H - Electricity – 02 – P
Patent
H - Electricity
02
P
318/78
H02P 1/00 (2006.01) H02P 1/50 (2006.01)
Patent
CA 1124781
Case 2549 ABSTRACT OF THE DISCLOSURE This invention relates to a control circuit for a rotor field winding of a synchronous motor. During motor acceleration at start-up, the rotor winding is discharged through a pair of thyristors connected in series across the rotor field winding. A varistor and a resistor are also connected in series across the rotor field winding and the junction between the varistor and resistor is connected by separate paths to each thyristor gate. As the voltage in the field winding increases, the varistor-resistor combination will conduct more current. When the voltage drop across the varistor reaches a first level it is suffi- cient to fire one thyristor. A zener diode in the path to the gate of the other thyristor blocks firing of that thyristor until the voltage across the varistor rises above the breakdown voltage of the zener, then the other thyristor fires. When both thyristors are fired or gated on they discharge the rotor winding. It was previously necessary to arrange for successive firing of the thyristors by using a pair of zeners whose breakdown voltage was selected by trial and error to ensure sequential firing at desired voltages. The present invention eliminates the need for selecting these matched but mismatched zeners and the related expense.
315582
Murdoch James C.
Nesbitt John J.
Stevenson Andrew C.
Canadian General Electric Company Ltd.
Eckersley Raymond A.
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