High voltage VLF test equipment with sinusoidal waveform

The problems associated with testing field aged XLPE cable using HVDC are now well documented. AC test equipment for field tests at power frequency also presents problems. The equipment required for such tests is large, heavy and expensive even with resonant test sets. Equipment producing very low frequency (VLF) high voltage has been used to some extent in the past. Typically this equipment produced 0.1 Hz voltage having a variety of waveforms. Squarewaves, triangular waves, etc. have been available. Such nonstandard waveforms complicate efforts to correlate VLF techniques with the results of power frequency tests. This paper describes AC test equipment utilizing a new approach to high voltage VLF in the range of 0.02 to 0.1 Hz. The equipment generates a sinusoidal waveform directly, without the additional complexity, cost and weight of HV filters. This not only saves weight and reduces cost but also simplifies its use in diagnostic tests such as partial discharge detection and site location. The design concept and application of the equipment to both voltage withstand testing and partial discharge testing are discussed.