Generator Protection PPT Turbo

8/13/2019 Generator Protection PPT Turbo

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PROTECTION OF 60MW TURBO

GENERATOR IN VSP


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POWER SYSTEM PROTECTION

The word 'protection' is generally used to

describe the whole concept of protecting a power

system.

Power system protection is the process of

making the production, transmission, and

consumption of electrical energy as safe as

possible from the effects of failures and events

that lace the ower s stem at risk.


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NECESSITY OF PROTECTION

Three main effects of fault, that state the necessity of

protection:

It is likely to cause the individual generators in a

power station, or groups of generators in different

stations, to lose synchronism and fall out of step with

consequent splitting of the system;

A risk of damage to the affected plant; and

A risk of damage to healthy plant.


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BASIC REQUIRMENTS OF

PROTECTION:

Speed

Selectivity

Sensitivity

Reliability

Simplicity

Economy


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BASIC COMPONENTS OF

PROTECTIONRelays

Instrument Transformers

Circuit breakers

Tripping Batteries


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-CIRCUIT BREAKER

COMBINATION


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GENERATOR FAULTS

Stator Faults

Rotor Faults

Faults Due To Mechanical Condition

External Faults


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GENERATOR DIFFERENTIAL

PROTECTION

For protection of stator windings against earth faults and phase to phase

makes use of circulating current principle

In this scheme of protection currents at the two ends of protected sections

are compared


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STATOR INTERTURN FAULT

PROTECTIONInterturn faults occur in the stator slots, they quickly

develop into faults to earth and are cleared by the stator earth

fault protection

There is,however,the possibility

that they may occur at the winding

ends and so cause extensive

damage to the generator before the

fault evolves to one detectable by

other protection.


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REVERSE POWER PROTECTION

The motoring of the turbine output can be detected by

reverse power protection relay which is powered by both

C.T and P.Ts.

To avoid false tripping due to power swings a time delay

is incorporated before tripping signal is generated. If the

unit trips on reverse power protection, the input power to

the turbine is increased as quickly as possible.


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AUTOMATIC FIELD

SUPPRESSION

In the event of fault on the

turbo generator winding even

if the generator C.B is tripped,

the fault continues to be fed as

long as long as excitation willexist because emf is induced in

the generator itself.

For the quick removal of fault during emergency, it is

necessary to disconnect the field simultaneously with the

disconnection of the generator


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LOCAL BREAKER BACK UP

PROTECTIONThe LBB protection is energized when the breaker trip

is initiated after a suitable time interval if conformation of

the breaker tripping from 3poles is not received

The energized tripping signal from local breaker back up

protection will trip all 220kv generator breakers and all

220kv feeder breakers through bus bar protection.


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STATOR EARTH FAULT

PROTECTION

If a faulty phase windingconnected to ground, the

normal low neutral voltage

could rise as high as line-to-

neutral voltage dependingon the fault location

The usual method of

detection fault is bymeasuring the voltage

across the secondary of

neutral grounding

transformer (NGT).


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NEGATIVE SEQUENCE OR

CURRENT UNBALANCE

PROTECTIONWhen the machine

delivering the equal currents

in three phases, no unbalance

are negative phase sequencecurrent is produced

An alarm will annunciate at

annunciation panel it negative

sequence currents exceed a

normal level


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ROTOR EARTH FAULT

PROTECTION

The rotor earth faultmay be caused due toinsulation failure ofwinding or inter-turn

fault followed by localheat.

The protection schemeconsists of a highresistance connectedacross the rotor circuitand its mid point isgrounded through asensitive relay


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OVER FLUXOR OVER

EXCITATION PROTECTION

This problem may occur in turbo generators that are

connected to the grid if they experience generating voltage

regulation problems

It may also occur for units during start-up or

resynchronizing following a trip.

A specialized volts/hertz relay is used to detect this

condition, and will trip the generator if excessive

volts/hertz conditions are detected


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STATOR FRAME OVER HEATING

PROTECTION

For the protection of the turbo generator against any

possible fire accident twelve fire detector relays are

provided on either side of the stator winding

The set of contacts will close when the temperature

surrounding the fire relay exceeds 80OC. The other relay

one when the temperature exceeds 100OC

These contacts are wired to CO2fire extinguishing

system


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ABNORMAL FREQUENCY

PROTECTIONThe abnormal over frequency on the machine may be

due to improper speed control adjustment or disoperation

of the speed controller or severe grid disturbance orsudden load thrown off.

If the unit trips due to abnormal frequency protectionthen change the governor speed until machine reaches full

speed. Even after 2to3 attempts the machine is running at

lower speed, probably the governor of the turbine is faulty.


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LOSS OF FIELD OR LOSS OF

EXCITATION PROTECTION

This fault is caused due to

open circuit of field, short

circuit of field, accidental

tripping of field breaker, poorbrush contact

The mho relay is placed which is designed to detect

the change of impedance from the normal load valuemay therefore be used to provide protection against

asynchronous operation resulting from the loss of

excitation.


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POLE SLIP PROTECTION

A generator may lose

synchronising with power

system without failure of

excitation system, becauseof severe fault disturbance

or operation at a high load

with leading power factor

and hence a relatively weakfield


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OVER SPEED PROTECTION

Bearing over heating can be detected by a

relay actuated by a thermometer-type bulb

inserted in a hole in the bearing, or by a

resistance-temperature-detector relay, such as

used for stator over heating protection, with the

detector embedded in the bearing


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PROTECTION AGAINST

VIBRATIONS

A vibration detector may be mounted on one of

the bearing pedestals in the case of a horizontal

shaft generating set, or on the upper guide-

bearing in case of a vertical shaft generating

set. It may be set to trip the machine or initiate

an alarm when the radial deflections of certain

duration exceed a per-determined value.


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BEARING OVER HEATING

PROTECTION

Bearing over heating can be detected by a

relay actuated by a thermometer-type bulb

inserted in a hole in the bearing, or by a

resistance-temperature-detector relay, such as

used for stator over heating protection, with the

detector embedded in the bearing


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ANTI MOTORING PROTECTION

In the event of prime-mover failurethe generator continues to rotate as a

synchronous motor drawing electrical

power from the system and driving theprime mover.

A single element directional powerrelay is used to sense (reverse power

relay)the direction of power flow in any

one phase.


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CONCLUSION

A generator is the most important and most costly equipmenentin a power system. It is subjected to more number of troubles

than any other equipment.

The basic function of protection applied to generators is

therefore to reduce the outage period to a minimum by rapid

discriminative clearance of faults.

While selecting the scheme for generator protection, theprotection of complete unit and the stability of the system due to

disturbance, in a generator should be considered in addition to

protection of the generator itself.


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QUERIES?


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THANK YOU

Documents

Generator Protection PPT Turbo