OVERTEMPERATURE PROTECTIVE GEAR FOR INDUCTION MOTORS Russian patent published in 1999 - IPC

FIELD: electrical engineering. SUBSTANCE: protective gear for induction motors 1 has semiconductor control unit 7 incorporating group of thermistors 6 whose number equals that of motor phase windings. Each thermistor 6 is, essentially, flat bifilar coil wound of copper wire. In addition, protective gear is provided with coils 4 each connected through current transformer 3 to motor phase winding. Rated current of transformer primary winding I_Itr.r is chosen from equation I_Itr.r = 8.I_m.r, where I_m.r is rated current of motor; cross-sectional area of additional-coil wire S_c.w equals S_c.w= S_m.w/K, where S_m.w is cross-sectional area of motor phase winding wire; K is rated transformation ratio. Grade of wire for motor phase winding and for additional coil is the same. Additional coils 4 are wound on common core 5 whose diameter is smaller than or equal to 0.1 of their total height. Thermistors 4 are stuck inside each additional coil. EFFECT: provision for replacing induction motor without changing its protective gear due to arrangement of thermistors beyond motor phase windings. 4 cl, 1 dwg