Page 317 - Practical Power System and Protective Relays Commissioning

Protection Relays Settings Chapter | 19 311

Relay set 5 47 Hz F 5 50 Hz
t set 5 4 seconds
Action:
1. Trip 220 kV CB. This protection works when load-shedding of the net-
work does not work.
8.Overfrequency protection
Under this condition the unit overspeed and trip are set as follows.
Relay set 5 54 Hz, F 5 50 Hz
Action:

1. Trip of 220 kV CB.
8. Undervoltage stator protection
This protection works as a backup for an HV network in two stages.
Stage 1 has a definite time uv set to 0.7 V n of the generator and trips the
HV CB.
Stage 2 trips the unit after 2.5 seconds.
Stage 1:

V set 5 0:7V n 5 0:7 3 100 5 70 V
t set 5 1.2 second
Action trip CB of 220 kV transformer (T 1 ).
Stage 2:
V set 5 70 V
t set 5 2.5 seconds
Action:
1. Turbine tripping;
2. Tripping of 6.4 kV transformer incoming;
3. Generator excitation tripping.
9. Overvoltage protection
This protection works when the Automatic Voltage Regulator (AVR)
maloperates or for manual operation of the excitation system.
First stage

V set 5 1:1 V n
5 1:1 3 100 5 110 V
t 5 4.5 seconds
Action: alarm
Second stage

V set 5 1:2 V n 5 120 V
t set 5 3 seconds