IJE TRANSACTIONS B: Applications Vol. 32, No. 5, (May 2019) 701-709 Please cite this article as: M. Ganji, M. Bigdeli, D. Azizian, Mitigation Transformer Inrush Current Using Modified Transient Current Limiter, International Journal of Engineering (IJE), IJE TRANSACTIONS B: Applications Vol. 32, No. 5, (May 2019) 701-709 International Journal of Engineering Journal Homepage: www.ije.ir Mitigation Transformer Inrush Current Using Modified Transient Current Limiter M. Ganji a , M. Bigdeli* a , D. Azizian b a Department of Electrical Engineering, Zanjan Branch, Islamic Azad University, Zanjan, Iran b Department of Electrical Engineering, Abhar Branch, Islamic Azad University, Abhar, Iran PAPER INFO Paper history: Received 04 August 2018 Received in revised form 09 January 2019 Accepted 07 March 2019 Keywords: Transformer Inrush Current Modified Transient Current Limiter Simulation Experimental Results ABSTRACT This study presents a modified transient current limiter (MTCL) for mitigation the inrush current of transformers. The MTCL is based on conventional transient current limiter (TCL), which, its configuration is modified to overcome the TCL drawbacks of operation. The proposed MTCL offers lower power losses and voltage/current THD during normal operation mode. It needs only one limiting reactor instead of two limiting reactors, which results in cost saving. The theoretical analysis of the MTCL for suppressing the inrush current has been presented and the performance was tested by PSCAD/EMTDC simulation anda experimental prototype. Both simulation and experimental results showed that the MTCL is effective for suppressing the transformer inrush current. Also, the capability of the MTCL for suppressing the transformer inrush current was compared with the conventional TCL. doi: 10.5829/ije.2019.32.05b.12 1. INTRODUCTION 1 Transformers are key equipments of power systems. Their availability and the life time have major impact on grid reliability and efficiency [1, 2]. The energization of power transformers can cause saturation of the transformer magnetic core and flux asymmetries. This saturation leads to large inrush currents flow with a high DC component and a wide harmonic spectrum. Depending on the instant of energization and grid voltage, the amplitude of the inrush currents may increase to several times (up to 10-15) of the transformer rated current. These large transient inrush currents will impose high thermal and electromechanical stress on the transformer winding and malfunction of differential and over current relays during the energization time [3, 4]. It may decrease the longevity of the transformer, and the system reliability. Therefore, to avoid these problems, the inrush current should be suppressed during the energization time [2–4]. In the literature, three main approaches have been proposed for limiting the inrush current of power *Corresponding Author Email: bigdeli.mehdi@gmail.com (M. Bigdeli) transformers, which can be categorized as three following approaches: Approach 1: Changing the internal structure of the transformer includes the winding structure and core magnetic characteristic [5–7]. Approach 2: Controlling the instant of the energization using a control circuit to control the switching angle [8, 9] and sequential switching of the phases [10–12]. Approach 3: Using impedance in the primary side of transformers [13–22]. The virtual air gap method has been present for limiting the inrush current of transformers [4]. In this method a DC current source uses to inject DC current in the auxiliary winding inside the core to reduce the permeability of the core. It has been reported in literature [5, 6], the primary and secondary coils of the transformer has been designed with an asymmetric winding distribution ratio to suppress the inrush current. In both solutions the transformer design consideration is more complicated, due to change in the transformer internal structure. Also, the efficiency of these methods for limitiging the inrush current is not significant.