Grounding of AC and DC low-voltage and medium-voltage drive systems

The grounding of AC and DC motor drive systems should detect and clear ground faults both on the source and load side of the power converters. Most drive systems are separately derived through a step-down transformer, which serves as a drive isolation, as well as rectifier transformer. Isolation transformers on individual or group drive systems, downstream of main substation transformers are also common. An output isolation transformer on an AC drive will isolate the drive electronics, step up the AC voltage from the inverter section and also serve to control high line-to-ground voltages on the motor windings. The grounding system has a profound effect upon the continuity of operations, loading of the solid-state devices and common-mode voltages. This paper discusses the various possibilities of grounding of low-voltage and medium-voltage motor drive systems and shows that a high-resistance grounding system can be often implemented to permit continuity of operations, allow fault detection and limit the transient overvoltage.