Page 171 - Practical Power System and Protective Relays Commissioning

Power System Fault Analysis Chapter | 16 171

FIGURE 16.12 Single phase to earth fault.

FIGURE 16.13 Phase-to-phase fault.

16.4.2 Unsymmetrical Phase-to-Phase Fault Analyses
This fault is unsymmetrical as it is from one phase to another phase and it
can be analyzed as follows (Fig. 16.13):
V R 5 V Y ; I R 52 I Y ; I 1 52 I 2 ; I B 5 0
E
I 1 5
2Z s 1 2Z 1

16.4.3 Unsymmetrical Phase-to-Phase Faults to Earth Analyses
This fault is unsymmetrical as it is on one phase to another phase to ground
and can be analyzed as follows (Fig. 16.14):
I 2 1 I 0 52 I 1
E
I 1 5
Z 1 1 Z s 1 ð Z s 1 Z 2 Þ Z s 1 Z 0 Þ
ð
2Z s 1 Z 2 1 Z 0