Some on-line monitoring and fault diagnosis methods of capacitive equipment are introduced.Some kinds of current sensors used by signal collection are introduced and compared

and the theory of electronic compensation zero-flux current sensor based on magnetic coupling mode is emphasized.And a method of judging capacitive equipment insulation based on the changing of three-phase leakage current sum is described as well as the influencing factors of measuring result.For the measurement of tanδ

the series equivalence circuit and on-line monitoring model

measuring theory and signal processing method are described

and the theory and its shortcomings of harmonic analysis based on Fourier transform are analyzed.Aiming at these shortcomings

the application of wave transform to extract the trend of tgδ is described as well as several methods of signal preprocessing

comb notch filter interference controlling method

Hanning-windowed interpolated FFT algorithm and correlation function method.