New Method for Thermal Aging Testing of Enameled Conductors Used in Liquid-Immersed Transformers

Abstract

Enameled wire is widely used as a conductor in liquid-immersed transformers and its performance is critical for the reliable operation of transformers. One of the major application characteristics of the enamel coating is its thermal endurance as it relates to the long term temperatures of the transformer windings. There are standards developed for the thermal evaluation of systems that combine transformer liquid and solid insulation materials, simulating the transformer insulating systems. The so-called sealed tube accelerated aging test is the method that is used most often. However, even though conductor materials are used as a part of the system in those evaluations, a review of available information confirmed that there is no standardized aging test method for the enamel coating itself (in systems with liquids) available. This paper proposes and describes a new method for accelerated aging testing and thermal endurance qualification of enameled wires for liquid-immersed transformers. The test set-up, test procedure and results evaluation methods are described in detail. The feasibility, applicability and accuracy of the proposed test is verified by aging experiments and the results are presented.