The A-C dielectric-loss and power-factor method for field investigation of electrical insulation

THE use of dielectric loss and power factor for testing the insulation of electrical equipment in service position in the field with one side grounded began with the advent of the apparatus and method described in this paper. Through its use, tables of standard values have been set up indicating when insulation is “good” for continued operation with an adequate factor of safety or when it is “bad” to a degree that warrants investigation and possible replacement in order to insure continuity of service until the next scheduled test. Types of insulation that were being discarded as inherently bad, judged by their high failure record, now are being re-established as good insulation after the tests have shown the defects to be largely of a secondary nature and removable or curable.