Type 1: Single Winding to ground

In this type of fault, one winding is shorted to the ground through a resistor Rfg as shown in the following schematic (rotoric circuit and windings’ resistance not illustrated). The faulted winding
is separated in two parts, Af1 and Af2. The same is also true for the related winding function. The two resulting winding functions are then used to calculate Af1 and Af2 self and mutual inductances.

Type 1 Fault in a Synchronous Machine with Two Parallel Windings and Neutral Impedance

During healthy behaviour, Rfg must be very large (> 1e6 pu) and to trip the faulty behaviour, it has to be stepped down to a very small value. This mechanism is valid for all types of fault.