The effect of high frequency, high voltage supply on the growth of electrical trees on cross linked polyethlyne insulation of power cables

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Abstract
Nowadays, all types of electrical equipment, including cables, are exposed to various power quality effects. The harmonics are among the severe power quality problems, which can directly affect the insulating material in cables and other power system elements. Cables are costly power system elements, which deserve special attention in this regard. Cross linked polyethylene cables are widely used in all parts of the power system. The insulation material of such cables is significantly affected by high frequencies appearing as harmonics in the supply voltage. In this paper, a high voltage, high frequency circuit is developed to create different voltage harmonic orders and to test cross linked polyethylene insulation under condition of 10 kV with frequency of 50, 150, 250, 350 Hz. Test circuit consists of high voltage resonance transformer and low voltage rectifier/inverter to generate high frequency waveform. This arrangement is a good simulation for the real life operation of such cables in harmonic-polluted grids. This paper shows the negative effect of high frequency, high voltage supply on the performance of cable appearing as a growth of electrical tree on XLPE insulation of power cables. Different shapes of electrical trees and growth patterns were obtained as a function of frequency variation. This is attributed to the intensive partial discharges and photo ionization occurring at high frequency. This work is of great importance for the transmission and distribution grids, which currently suffer from a high penetration level of harmonics exceeding the standards limits.

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