Electrical Engineering ⇒ Topic : Synchronous motor ratings

SYNCHRONOUS MOTOR RATINGS

Synchronous motors may be purchased in three standard ratings namely :

1. unity power factor;
2. 90% leading power factor; and
3. 80% leading power factor.

Other ratings are obtainable from motor manufacturers by special quotation.

If a motor is rated at unity power factor it can be operated with a leading power factor.However the mechanical load must be decreased sufficiently so that no more than rated A.C. stator current will flow at the reduced power factor. In other words, the mechanical load in horsepower output and the electrical load in not exceed the rating of the leading kVARs must motor. When a synchronous motor is rated at 80 or 90 percent leading power factor it will have a large current capacity for a given horsepower output. This is necassary in order to supply rated horsepower output with the larger current at the reduced power factor.