An Improved Space Charge Measurement Approach for Power Cables

With the increasing use of high-voltage direct current (HVDC) and MVDC assets, the fundamental topic of space charge measurements in full-size cables has to be faced properly. Space charge can be a significant threat to dc insulation system reliability. In this article, the development of an innovative pulsed electro-acoustic (PEA) device to measure the space charge distribution of HVDC and MVDC cables is presented. Issues related to the real cable structure, thickness (and thus signal attenuation), and noise are dealt with. Specifically, the effect of different types of electrodes, thickness, and materials on PEA signal measurement accuracy is discussed. It is shown that the measurement results can be still effective and accurate in a simpler and smaller structure than those used at present for flat specimens or model cables. To mitigate the influence of environmental noise and multiple reflection waves, a new adaptive algorithm based on wavelet analysis is proposed. By combining time-frequency analysis with the adaptive filtering (AF) method, space charge signals can be extracted from noise in a lossless way. The study also shows that the new algorithm has a better performance and stability as regards attenuation and dispersion factors. The validity of the improved recovery technique is proved by testing on polymeric cable.