Analysis Of Partial Discharge Characteristics Of Oil-Paper Insulation Of Transformer At High Frequency

High frequency transformer,as an important electrical component in power electronics,has the function of electrical isolation and voltage regulation.As the requirements for voltage frequency become higher and higher,the proportion of high frequency transformer in production and life is becoming larger and larger.However,partial discharge phenomenon will cause transformer oil to heat up and crack to produce bubbles,and space electric field distortion will eventually evolve into arc discharge to breakdown insulation,which will affect economic production and life safety.In the past,the research on oil paper insulation partial discharge of oil immersed transformers was mainly based on simulation or experimental research under the premise of DC and power frequency AC.For the high-frequency situation,it mainly focused on the high-frequency partial discharge of gas-solid insulation system,focusing on the influence of voltage form,temperature and other factors on the discharge macro characteristics.There were few research reports on the discharge amount and discharge times of partial discharge under highfrequency voltage.In this paper,the characteristics of oil paper insulation partial discharge at high frequency are studied by finite element simulation and experiment.Firstly,based on the finite element simulation model of oil paper insulation partial discharge under different high-frequency voltage,the relationship between the initial discharge voltage amplitude,electronic charge density and frequency of oil paper insulation partial discharge under high-frequency voltage was obtained.At the same time,the phenomenon of ion recombination and residual charge was found in the discharge process and its mechanism was analyzed;Then through the oil paper insulation partial discharge experiment platform at high frequency and power frequency,it is found that partial discharge at high frequency mainly occurs at the rising edge and falling edge of the applied voltage,and when the frequency is higher than 10 k Hz,there is a frequency induced inflection point on the rising edge and falling edge of the occurrence of partial discharge,and the trend of the maximum discharge amount and discharge times of partial discharge with the applied voltage at high frequency and power frequency is analyzed,As well as the relationship between the discharge voltage and current of partial discharge under different high-frequency and the applied voltage,it is concluded that the applied voltage of 10 k Hz and 4k V has the smallest impact on the insulation performance of oil paper composite insulation in the high-frequency range of 1～10k Hz;Finally,the bubble characteristics of partial discharge at high frequencies are studied.Based on the establishment of a separated multiphase flow finite element simulation model,the bubble movement trajectory in transformer oil,the impact of bubbles on the discharge channel,and the impact of different high frequencies on the bubble’s own shape,gas production rate,and movement rate are obtained.In this paper,the characteristics of initial voltage,electronic charge density,discharge voltage,discharge current,maximum discharge amount,discharge times,single bubble and multi bubble motion and shape change of oil paper insulation partial discharge at high frequency are studied by combining experiment and simulation.The main innovation of the simulation part is to divide the oil paper composite medium into three areas,which makes the simulation data more realistic,and provides theoretical support for the deterioration protection of oil paper insulation of high-frequency transformers and the improvement of the dielectric properties of oil paper insulation;In the experimental section,the maximum discharge amount and discharge frequency under different high-frequency conditions were studied to obtain the frequency value that has the smallest impact on the insulation performance of oil paper within the specified frequency range.This provides a reliable frequency reference for the use of high-frequency transformers in industrial life and provides data support for future researchers on high-frequency partial discharge.