ELECTRIC MOTOR PHASE-FAILURE AND SUPPLY-VOLTAGE UNBALANCE PROTECTIVE DEVICE Russian patent published in 2003 - IPC

FIELD: electrical engineering; phase-failure and voltage unbalance protection of farming motors powered from three-phase, solidly grounded neutral mains. SUBSTANCE: device has emergency transducer with two-winding transformer whose primary is connected in series with diagonally opposite ac ports of power-supply rectifier bridge. Connected across diagonally opposite DC ports of bridge are storage capacitor, discharge resistor, and series-connected coils of individual point relay incorporating provision for operation storage and thyristor anode-cathode. Operating threshold of device is adjusted by means of resistor inserted between plus terminal of other rectifier bridge of emergency transducer and gate electrode of thyristor whose anode circuit incorporates individual point relay coil. Noise suppression capacitor is inserted between cathode and gate electrode of thyristor and zero-sequence voltage filter is built around capacitors. Upon occurrence of phase failure or inadmissible unbalance of supply voltage capacitor is placed at potential and control pulses arrive at thyristor gate electrode. Capacitor charge to operating potential of circuit drives thyristor in conduction and pulsed discharge of capacitor through individual point relay coil takes place with the result that this relay operates and motor is disconnected from faulty mains. EFFECT: enhanced reliability and facilitated manufacture of device. 1 cl, 1 dwg