Ground Fault Detection Method for Variable Speed Drives

The use of variable speed drives made essential the presence of power electronic in electrical systems. The ac to dc and dc to ac conversions, thanks to rectifiers and inverters cause difficulties in the ground fault detection. In this article, a new method to detect ground faults in variable speed drives is presented. It is based on the analysis of the terminal voltage signal of a grounding resistor connected between the neutral at the secondary of the main power transformer and ground. Attending to the waveform, the ground fault can be detected on the ac grid side, dc positive or negative terminals, or ac inverter side. To verify the method, numerous simulations and experimental tests in a 140-kW power converter were carried out achieving satisfactory results.