Arrangement for testing breakdown of the insulation of a conductor utilizing an alternating current circuit to eliminate stray capacitance effects

Claim 1

An arrangement for testing breakdown of the insulation between a conductor under test and an adjacent second conductor, said two conductors having a certain amount of stray capacitance therebetween, an alternating current source connectable across said conductors for impressing thereacross an alternating current voltage of a magnitude to place said insulation under breakdown stress whereby alternating current potential is permitted to flow over said two conductors and said stray capacitance in series; apparatus for rendering said breakdown tests substantially independent of said stray capacitance, said apparatus including: sensing means connected between said alternating current source and said second conductor; synchronizing means connected to said alternating current source operated to periodically generate control pulses in response to current reversals of said alternating current source; amplifying means comprising an inverting amplifier and a non-inverting amplifier each having input connections to said current source and said sensing means, said amplifying means further including an output circuit; switching means connected between said synchronizing means and said amplifying means operated in response to said periodic pulses from said synchronizing means to alternately short circuit said inverting amplifier input and said non-inverting amplifier input whereby signals representative of the magnitude of current flowing through said conductors under test are alternately conducted to said inverting amplifier and to said non-inverting amplifier; and magnitude measurement means connected to the output of said amplifier means operated to indicate the magnitude of current flowing over paths between said conductor under test and said adjacent second conductor to indicate the magnitude of leakage condition between said conductors.