Page 305 - Practical Power System and Protective Relays Commissioning

Protection Relays Settings Chapter | 19 299

FIGURE 19.5.5 Detailed connection diagram of three-winding transformer differential
protection.

400 3 10 3
I 2 5 p ffiffiffi 5 954:3A
3 3 242
954:3
I Relay5 0:95 3 5 0:906 A
1000
Min Bias 5 2 I R at nominal I R at Vmax Þ
ð
5 21 0:906Þ 5 0:188
ð
Minimum voltage at the low-voltage side:
V min 5 220 kV 3 0:9 5 198 kV
400 3 10 3
I 2 5 p ffiffiffi 5 1166:4A
3 3 198
1166:4
I R at min voltage 5 0:95 3 5 1:108 A
1000
Min Bias 5 2 ðI R at min voltage I R at nominal voltage Þ
5 21:108 1Þ 5 0:218
ð
For the low-voltage side choose bias 5 22%.