A static dynamometer for load testing large variable frequency motor drives

The static dynamometer, an apparent oxymoron, is a system which allows full load testing of variable frequency motor drives with no rotating equipment and only minimal demand from the power line. By inserting a reactor between the drive output and the line from which it is powered, the drive can be made to appear as a synchronous generator. This arrangement offers a practical alternative to the motor-generator sets usually employed for load testing. The required equipment consists of a set of power reactors approximating 10% of the drive rating, a contactor and a phase locked loop circuit for regulating the drive phase relative to the line. The static dynamometer is in production use on variable speed drives from 20 to 5000 hp and 480 to 4160 V. There are no intrinsic limits to either power or voltage for its application.