On-line fundamental waveform and symmetrical components filtering for digital current comparison protection

The real-time evaluation of the measuring signals (voltages and currents) fundamental waveforms is essential for the control and protection of the electrical power systems. Some specific requirements, concerning filtering speed and accuracy, appear when the fundamental sinewave of current signals distorted by high frequency oscillations, harmonics and aperiodical components is to be applied in the high-speed differential protective algorithms. Moreover, the above mentioned protective schemes may be realised in a non-segregated version, which requires fast and reliable calculation of currents symmetrical components. The linear combination of these components is used by the fault detection criteria instead of the separate signals analysis for each phase of the protected unit. In the paper the FIR filter solution as well as a fast algorithm of the symmetrical components calculation, applied to the transmission line phase/current comparison protection (PCCP) are described. Moreover, the results of the non-segregated protective algorithms performance analysis also by distorted measuring signals are presented.