Breakdown voltage calculation of sphere-planesphere air gap in slightly uneven electric field

The breakdown voltage of typical electrode structures is important for the design of external insulation, but little attention is paid to the analysis of floating metals, which is common in high voltage transmission and transformation projects. Thus, photoionization criterion was adopted in this paper to calculate the breakdown voltage of sphere-plane-sphere air gap in slightly uneven electric field with the consideration of floating metals, and the power-frequency withstand voltage tests were carried out for the comparison. The results indicate that the calculation results agreed well with the test ones, where the mean absolute percentage errors are less than 3%. The study verifies the validity and generalization values of photoionization criterion within a certain range, and contributes to explaining the discharge mechanism of complex air gap in slightly uneven electric field.