| 摘要 |
<p>PURPOSE:To prevent phase shift and make an exact measurement of insulation resistance possible, by adding a current nearly equivalent to a zero-phase current at the commercial frequency and a fixed current of low frequency voltage for measurement, and making them flow simultaneously, the zero-phase current being fed back to the ground line of a second zero-phase current transformer (ZCT) having almost the same characteristics as a first ZCT. CONSTITUTION:An output of commercial power source component applied to a zero-phase current fransformer ZCT 6 is selected by a filer 15, and then delivered, as the output of an amplifier 13, to a loop signal line 14 penetrating through a second zero-phase current transformer ACT 11. A low frequency signal for measurement is also applied to the signal line 14 through an injection transformer 10, and both signals are input to a synchronous detector 9 through the second zero-phase current transformer. When each amplifier and a resister R12 are so adjusted that almost the same commercial power source components flow through the first and the second zero-phase current transformers, the phase shifts due to the commercial power source components of the low frequency signals for measurement derived via these zero-phase current transformed become equal to each other. Consequently, the phase relation between both signals in the synchronous detector 9 is kept in a desired state, and both signals are affected in a similar manner by temperature change, which gives no bad effects.</p> |
