Examination of the discharge capacitor of the current impulse generator in time and frequency domain

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Cselkó Richárd
Department of Electric Power Engineering

In my work my goal is to define the electric model of the discharge capacitor of the current impulse generator which is took place in the High Voltage Laboratory of the Budapest University of Technology and Economics. It is important to know the real electric parameters of the capacitor, because various measurements are performed in the laboratory with the impulse generator; without an appropriate model, the shape of the real current impulse is different from the desired one. However, if the real model is known, the parameters of the generator can be adjusted to result the expected waveform. The specialty of the current impulse generator is that the permittivity of the applied oil-paper insulator in the discharge capacitor is strongly frequency dependent in the relevant frequency band.

My work started with reviewing high number of references about high voltage laboratory equipment. After that I carried out various measurements on the oil insulated discharge capacitor in the High Voltage Laboratory. In time domain I performed switch-on, switch-off and transfer measurements. I applied a carbon dioxide insulated capacitor for the transfer measurement because this capacitor type is frequency independent in this range. Based on the results I established an electric model of the capacitor. I implemented a simulation in Matlab with a simple model and then I compared the simulation and the results of the laboratory measurements. Based on the experiences I was able to improve the electric model.

With another measurement method I performed investigations in frequency domain. The oil-paper insulated capacitor, a wideband signal generator and a frequency-independent resistor were used in the measurement. I made a multi-frequency measurement and measured the voltage of the resistor, the voltage of the capacitor and the angle between the two vectors. At every frequency I was able to establish a series/parallel R-C electric model which contains the effect of polarization modes that could form at that dedicated frequency. After that I could establish the electric model of the impulse generator which contains all of the polarization effects. Finally I defined a more complex electric model of the current impulse generator.


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