Evaluation of controlled energisation of an unloaded power transformer for minimising the level of inrush current and transient voltage distortion using PIR-CBs

This study presents an evaluation of the application of the controlled switching device for reducing the level of inrush current and transient voltage dip (TVD) during energisation of an unloaded power transformer using circuit breaker having pre-insertion resistor (PIR-CB). This evaluation is achieved by analysing the effect of statistical scatter of mechanical operating time (MOT), tolerance of auxiliary contact used as a feedback for a controlled switching device, and variation in mechanical insertion time (MIT) and electrical insertion time (EIT) of the PIR-CB. The modelling of a complete system consisting of a power source, PIR-CB, and two types of power transformers (electrically and magnetically coupled) is carried out using power systems computer-aided design/electro-magnetic transient design and control (PSCAD/EMTDC) software package. The results obtained from the simulations are compared with the results obtained during energisation of similar transformers in the real field. Finally, the performance of PIR-CB-based proposed methodology has been compared with the conventional methodology (non-PIR-CB) with reference to mitigation of inrush and TVD. The close match between field results and that obtained with simulation for both electrically and magnetically coupled transformers authenticate the proposed methodology.