Simulation modeling of polarization and depolarization current analysis for underground cable insulation

High voltages, when applied continuously to an underground cable, leads to the deterioration of its insulation. Gradual yet permanent changes are made to its dielectric properties, caused by electronic charges created within the insulation material; affecting its ability to withstand high electrical stresses. Over an extended period of time, this continual insulation degradation plays a major role in its eventual cable breakdown. Therefore the monitoring of insulation condition is essential to power utilities, to avoid costly disruptions. One of the techniques developed to assess the insulation condition of underground cables is the polarization and depolarization current (PDC) analysis. This technique, executed by measuring the insulation´s polarization and depolarization currents, is commonly used to assess degradation in the transformer insulation. However it can also be used to monitor the degradation within cable insulation to a certain degree. This paper attempts to describe how PDC can be used to determine the condition of cable insulation via simulation modeling, developed based on the PDC theory for an ideal cable. The simulation results are then compared with experimental PDC measurements to determine the severity of insulation degradation.