Study on Impulse Discharge Voltage Calculation of Environmentally Friendly Insulation Gas in Slightly Non-Uniform Electric Field

The environmentally friendly insulating gas C4F7N/CO2 has become a popular alternative to the insulating gas SF6 in recent years. The internal structure of electrical equipment should be taken into account in normal operation, and its electric field distribution is designed and manufactured according to a slightly non-uniform electric field. A large number of high-voltage experiments are usually needed to study the impulse discharge voltage of gases, while new environmentally friendly insulating gases are expensive and have a large amount of experience. The current calculation model of gas discharge voltage is only suitable for special gases, and the calculation conditions (electric field non-uniformity, air pressure, polarity) are specific, making it difficult to match engineering. In this paper, the calculation model of impulse discharge voltage is established with a sphere–plane electrode in a slightly non-uniform electric field, and the calculation formula for key parameters is deduced. SF6 gas and C4F7N/CO2 mixed gas were used as cases to calculate, and the calculation model was verified to be effective via comparison with the experiment.