Protection Against Abnormal
System Frequency
Effect Of Over Frequency
Effect
Remedial process
May result in
High Speed and
Increased Cooling
Automatic unloading of
Generator
Turbine Speed Governor
Unit tripping due to
turbine High speed
High Voltage
AVR to Control the raise
in Voltage
Unit tripping due to
Loss of excitation,Due
to High Voltage if AVR
not in service
Generator tripping under Such circumstance may not pose major
problem to the grid since this part of the power system will have Excess
generation and it will be a Isolated event
Effect of Under Frequency
Effect
Remedial process
May result in
Low Speed and
Decreased
Cooling
Turbine Speed Governor
Low Voltage
AVR to Control the
Unit tripping due to
•Thermal over load
•Over heating of Both
Stator and Rotor
•Over fluxing of
generator and GT
Generator tripping under Such circumstance may further worsen the
situation and lead to cascade tripping.
Continued operation of the System at low frequency reduce the life of
the turbine. Diagm
• Pic 20.28