Fault Types

Consider a single line-to-ground fault from phase a to ground at a three-phase bus, including a fault impedance. This impedance is zero for a bolted fault, is equal to the arc impedance for an arcing fault, and represents the total fault impedance during a transmission-line insulator flashover.

Fault conditions in the phase domain are translated to the sequence domain, deriving sequence and phase currents.

Line-to-line faults occur between phases b and c. As before, phase domain conditions are converted to the sequence domain to establish the relationship between phase and sequence currents.

These fault conditions are satisfied by connecting positive and negative-sequence networks in parallel at fault terminals through fault impedance.

Finally, a double line-to-ground fault occurs from phase b to phase c via fault impedance to ground.

Fault conditions in the phase domain are then determined and transformed to the sequence domain, satisfied by connecting the zero-, positive-, and negative-sequence networks in parallel at the fault terminal.

This process determines sequence fault currents and line-to-ground voltages.