Field studies on the Inrush Current for 33/11kV transformer and the effect on voltage interruption during switching operation of 10MW wind farm

The Inrush Current for transformer switching operation study is an electromagnetic transient analysis (EMT) and are performed in order to investigate the network response after the energized the two 33/11 kV, 7.75MVA transformers in the Layafa S/S. The Inrush current associated with transformer energizing can cause some reactions that may adversely affect other loads in the power networks system, for instance voltage sags or over-voltage phenomena which could cause nuisance tripping for protective devices or loads. Protection devices may mis-interpret these events as fault currents, if the protection devices are not properly coordinated well. In this paper, the inrush current analysis was performed for the generators-transformers of the wind farm switching operation. In the study analysis, the 33/11 kV transformers will not be energized at the same time. Each transformer will be energized at no load condition, with the tap changer set to the maximum step of the HV side (higher voltage) in order to minimize the inrush current values. The simulation analysis was performed which the aid of DigSilent and EMT computer simulation to establish this study while considering the minimum short circuit power in the grid and the Wind Farm disconnection from the system. This paper is based on the field results test of the newly installed wind farm generator-transformer in relation to network interruption on the 33 kV and 11 kV systems during the switching on operation especially transient voltage phenomena.