Analysis of the Effect of UHV Series Compensation Capacitor on Distance Protection

The use of a series compensated capacitor causes damage to the intrinsic impedance of a power transmission line and affects operation actions of protection such as distance, etc. For this problem, a model whose operation mode is the same as the one at a site is built. The effect of the series compensated capacitor on directional circle characteristic impedance relay distance protection is summarized by inputting actual parameters and via simulation analysis. The position of different failures and protection action logic and method under different capacitor compensation degrees are studied by using the software PSCAD; the FFT transformation of data is made by using MATLAB, and then the spectrum characteristics of data are further analyzed; the use of a series compensated capacitor bank reduces the range of distance protection; and possible protection malfunction under special conditions in case of an external or reverse fault is pointed out. Spectrum characteristics are studied and discussed in a failure state. When the positive direction of a capacitor bank suffers a short-circuit failure, there is no low-frequency current component; on the contrary, when the rear of the capacitor bank suffers a short-circuit failure, the low-frequency component accounts for a certain ratio. Finally, the countermeasure and solution to series compensated protection are studied according to the characteristics of line protection with the series compensated capacitor added.