Method for Internal Fault Testing of Instrument Transformers With Sectioned Active Parts

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, testing, as currently defined, is mostly inapplicable. The purpose of this paper is to address this issue by presenting a testing sequence that is applicable for verifying the behavior of transformers with sectioned active parts that contain energy-limiting features. Furthermore, the acceptance criteria for the successful completion of the test are also introduced. Every step of the proposed test sequence is discussed in detail and presented on a 145 kV inductive transformer, selected specifically for this purpose. This paper is a part of a continuous broad research with the aim of developing and specifying adequate routine, type and special testing sequences for qualifying paper-oil insulation systems that limit internal arc energy, with the aim of improving the performance of such systems and introducing test methods and criteria that exceed the practices of current standards.