High Resistance Grounding (HRG) and Adjustable Speed Drives (ASD)

This paper provides an analysis of the use of a high resistance grounded (HRG) power system for supplying power to adjustable speed drive (ASD) loads. First, the paper provides a brief discussion on the use HRG on a power system and in particular to understand how the system works in the zero sequence plane. A path is required for the ground fault current to flow and an understanding of the path is better realized with the use of symmetrical components and the use of the zero sequence plane. Next, the paper will present a brief discussion on the use of a standard six-pulse rectifier which is commonly used on small, low and medium voltage drives. Using the basic understanding of the HRG system and the ASD, the flow of ground current from the load side of the ASD to the power system is shown. In particular, the paper will show that the ASD will most likely trip immediately for a ground fault due to the self-overload protection of the ASD whereby the system should continue to run using an HRG power system.