A new DFT-based phasor computation algorithm for transmission line digital protection

This paper presented a new DFT-based phasor computation algorithm named as EDFT for computing accurately fundamental and harmonic phasors when a sampled signal contains exponential decaying DC offset. Using three consecutive phasors computed by DFT, EDFT estimates the time constant of the exponential decaying DC offset and achieves complete elimination of the error caused by exponential decaying DC offset in computation of phasors. The EDFT is superior to traditional DFT-mimic circuit configuration since it is not affected by the uncertainty of time constant of exponential decaying DC offset. The results of computer simulation show that the EDIT can provide accurate phasors for transmission line digital protection when the exponential decaying DC offset occurs.