Research On The Equivalence Of Damped Oscillation Voltage And AC Voltage To Withstand Voltage Test Of XLPE Cable

The current XLPE cable withstand voltage test method mainly uses AC resonance method,but this method needs high power,large equipment volume,and field test is extremely inconvenient.The oscillation wave method,which is often used to detect partial discharge,is easy to operate,light and flexible,and easy to carry and transport.If the oscillation wave method can be used to replace the AC resonance method for withstand voltage test,it will greatly improve the test efficiency The equivalence between oscillatory wave method and AC resonance method is of great significance.In this paper,an improved needle plate electrode model was designed and fabricated,which can accurately adjust the depth of the needle tip in XLPE tablet,Power frequency voltage withstand platform and oscillating wave voltage withstand platform are built.The voltage withstand process of pin plate electrode model is observed from Weibull distribution,partial discharge before breakdown and discharge channel after breakdown.The effects of oscillation frequency,pre pressurization time and multiple oscillation pressurization on the breakdown process under oscillating wave voltage are studied,and the equivalence with power frequency voltage withstand is analyzedThe results show that the size and shape parameters of Weibull distribution are affected by the insulation distance of XLPE laminate and the frequency of oscillation wave.The partial discharge of power frequency is large and dense,and the number of oscillation wave partial discharge increases with the increase of frequency.The breakdown channel of XLPE laminate has obvious carbonization track under power frequency voltage,while only cracks along the periphery of the channel appear under oscillation wave voltage.For the XLPE laminate with 0.2mm insulation distance,the equivalent coefficients of the average peak value of the breakdown voltage of 42Hz,216Hz and 375Hz oscillation wave and the peak value of power frequency 2U0 are 2.0,2.2 and 2.7 respectively.When the DC voltage is preloaded for 15min at 375Hz oscillation wave,the equivalent coefficient becomes 2.4.It is considered that the increase of DC withstand time will lead to the decrease of the breakdown voltage of oscillation wave.The oscillation wave voltage lower than the breakdown voltage has little effect on the insulation damage and will not lead to the breakdown.Increasing the DC preloading time can reduce the equivalent coefficient and improve the equivalence between the oscillation wave and the power frequency withstand voltage.