Ground fault detector apparatus including a pair of complementarily connected bridge detector means for isolated electrical power systems

Claim 1

A ground fault detector comprising: first phase sensitive bridge detector means producing a signal relative to impedance to ground of the lines of an isolated alternating current source, circuit means having a normal output signal level for generating a change in the output signal level whenever the signal reaches a predetermined threshold value corresponding to the impedance to ground being below a minimum level, and switching mean responsive to the change in output signal level for indicating the minimum level impedance to ground; the improvement comprising, a second complementary phase sensitive bridge detector means parallel connected across the first phase sensitive bridge detector means for indicating the presence of phase balanced ground faults and wherein the first phase sensitive bridge detector means includes serially arrayed capacitor and resistor bridge elements connected across the lines of said alternating current source, and the second phase sensitive bridge detector means includes, second serially arrayed capacitor and resistor bridge elements complementarily connected across the lines of said alternating current source so that the first serially array capacitor and resistor bridge elements and the second serially arrayed capacitor and resistor bridge elements are in parallel, but inversely connected across the lines of said alternating current source.