The influence of a pretreatment on the loss behavior of watertree retardent XLPE insulation materials

Investigations were carried out to determine the loss behavior of water tree retardent XLPE (cross-linked polyethylene) insulating materials. The parameters are temperature, frequency, and field strength. At a field strength of 5 V/mm, the dissipation factor of WTR XLPE plates was determined in the temperature range from -10 up to 120°C, while the frequency varied from 50 Hz to 100 kHz. The measurements were carried out on plate specimens immediately after production as well as after vacuum drying and humidity storage. To clear up the question of the influence of the field strength, specimens with a Rogowski electrode configuration were used. These specimens were pretreated in the same manner as the plates and tested under high voltage up to 30 kV/mm with a frequency of 50 Hz within a temperature range of 20 to 100°C. The results of the low and high voltage measurements are compared and discussed. A description of the possible physical processes is given concerning the question of the dissipation factor behavior as a function of temperature, frequency, and field strength. The results are discussed in relation to insulating materials of HV cables