Research On On-line Monitoring Method Of Solid Insulation Dielectric Loss

The on-line monitoring of electrical equipment insulation is one of the most importantways to find out the potential hazards and ensure the reliability of power systems supply.The dielectric insulation characteristics of electrical equipment insulation matter thereliability of power systems operation, in which the dielectric loss angle tangent tanδ is animportant index to reflect insulation dielectric loss properties comprehensively, thechanges of insulation dielectric properties (especially the insulation aging properties) canbe monitored by real-time monitoring of tanδ, and thus the deterioration of insulationperformance and other hazards can be detected in time. Present on-line monitoringmethods of calculating dielectric loss angle is easily influenced by power systemsfrequency fluctuation and higher harmonics which result in great measurement errors,therefore, the research on high-precision dielectric loss angle measurement algorithm hassignificant engineering application value.Based on the analysis and comparison of common on-line monitoring methods, WhenFast Fourier Transform(FFT) algorithm is directly applied to measure the dielectric lossangle, the measurement accuracy is influenced by leakage effect of asynchronous sampling,two high-precision dielectric loss angle measurement algorithms based on FFT arepresented. One is a FFT algorithm of dielectric loss angle measurement based oncorrelation blackman window, the simulation results show that frequency fluctuation andthird-harmonics has little affected on the dielectric loss angle measurement algorithm,therefore, the method can effectively against above interference impact. Another is fivepoints weighted FFT algorithm for measurement of dielectric loss angle, this simulationresults show that the influence of the changes of power systems frequency, initial phaseangle, sampling frequency, higher harmonics, direct bias, the insulation dielectricstate(theoretical value of dielectric loss angle) and other factors on the measurementaccuracy of dielectric loss angle can be effectively reduced by this method.In this paper, the laboratory dielectric loss angle on-line monitoring system whichadopts five points weighted FFT algorithm is developed based on LabVIEW platform, including hardware design and software main interface.