Investigations of the Electrical Tree Growth at Different Voltages and Frequencies

Considering high voltage direct current (HVdc) link cables, transient overvoltage can occur during fault situations. Electrical trees can be incepted by these transient effects characterized by frequency components of several kHz. Normally, a higher voltage frequency is associated with faster polymeric insulation materials degradation. To better investigate the relationship between applied voltage and frequency and the growth of the electrical trees, cross-linked polyethylene (XLPE) samples obtained from a commercial HVdc cable have been tested in different conditions. The partial discharge (PD) activity was monitored along with the degradation of such samples. The results show that both voltage amplitude and frequency influence the tree shape and consequently the time to breakdown: the increase of the frequency does not lead to a faster degradation and to a faster breakdown of the sample.