In on-line monitoring tanδ of power equipment

the harmonic analysis based on conventional FFT brings significant errors because of the truncation of power frequency signal and unsynchronized sampling sequence.In this paper

the window and interpolation algorithm is derived

and a practical interpolation formula with Blackman-Harris window is proposed.For the unsynchronized sampling sequence caused by frequency fluctuation of power system

the simulation is performed via MATLAB code on the conventional FFT algorithm the interpolation algorithm with Blackman window

and the interpolation algorithm with Blackman-Harris window

respectively.The simulation results show that the interpolation algorithm with Blackman-Harris window can effectively reduce the measurement error and increase the precision

which satisfies the requirement for on-line monitoring tanδ of power equipment.