AC Ground Fault Location Method through Voltage Frequency Components Analysis for Variable Speed Drives

Variable Speed Drives (VSDs) are key pieces in most of the industrial processes and thus, a secure operation must be ensured against possible harmful events such as ground faults. Fault location is a complex task that has been aggravated by the increasing presence of power converters. The switching commutations as long with the high frequency leakage currents can cause the malfunction of protection relays. This paper proposes a ground fault location method in the AC drive side of VSDs. The method is mainly based on a grounding resistor connected to the midpoint of the DC bus. Measuring the phase-to-neutral voltages of the AC drive side and the grounding resistor voltage, the method can determine the faulty phase. Moreover, it can estimate the fault position and fault resistance applying phasors equations with the fundamental and the switching frequencies. The method has been validated by means of computer simulations and experimental tests using a 140 kW power converter showing promising results for both fault position and fault severity estimations.