Spark Breakdown in Gas-Discharge-Tube Surge Arrester at Voltage Pulse

The sparkover voltage of gas discharge tubes for surge voltage protection has been found to be dependent on the rate of voltage rise. At slow voltage increase, it is close to stationary voltage conditions and is assumed to be the breakdown voltage at a given pd regarding Paschen law. The deviation of stationary sparkover voltage measured on test samples is assigned to the variation of electrode conditions and illustrated as the effect of the Townsend coefficient γ. The increase of impulse sparkover voltage at fast voltage rise depends on the time lag of the spark breakdown where the effect of statistical and formative time lag is assessed. As an origin of ion avalanche and streamer formation, the cold-field electron emission process is considered where the Poisson probability function for rare stochastic events is concerned for the evaluation of emitted electron current. Due to the absence of applicable values for relevant system parameters, the relationship between the impulse sparkover voltage and the rate of voltage rise obtained by simulation have more or less qualitative character. Values taken for the coefficients of simulation are chosen by fitting the simulated results to the measured ones. Their relevance is verified by comparing it with the typical values of discharge quantities found in the literature.