CALIBRATION OF EXPERIMENTAL INSTALLATION FOR MEASURING PARTIAL DISCHARGES IN LOW CAPACITANCE INSULATION SAMPLES

Abstract

Purpose. The method for calibrating an experimental installation for studying the patterns of partial discharges aris-ing in samples of paper insulation having low capacitance was developed. Methodology. In order to verify the proposed method, a physical experiment was carried out in a high-voltage laboratory to measure partial discharge parameters using a digital oscilloscope. Free software for circuit simulation was used to create high-pass filter schematics. Results. The task of calibrating the systems for measuring partial discharges of low capacitance insulation samples (for example, ranging from 1 pF to 5 pF) is characterized by high complexity, because the calibration capacitor must have a capacitance an order of magnitude smaller than the capacitance of the test sample (from 0.1 pF to 0.5 pF, accordingly), which sometimes cannot be achieved practically. Moreover, in such case the stray capacitance will obviously be of the same order as the capacitance of calibration capacitor, or even greater. In such cases traditional calibration circuits where calibration generator is connected in parallel with the test object cannot be applied. Originality. Alternate calibration circuit was proposed, implemented and tested in the work, where the calibration generator is connected in series with test object. Practical value. Studies of the proposed calibration method have shown that it can be used quite effectively in cases when test object have low capacitance. The results of recording the calibration pulses showed that they can be reliably recorded and measured with a minimum error (oscilloscope error), and errors associated with parasitic parameters of the recording circuit are automatically taken into account when calibrating by this method and do not require additional adjustments. Conclusions. There is a possibility to increase the sensitivity of the measuring circuit to 0.05 pC/V, primarily by increasing the gain of the oscilloscope at least 100 times without repeating the calibration procedure. This will make it possible to study insulation samples of fairly high quality in which the level of partial discharges is much lower than in those samples used in this work. The experimental installation can be used to analyze different ways of modeling partial discharges on a personal computer and comparing their results with a real experiment. References 15, figures 12.