In order to meet smart substation new demands on phasor extraction algorithm for completely digital relays in face of the poor filtering performance of the short-window algorithm and Fourier algorithm’s long time-delay and fixed data-window

a phasor extracting algorithm with narrow band-pass digital filter (NBDF) and variable data-window combined is proposed. Primarily

the NBDF filters the original sequence of sampled values

with the initial values of NBDF estimated by the short-window algorithm to reduce the impact of NBDF’s transient process and shorten the filter’s time-delay. Then the variable data-window algorithm based on least squares method is applied to the output sequence of NBDF. As a result

the phasor magnitude and phase are acquired. The new algorithm that takes into full account the characteristics of the smart substation mentioned above realizes the phasor extraction of variable data-window

increasing the phasor extracting speed while ensuring filtering precision. Digital simulation and verification by record data show that the proposed algorithm is capable of accurately extracting the fundamental phasor

improving the rapidity and adaptability of completely digital relays in smart substations. This work is supported by Shandong Provincial Natural Science Foundation of China (No. ZR2014EEM039) and Doctoral Scientific Research Foundation of University of Jinan (No. XBS1408).