Arthur Kaindl

Influence of processing parameters on electrical insulation properties for epoxy-resin materials-an investigation by experiment and finite element analysis simulation

This paper discusses the influence of the speed of the heating process upon epoxy casting of special test specimens on generating mechanical stresses inside a mold. Higher speed leads to higher temperature gradients and therefore to larger internal stresses which by itself promotes cracking in the solid epoxy material. As a consequence of that, the partial discharge inception voltage is decreased. Finite element analysis shows that differences in the thermal expansion coefficient of the materials in the mold together with the absolute temperature level are responsible far the degree of mechanical stresses and finally for the partial discharge behavior of the solid product.

A novel method for noise rejection during PD measurements in combination with pulse-width-modulation amplifiers

This paper describes a new method to avoid the noise influence on partial discharge (PD) measurements upon using pulse-width modulation (PWM) amplifiers. This is achieved by a special PD test set-up, where the test object, a coil with high inductivity, and a capacitance are put together to form a series resonance circuit. Energy is only applied to the measurement circuit by the PWM amplifier during a short period of time (e.g., between 0 and 90/spl deg/ phase angle). To avoid the noise generated by the PWM amplifier, the PD measurement is only carried out during its switch-off period. With this measurement set-up, it was possible to measure the PD behavior of the test object under high voltage as well as under high current conditions. By this, a new method was found to conduct PD measurements of coils with high inductivity and high capacitance under operation conditions.

Practical application of partial discharge measurements at epoxy impregnated coils for analyzing signal noise in the radio frequency range

In order to analyze the partial discharge signal noise in the radio frequency range, the signal characteristics of partial discharge pulses generated in a large-scale epoxy-resin impregnated coil are analyzed in this paper and compared with the partial discharge behavior at lower frequencies. Partial discharge inception voltages generally are higher when measured at radio frequency level compared to standard measurements. Two different pulse types, single and double pulses or different void types account for the variations in the partial discharge behavior.

Influence of chemo-rheological properties of silica-filled liquid epoxy resins on partial discharge behavior of coils

This paper describes the investigation of chemo-rheological properties of silica-filled liquid epoxy resins and its correlation to electrical properties of solid insulation, such as the partial discharge behavior of epoxy resin coils. Results of this investigation show that low viscosity is absolutely essential for a good impregnation of insulation layers. High maximum viscosity values, high surface energy of the resin part as well as filler morphology cause poor impregnation behavior. Optimum partial discharge properties may only be obtained if full impregnation within the insulation layer is achieved. As soon as one single void is left in the insulation, the partial discharge inception voltage drops by a factor of 10. Partial discharge data from the epoxy-resin impregnated coil show a significant improvement upon applying epoxy systems with excellent impregnation characteristics.