Dielectric response measurements utilizing non-sinusoidal waveforms

In order to assess the effect non-sinusoidal high voltages impose on electrical insulation systems, new methods for material characterization and diagnostics are needed. The method developed in the work presented here utilizes arbitrary non-sinusoidal voltage waveforms. It thereafter makes use of the fast Fourier transform (FFT) analyses for extracting the harmonic contents of the applied voltages and the resulting currents. In this way the response spectrum for the harmonic frequencies is obtained. The method puts high demands on the measurement instrumentation as well as on the calibration and correction procedures for obtaining reliable results. One of the main advantages with the measurement system developed is that it does not require a precise and well controlled voltage source. This provides new possibilities for on-line monitoring and diagnostics, when any voltage appearing in the system can be utilized. It is shown that measurement results obtained by the new method are in good agreement with results obtained by means of the conventional frequency response techniques.