Page 246 - Practical Power System and Protective Relays Commissioning

Protection Relays Chapter | 18 243

FIGURE 18.7.10 Voltage-controlled OC relay for generators.

18.7.7 REVERSE POWER PROTECTION

Reverse power protection is taken against generator prime mover failure.
The motoring allowable for generator units as follows:
Steam turbine and gas turbine units: 5% only;
Diesel-driven sets: 25% only;
Hydro units reverse power protection is not required.
In this case there is a field current but there is no steam to drive the
turbine, this condition leads to reversing the active and reactive power
and the generator runs as a synchronous motor, leading to a condition
in which the turbine blades are not cooled and can be distorted and
damaged.