Research On Overvoltage Online Monitoring And Its Data Analysis And Application

Overvoltage, one of the factors that affects the safety and stability of the operation of power system, is also the main cause for insulation fault. Actual overvoltage waveform data is of great importance for insulation evaluation, insulation coordination, fault analysis and standard revision etc., and cannot be replaced by simulation data. Therefore, it has practical significance to carry out overvoltage online monitoring. However, the existing overvoltage online monitor cannot effectively detect overvoltage when the voltage level is 220 k V and above. To solve the problem, this paper, based on the principle of zinc oxide varistor voltage dividing, puts forward an improved method to monitor overvoltage and obtain data by using zinc oxide varistor voltage divider.In this paper, the basic principle of zinc oxide varistor voltage dividing is explained,equivalent circuits of zinc oxide varistor in various current areas are built, and corresponding voltage ratio calculation formulas are derived. The results show that the voltage ratios are all the same in different current areas, accordingly, zinc oxide varistor voltage divider is feasible for online overvoltage monitoring.Circuits are built in the ATP-EMTP program to simulate zinc oxide varistor voltage ratios which the results show are the same, no matter the zinc oxide varistor is under power frequency voltage, switching impulse voltage or lightning impulse, conducted or not. And it proves that voltage calculation formulas are correct. Considering that the main varistors of lightning arrestor could be made of multiple columns, the paper also simulates the voltage ratio of two parallel columns zinc oxide varistor and this time the voltage ratio turns out different. Reasons for the difference are analyzed and the actual way of varistor voltage dividing in engineering application is demonstrated.Experimental circuits are built in the laboratory to respectively test the voltage ratio under the impact of power frequency voltage and impulse voltage. The test shows that voltage ratios are basically stable and the tolerances are calculated and analyzed. Voltage ratios under various sinusoidal voltage waves of different frequencies are tested to obtain frequency response curve. This paper combines the frequency characteristics curve with the voltage ratio differences under power frequency voltage and impulse voltage to put forward an improved method to calculate the primary terminal voltage by using different voltage ratios.Zinc oxide varistor is connected in series with lightning arrestor, right at the bottom of it, to test the voltage ratio, with high voltage applied by impulse voltage generator and high voltage transformer, under frequency voltage, switching impulse voltage and lightning impulse. Tests show that the actual voltage ratio is basically in accordance with thetheoretical value, which proves that it is feasible and accurate to monitor online overvoltage by zinc oxide varistor voltage divider.Finally, in this study, wave analysis of overvoltage data obtained by online monitoring is done and typical cases are presented to demonstrate the overvoltage online monitoring data's application value in fault analysis and responsibility definition.