Page 251 - Practical Power System and Protective Relays Commissioning

248 Practical Power System and Protective Relays Commissioning

With undervoltage protection there is no danger for the generator but it
causes stalling of motors in the generator’s service motors.

18.7.14 INTERTURN FAULT PROTECTION

Normal differential protection cannot detect this fault which is rare in
generators and quickly develops to an earth fault.
The generator can be protected against this fault by zero-sequence
voltage protection, as shown in Fig. 18.7.16.

FIGURE 18.7.16 Interturn fault protection for generators by zero-sequence voltage.

Also, this fault can be detected by differential protection in double-
wound generators, as shown in Fig. 18.7.17.

18.7.15 POWER FACTOR RELAY (32R) PROTECTION

This protection works for reverse reactive power (Q) as is the case in
loss-of-field current for generators (the generator absorbs Q (MVAR) from
the power system).