Arrangement for testing breakdown of the insulation of a conductor utilizing a direct current circuit to minimize 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 CONNECTIBLE ACROSS SAID CONDUCTORS FOR IMPRESSING THEREACROSS AN ALTERNATING CURRENT VOLTAGE OF A MAGNITUDE TO PLACE SAID INSULATION UNDER BREAKDOWN STRESS WHEREBY A PREDETERMINED AMOUNT OF ALTERNATING CURRENT IS PERMITTED TO FLOW OVER SAID TWO CONDUCTORS AND SAID STRAY CAPACITANCE IN SERIES; APPARATUS FOR RENDERING SAID BREAKDOWN TEST SUBSTANTIALLY INDEPENDENT OF SAID STRAY CAPACITANCE, SAID APPARATUS INCLUDING MEANS FOR ADDITIONALLY CONNECTING A DIRECT CURRENT SOURCE ACROSS SAID CONDUCTORS SO THAT A DIRECT CURRENT IS CAUSED TO FLOW IN A CIRCUIT EXTENDING OVER SAID TWO CONDUCTORS, AND THE LEAKAGE RESISTANCE THEREBETWEEN IN SERIES, AND AN AMPLIFYING DEVICE HAVING FIRST AND SECOND OUTPUT ELECTRODES AND A CONTROL ELECTRODE, SAID OUTPUT ELECTRODES BEING SERIALLY INCLUDED IN SAID DIRECT CURRENT CIRCUIT, AND MEANS BEING PROVIDED FOR APPLYING A BIAS POTENTIAL TO SAID CONTROL ELECTRODE SUCH THAT FOR RELATIVELY HIGH RESISTANCE OF SAID LEAKAGE PATH THE AMPLIFYING DEVICE IS MAINTAINED NEAR CUTOFF BUT THAT FOR RELATIVELY LOW RESISTANCE VALUES OF SAID LEAKAGE PATH SAID AMPLIFYING DEVICE IS PERMITTED TO OPERATE IN RESPONSE TO SAID FLOW OF DIRECT CURRENT TO INDICATE THE EXISTENCE OF THE HIGH LEAKAGE CONDITION BETWEEN SAID CONDUCTORS.