Effects of Thermal Accelerated Ageing on a Medium Voltage Oil-Immersed Current Transformer

Asset management and preventive maintenance tendencies in the electrical power industry lead towards increasing exigencies of operational equipment condition assessment. There is a big interest in confirming loading limitations of different components of the electrical system whether related to generation, transmission or distribution of electric energy. One of these components is the oil-immersed current transformer, which plays a very important role in the optimal operation of substations. Power and distribution transformers have largely been investigated thereby leaving an opportunity for research in instrument transformers. Efforts are currently underway to obtain guidelines for estimation of ´loss of life´ of a current transformer as a result of short term overloading. Such guidelines will have a direct impact on maximizing an important asset in the form of a current transformer. This paper provides a detailed description of the technical approach taken at the Tennessee Technological University in order to implement and carry out thermal accelerated ageing procedures on medium voltage oil-immersed current transformers and the corresponding validation tests performed. The use of typical & non-typical load profiles, state-of-the-art DC & AC testing practices, same as on-line gas monitoring and temperature data acquisition is being described. Results will be presented in the context of ageing of the medium voltage current transformer.