POSITIVE DISCHARGE DEVELOPMENT IN INSULATING OIL - OPTICAL OBSERVATION AND SIMULATION

Results of optical investigations of positive discharge channel develo pment in transformer oil under divergent field configuration and impul se voltages to 650 kV are presented. The propagation of two different discharge structures (bush-like, tree-like) and the transition between these structures were observed. The conditions of their development a nd boundary of the bush-to-tree transition were determined. Anomalous behavior of the breakdown time dependence on applied voltage, consisti ng of a sharp drop in time at a critical voltage, was found. The diele ctric breakdown model modified by introducing the varying channel cond uction is presented. In the model discharge channel propagation is des cribed by stochastic development of current and field instabilities. T he model describes adequately the main spatial and temporal features o f the various discharge structures observed in the experiments. The cu rrent and field characteristics of the simulated discharge channels wh ich belong to different structures are compared. The bush-to-free tran sition and the anomalous dependence of the breakdown time on voltage w ere explained by current instability in bush-structure channels.