New approach for assessment of positive streamer penetration of long air gaps under impulse voltages

The paper comprises a new systematic approach to determine the critical ambient field needed for positive streamer propagation in nonuniform field gaps. It is shown that such critical streamer penetration field is a function of the basic value previously established for uniform field gaps and the degree of ambient field nonuniformity. The latter quantity is defined by the ratio of the maximum to mean ambient electric fields along the streamer propagation path, which can be determined either analytically or by charge simulation. Such functional dependence of the critical streamer penetration gradient on field nonuniformity has been determined for different rod topologies of rod-plane gap as well as for single and bundle conductor plane gaps. The model is used to determine critical streamer penetration fields and streamer lengths under different impulse voltage levels for different gap configurations and for a tall ground structure exposed to ambient impulse field. The findings of this method are compared to available experimental results and the agreement is found satisfactory.