Research On New Characteristic Quantity For AC Contamination Forecast Of Line Insulators

The contamination flashover accident of power transmission lines insulators has been a serious threat to the security and stability of the power system. How to predict and prevent the flashover occurrence by monitoring the insulator contamination extent has been a problem urgent needed to solve. The extreme result of contamination discharge is contamination flashover, and the leakage currents in the discharge process have very close links with contamination flashover. So, through in-depth study of the leakage current characteristics and extracting effective new features, the insulator pollution state forecast can be realized, this has been a continuing research subject of transmission line pollution flashover prevention all the time.Based on artificial pollution tests in this paper, the time domain and frequency domain characteristics of leakage current were researched, and 4 characteristic quantities reflecting the insulator pollution degree in the safety zone were obtained: the mean value, maximum and standard deviation of leakage current effective value, and the amplitude ratio between the 3rd harmonic and the fundamental wave of leakage current. The relationship between the four feature quantities and contamination degree was analyzed in deep, values of the 4 characteristic quantities increasing with the increase of the insulator contamination degree was obtained, being exponential fitting relationship approximately, and having a high fitting degree. It is proved that these four characteristic quantities can well realize the insulator contamination state forecast.For the reliability problem of contamination degrees forecast by a single characteristic quantity, combined with the contamination insulator leakage current having the fractal-body characteristics of nonlinear, irregular, and self-similarity, the leakage current signal characteristics are described by fractal ideology based on fractal theory in this paper. The appropriate calculation methods of fractal dimension and multi-fractal were select, the fractal dimension, generalized fractal dimension and multi-fractal spectrum characteristic quantities of insulator leakage current waveform were extracted as prediction parameters for contamination discharge development sections and contamination levels, the relationship between the fractal characteristic quantities and the contamination levels, contamination discharge development phases was analyzed in deep. The fractal dimensions of different contamination degrees and different contamination discharge development stages are different and varying significantly, and the generalized fractal dimensions and multi-fractal spectrum feature quantities also have a certain variation law.Through in-depth analysis of the leakage current characteristics, the time and frequency domain and fractal characteristic quantities of the leakage current extracted in this paper have been the supplement for characteristic information investigation of polluted insulator leakage current, and provided a new idea and new characteristic quantities for predicting the insulator contamination discharge development stages and the severity of contaminations.