Online monitoring of power transformers for detection of internal winding short circuit faults using negative sequence analysis

Abstract

As a recent trend, online monitoring techniques for electrical machines, mainly including power transformers, has been considered very important. This paper presents a new online method for detection of interturn faults in the power transformers using the ratio of negative sequence components of the primary and secondary line currents. The ratio is equal to the turn ratio during external faults as well as in the supply or load imbalance conditions, while it differs from the turn ratio when interturn winding faults occur. The main feature of the proposed method is its capability to detect low level interturn faults which typically cannot be detected by the traditional transformer protection devices before they developed into high level faults with more severe damage to the power transformer. In this work, a major improvement has been suggested to overcome this problem to a great extent. The proposed method can unambiguously detect interturn faults even down to two shorted turns along the winding. The method is not influenced by the supply and load harmonics even under heavily distorted conditions. The performance of the proposed technique was studied for a variety of operating conditions using data generated by simulations on a finite element model. Copyright © 2010 John Wiley & Sons, Ltd.