A Case Study of Transformer Inrush Current Analysis in Java-Bali Power System

Energizing transformer is a common process in power systems; however, the presence of transient phenomena during energizing process must be taken into account. This paper presents general overview about inrush current and several factors that influence its magnitude. Those factors were evaluated by using transient analysis simulation based on the field data (transformer factory acceptance test data and short circuit impedance on 150kV bus of Java-Bali Power System). According to the simulation result, it was found that greater voltage ratio during energize will generate smaller inrush current, and vice versa. Greater inductive load will increase inrush current, while greater capacitive load will reduce inrush current. Higher source impedance value will reduce inrush current, and vice versa. Energizing transformer at zero crossing of the voltage wave will generate maximum inrush current, while energizing at the peak value of the voltage wave will generate minimum inrush current. Inrush current with high magnitude can cause deterioration of paper insulation which affect transformer lifetime. Therefore, factors that cause higher inrush current must be mitigated.