Investigation of the Loss Tangent and Permittivity of Solid Insulation Materials at Medium Frequency

The increasing use of power electronic components for higher voltage levels, such as power electronic transformers, imposes new requirements on insulating materials. Higher operating frequencies require an electrical characterization of the insulation materials, such as loss tangent and permittivity, beyond the classical power system frequencies of 50 Hz or 60 Hz. Therefore, this paper presents investigations on the loss tangent and permittivity of three different solid insulating materials at frequencies between 50 Hz and 40 kHz. The paper focuses mainly on the experimental methodology and its effects on the measurement results. For this purpose, the results of a parameter variation according to the principle of Design of Experiments are presented. Furthermore, the frequency-dependent variation of loss tangent and permittivity for the investigated materials is presented. In particular, the contacting of the test specimens has shown a great influence on the measurement results in the investigations carried out.