

Overview of Generation & Distribution busControl philosophy of GIS

Brief about DAVR

Overview of Generator & Generator Transformer

ProtectionProtection chart of Generator & Generator Transformer

WHY & HOW of each type of protection

Generator CO2 system


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GENERATOR MODULES

Air Cooled Turbogenerator : TARIHydrogen Cooled Turbogenerator : THRI

Hydrogen/Water Cooled TG : THDF

MODULE NOMENCLATURE (EXAMPLE)

TARI 108/46 Paradip Refinery : TARI 1080-36P for GTGTHRI 108/44 TARI 800-20P for STG

THDF 115/59

MW CAPACITY RANGE OF TURBOGENERATOR

Air Cooled Turbogenerator : 80MW 240MWHydrogen Cooled Turbogenerator : 100MW 350MW

Hydrogen and Water Cooled Turbogenerator : 450MW 1000MW

GENERATOR DETAILS


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PARAMETERS OPERATION VALUES ALARMS

Stator teeth temp. 50-100 deg. C 120 deg.C

Generator winding temp. 50-100 deg. C 120 deg. C

Stator core temp.

50-100 deg. C

120 deg. C

Cold air temp. < 55 deg. C

Hot air temp.


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PARAMETER OPERATING VALUE ALARM TRIP

Bearing vib < 10 mm/sec 12.5 mm/sec. 25 mm/sec (peak)

Bearing temp < 85 deg. C 100 deg. C 120 deg. C

Load Limits : As per the capability curve

Rate of loading : Permissible rate of loading depends on the condition of the winding

Insulation

Space Heater : when generator is not running space heater should be ON

Monitoring:

a) Temperature monitoring of components (through temp scanner)

b) Generator hot air temp

c) Shaft grounding brushd) Rotor vibration

e) Fuse of brushless exciter with the help of stroboscope

Generator IR value : Min. IR value = (KV rating +1) M Ohm @ 40 deg C with 5 KV IR tester

Action required if IR value is less than min : Identification of low IR section , if found in winding

drying out to be adopted.

CHECKS ON GENERATOR DURING NORMAL OPERATION :


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PERMISSIBLE SYNCHRONISING CRITERIA


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PMG

Main Exciter

Rotor winding

Rectifier Wheel

Ring for rotor earth

fault

EXCITER ROTOR


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BRUSHLESS EXCITATION SYSTEM


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ECS panel

in CPP

C/R

I/O

panel

SCAP

Toshiba GIS

I/O

panel

ECS panelsin GIS

building

Operator

work

station

EEP panel

Control & Monitoring Architecture

FOcable


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66KV BUS 1

66KV GIS SLD CPP Generation Bus & S/S-303 Distribution Bus

66KV BUS 3

66KV BUS 4

11 /66 KV

10 MVA

(ONAN)

YnYn0,Z=12%

66KV BUS 2

To Transformers at downstream distribution sub-stations

X

118.3 MW

GTG 1 GTG 2

X

X

X

11 /69 KV

148/118 MVA

(ONAF/ONAN)

OCTC

YNd11,Z=14.8%

STG 2

X

X

STG 1

X

X

GTG 3

X

X X

X

X

X

3150 A 40 KA ,1 SEC 3150 A

11 /69 KV

37.5 MVA

(ONAN)

OCTC

YNd11,Z=11.2%

118.3 MW 118.3 MW 30 MW 30 MW

BS 1

BS 2

X

x xx

66KV BUS 2X X

x

x66KV BUS 1

SS 303 GIS -66kV,3150 A,40kA for 3 sec3150 A 3150 A

X X X X XX X XX

O

/

gF

D

R

O

/

g

F

D

R

O

/

g

F

D

R

O

/

g

F

D

R

O

/

g

F

D

R

O

/

g

F

D

R

O

/

g

F

D

R

O

/

gF

D

R

O

/g

F

D

R

O

/

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F

D

R

Generation Bus

Distribution Bus

X

x

BC 1

X

x

BC 2


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GIS control philosophy

Synchronisation facility is provided to generators, sectionalisers, bus couplers and Tie-

transformer breakers

Synchronisation can be performed from SCAP as well as ECS in Auto as well as in manual

mode.

SCAP /ECS/OFF selection switch provided on SCAP

All breakers can be controlled from SCAP as well as ECS with Remote in LCC

All isolators can be controlled from SCAP as well ECS with Remote in LCC

All earthing switch can be controlled from LCC only with Local selection in LCC

All breakers can be controlled from LCC in maintenance mode (line & breaker side earthswitch connected) with Local selection in LCC

All isolators can be controlled from LCC with Local selection in LCC


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A section of 66kV TOSHIBA GIS Generation Sub-Stations Bays Local Control Panels


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CPP Synchronisation Control & Annunciation Panel (SCAP)


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Block Diagram of DAVR with Dual Auto (inbuilt Manual) Channels & Dual PLC


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21G,27G,32G,37G,40G,46G,50GDM,51G,59G,60G,64G(95%),64G(100%),64F,78G,81G,87G & 99GT

Y

G

x

P345 P345

P127

P633

P633

P141

P127

66 Kv GIS Bus

87GT

51GT/ 64RGT

870A/ 51NGT

P345

51VG 51VG

3 nos VTs for AVR Ch1, Ch2,

Met & Prot

To rotor E/F protection

GENERATOR & GENERATOR TRANSFORMER PROTECTION OVERVIEW

66/11 KV transformer


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Integrated Numerical generator protection relay

Areva Make Model P345 (two independent relay GR1 & GR2)

Protection code Description21G: Generator backup impedance protection

27G: Under voltage protection

32G: Reverse power protection

37G: Low forward power protection

40G: Field failure protection46G: Negative sequence current protection

50GDM: Dead machine protection

51G: Definite time overload protection

59G: Overvoltage protection

60G: Voltage balance relay (fuse failure)

64G(95%): Stator earth fault protection(95% winding)64G(100%): Stator earth fault protection(100% winding)

64F: Rotor earth fault protection

78G: Out of step(pole slipping) protection

81G: Under/Over frequency protection

87G: Differential protection

99GT: Gen & Gen Transformer Overfluxing protection

PROTECTION RELAYS


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Protection Relay Protection

Code

Description of protection

Areva Make P127 Numerical

protection relay(two

independent relay)

51VG Generator voltage restrained over

current protection


protection relay

51GT/64RGT Generator Transformer HV side over

current & restricted earth fault

protectionAreva Make P633 Numerical

protection relay (1strelay)

870A/51NGT

Overall differential & Generator

transformer backup earth fault

protection


protection relay (2nd

relay)

87GT Generator Transformer differential

protection

Areva Make VAEM21 relay 64F1A 1strotor earth fault relay

Areva Make CAEM33 relay 64F2 2ndrotor earth fault relay

PROTECTION RELAYS


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Important Accessories for

protection relays

Code Description of code

Areva Make P931 RGR2 low frequency square wave generator

for rotor E/F

Areva Make PR5104 REP Repeater for rotor E/F protection signal

Siemens Make 7XT3300 G20Hz 20Hz generator for 100% stator E/F

Siemens Make 7XT3400 FGR2 Band pass filter with built in voltage

divider for 100% stator E/F protection

PROTECTION RELAYS

OVERVIEW OF GENERATOR PROTECTION


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OVERVIEW OF GENERATOR PROTECTION


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GENERATOR PROTECTION

Electrical protection provided - To quickly detect & initiate shut down for

major electrical faults associated with the generating plant.Abnormalelectrical conditions arise as a result of some failure with the generatingplant itself,but can also be externally imposed on the generator. Commoncategories of faults and abnormal conditions to be detected are:

1. Internal Faults

Phase and /or ground faults in the stator and associated protection zone

Ground faults in the rotor (field winding)

2. Abnormal Operating Conditions.

a. Loss of field.

b. Overload.

c. Overvoltage.

d. Under and over frequency

e. Unbalanced Operation e.g. single phasing.

f. Loss motoring i.e. loss of prime mover.

g. Loss of synchronization (out of step).

h. Subsynchronous oscillation.


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GENERATOR DIFFERENTIAL (87G)

WHY

For protection of the stator windings against internal faults- to detect stator

winding multi phase and earth faults . Normally involves high fault current ,

so fast clearing required.

HOW Based on the principle of circulating currents. The difference of two currents

of the two sets of CTs (one set on the neutral side & other set on line side of

generator) flow through the relay.

Operates only with in the protected zone for internal faults.

Stability to be ensured for stability against out of zone fault



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VOLTAGE DEPENDENT OVERCURRENT (51VG)

WHY

A fault close to the generator will result in a fault current decrement since

the armature reaction of the generator significantly reduces the fault current.

Provides back up protection for uncleared downstream faults with time

delay.

HOW

Voltage restrained over current relay. When voltage is low, relay will operate

on low current


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STATOR EARTH FAULT PROTECTION (64G)

WHY

Most faults in a generator are a consequence of insulation failure. They may

lead to turntoturn faults and ground faults. Required for the earth fault ingenerator stator windings, potential transformers, lightning arrestors, surgecapacitors & neutral bus duct. Fault current must be low as it may damage thecore , which is very costly affaire. Hence ground fault protection is veryessential for generators.

HOW Maximum resistive fault current limited to 7.8 Amp (under field forcing) by

neutral grounding transformer & secondary loading resistor.

95% of stator winding is protected by sensing voltage (overvoltage) acrosssecondary loading resistor.

100% of stator winding is protected by low frequency injection method.

100% stator earth fault protection can be provided by injecting an external lowfrequency alternating voltage into the starpoint or the terminals of themachine. Under normal healthy conditions only a very small current flows viathe stator earth capacitance due to the high impedance of this path at lowfrequencies (Xc = 1/2fc). In the event of an earth fault the measured currentincreases due to the smaller impedance of the earth fault path.


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STATOR EARTH FAULT PROTECTION (64G)


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ROTOR EARTH FAULT PROTECTION (64F)

WHY

An earth fault in the rotor winding does not cause immediate damage;

however, if a second earth fault occurs it constitutes a winding short-circuit of

the excitation circuit. The resulting magnetic unbalances can cause extreme

mechanical forces which may cause damage to the machine.

HOW

The rotor earth fault protection injects a DC voltage into the rotor circuit; the

polarity of the voltage is reversed at low frequencies and the frequency is

selectable by the user through a link selection.

Every time the DC voltage is reversed in polarity, a charging current is applied

due to the capacitance of the rotor windings to earth. Under no fault

conditions, the charging current should be discharged to zero.

When a rotor earth fault occurs, the steady state current will no longer be zero,

the magnitude of which can then be used to calculate the fault resistance.

Other method: -ve biased voltage injection(VAEM) for 1strotor earth fault and

potentiometer method(CAEM) for 2ndrotor earth fault.


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ROTOR EARTH FAULT PROTECTION (64F)


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REVERSE POWER PROTECTION (32G)

WHY

In the event of prime mover failure, a generator connected in parallel with a

power system - will begin to run as Motor . The active power is drawn fromthe power system to cover alternator & failed prime mover mechanical losses.

HOW

A time delay provided to reverse power protection tripping - to prevent false

tripping during some system fault conditions & power system swings.

A typical setting for reverse power protection - with 0.2% to 0.5% of the rated

power of the generator.

A time delay provided for operation without turbine trip.


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LOW FORWARD POWER PROTECTION(37G)

WHY

To avoid over speed damage to Large turbo alternators, with slender, low

inertia rotor designs like that of steam turbines - do not have high over speedtolerance , non urgent tripping of the generator breaker & the excitation

system can be interlocked with a low forward power function.

HOW

Measurement of the low power - done similar to that of reverse power

function

A typical under power setting : 0.5% of rated power.

A time delay provided for operation without turbine trip.

In gas turbine driven generators - Low forward power protection not required.

NEGATIVE PHASE SEQUENCE PROTECTION(46G)


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NEGATIVE PHASE SEQUENCE PROTECTION(46G)

WHY

Negative sequence currents create an mmf wave in opposite direction to thedirection of rotation of rotor. This cuts the rotor at twice the rotational speed,

and induces a 100 Hz eddy current flows in the outside skin of the rotor body, onthe wedges & in the top winding conductors and cause heating which can causesevere over heating and ultimately, the melting of the wedges in the air gap.

HOW

Negative sequence current is measured by the relay. An inverse-time overcurrent

relay excited by negative sequence current can be used for this protection. Themachine designer establishes constant k. It can be in the range of 550.

8% continuous negative sequence current can tolerated.

UNBALANCED LOAD TIME CURVE


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UNBALANCED LOAD-TIME CURVE

FIELD FAILURE PROTECTION (40G)


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FIELD FAILURE PROTECTION (40G)

WHY

When the excitation of a generator fails - its internal e.m.f. will decay. Thisresults in fall of active power output (accelerate to super synchronous speed)

& increasing level of reactive power being drawn from the system. In the lagging power factor-operating region, limits are determined either by

rotor field heating limit or by stator armature heating limit. During the leadingpower factor-operating region, it is the iron end region-heating limit due toeddy currents that is detrimental to the machine. Turbo-alternators may nothave adequate reactive power absorption capability. Hence, they are seldomoperated with leading power factor.

HOW

This protection function - measures the impedance at the terminals of agenerator to detect failure of the generators excitation.

During loss of excitation - the terminal impedance of the generator undergoesa transition from the first quadrant to the fourth quadrant.

Offset Mho relay Xa= 0.5 Xd , Xb= Xd

Time delay used. But in case of U/V no time delay.


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X

R-Xa

Xb

Load Point

Machine terminal

loss of fieldlocus

Field Failure protection function characteristic with typical machine impedance

TRIP

NO TRIP


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UNDER VOLTAGE PROTECTION (27G)

WHY

Under voltage - can be used to detect abnormal operating conditions, AVR failureor an un-cleared power system fault by other generator protection.

It can be interlocked with the field failure protection - to prevent its operation

during stable power swings.

Under voltage protection - not a commonly specified requirement for generator

protection.

HOW

Operates when the three phase voltages fall below the common set point. An

adjustable timer is available .

Under voltage threshold ( V< ) setting - set below the steady state phase-phase

voltage seen by the relay for a three-phase fault at the remote end of any feeder

connected to the generator bus.

70% of normal voltage.


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OVER VOLTAGE PROTECTION (59G)

WHY

Over voltage protection - set to prevent possible damage to generator insulation,prolonged over fluxing of the generating plant or damage to isolated power system

loads.

HOW

Over voltage operates when the three phase voltages are above their commonthreshold setting.

At 105% voltage , alarm with 2 sec delay

At 140% voltage, Trip without delay


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UNDER FREQUENCY PROTECTION (81GUF)

WHY

Under frequency operation of a generator - occurs when the power system

load exceeds the prime mover capability of the generator.

Under frequency running at nominal voltage - will result in over fluxing of the

generator.

Unsafe for turbine

HOW

The under frequency protection function of the relay - utilises the AC voltage

input signals as the frequency measurand.

Two independent time-delayed stages of under frequency protections.

First stage48.5 Hz, Alarm with 2.5 Sec delay

Second stage47.5 Hz, Trip with 2 sec delay.


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OVER FREQUENCY PROTECTION (81GOF)

WHY

Over frequency running of a generating set arises when the mechanicalpower in put to the generator is in excess of the electrical load & mechanical

losses.

Over frequency protection - a back up protection function to cater governor

or throttle control failure following loss of load & prevent over speeding.

HOW

Over frequency protection function of the relay - utilises the AC input signals

as the frequency measurand.

A single time delayed stage of over frequency protection , with an over

frequency threshold setting ( F> ) and a time delay setting ( t ). 51.5 Hz, Alarm with 2 sec delay.


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VOLTAGE BALANCE FUNCTION (60G)

WHY

Voltage balance function - provided to detect PT fuse failure so that an alarm

can be raised & unwanted generator shut down by the voltage sensitive

protection function can be prevented.

HOW

The voltage balance protection function - operates from signal derived fromthe relays two main PT secondary inputs and signals derived from an

additional pair of reference PT secondary inputs.

The level of voltage difference is determined between each of the two main &

reference voltage inputs.

When a voltage difference in excess of an adjustable threshold ( Vs ) isdetected - an alarm is raised.

( )


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GENERATOR BACKUP IMPEDANCE PROTECTION(21G)

WHY

Back-up protection must be applied at the generator so that faults are cleared

in the event of downstream protection/circuit breakers failing to operate. Also

current will come down with time.

HOW

Under impedance protection. This element is set to monitor the system

impedance at the terminals of the machine. If the impedance measured fallsbelow a set threshold then the element will operate.

System back-up protection must operate quickly during a fault and must not

operate for load conditions.

( )


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GENERATOR DEAD MACHINE PROTECTION(50GDM)

WHY

To provide fast protection for accidental energization of a generator when the

machine is not running condition.

HOW

Instantaneous overcurrent element that is gated with a three-phase

undervoltage detector and is blocked by the VT supervision element.

GENERATOR OUT OF STEP PROTECTION(78G)


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GENERATOR OUT OF STEP PROTECTION(78G)

WHY

A generator might pole slip, or fall out-of-step with other power system

sources, in the even of failed or abnormally weak excitation or as a result of

delayed system fault clearance.

HOW

To detect this condition, distance relay looking into the generator (or into the

transformer-generator unit) should be installed. Even a distance relay used forloss-of-field protection will pick-up on such power swing.

If the swing moves out of the relay characteristic, before the timer runs down,

then, no trip action will be initiated. However, if the swing persists for

sufficient time, the loss-of-excitation distance relay will operate on power

swing.

GENERATOR DEFINITE TIME OVERLOAD PROTECTION(51G)


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GENERATOR DEFINITE TIME OVERLOAD PROTECTION(51G)

WHY

To protect the generator from going out of the capability and safe operation

limit.

HOW

Thermal modeling of the generator as per the given data and

recommendation of supplier.

GENERATOR & GENERATOR TRANSFORMER OVERFLUXING


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PROTECTION PROTECTION (99GT)

WHY

High voltage or low frequency, causing a rise in the V/Hz ratio, will produce high

flux densities in the magnetic core of the machine or transformer. This could

cause the core of the generator or transformer to saturate and stray flux to be

induced in un-laminated components that have not been designed to carry flux.

The resulting eddy currents in solid components (e.g. core bolts & clamps) and

end of core laminations can cause rapid overheating and damage.

HOW

V/f element of the relay set as per the overfluxing withstand capability of the

generator & generator transformer.

Time delayed Alarm is used to take action

Inverse characteristics is used for trip

GENERATOR STATOR FRAME OVERTEMPERATURE PROTECTION


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(CO2 SYSTEM)

WHY

To provide protection against fire/ hot spots inside generator enclosure.

HOW

80 deg C & 100 deg C fire detectors installed at equal distance along the

periphery of generator frame /enclosure (Turbine end & Exciter End).

Logic formed to avoid mal-operation of detector for release CO2 in thegenerator enclosure and class A tripping.

CO2 is also released in case of actuation of generator differential protection.


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Fire Detector arrangement inside generator enclosure(Turbine side)


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Fire Detector arrangement inside generator enclosure (Exciter side)

GENERATOR CLASS A PROTECTION TABLE


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GENERATOR CLASS-A PROTECTION TABLE

ORlogic for class

A trip

GEN WINDING DIFFERENTIAL 87G

GEN TR DIFFERENTIAL 87GT

STATOR EARTH FAULT 64G

GEN TR REF 64RGT

OVERALL DIFFERENTIAL 870A

GEN FRAME TEMPERATURE 100 DEG

CELSIUS

ROTOR E/F 64F

Tripping of both generator breaker and turbine occurs for any of the following conditions

EMERGENCY PUSH BUTTON


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THANK YOU

generator operation and protection

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