Influence of Start Electron Provision Parameters on Breakdown Strength in Pressurized Synthetic Air Under Lightning Impulse Voltage Stress

Future generations of gas-insulated metal-enclosed switchgear (GIS) should be operated with an environmentally friendly alternative insulating gas instead of sulfur hexafluoride. A promising alternative is pressurized synthetic air. To reliably design these systems, it is essential to predict the breakdown probability. For this purpose, the breakdown probability of a weakly nonuniform, polished hemisphere-plate electrode arrangement is evaluated through voltage rise tests. These tests are conducted under negative and positive lightning impulse (LI) voltage stress at pressures up to 1.0 MPa and room temperature. Alongside the experiments, a simulation model is developed using the volume-time law to predict the breakdown probability based on the start electron provision. The simulation parameters are empirically adjusted to ensure a high degree of agreement between the measured and calculated breakdown probabilities. This adaptation enables the determination of pressure- and polarity-dependent effects on the field stress enhancement factor, the minimum macroscopic background field strength, and the negative ion density.