A single phase transformer equivalent circuit for accurate turn to turn fault modeling

Abstract

Recently, an increasing concern has been raised about turn-to-turn faults (TTFs) in power transformers, because these faults can lead to severe transformer insulation failure and consequently, its outage. Generally, it is impossible to experimentally analyze the transformer behavior under such faults, since the implementation of those experiments may be substantially destructive. Therefore, computer-aided models should be developed to investigate the performance of transformer protective relays under turn-to-turn faults. So far, existing transformer models are mainly formulated to implement in the EMTP-based softwares. However, most of power system protection engineers and researchers develop their protective algorithms in other softwares, such as MATLAB. In this paper, two simplified and accurate equivalent circuits of single phase, two winding transformer (under TTF condition) are proposed. These equivalent circuits can be simply simulated in any desired software. This accurate model closely translates the state-of-art existing TTF models into a comprehensive equivalent circuit. However, precise estimation of its parameters requires a supplementary finite element analysis. This paper employs some justifiable simplifications to the accurate model and results in a simple TTF equivalent circuit. The parameters of this model can be obtained by employing just the transformer routine test datasheet. The simple equivalent circuit is simulated under several turn-to-turn fault conditions and its accuracy has been validated.