Error Ratio Evaluation of Protection Core of Selected Older Distribution Current Transformers

Current transformer (CT) is one of the vital devices for metering electrical parameters of distribution and transmission networks. Requirements and specification are described in technical standards for 60 years at least, but ageing 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 Czech Republic. Due to the intended aim of using output values for technical state estimation of network components in RCM strategy development, only protection cores measurement for error ratio evaluation was proposed. The results of two selected older oil-insulated current transformers (5P10 class) from distribution network are presented in the paper. The cores are measured according to the protection CT accuracy class, and also, matching measuring CT accuracy class for a general overview of CT accuracy only. The equipment used for measurement is described. The highest current recordings, ratio error evaluation and values are presented and depicted. Results applicability is discussed.