METHOD FOR IN-SERVICE HEATING OF AC MOTOR WINDINGS BY ELECTRIC CURRENT Russian patent published in 2004 - IPC

FIELD: electrical engineering; in-service protection of three-phase motors.

SUBSTANCE: additional heating circuit is set up from heat source and series connected windings 4, 4', and 4" of motors of different rated power and speed, capacitors 5 and 5' are connected in parallel to them, and ac voltage is applied to this circuit. Prior to setting up this circuit type of winding connection and rating of capacitors to be connected are chosen so as to ensure heating current chosen not to exceed 0.35 of motor rated value at hottest spot of windings. Motors are automatically switched over for heating: switching devices 1, 1', and 1" disconnect them from supply mains U₁, and additional heating circuit is connected to supply mains U₂ through contacts 7, 7', 7", 7''', and 7"" of switching device 6. Heating is ceased automatically: turning on switching devices 1, 1' and 1" when any motor is to be thrown in operation makes their auxiliary contacts 3, 3', and 3" open circuit of device 6, contacts 7, 7', 7", 7''', and 7"" disconnect additional circuit from supply mains U₂, and heating process is discontinued.

EFFECT: reduced cost.

2 cl, 1 dwg