초록 ▼

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 s

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.

대표청구항 ▼

Detector apparatus for registering ground faults on either terminal of a direct current energy source, comprising, (a) a pair of switching means, each when active coupling a different terminal of said energy source to a common bus of said detector apparatus for producing a fault current signal havin

Detector apparatus for registering ground faults on either terminal of a direct current energy source, comprising, (a) a pair of switching means, each when active coupling a different terminal of said energy source to a common bus of said detector apparatus for producing a fault current signal having a level in accordance with the impedance of any ground fault on the opposite source terminal, (b) a pulse generating means coupled for alternately activating said pair of switching means at a preselected rate, (c) a current pump means controlled by said pulse generating means for alternately supplying a first and a second reference current signal, each having a preselected level and associated in time with a different one of said fault current signals alternately produced by said switching means, (d) a comparator means coupled for alternately receiving said first and second reference current signals, each jointly with the corresponding fault current signal, and responsive to each pair of received corresponding signals for generating a first or a second output signal in accordance with a predetermined comparison level of that pair to indicate the absence or presence, respectively, of a ground fault on the corresponding terminal of said energy source, (e) a register means normally occupying a first condition and operable to a second condition for registering a ground fault indication, and (f) a synchronizing means jointly controlled by said switching means and said pulse generating means and coupled for applying the output signals of said comparator means to hold said register means in its first condition only when said comparator output is a sequence of first signals in synchronism with the operation of said pulse generating means.