ASYMMETRIC MODE PROTECTIVE DEVICE FOR THREE-PHASE MOTOR Russian patent published in 2004 - IPC

FIELD: electrical engineering; asymmetric mode protection of three-phase motor at reduced voltage across supply mains. SUBSTANCE: newly introduced in proposed device is phase generating unit incorporating power bridge rectifier connected to capacitor of phase-shifting L-C control circuit, to phase A terminal of supply mains through making contact of first auxiliary relay and making contact of fourth auxiliary relay, and to phase B terminal of supply mains through making contact of second auxiliary relay and making contact of fourth auxiliary relay. Same input of power bridge rectifier is connected through making contact of third auxiliary relay and making contact of fourth auxiliary relay to phase C of supply mains. Other lead of power bridge rectifier is connected to inductance coil of phase-shifting L-C control circuit and through making contact of first auxiliary relay and making contact of fourth auxiliary relay, to phase B terminal of supply mains, through making contact of second auxiliary relay and making contact of fourth auxiliary relay, to phase C terminal of supply mains, and through making contact of third auxiliary relay and making contact of fourth auxiliary relay, to phase A terminal of supply mains. Output of power bridge rectifier is connected to power terminals of push-pull power amplifier. Output of phase-shifting L-C control circuit is connected to one lead at input of push-pull power transistor amplifier whose other lead is connected to neutral wire N of supply mains. One lead at output of push-pull power transistor amplifier is connected through making contact of first auxiliary relay to motor connecting terminal which is connected through breaking contact of first auxiliary relay and making contact of fourth auxiliary relay to phase C terminal of supply mains. Output of push-pull power transistor amplifier is connected through making contract of second auxiliary relay to motor and the latter is connected through breaking contact of second auxiliary relay and making contact of fourth auxiliary relay to phase A terminal of supply mains. Output of push-pull power transistor amplifier is connected through making contact of third auxiliary relay to motor and the latter is connected to phase B terminal of supply mains through breaking contact of third auxiliary relay and making contact of fourth auxiliary relay. EFFECT: enhanced operating reliability; enlarged functional capabilities. 1 cl, 1 dwg