An Update on Surge Protection of Medium Voltage Motors: A Comparison of the Standrads and Applications

Much research has been done in recent years to aid in the determination of surge protection requirements for medium voltage (MV) motors rated typically between 500-20,000 HP range, and at 4.16-13.2 kV. In order to determine the actual surge magnitude and the corresponding rise time seen by the motor windings, the sources of surges and the factors affecting the surge transmission to the motor terminals are examined. The actual surge-withstands capability of the motor windings, both in terms of magnitudes and rise-times are also reviewed. Based on the probability of such surge occurrences and the surge withstand capability of the motor winding, decisions about additional surge protection requirements can be made. This paper summarizes such activities, compares the IEEE and IEC requirements and provides some application guidelines. Numerical examples are included to enhance the understanding and the design needs.