Condition assessment of XLPE insulated cables using isothermal relaxation current technique

The isothermal relaxation current (IRC) method of assessing the condition of power cable insulation has been in use for more than 10 years. The method is based on a relaxation model of the thermal release of carriers from traps. An empirical aging factor often called A-factor determined from IRC analysis is investigated using measured depolarization currents from laboratory and field aged cables. Measurement results presented here indicate that calculation of A-factor depends on how well the software of the measuring system in IRC test set is able to approximate the measured depolarization current data. It is found that wrong approximation of measured data may result especially when the current decay is not monotonically decaying with time. For a better use of this equipment it is propose that the user make use of the raw depolarization current data instead of the A-factor output from the test system