Medium Voltage Motor Surge Protection

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 500-10,000 HP ranges at 4.16 kV-13.2 kV. This paper summarizes all such activities and provides some application guidelines. 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 capabilities of the motor windings, both in terms of magnitudes and rise-times are also reviewed. Based on the probability of such surge occurrences, decisions about additional surge protection requirements can be made.