An Approach to Thermal Analysis of Current Transformers of Rating 170 kV and Above

Current transformers are core of electrical systems functioning to provide required inputs for metering and measurement purpose. Generally the current transformers are tested for electrical integrity by way of di-electric measurements such as capacitance tan delta, partial discharge, accuracy and others. Although these tests fairly determine di-electric/insulation co-ordination of current transformer they do not reveal thermal condition of current transformers. In this study attempts are made to understand thermal integrity of current transformers by way of temperature measurements and temperature rise of primary and secondary winding which are main constituents of current transformers. The current transformers though are of different type such as winding, bar type, window. The thermal performance is equally important for all these types of current transformers. The general approach is to measure temperatures at accessible regions such as tank surface if it is live tank type current transformer and also at the axel points of protruding outside the tank which are internally connected to conductors. The temperatures before energizing of current transformer and after temperature rise test are measured by resistance method in accordance with international standards. In this work, temperature mapping at steady state for several current transformers of 200 kV rating have been studied in the light of IEC standards and results are more discussed and analyzed to determine the thermal condition of current transformers.