The field testing of electrical insulation by D-C methods

The thought has been expressed that the manufacturer and user of insulating materials, who may use electrical resistance measured in accordance with ASTM D-257(1) as one means of evaluation and control, may not be familiar with the d-c tests that these materials are subjected to after assembly into insulation systems in apparatus. One of the purposes of this paper is to review d-c tests as they are used in the field to evaluate the condition of the insulation in power apparatus. It is largely in power equipment such as rotating machinery, switch-gear, cable and transformers that such field tests can be economically justified (2).