PHASE TO PHASE SHORT CIRCUIT BASIC INFORMATION

Phase to phase short circuit is also known as line to line fault.

Faults involving abnormal conduction from one phase to another without involving ground may be represented using the interconnection of Figure below.

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Sequence interconnections for a phase-to-phase fault not involving ground

The zero-sequence network is not involved and may be ignored. As for the three-phase condition, Zf would normally be the fault impedance, but it could also be a phase-to-phase load impedance if the problem of interest is the response of the system to a phase-to-phase-connected single-phase load.

An interesting and often useful relationship develops from Figure.

In the special case of a zero-impedance phase-to-phase fault, if the negative-sequence impedance of nearby synchronous machines is approximately equal to the positive-sequence impedances of such machines or if no synchronous generators are nearby at all, then the phase-to-phase fault current will be 0.87 times the corresponding three-phase fault current.

This relationship can be proven by calculating sequence currents in Figure for the specified condition and then converting them to phase currents using symmetrical components equation.