| 摘要 |
<p>1,183,294. Control of A.C. motors. DANFOSS A.S. 18 June, 1968 [6 July, 1967], No. 28911/68. Heading H2J. The auxiliary winding 3 of an asynchronous motor is energized via a symmetrical controlled semi-conductor device (Triac) 7 in series with an ohmic resistor 8 (which may provide the necessary phase splitting), the control electrode 11 being supplied via a PTC resistor 10. At switch-on, the PTC resistor 10 passes sufficient current to trigger device 7 on, but the temperature and resistance of 10 rises until a point is reached when the current through it is insufficient to trigger 7 and the auxiliary winding is then effectively disconnected. A small current continues to flow through 10 thereby maintaining its temperature. The PTC resistor 10 is heated either by its own current, by resistor 8, by a separate resistor in series with the main winding or by the heat produced by the motor. Because of the time required for 10 to cool, too frequent starts are prevented.</p> |
