Assessment of the State of Electrical Insulation by Measuring Isothermal Relaxation Current.

Experimental data on measurements of isothermal relaxation current (IRC) are presented for different kinds of industrial electrical insulation: cross-linked polyethylene (XLPE) 6-kV power cables and thermosetting insulation for the stator windings of high-power rotation machinery. The ageing of and damage to electrical insulation was assessed using indicators derived from the so-called distributed charge current. An analysis of the experimental data shows that the IRC method is highly sensitive for detection of incipient defects in these insulating materials and can be used to determine the indicators of ageing in XLPE insulation and their initial and limiting values. [ABSTRACT FROM AUTHOR]