AC Ground Fault Location Method for Variable Speed Drives Using Lissajous Curves

The increasing presence of electric drives demands the development of new detection and diagnosis methods of electrical faults. In particular, ground faults are the most common type of faults in electrical systems. Locating these faults is not trivial, as they depend not only on the position, but also on its fault resistance. This paper proposes a new method to detect and locate ground faults in the AC side of an electric drive. The method is based on the ground connection of a high value resistance between the midpoint of the DC bus and ground. By means of the study of the relations between the DC voltage on this resistance and the phase-to-neutral voltages in the AC side of the drive, the location of the fault can be determined. This method has several advantages, as it does not require to know the phase impedance or to estimate an initial ground resistance. The method has been validated by means of computer simulations and in an experimental test bench using a 140-kW power converter obtaining satisfactory results.