Breakdown characteristics of transformer oil in a uniform field under oscillating impulse voltage

The field impulse voltage test plays the most important role to ensure the safe of the power transformer. It is hard to carry out the standard impulse voltage test for the power equipment because the generator is very huge. The oscillating impulse voltage waveform has high efficiency and be recommended by IEC 60060-3 as the field test waveform. Transformer oil is the main insulation part of power transformer insulation system. The insulation characteristics of transformer oil under different type impulse waveform have great influence to the design, operation and test amplitude for the power transformer. This paper focuses on the breakdown characteristics of transformer oil in a uniform field under oscillating impulse voltage (OIV). Three type oscillating impulse voltage waveforms with oscillating frequency of 14, 117 and 373 kHz were adopted as the test waveforms. The standard lightning impulse (SLI) voltage was also adopted as the reference waveform. The experiment results show the breakdown waveforms have large oscillation under OIV but little oscillation under SLI for the influence of circuit inductor. The minimum breakdown voltage increase with the increase of oscillating frequency and the 117 kHz impulse waveform has the similar breakdown voltage with SLI waveform. The voltage-time distributions were obtained through lab test and the results shown that the OIV have the longer time lag than SLI for the influence of the oscillation of waveform. The experimental results were explained through streamer mechanism. The study provides the foundation for the field impulse test using oscillating impulse waveform.