TCSC impact on communication-aided distance-protection schemes and its mitigation

The paper analyses the impact of the thyristor-controlled series capacitor (TCSC) on the performance of conventional communication-aided distance-protection schemes and proposes new schemes for its mitigation. The associated TCSC control actions introduce rapid changes that create certain problems in the primary-system parameters such as line impedances and load currents, causing the apparent impedance seen by the distance relay to be affected during the fault period; hence the positive-sequence impedance measured by the traditional stand-alone distance relays is no longer an indicator of the distance to a fault. It is shown that communication-aided distance-protection schemes that perform successfully in lines with fixed series capacitors have problems in lines with TCSC. This impact is observed not only on the relays of the compensated line with TCSC, but also on the relays of adjacent lines. Mitigation of this problem is proposed by using new communication-aided schemes. The proposed schemes use the information available at the substation to inhibit relay malfunctions. The performance of the techniques is studied for different TCSC locations in the transmission line. Real-time digital simulation and commercial relays are used to perform the analysis. The results indicate the effectiveness of the proposed methods to be applied in the power systems equipped with TCSC.