Page 315 - Practical Power System and Protective Relays Commissioning

Protection Relays Settings Chapter | 19 309

FIGURE 19.6.2 Loss of excitation impedance protection for generators.
xd 0
X 2 5
2

Xd 5 191% on 417 MVAb.
Z% MVAb:100
Z ðΩÞ 5
ðVLÞ 2
33 3 417:100
Xd ΩðÞ 5 5 28:43 Ω
0
100ð22Þ 2
xd 0 28:43
X 2 5 5 5 14:21 Ω
2 2
X 1 5 xd x 2
191:417 3 100
Xd ΩðÞ 5 5 164 Ω
100:ð22Þ 2
X 1 5 164 14.21 5 150.35 Ω
X 1 5 150.35 Ω primary, secondary x 1 5 887.065 Ω
x 2 5 14.21 Ω primary, secondary x 2 5 83.839 Ω

NV
t 5 1 second; Z s 5 Z P 5 5:9 Z P
NC
220; 000=O3
VT ratio 5 5 2200 5 NV
100=O3
CT ratio 5 13,000/1 5 NC
6. Underimpedance protection
This relay is used as a backup protection for external faults on the high-
voltage side (220 kV) of a transformer (T 1 ), as shown in Fig. 19.6.3.