Development of high frequency Tan Delta measurement method for 132kV transmission underground cables

Abstract

Tan Delta testing is a diagnostic method of testing cables to determine the quality of the cable insulation. This helps create a systemized method to analyse aging of cables in the long run. It utilizes the phase shifts caused by the displacement current induced due to the existence of impurities in the insulation or stress on the cable. Current method for tangent delta measurement is performed at VLF (0.02 and 0.1 Hz) or power frequencies of 50 and 60 Hz. However the usage of high voltage at VLF or power frequency will require large cost and space. Alternate method is by using High frequency. The novel part of the HF experiment setting is that short samples of cables will be used (1m).A smaller testing environment is needed compared to LF experiment setting. Thus cost and space will be saved. However the utilization of short cables reduces the total capacitance of the cable. Therefore frequency (ω) has to be increased from power frequency to high frequency to obtain sufficient induced current. The utilization of HF will create high electric stress on the dielectric thus inducing dielectric current that is measureable which proves crucial in determining actual Tan delta values to indicate the real condition of the cable for diagnostic purpose. © 2014 IEEE.