Why We Should Not Rely Upon the Paschen Law to Estimate Partial Discharge Inception in Electrical Insulation Systems and What We Should Use Instead

Partial discharge inception in insulation systems is often handled using estimates coming from the application of the Paschen law. In this paper, the estimates provided by the Paschen law for discharges in bulk insulation defects (internal discharges) and on insulation surface, at triple points (surface discharges) are theoretically compared with those provided by a new partial discharge inception model yielding proven accurate estimates, and experimentally validated. It is shown that the use of Paschen law can cause significantly inaccurate estimates of partial discharge inception voltage, especially in small cavities embedded in bulk insulation or on insulation surface. The larger the cavity size and the smaller the surface field gradient, the closer the estimates coming from the new discharge model and Paschen law. On the whole, the predictions provided by the new discharge model fit very well to experimental results for any testing condition.