Power Swing Detection Using Concentric Characteristics Method: Challenges and Solutions

The power swing detection (PSD) block plays an important role in the security and dependability of distance relays. In most commercial distance relays, power swing is detected using the concentric characteristics method. On the one hand, incremental demand for electrical energy has led that the load area gets closer to the relay operational zones in the R-X plane. Meanwhile, some grid codes requirements, such as detecting high-resistance faults, necessitate that distance operational zones (particularly zone-3) become larger in the resistance direction of the R-X plane. Considering these points, the resistive distance between the load area and distance relay zones, and accordingly, the setting time of the conventional concentric characteristics method decreases. Consequently, the correct operation of PSD function under different conditions, e.g., heavy loadings, fast power swings, fault resistance variations during the fault, evolving faults, and the effect of instrument transformer<strike>s</strike> transients, would be faced with some challenges. In this article, a new PSD method is proposed by investigating the impedance trajectory during power swing conditions. A novel index named the ratio of resistance variation speed is suggested, which improves not only the security of distance relays for fault conditions including the transient behavior of current and voltage transformers and fault resistance variations, but also their dependability for power swing conditions during heavy loadings and fast swings (up to 7 Hz). The method's efficiency is evaluated on two single-machine and three-machine test systems using the PSCAD/EMTDC software. The obtained results verify the superior performance of the proposed method in different scenarios.