C.-S. Yu, J.-Z. Yang, and C.-W. Liu
Distance protection, discrete Fourier transform, thyristor-controlled switched capacitor, decaying DC component, subsynchronous fre- quency component
In computer relaying scheme, discrete Fourier transform (DFT) is the most widely used filtering algorithm for computing the fundamental frequency components, especially in distance protection. However, in recent developed thyristor-controlled switched capacitor (TCSC) compensated lines, the fault currents contain a large number of unwanted subsynchronous frequency or decaying DC components. It always needs 0.5–5 cycles for decaying DC component or 10– 20 cycles for subsynchronous frequency component to obtain the accurate fundamental phasor by DFT algorithm. The vital slow convergence problem will degrade the performance of fault locator or distance protection scheme. To overcome the problems, this work presents a new design of Fourier filter for series transmission lines protection. By the proposed scheme, we only need one-cycle-plus- four samples to obtain the accurate fundamental phasor. To increase the flexibility in further design, both the non-recursive and recursive forms are developed. Meanwhile, the resolution of the analogue- to-digital (A/D) converters and the designing of pre-filter are also considered in this work. Some specific test signals and 100 km, 345 kV TCSC transmission line modelled by MATLAB/SIMULINK power system blockset are used for performance evaluation. The results indicate the effectiveness of proposed filtering scheme.
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