PROTECTIVE RELAY WITH IMPROVED DFT FUNCTION

A method for applying a modified Discrete Fourier Transform (DFT) in a protective relaying system involves five basic steps: The first step, S1, comprises measuring voltage and current time-domain samples v(k), i(k). The next step, S2, involves the computation of the DFT of the DC component(s) (V.sub.DC (k), I.sub.DC (k)) of the voltage and current samples. The next step, S3, comprises the computation of the regular DFT (V(k), I(k)). Next, in step S4, the modified DFTs are computed as, V.sub.m (k)=V(k)-V.sub.DC (k), and I.sub.m (k)=I(k)-I.sub.DC (k). In step S5 the modified DFT values representing the desired phasors are employed to carry out various protective relaying functions.