| 摘要 |
A pair of transistors, alternately activated by a low frequency generator, alternately connect the positive and negative terminals of the monitored DC source to the common bus of the ground detector apparatus. Each produces a fault current signal flow through any ground fault existing on the other source terminal, with the return circuit including a permanent ground rod, the input of a comparator, and apparatus common. An opposing reference current signal of preselected level is applied to the comparator input, at the same time as each fault signal, from a current pump network driven by the low frequency generator. If each reference current signal is larger than the corresponding fault current signal, the comparator output is a square wave signal of alternate plus and minus pulses which is applied to a negative voltage generator network controlled by contacts of two synchronizing relays alternately driven by the low frequency generator. If the comparator square wave output is synchronized with synchronizing relay operation, a registry relay is held energized to indicate the absence of ground faults on the source. If either or both fault current signals are greater than the corresponding reference current signal, the output is either of one polarity or is not synchronized with the relays so that the registry relay is deenergized and releases to indicate a ground fault condition.
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