Influence of Variation in Rain Parameters on Insulator Flashover Voltage

Insulators

Several years ago, a Round Robin Test (RRT) of insulator flashover was organized among four internationally recognized, fully accredited high voltage laboratories. Comparison of test outcome for the 400 kV insulator set being tested showed a large spread among the individual laboratories (see Fig. 1).

Fig. 1: Maximum relative difference between different laboratories.

For example, maximum relative differences showed large deviations, especially for tests under wet conditions, i.e. up to 22% for the wet switching impulse tests (wet SI) and nearly 29% in regard to the wet power-frequency tests (wet AC). The main aspects that may have affected these measured values were discussed and it was suggested that differences in reproducibility could be reduced by keeping variations in test set-up to a minimum.

In the light of these results, it was also decided to perform a new set of tests on a smaller set-up, such as a short string of cap & pin insulators. Doing this would make it easier to evaluate the influence of individual parameters on flashover voltage. IEC 60060-1 states the requirements for the rain when applied to a test object. These parameters where varied within the ranges specified. In addition, the type of nozzle and front time was varied as well.

Fig. 2: Test set-up for short string.

In order continue investigating this important topic, one of the laboratories involved in the RRT – STRI in Sweden – subsequently performed further tests on a shorter insulator configuration in order to vary more parameters, such as front time of the switching impulse voltage as well as rain intensity and conductivity. A short string consisting of 8 glass insulator units was tested in a set-up in accordance with IEC 60383-1.

Attend the 2022 INMR WORLD CONGRESS in Berlin where Dr. Dan Windmar of STRI will present how this additional testing was performed as well as the findings in values of wet switching impulse flashover voltage.