Evaluation of Current Transformers and Protection Relay Circuit

Current transformers (CTs) as same as protection relays are vital devices in electrical networks. Requirements and specification for CTs are described in technical standards for 60 years at least, but aging and performance after some time of on-site operation have not been described in recent works well, especially in conditions similar to network and climate situation in the Central Europe. In case of protection relays, there are not many papers describing the fault recording function, especially with real data. Therefore, this paper presents a combination of both above-described problems. Due to the intended aim of using output values for technical state estimation of network components in Reliability Centered Maintenance (RCM) strategy development, only protection cores measurement for error ratio evaluation was proposed. The results of two selected older oil-insulated current transformers from distribution network and four protection relays are presented in the paper. The highest current recordings, ratio error evaluation, and values are presented, depicted, and discussed.