Internal Fault Performance of Instrument Transformers with Sectioned Active Part

Relevant international instrument transformer standards specify internal arc testing to prove the transformer behavior under internal fault conditions. However, the test is defined in a way that does not recognize that it is possible to limit and reduce the total fault energy. For such instances, currently defined testing is mostly inapplicable. The purpose of this paper is to provide a theoretical background on behavior of units with sectioned active part under fault conditions, aided by numerical analysis of different fault scenarios on a variety of inductive voltage transformers, spanning from 72.5–550 kV. Numerical calculations are verified with several tests performed on a 123 kV inductive voltage transformer. This paper is a part of a continuous broad research with an aim to develop and specify adequate routine, type and special testing sequence for qualifying the paper-oil insulation systems that limit internal arc energy. Furthermore, the idea is to prove performance of such systems by introducing criteria that exceed the practices of current standards and aim to improve the instrument transformer fault statistics.