Local Electric-Field Direction Measurement in SF6 Based on Electric Field-Induced Second-Harmonic Generation

Non-intrusive measurement of the local electric-field direction in SF6 gas-insulated equipment is important for insulation-condition assessment and electric-field distortion analysis. In this study, a three-projection electric-field direction measurement method based on electric field-induced second-harmonic generation is proposed. The feasibility of the method is validated using a known reference electric field, and the effects of electric-field strength, laser pulse energy, SF6 pressure, and spatial electric-field non-uniformity on the direction-retrieval results are systematically investigated. The results show that increasing the electric-field strength or laser pulse energy enhances the second-harmonic modulation signal and thus reduces the direction-retrieval deviation. SF6 pressure has a non-monotonic influence on the effective accumulation of the second-harmonic signal and the direction-retrieval accuracy through the competition between increased molecular number density and enhanced phase mismatch. Spatial electric-field non-uniformity weakens the ability of the three-projection retrieved direction to represent the local electric-field direction at the focus. Under the present experimental conditions, the maximum absolute angular deviations in the strongly non-uniform edge regions of the cylindrical and hemispherical electrodes are 6.68 ± 1.62° and 9.20 ± 1.84°, respectively.