Nondestructive testing of insulation

THE USER OF ELECTRIC APPARATUS is constantly in need of information concerning the condition of insulation. This information, at the present time, is supplied by such tests as insulation resistance, power factor, capacitance, or by more severe tests such as “high-pot.” Unfortunately, none of these tests gives a true indication of the “health” of the dielectric, but rather indicate its present condition — a condition that may exist only temporarily and can be corrected by suitable action. It is important, of course, to have this information; however, it is of equal importance in many applications to have an indication of the useful life that can be expected from the dielectric at any time during its use.