PREDICTIVE MODELING OF POSITIVE LEADER PROPAGATION UNDER STANDARD ANDOSCILLATORY IMPULSE SHAPES

First we define an optimum discharge corresponding to a minimum energy consumption (optimum discharge), which may not necessarily correspond to the shortest discharge path. The definition results from charge an d voltage measurement in a 2.2 m point-to-plane air gap energized by s tandard and oscillating impulse shapes. The second step is the creatio n of a macroscopic model and fitting it, to compare actual discharges with the optimum one. The variation of observable discharge parameters such as axial length of the leader channel, velocity of the leader ti p, apparent injected charge, time-to-breakdown and applied voltage val ue just before breakdown are readily simulated using this model, whate ver the waveshape. The third step is to validate the model using previ ous experimental results on several gap spacings: 5, 10 and 17 m (stan dard impulse shapes) and 2.2 m (oscillating impulse shapes). Two main phases are shown to exist in both experiment and model: an unstable on e resulting from the first corona event and, in some cases, a quasi-st eady one occurring before the final jump (breakdown cases). For a brea kdown case, the U50 value can be deduced from a U0 value, the withstan d level, given by this model. Finally, the well-known U curves for swi tching impulses are easily reproduced using our modelling work.