## 1 Introduction  
Transformers are essential components of power systems. However, energization of the transformer is necessary for the operation of power systems. When the transformer is energized, an inrush current of large magnitude and rich harmonics is generated. This current adversely affects the power system causing a reduction in the lifetime of the transformer, damage, and mal-operation of the protective relay. Therefore, several studies have been carried out on the inrush current of a transformer to counteract these adverse effects. References [1; 2; 3; 4; 5] studied the discrimination strategies between transformer faults and inrush current. References [6; 7; 8; 9; 10; 11; 12; 13] studied the reduction techniques of inrush current. Moreover, [6; 7; 8; 9] studied the controlled energization of transformers, while [10; 11] studied the utilization of uninterrupted power supply and photovoltaic systems. In addition, [12; 13; 14; 15; 16; 17] studied the power quality and protection of power systems by inrush current. The studies above were performed using a power system simulation program. [1; 3; 4; 9] used Power Systems Computer Aided Design Electromagnetic Transients including DC (PSCAD/EMTDC). References [2; 5] used MATLAB. References [6; 7; 10; 14; 15] used Electromagnetic Transients Program (EMTP). Reference [16] used Electromagnetic Transients Program--Restructured Version (Emitter-RV). Reference [17] used DigSIENT software, and [11] performed laboratory experiments. References [8; 12; 13] did not provide any simulation software information. References [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17] did not provide detailed information for the simulation of the transformer inrush current.  
For a transient simulation program, it is necessary to derive the data based on the current-flux curve necessary for simulating the transformer inrush current. In addition, data such as impedance ratio, impedance voltage, no-load losses, and winding resistance in transformer test reports are required. However, it is often difficult to determine what data should be used and how they should be processed when the power system operator performs transformer inrush current simulations. Therefore, this paper provides detailed information on the simulation of transformer inrush current to power system operators. The novel contribution of this paper is as follows:  
1. The simulation process of transformer inrush current using EMTP has been systematized.
2. The necessary data for the simulation are derived from the test report.
3. The method for simulating transformer inrush current using these data is described in detail.
4. Based on the method proposed in this paper, the power system operator can easily perform the inrush current simulation.  
Therefore, this paper establishes the simulation process of transformer inrush current using EMTP, which simulates transient electromagnetic phenomena and is one of the most widely used electric utilities programs. Alternative Transients Program Draw (ATPDraw) is a graphical, mouse-driven pre-processor to the ATP version of EMTP [18; 19; 20]. Based on the established simulation process, the simulation example of transformer inrush current is presented using 154 kV transformer test data in Korea.  
The remainder of this paper is organized as follows: Section 2 discusses the inrush current. In Section 3, two methods of the simulation process of transformer inrush current using EMTP are introduced. Section 4 discusses the simulation results using 154 kV transformer test data in Korea. Finally, the conclusions derived from the study are presented in Section 5.