Page 316 - Practical Power System and Protective Relays Commissioning

310 Practical Power System and Protective Relays Commissioning

FIGURE 19.6.3 Backup impedance protection for generators.
Z set 5 0:7 3 0:36 5 0:252- 5 25:2%

25:2 3 417 3 100
Z set ΩðÞ 5
100ð220Þ 2
ð
5 0:217 Ω primaryÞ
Z set ΩðÞ secondary 5 5:9 Z primary
5 5:9 3 0:217
5 1:2803 Ω
Z set

Z set 5 0:7 Z Load
Z Load min 5 XG 1 XT
5 Xd} 1 XT
5 0:22 1 o:14
5 0:36
Set time 5 3 seconds.
Action:
1. Turbine tripping;
2. Tripping of 6.4 K unit transformer incoming;
3. Generator excitation tripping.
7. Generator frequency protection
A. Underfrequency protection
This protection is required for load-shedding to allow unit frequency
recovery.