A New Strategy to Reduce Inrush Current Fixing Residual Flux in Power Transformers

In this paper, inrush current reduction in power transformers has been analyzed and a new strategy is proposed for effective reduction of this current. Residual flux has an important role in the amplitude of inrush current in power transformers. Therefore, first, analytical method has been introduced for estimating residual flux using the information during deenergizing. In the next step, another method has been introduced using residual inductance concept for estimating residual flux when there is no access to the information during deenergizing. Considering some limitations in this method and also possessing the required information and the way of deenergizing in most cases, a new strategy is proposed to mitigate the inrush current. In the proposed strategy, instead of estimating the residual flux, its value is fixed and used in energizing process to reduce inrush current. Additionally, the proposed strategy can be used in different types of power transformers and connections with no need to the neutral point. Simulation results exhibit effective reduction in inrush current using the proposed strategy.