Motor controller with instantaneous trip protection

摘要

A motor control unit for protecting a motor against overload, short circuit and ground fault currents. The unit monitors the currents in each phase of the motor to provide values representative of each phase current. The unit also includes a contactor for opening and closing each phase, wherein the unit controls the contactor based upon the values representative of the phase currents. The contactor is opened where the phase currents exceed limits which indicate that either an overload, short circuit or ground fault situation exists at the motor. A magnetic trip circuit breaker can also be provided to operate in cooperation with the unit to provide instantaneous trip protection for current levels which are relatively high in relation to those for which the contactor is rated.