Evidence theory-based fake measurement identification and fault-tolerant protection in digital substations

Protective relay is designed to make a trip decision based on calculation of collected measurements, and thus, the quality of data plays an important role in ensuring the reliability of protective relay. However, abnormity of any part of the data acquisition system (DAS), especially cyber risk, may make the protection system receive fake measurements and misoperate. Besides those efforts spent on the reliability of DAS and cyber security, protective relay itself should be able to tolerate fake measurements and actively minimise the impacts associated with bad data. Based on evidence theory, this study proposes an approach taking advantage of abundant information in digital substations to identify fake measurements and avoid misoperation of protective relay. When protective relay is prone to misoperate after the analysis of fake measurements from several current transformers (CTs) or voltage transformers (VTs), measurements from other CTs/VTs are rapidly collected to indicate whether there is a real fault in the power system. In this way, misoperation because of fake measurements can be prevented and CTs/VTs providing bad data can also be identified. Simulation tests demonstrate the effectiveness of the proposed approach.