Space Charge Distribution Characteristics under Ultra-Low Frequency Voltage in XLPE

There is a risk of space charge accumulation under ultra-low frequency voltage, which may cause electric field distortion and destroy the cable insulation. In this paper, a space charge measurement system with high phase resolution is established based on electroacoustic pulse method (PEA). XLPE samples were prepared to test the space charge distribution at 0.02, 0.1 and 50 Hz. The characteristics of space charge distribution and average bulk charge density at different frequencies, amplitudes and phases were obtained. The results show that the distribution of space charge varies periodically with the phase change under different frequency AC stress. The space charge distribution characteristics are different at 0.1 Hz and 0.02 Hz, which may be related to the effective time of charge injection. The accumulation of heterocharges at 0.1 Hz may be the result of impurity ionization. Besides, the average bulk charge density increases with the decrease of applied voltage frequency, and the space charge accumulation at 0.02 Hz is several times higher than that at 50 Hz.

I. Introduction

Crosslinked polyethylene (XLPE) is commonly used in power systems because its excellent insulation, mechanical performance. It is common knowledge that the space charge accumulation in insulating materials can significantly reduce their effectiveness and even cause insulation breakdown [1].