Page 172 - Practical Power System and Protective Relays Commissioning

172 Practical Power System and Protective Relays Commissioning

FIGURE 16.14 Phase to phase to earth fault.

FIGURE 16.15 Single-phase open-circuit fault.

16.4.4 Unsymmetrical Single-Phase Open-Circuit Fault
Analyses
This fault is unsymmetrical as it is on one phase only and can be analyzed as
follows (Fig. 16.15):

I 2 1 I 0 52 I 1

16.4.5 Three-Phase Equivalent Fault Level and Fault Current
To make the calculation simple, a single-phase fault can be represented
approximately as three-phase faults, for example:
h i
MVA 3Φ equivalent to 1Φ fault 5 3 MVA b 3 100
2Z 1 1 Z 0
MVA3Φequivalent
I F 5 p ffiffiffi
3V L
Sequence voltages for different fault types.