A potentiometer and voltage gradient method for locating ground faults in a wound electrical machine stator

The location of ground faults in a wound stator is essential for a partial rewind of a new or old winding. The objective is to perform such a test without further damage to the winding. For this purpose, a potentiometer with a sensitive voltmeter has been found to be very accurate in locating a ‘dead short’ as well as a resistive short. Other methods such as the electromagnetic probe and high frequency detector are limited by the nature of the fault and sensitivity. The conventional method of electrically creating a hot spot in the fault area may damage the core iron or the adjacent coils. The proposed test involves two steps. The first step is to locate the pole phase group in question. The second step is to confirm and plot the voltage distribution of this coil group and finally deduce the exact location of the fault in the iron core.