Research On The Monitoring Technology Of Dielectric Loss Factor Of Capacitive Equipment

The reliability of electrical equipment depends on the performance of insulation to a large extent.During the work of HV capacitive equipment,there will be a series of chemical and physical changes happening to insulation dielectric due to some factors like chemical corrosion and mechanical loss,causing the performance deterioration,which is called aging.If serious,the aging of insulation dielectric in the electrical equipment may lead to the loss of the function of insulation,thereby causing equipment fault.However,with condition monitoring technology,the real-time monitoring of the insulation condition of capacitive equipment will be available and some fault of insulation performance can be found promptly.At present,Discrete Fourier Transform is the main algorithm for dielectric loss angle,with the advantages of high precision and speedy calculation;yet the error is comparatively big when frequency fluctuation of power system occurs.Therefore,it is of great value in engineering application to conduct research on how to improve the precision of the algorithm for dielectric loss factor.This paper gives the introduction of the theory of dielectric loss of capacitive equipment and the main algorithm for dielectric loss factor,as well as the analysis on various factors affecting the calculating precision of the algorithm for dielectric loss factor,along with providing the introduction of domestic and overseas relevant literature and conducting analysis on the development and optimization made by researchers to improve the calculating precision of the algorithm for dielectric loss factor.Furthermore,this paper illustrates the theory of DFT and its problems in the calculation of dielectric loss factor under the dynamic condition of power system and comes up with optimization scheme.Under the condition of non-integer-period sampling,the traditional DFT may cause the problem of spectrum leakage and big error.As to this problem,this paper points out the DFT algorithm based on Nuttall Window-Five points' Polynomial Transform.Spectrum leakage is restrained through Nuttall Window which can reduce the restraint of signal truncation error and which accelerates the decay rate of the signal in frequency domain via applying Five Points'Polynomial Transform using the main frequency point and other four frequency points around by.The calculation of dielectric loss factor is conducted by using traditional DFT,Five Points' Polynomial Transform-DFT and Nuttall Window-Five Points' Polynomial Transform respectively under various simulation disturbance environment of Matlab.The result shows that the precision of Five Points' Polynomial Transform-DFT is slightly higher than that of traditional DFT,while the precision of Nuttall Window-Nine points' Polynomial Transform is highest and its error is slightest.Finally,a dielectric loss angle measurement test platform based on Lab VIEW is designed,with the core part of Nuttall Window-Five Points' Polynomial Transform.And the validity of proposed algorithm is verified by this platform.The data was collected via the PCIE1816H acquisition card from Advantech Corporation and the platform was designed through Lab VIEW.