Вот определение, посмотрите, может поможет:

The "c" factor is the voltage factor. It is the ratio between the equivalent voltage source and the nominal system voltage (Un).

The explanation of the voltage factor implies that the prefault voltages should be based on a power flow solution. In the abstance of a prefault power solution, the prefault voltage (Un nominal voltage) would be approximately 5% lower than the no-load voltage (Ur rated voltage) The allowance for high system voltages is accounted for by the voltage factor "c" shown below. The voltage factor cmax is used for maximum currents and the factor cmin is used for minimum currents.

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