Study on Breakdown Characteristics of Transformer Oil under Negative Oscillation Lightning Impulse Voltage

Abstract

Field impulse voltage withstand test is an important step to ensure the safety of a transformer. The double exponential impulse voltage generator has large volume and low efficiency, which is hard to adjust the output waveform and is not convenient for field test. IEC 60060-3 recommends that the oscillating impulse voltage can be used in filed test and the generator has high efficiency. This paper constructs a generator which can output 5 kinds of Negative lightning impulse voltage waveforms and studies the breakdown characteristics of transformer oil under these lightning impulse voltages. The five types of lightning impulse voltages are standard lightning impulse (LI) voltage and oscillating lightning impulse (OLI) voltages with the oscillation frequency of 100 kHz, 200kHz, 300kHz and 400 kHz. The results prove that, in oscillating lightning impulse voltage test, the breakdown point always occurs at the peak of the oscillation period. And as the oscillation frequency increases, the maximum discharge time delay decreases, the voltage-time curve moves up, the slope of the probability curve of the Weibull distribution decreases, the scale parameter of the Weibull distribution curve decreases, and both the initial breakdown voltage and the 50% breakdown voltage increase gradually. Comparing with the standard lightning impulse voltage test, the results of the oscillating lightning impulse voltages test has larger maximum discharge delay, higher voltage-time curve and higher slope and scale parameter of the Weibull distribution curve. The probability curve of the Weibull distribution converges in high voltage.