New Procedure in Impulse Evaluation - a Change in the Electrical Breakdown Test Results?

The actual recommendation is ambiguous concerning the evaluation of the test voltage of lightning impulses with oscillations or overshoot near the peak. Based on measurements within an European Research Project a new evaluation procedure is proposed using the k-factor as a measure of the influence of the superimposed oscillating voltage on the breakdown behavior of insulating materials. The k-factor is frequency dependent and a function is developed which can be used as filter characteristics. Some examples show the evaluation procedure and the results in comparison with the actual evaluation recommendation. Assuming the same behavior at withstand tests the k-factor can be used for the evaluation of the test voltage during withstand or breakdown tests. A comparison between the results using the actual procedure and the results using the new proposed method on lightning impulses applied on a power transformer shows clearly that the new procedure is reliable, reproducible and will not lead to changes in withstand voltage and test results