Development of a Measuring System to Detect and Localize Partial Discharges in a Termination with UHF-Sensors

Terminations are used to control the electrical field at the end of cables in the medium-voltage sector as well as in the high-voltage sector. Field control is mostly achieved by semiconducting silicon deflectors. The terminations in the high-voltage sector are often filled with silicone oil as insulating liquid. Impurities that can occur because of installation failures, mechanical stress, production conditions or aging, can result in partial discharges (PD) which are stressing the silicone oil and the deflector until it comes to a breakdown. To avoid this breakdown and the associated cable termination failure it is necessary to detect the partial discharges before the breakdown process begins. For the detection and the localization ultra-high frequency (UHF) sensors may be used. The target of this investigation is to develop a measurement system that "scans" the termination and monitors the position of the partial discharge by use of simple capacitive sensors. In preparation for this project, a partial discharge source has been developed that generates partial discharges by around 1 pC in air. This source should be used to get reference measurements and a directional receiving pattern of the UHF-sensors. In order to generate these defined, reproducible partial discharges with this source, the ambient conditions such as air pressure, humidity and temperature must be observed and taken into account. If this is ensured, the partial discharges of this source should be measured with different positions of the sensors to get a reference dataset of the sensitivity of the sensors. Since the aim is to identify and locate PD in terminations by use of three or more UHF-sensors and overlaying the known directional receiving pattern, the measurement data of reference measurements deliver the basics for this. The paper reports about the steps to achieve first results for the sensitivity check, the directional characteristic of the UHF-sensors and the PD-localization.