Internal Fault Detection/Classification System for Permanent Magnet Machines

A high response internal fault detection (IFD) and classification system is designed for large permanent magnet synchronous machines using multiple electromagnetic detection methods and thyristor controlled stator winding isolation techniques. Four broad categories of stator faults including dielectric failures, short circuit faults, core failures and open circuits are covered by the IFD. Three IFD control schemes are to be investigated and designed for specific application to the 25,000 HP class PM machines of the Navy ASMP project; these schemes include field oriented vector (FOV) detection and magnetically polorized fiber optic detectors to determine unbalances in the machine airgap flux and magnetic core flux. The result of using a field oriented vector yields optimum values for terminal excitation in Volts/Hertz when the PM motor is operated by inverter dirive under abnormal conditions occuring with stator winding isolation. The novel aspects of the approach in addition to the 150-300 microsecond response time include the ability to modulate the thyristor-stator winding switching to avoid step functions in terminal voltage or power and the ability to control the machine reactive power flow in an optimum fashion.