Generator Protection for Differential and Over Current Relay includes:Abnormal Condition, Aspects: Generator Problem, Generator Fault Current, Voltage Controlled Over current Relay, Differential Protection, Generator Differential Scheme

1. Generator
Protection for
Differential and
Overcurrent Relay
Toshali Mohapatra, BT18EE004

2. Contents
Introduction
Abnormal
Condition
Aspects:
Generator
Problem
Generator
Fault
Current
Voltage
Controlled
Overcurrent
Relay
Differential
Protection
Generator
Differential
Scheme
Conclusion
References

3. Size of individual
generating unit
30 MW to
500/1000 MW
Loss of even a
single unit
serious problem
Protection
systems of
generators: more
stringent
Required to
reduce the
outage period to
a minimum
Achieved by rapid
discriminative
clearance of all
fault conditions
associated with
the units
Damage due to
faults is none or
to the minimum
Introduction

4. Loss or insufficient excitation
Overload
Overvoltage
Under and Over frequency
Unbalance current
Inadvertent energization
Out of step (loss of synchronism)
Loss of prime mover (motoring)
Abnormal Condition

5. Internal faults
Abnormal Service conditions
External Faults (as back up protection)
The hazards and problems considered
Phase to phase faults in winding
Phase-ground faults in winding
Ground faults in the rotor
Aspects: Generator Protection

6. Sub transient
current
Transient
current
Steady state
current
Generator Fault Current

7. Voltage restrained –
If the voltage falls,
the pickup will be at
the reduced current.
Voltage controlled –
Enabled if the
voltage falls below
the pre-set value.
Voltage Controlled Overcurrent Relay

8. Flux
summation CT
acts as
sensitive
differential
protection.
Differential Protection

9. Only generator is
covered in case of
generator breaker
Generator and
generator
transformer are
covered in case of
breaker only at HT
side.
Overall differential
protection covers
generator,
generator
transformer and
UAT.
Generator Differential Scheme

10. Conclusion
Complexity can be made simple with
the correct user tools
Modern element design matter for
security and dependability
These protections are for in-zone
and out of zone events
Generators require special
protection for faults and abnormal
operations

11. References
1. IEEE Guide for Generator Ground Protection, ANSI/IEEE C37.101-2006.2.
2. IEEE Guide for AC Generator Protection, ANSI/IEEE C37.102-2006.
3. Protection Analytic Tool, Power Research and Development Consultants, PRDC
4. General Electric(GE) Grid Solutions
5. Electrical-engineering-portal.com