This document discusses the main components and construction of generators, how generators produce power, and generator protection systems. It describes the rotor, stator, and other main generator parts. It explains how generators work using the principle of electromagnetic induction. It then discusses various electrical, system, and mechanical faults that can occur in generators. Finally, it provides details on primary, backup, and different classes of protection systems for generators, including differential protection, earth fault protection, loss of excitation protection, and more.
5. GENERATION OF POWER
TURBINE
GENERATOR
TRANSFORMER CB
ISOLATOR GRID/
BUS
THE ELECTRICAL MACHINE WHICH CONVERTS MECHANICAL ENERGY INTO
ELECTRICAL ENERGY WHICH IS AN ALTERNATING CURRENT (AC) IN NATURE
IS CALLED AS AN AC GENERATOR OR ALTERNATOR.
6. BASICS OF GENRATOR
PRINCIPLE:
ALL ELECTRICAL GENERATORS, WHETHER DC OR AC, DEPEND UPON THE PRINCIPLE
OF ELECTROMAGNETIC INDUCTION. AN EMF IS INDUCED IN A COIL AS A RESULT OF
A COIL CUTTING THROUGH A MAGNETIC FIELD, OR A MAGNETIC FIELD CUTTING
THROUGH A COIL. AS LONG AS THERE IS RELATIVE MOTION BETWEEN A
CONDUCTOR AND A MAGNETIC FIELD, A VOLTAGE WILL BE INDUCED IN THE
CONDUCTOR.
THAT PART OF A GENERATOR THAT PRODUCES THE MAGNETIC FIELD IS CALLED THE
FIELD. THAT PART IN WHICH THE VOLTAGE IS INDUCED IS CALLED THE ARMATURE.
FOR RELATIVE MOTION TO TAKE PLACE BETWEEN THE CONDUCTOR AND THE
MAGNETIC FIELD, ALL GENERATORS MUST HAVE TWO MECHANICAL PARTS — A
ROTOR AND A STATOR.
8. Protection System
Generator must be protected from electrical faults,
mechanical problem and adverse system conditions
Some fault require immediate attention (shutdown) while
others just require alarming or transfer to redundant
controllers
Avoid outage of time
Cost
9. FAULTS IN GENRATOR
Electrical Faults
Phase to Phase Faults
Inter turn faults
Stator Earth fault
Rotor Earth faults
10. FAULTS IN GENRATOR
SYSTEM FAULTS
Over Voltage
Under Voltage
Over Frequency
Over loading
Unbalanced loading
Reverse power
Loss of Excitation
Under Frequency
11. FAULTS IN GENERATOR
Mechanical Defects
Bearing temperature
Vibration
Prime mover failure
Winding temperature
Lube oil problems
13. GENERATOR DIFFERENTIAL PROTECTION (87G)
Acts for Phase to Phase faults
Acts for earth faults
Do not act for inter turn faults
Fault
Pick Up value of high set point, I-Diff>> 7.5I, Time Delay 5.00Sec.
14. GENERATOR STATOR EARTH FAULT RELAY (59 N & 27-3N)
• Acts for any Earth fault in
Stator
Potential transformers
Lightening Arrestors
Bus ducts
Generator Transformer 11
KV side
15. GENERATOR STATOR EARTH FAULT RELAY (59 N & 27-3N)
Stator Earth fault
Pickup 6V, time delay 0.50Sec
16. ROTOR EARTH FAULT PROTECTION (64R)
First Stage
IR Value less than K OHMS- ALARM
Second stage
IR Value less than K OHMS - TRIP
Excitation
supply
17. BACKUP PROTECTION
Negative Phase sequence
Over current relay with voltage Restraint (51V)
Distance relay (21)
Over excitation protection
18. NEGATIVE PHASE SEQUENCE (46G)
One open phase of the line
One open pole of the circuit breaker
Unbalanced faults
Stator winding faults
Single phase Traction loads
Single Phase Arc furnaces
Continuously Permissible Current
I2>12.3%, Time delay 10.00Sec-
Alaram.
Pick Up value,I2>> 60%,Time delay
3.00Sec-Trip.
19. OVER CURRENT RELAY WITH VOLTAGE
RESTRAINT (51V)
Heavy over loads
Short circuits
Dip in Grid voltage
Failure of voltage regulator
Setting: 105% IN
Standard inverse characteristics
20. REVERSE POWER (32)
Prime mover failure (inadvertent closure of steam control valves)
Protection against motoring
Over heating of turbine low pressure blades
P> Reverse power pickup - -2.43% of the rated power for 5 sec.
21. DISTANCE PROTECTION (21)
Back up protection
Co-ordination with other relays
Impedance below 70% of generator
22. LOSS OF EXCITATION (40 G)
Open field winding
Malfunction of AVR
Generator will operate as a
induction generator
Heats up rotor
May create instability
23. OVER FLUXING (24)
Voltage / frequency
Core saturation in transformer
Stage 1 : 115%
Stage 2 : 120%
24. UNDER /OVER FREQUENCY (81)
Load rejection / tripping of transmission lines
Turbine problem
System over load
Over frequency will lead to over speeding
Under frequency will damage low pressure
stages
Stage 1 : 48.5 Hz and 51.5 Hz - Alarm
Stage 2 : 47.5 Hz and 52.5 Hz - Trip
25. GENERATOR OVER VOLTAGE
PROTECTION (59)
Mal operation of AVR
Sudden load variation when generator on
manual regulation
Lead to insulation damage
First Stage
110% En : Auto to manual c/o of regulation
Second Stage
120 % En : TRIP
Under voltage protection (27) : 90% En,
Disabled
26.
27. CLASSES OF PROTECTION (STG)
CLASS A (Generator breaker trip, Excitation trip, Turbine trip)
Generator Differential relay (87G)
Overall Differential relay (87 O)
Backup impedance relay (21)
Second rotor Earth fault (64R)
95% stator earth fault (64G)
Over voltage (59)
Low forward power (32)
Over fluxing (24)
Loss of Excitation (40)
Under voltage (27)
Generator Transformer Faults
28. CLASSES OF PROTECTION (STG)
CLASS B (Turbine trip)
100 % Stator earth fault
Loss of Excitation (40)
Stator over current (51)
Voltage restrained Over current
Under frequency
CLASS C (Generator breaker trip)
Over load (51)
Negative Phase sequence (46)
Dead machine protection
Pole slipping (78)
Off from AVR
Generator winding temperature High
30. PROTECTION IN GTG
Generator Tripping (86G)
Generator over voltage (59)
Generator under voltage (27)
Reverse power (32)
Loss of Excitation (40)
Negative Phase sequence (46)
Under frequency (81U)
Off from AVR
Pole slipping
External trip