Space charge monitoring in cables at low DC electrical field

Space charge measurements based on the Pulsed Electro-Acoustic (PEA) method were performed on a XLPE based mini-cable at low applied DC voltages and under isothermal temperature (60°C). This work was to study the transient of the space charge accumulation due to the field dependent conductivity of the cable insulation. Considering the small charge quantity of charge accumulated and the resulting difficulties in accurate data acquisition, a new method is proposed based on using the peak area ratio of the electrode peaks to characterize the transient behavior of charge accumulation. The experimental results show that the peak area ratio decays exponentially to an equilibrium value determined by the cable cylindrical geometry and therefore a time constant for space charge accumulation can be estimated. Moreover, the measured peak area ratios, which reflect the ratios of electrical fields at two interfaces, from different initial conditions (charge-free, charged steady-state and following polarity reversal) coincide with that calculated from theory published in the literature.