Novel 0.1 Hz exponential wave generator based on semiconductor switch

Abstract

Very low frequency (VLF) high voltage technique has been used to some extent in the past for the field test of XLPE power cables. Equipment available has used 0.1 Hz voltage having a variety of waveforms such as square waves, triangular waves, etc. This paper describes a novel laboratory test system conducted with the objective to develop an exponential wave generator as the complement of existing VLF test waveforms. The generator consists of a high voltage (HV) 50 Hz AC source, a HV semiconductor switch unit based on the series-connected IGBTs, and shape-control resistors. The proposed HV switch can block 20 kV rated voltage and has the current capacity of 40A. Finally, the new designed approach permits the cable load of up to 1μF to be tested at a withstand voltage level of 20 kV. Preliminary experiments are performed in the laboratory using the proposed generator and the output waveforms are presented. The experiment results show that the exponential wave appears to be a satisfactory alternate to the waveforms used in the traditional VLF test and the generator is a utility installation for the diagnostic test of power cables. Keywords-VLF; test systems