Partial discharge inception voltage modeling in air gaps at low to atmospheric pressure

Abstract Accurately predicting the partial discharge inception voltage (PDIV) of gas-filled gaps is crucial for various high-voltage applications, including determining clearance distances in air insulated medium-frequency transformers (MFTs). This paper addresses this challenge by assuming the PD inception mechanism in non-uniform fields to follow a multi-avalanche process, with photons as the primary contributors to secondary avalanche generation. This enables the adaptation and extension of a physics-based parametrization for the secondary feedback coefficient, originally developed for static breakdown modeling in (quasi-) uniform fields, to non-uniform fields. Consequently, a generalized methodology for the PDIV prediction in arbitrarily shaped gas gaps is obtained. The proposed model is validated against a wide range of measurements on various geometries, incorporating data from both literature and own experiments. These geometries include standard setups such as rod-plane, cylinder-plane, and needle-plane configurations. The average relative error between measured and predicted PDIV at these setups is below 5%. Additionally, a case study is conducted on an electrode setup emulating a foil-winding of an MFT to investigate the model’s applicability for determining clearance distances. A notable influence of the copper foil’s microscopic structure on the PDIV is observed. When this structure is incorporated into the model, the error between the predicted and measured PDIV remains well below 5%. However, assuming a simplified geometry results in an increased error of approximately 10%. Furthermore, the good accuracy of the proposed model is maintained for pressures ranging between 6.5 mbar and 1 bar.