| 摘要 |
<p>An insulation monitoring circuit for use with three phase motors fed from a supply in which one motor phase lead (2) is solidly earthed, has two semiconductor switching elements (4, 5) in series with, and at each of end, the earthed phase. At the main switch (3), a two phase tapping continuously feeds an insulation resistance measuring circuit (29) of the d.c. bias type, one of the phases being also connected to the earthed motor lead (2). A trigger pulse unit (10), with a synchronising signal obtained from a current transformer (6) in the earther phase, controls the firing of the thyristor in the outer switching element (4), and triggers it once every two cycles. In the alternate cycle the earthed section is thus isolated, and an insulation measurement takes place on the rest of the circuit. The motor performance is not interrupted.</p> |
