A New Method of Electrical Testing, Applied to Insulated Wires

Abstract

A DIFFICULTY was experienced recently in carrying out some electrical tests on enamelled wires at temperatures up to about 120° C. Pairs of wires were twisted together in accordance with B.S. Specification 156, Appendix A, and although it was possible to obtain all the required electrical properties at atmospheric temperatures, this was not so with some classes of enamel when the same tests were attempted in rising temperatures. As changes in power factor were being followed, a relatively high voltage between wires was used (about 1.2 kV.), and it was found impossible to avoid premature breakdown of some classes of enamel when the temperature was raised rapidly. Evidently a means of controlling the voltage applied between wires was wanted so that as the temperature rose, the voltage would fall off; but it was not practicable to do this accurately and quickly enough with ordinary hand control.