A novel physical model for partial discharge in narrow channels

In order to reveal the mechanism of partial discharge (PD) in electrical trees, an artificial single channel is studied as model for tree channels. In a long-narrow channel, the behaviour of PD is similar to that in an actual tree. When the length of the channel is decreased, the φ-q-n pattern of PD in the channel changes from wing to turtle or rabbit like, and the range of light emission in the channel increases when the applied voltage is increased. Considering the influence of a PD on the total field distribution and thus on a later PD, a physical model is put forward to describe the PD behaviour. It is assumed that PD is induced by the high field at the needle tip, then propagates along the channel, and stops propagating when the field in the channel becomes lower than a critical value due to field divergence. Mathematical analysis on an ideal needle-plane electrode system clearly explains the physical meaning of the model. And the computer simulation by using the superposition method agrees with the experimental results very well. This model is also valid to describe the behaviour of PD in electrical trees