Limiting inrush current in power transformers by using a pre-magnetizing transformer

During energization of power transformer transient inrush currents may arise up to 20 times the rated current. This phenomenon can be detrimental to certain applications and with frequent switching operations may reduce transformer’s life cycle. Using a Pre-Magnetizing transformer reduces the inrush current quite significantly, in most of the cases below the rated current, hence improving the lifetime, availability & reliability of power transformers. In this paper challenges with respect to high inrush current are discussed in detail. Practical implementation of Pre-Magnetizing Transformer (based on experience in actual implementation at site installed transformers) is discussed and explained. Finally, it highlights the advantages of this arrangement with recommendations as to in which applications this must be implemented.