Experimental setup for measuring the dielectric properties of solid insulating materials under high frequency and mixed frequency high voltage stress

Due to an increased integration of power electronic components in power grids and the continuous development of power semi-conductors, insulating materials are exposed not only to high electric fields but simultaneously to strongly increased frequencies. This combination poses a different stress on most insulating materials compared to conventional operation. This stress is based on the dependence of the dielectric parameters of an insulating and field grading material on the electric field strength and the frequency of the applied electric field. In order to investigate the influence of high electric fields and simultaneously high frequencies on these materials, this work introduces an experimental setup for measuring the relative permittivity and the dissipation factor for frequencies up to 10 MHz and voltages up to 20 kV. The test setup is based on high frequency transformers or tuned resonant circuits, respectively. It can be used for both, sinusoidal high frequency high voltages as well as the application of mixed frequency high voltage. For measuring the relative permittivity and the dissipation factor, a measurement concept based on a reference path consisting of shielded vacuum capacitors was developed and validated. In addition to the dielectric measurements, the setup can also be used to determine the breakover and breakdown field strength of the materials as a function of the frequency.