Load monitor for the TFTR motor-generator sets

Two parallel-operated motor-generator (MG) sets are used to provide pulsed AC power to the Tokamak Fusion Test Reactor (TFTR). The MG sets are vertical shaft machines adapted for the pulsed duty; each is nameplate-rated 475 MVA, 13.8 kV, 0.7 pF, 60 Hz, 7 s, and can deliver 2.25 GJ of energy during an excursion from 87.5 Hz to 60 Hz once every five minutes. In order to better quantify the machines´ actual operating limits, a study was undertaken to determine what subset of all conceivable performance-limiting factors might come into play to limit the overall machine performance envelope throughout the nominal range of speed and power factor, with consideration of pulsed operation. Seven critical factors were identified: (1) instantaneous stator current, (2) stator winding temperature, (3) instantaneous field current, (4) field winding temperature, (5) exciter thyristor junction temperature, (6) prospective stator overvoltage, and (7) instantaneous torque. An MG load monitor will be built to provide real time monitoring of all seven quantities by direct measurement and simulation, where necessary. The preliminary design of the MG load monitor is described