| 摘要 |
<p>When a three phase induction motor is connected by three wires only, and its power factor is controlled by triggering triacs or other thyristor arrangements in response to deviation from a required value, a triac may cease to conduct prematurely because no other triac is conducting. Also the phase lag monitoring for control purposes may be incorrect through premature triac turn-off. If a triac 50 for one phase receives a trigger signal from a generator 16 and at the same time another triac 51 or 52, depending on direction of motor rotation, also receives a trigger signal from one of gates 75 and 76, the effect of premature turn-off is overcome by a further firing. Gates 84 and 85 are used to suppress erroneous phase-lag monitor signals from the comparator 21 when current in another phase, selected according to direction of motor rotation, has ceased. Other phases have similar arrangements. <IMAGE></p> |
