Study On The Influence Of Voltage Frequency On The Development Of Partial Discharge And Breakdown In Oil-paper Insulation

Harmonics,pulses and transient voltages in the power network lead to the long-term operation of high-voltage bushings,shunt capacitors,filter capacitors,reactors and other electrical equipment in the AC and DC networks under the voltage condition of nonsingle power frequency or non-steady DC.At present,the research on the breakdown characteristics of oil-paper insulation is only confined to the electrical strength test under the influence of voltage waveform,temperature and other factors.However,the influence of equipment loss enhancement effect under harmonic voltage on the development process of partial discharge of insulation and its breakdown characteristics need to be further studied.At the same time,although a large number of studies have been carried out on the damage effect of partial discharge on insulating paperboard,there is still a lack of exploration on the correlation between the partial discharge and the defect development of oil-paper insulation.In view of the shortcomings of the above research,this paper takes oil-impregnated paperboard as the research object,characterizes the thermal effect corresponding to power loss as a temperature factor and carries out the experimental research on the partial discharge and breakdown characteristics of oil-paper insulation under the action of frequency variation and temperature variation,and deeply analyzes the dielectric loss enhancement effect under harmonic voltage.Based on the development process of dielectric defects,the partial discharge and breakdown mechanism of oil-paper insulation under frequency change and temperature change is discussed in depth.The main work of this paper is as follows:(1)Taking capacitor element as research object,the calculation method of dielectric loss of insulation and conductor loss of aluminum foil plate under periodic voltage based on FFT decomposition principle is proposed,and the eclectrothermal coupling simulation model of capacitor element is established to analyze the temperature field distribution of capacitor element ubder high-frequency voltage.(2)A combined electrical-thermal breakdown test platform for oil-paper insulation is built to obtain the partial discharge and failure test data of oil-paper insulation under different voltage frequencies and temperatures.The phase resolved partial discharge is constructed,and the relevant discharge characteristics such as partial discharge initial voltage,discharge pulse repetition rate,maximum discharge amplitude,the average discharge amplitude are obtained.By dividing the development stages of discharge,the influence of frequency and temperature on the partial discharge and failure time of oilpaper insulation are analyzed.(3)The damage of oil-paper insulation under different discharge time is studied from the two aspects of surface morphology and characteristic of frequency domain dielectric response.The development law of internal defects caused by discharge degree is analyzed,and the mechanism of partial discharge damage to oil-paper insulation system is discussed.(4)The change of partial discharge energy in the process of oil-paper insulation failure is calculated and analyzed,and the development model of dielectric defects is proposed.The correlation between the defect development and partial discharge is analyzed by combining the energy change and the internal electric field change law of dielectric defect.The mechanism of frequency and temperature on the breakdown of oilpaper insulation is discussed.