Error analysis for dielectric loss factor measurement based on harmonic analysis

Dielectric loss measurement is an important index in assessing the insulation performance of power equipment. With the development of condition-based maintenance, the on-line diagnostic technologies for dielectric loss measurement are regarded more and more. Many methods have been developed in this field in which harmonic analysis is prevalent due to its perfect performance of resisting disturbance and stability relative to others Harmonic analysis includes measuring the operating voltage and the current of the specimen by some sensors firstly, then transforming the analog signal into digital signal. Finally the dielectric loss angle could be calculated by means of digital frequency analysis. According to the digital spectrum analysis theory, accurate analysis can be conducted if the sampling length is the integral multiple of the signal cycle. Actually, as the frequency of power system is often fluctuant, the condition of the sampling of integral multiple is difficult to satisfy. Therefore the frequency fluctuation is an important factor which greatly influences the precision of dielectric loss detection based on harmonic analysis. Discrete Fourier transform (DFT) is the most fundamental method in digital spectrum analysis but is too difficult to use conveniently. So a new method, quadrature filtering algorithm, is used in this paper. Then, two preprocessing methods to improve the precision of dielectric loss detection are put forward.