Experience With On-Line Ground Fault Protection in Medium Voltage Drive Systems

The uniqueness of medium voltage AC drive systems requires attention to ground fault protection. Most often these power conversion topologies include an isolation rectifier transformer with multiple secondaries, a converter-inverter, and the motor stator windings. The internal ground fault protection of the adjustable frequency drive can be configured for continuity of operation or immediate shutdown to ensure personnel safety and minimize equipment damage. Ground fault protection included within the AFD electronics can be configured for programmable voltage pick up thresholds. This paper will introduce the many topologies of MV AFDs and then presents protection results from multiple locations from a high-impedance to frame ground system.