Study On Discharge Characteristics Of Liquid Dielectric Under Nanosecond Impulses

Research of liquid dielectrics discharge characteristic has been focused on the field of electrical insulation,the main purpose is to take full advantage of the insulating properties of the liquid medium,and optimize the insulation design.With the rapid development of pulsed power technology,people has been concern the research of liquid dielectric discharge process under nanosecond-pulsed voltage.In this dissertation,the two-dimensional hydrodynamic fluid model is established,the needle-needle electrode gap transformer oil is used as the research object.A numerical simulation of transformer oil is made by positive and negative nanosecond pulses.The effects of different voltage polarity,voltage amplitude and pulse rising time on the formation and development of oil discharge were investigated.The results show that under the condition of positive polarity pulse voltage,the space charge strengthens the electric field in front of the head.The larger the voltage amplitude,the faster the streamer rate.When the discharge reaches the same position,The shorter the rising edge of the positive pulse,the larger the radius of the streamer formed.Under the condition of negative polarity pulsed voltage,the space charge attenuates the electric field in front of the head of the streamer.The larger voltage amplitude,the faster streamer rate.The rise time is longer,the streamer propagation distance is shorter,when the rise time is 100 ns the streamer disappear easily.The initial velocity of the streamer injection is larger than the initial velocity of the positive streamer injection under the negative polarity condition,and the axial propagation distance of the negative streamer injection under the same amplitude condition is smaller while the radial propagation distance is large,the generation and propagation of the negative streamer injection requires a higher amplitude voltage.In addition,the process of discharge in the transformer oil temperature rise phenomenon.The numerical simulation can be used to analyze and understand the pre-discharge process of liquid medium from the microscopic point of view,which can help to deepen the understanding of the starting and developing process of the transformer oil and the understanding of the ionization mechanism in the liquid dielectric.In addition,equipped with a breakdown test system,the use of pulse powersupply device output positive and negative polarity pulse voltage,positive and negative DC voltage,breakdown needle-needle electrode with transformer oil.Spectrum measurement system of the 45# transformer oil discharge is designed,the spectral measurement apparatus comprise spectrometer,ICCD,optical fiber and computer.The most spectral data of the experiment is the?H spectral line,and the intensity is very large,which indicates that the largest number of particles are involved in this transition.We can also get the information of the discharge area of electronic density by spectrum to calculate.Get the breakdown voltage of different electrode gap,the electrode of small radius of curvature with negative polarity breakdown voltage is high,indicating the polarity effect;the breakdown pulse voltage is different,if the pulse frequency is different,breakdown voltage of high frequency is low,indicating a heavy frequency effect.Liquid discharge spectroscopy provides an experimental method to analyze the discharge from the microscopic point of view.The polarity effect and the frequency effect of the breakdown process are helpful to understand the discharge mechanism of the liquid medium.Under the nanosecond pulse the discharge study is more conducive to reveal the essence of liquid discharge.