Characterization of the Pulsed Electro- Acoustic Method in HVDC Materials

Abstract

The Pulsed Electro-Acoustic (PEA) method is a non-destructive technique used to measure space charge accumulation in polymeric insulation materials used for extruded high voltage direct current (HVDC) power cables. However, the measured space charge profiles are sensitive to the measurement setup. In this work, the influence of electrode configurations and acoustic coupling media (ACM) on PEA measurements has been investigated using commercial grade HVDC crosslinked polyethylene (XLPE) materials supplied by Borouge International. PEA measurements were performed using four different electrode configurations to assess the influence of semiconductive and metallized interfaces on charge injection and space charge accumulation. The measurements were conducted at two electric field strengths and two temperatures. In addition, three acoustic coupling media were evaluated based on a pre-screening procedure. The results show that the electrode configuration has a significant impact on the space charge profile of the XLPE insulation. Configurations utilizing metallized semiconductive electrodes reduced the overall charge injection compared to configurations using semiconductive electrodes without metallization. When the electrodes were sputtered direcetly onto the XLPE insulation, the influence of both the semiconductive electrode and the acoustic coupling medium was decoupled from the insulation sample, therefore reflecting the intrinsic space charge dynamics of the XLPE insulation. The acoustic coupling media were also found to influence the measurements. One of the acoustic coupling medium tested was observed to migrate into both the XLPE insulation and the XLPE semiconductive electrode materials, resulting excessive material swelling at 70 ◦C. Acoustic coupling media with higher viscosity was found to increase overall homocharge injection at 25 ◦C, and contribute to heterocharge accumulation at the high voltage electrode at 70 ◦C, indicating increased Maxwell-Wagner polarization at the ACM-insulation interface.