By tracking and measuring the ground parameters of the system, the correct phase selection is achieved when neutral point ungrounded system single-phase fault occurs. Because of the asymmetry of the system parameters, the neutral point of the system will produce a certain voltage shift during normal operation. When the neutral point power frequency voltage changes, by adding a resistor with appropriate resistance in the neutral point and gathering the amplitude and phase of the neutral point voltage before and after inputing resistance, accurat...
