Digital impedance protection of power transmission lines using a spectral observer

A recursive discrete-time filter for calculating the impedances from digitized voltage and current samples at relay location is derived. From an interpolating signal model comprising a delaying DC component and components of fundamental harmonic frequencies, an interpolating spectral observer is constructed to give the desired Fourier coefficients recursively. The interpolators are also useful for sampling rates other than Nyquist rate and unevenly spaced samples. The proposed algorithm is tested using fault data recorded at the Saskatchewan Power Corporation, resulting in fast and reliable tripping conditions. The performance of the spectral observer is enhanced by suitable placement of poles of the observer, producing a fast operation of the digital relay. The performance of the protection scheme with evenly spaced data samples is presented