Study On The Insulation Characteristics Of Mixed Gas Based On Perfluoroisobutyronitrile And Its Application In Pulsed Power Generator

In the continuous progress process of pulsed power technology,insulating medium has become one of the most popular research directions.Among them,insulating gas is an effective substitute for transformer oil because of its light weight and easy monitoring and maintenance characteristics.Perfluoroisobutyronitrile（C₄F₇N）is a newly emerging environmental-friendly insulating gas in recent years,which has better insulating properties than sulfur hexafluoride.This thesis studied the insulation characteristics of the perfluoroisobutyronitrile mixed gas,applied the perfluoroisobutyronitrile mixed gas to the pulse power generator,and carried out experiments on its breakdown characteristics,insulator flashover characteristics,and trigger switch jitter characteristics.The high and low temperature characteristics are calculated and analyzed,and the pulse power generator using perfluoroisobutyronitrile mixed gas is employed for repetitive frequency experiments.The research results show the application of perfluoroisobutyronitrile gas in the field of pulsed power technology has great prospective,which has important practical significance and application value.The research content specifically includes the following aspects:（1）Under a uniform electric field,the electrode spacing,gas pressure,and the volumn fraction of C₄F₇N in the C₄F₇N/CO₂ mixed gas were changed,and the breakdown characteristics of the C₄F₇N/CO₂ mixed gas were tested.The experimental results show that when the C₄F₇N/CO₂ mixed gas pressure and the volumn fraction of C₄F₇N remain unchanged,the breakdown voltage decreases with the decrease of the electrode spacing;when the electrode spacing is fixed and the C₄F₇N/CO₂ mixed gas pressure does not change,the breakdown voltage increases with the increase of the volumn fraction of C₄F₇N in the C₄F₇N/CO₂ mixed gas.Under the same volumn fraction of C₄F₇N,the breakdown voltage between the electrodes decreases with the decrease of the electrode spacing.When the the volumn fraction of C₄F₇N in the C₄F₇N/CO₂ mixed gas is lower,the breakdown voltage dispersion is higher.Under the same electrode spacing,the lower the volumn fraction of C₄F₇N in the C₄F₇N/CO₂mixed gas,the shallower the carbonization traces remaining on the electrode surface after the breakdown experiment,and as the electrode spacing decreases,the carbonization traces remains on the copper plate electrode after breakdown experiment are shallower.（2）Insulators made of three insulating materials:Poly tetra fluoroethylene（PTFE）,Polyformaldehyde（POM）,and polyamide（PA）were used to carry out the flashover test along the surface of the insulators with C₄F₇N/CO₂ mixed gas.The insulators were in smooth and grooved shapes.The results show that when the insulator flashover occurs along the surface,the voltage will be greatly reduced.Under the same conditions,when the length of the insulator decreases,the flashover voltage along the surface decreases.When the C₄F₇N content in the C₄F₇N/CO₂ mixed gas decreases,the insulator flashover voltage decreases.In terms of insulation recovery after the occurrence of flashover along the surface,PTFE material is the best,POM material is the second,and PA material is the weakest.Grooving treatment of insulators will slow down the voltage drop rate of the surface flashover phenomenon and increase the value of the surface flashover voltage,which is essential to the improvement of the insulation recovery performance of the insulator.（3）Use the Antoine equation to calculate the saturated vapor pressure values of pure C₄F₇N and pure CO₂ gas at different temperatures,and obtain the relationship between the saturated vapor pressure and temperature of the mixed gas under the condition of different proportions of C₄F₇N in the C₄F₇N/CO₂ mixed gas.The results show that when C₄F₇N gas is mixed with CO₂ gas,the saturated vapor pressure of the mixed gas increases significantly.From the calculation results,the liquefaction temperature changes of the mixed gas under different C₄F₇N content at different gases are obtained.The results show that if the temperature is below-40℃,the maximum pressure should not exceed 0.2MPa when the C₄F₇N content is 10%,and the C₄F₇N content is 8%.The maximum air pressure shall not exceed 0.25MPa when the C₄F₇N content is 5%,and the maximum air pressure shall not exceed 0.4MPa when the content of C₄F₇N is 5%.At the same time,a mixed gas high and low temperature test experimental platform was established,and the C₄F₇N/CO₂ mixed gas high and low temperature characteristic experiment was carried out,and the experimental values of the C₄F₇N/CO₂ mixed gas liquefaction temperature under different mixing ratios and different pressures were obtained.The calculation and experimental results of the high and low temperature characteristics of the C₄F₇N/CO₂ mixed gas have guiding significance for determining the mixing ratio of the mixed gas in practical applications.（4）The switch triggering experiment of C₄F₇N mixed gas under different pressure and different volumn fraction was carried out.The study found that when there is no switch self-breakdown,the corona stabilized gas switch has a low jitter characteristic,and the minimum trigger voltage standard deviation to the mean value is 4.7%,the maximum value is 7.5%,and the average value is 6%.When the switch self-breakdown phenomenon occurs,the minimum ratio of the trigger voltage standard deviation to the average value is 15.6%,the maximum is 52.3%,and the average is 26.9%.When the content of C₄F₇N is less than 3%,the probability of switch self-breakdown is greater,the gas switch jitter degree is serious,and the instability is strong.As the volumn fraction of C₄F₇N gradually decreases,the jitter of the trigger voltage in the re-frequency experiments basically show a gradual upward trend,and the switch self-breakdown phenomenon is more likely to occur,making the jitter more serious.When the repetition frequency continues to increase under the consition of the switch self-breakdown not occurring,the correlation coefficient between the jitter of the trigger voltage and the repetition frequency is 0.4659,showing a moderately positive correlation trend.It expresses that there is probably a"memory channel"effect.（5）Apply the C₄F₇N/N₂ mixed gas to the high-power pulse drive source as the insulating medium of the gas switch,and carry out a long-term re-frequency experiment with a repetition frequency of 600 times at 10 Hz.The experimental results show that the 10%C₄F₇N/N₂ mixed gas has better stability in the long-term re-frequency experiment when the switch self-breakdown does not occur,and the jitter is 7.55ns.This has important practical significance for exploring the application of C₄F₇N mixed gas in pulsed power devices.The research results of this thesis provide a useful reference for the use of the new environmentally friendly insulating gas C₄F₇N in the field of pulsed power technology.