Efforts on Improving the Performance of Superimposed-Based Distance Protection

Existing superimposed-based distance protection possibly maloperates due to some extreme conditions, for instance, an external earth fault occurring while the transmission system operates at a large phase difference between the sources at two sides of the protected line. To solve this problem, an adaptive distance relay using the superimposed component and the information of the opposite end is put forward. The shortages of the existing schemes are first investigated, and the scenarios leading to the maloperations of those schemes in theory are clarified. Furthermore, corresponding countermeasures by means of the floating threshold and criterion switching are introduced. In this case, the reliability and the sensitivity of the superimposed-based distance protection are improved. By means of a variety of comprehensive tests, the feasibility of the proposed scheme is verified.