Controlled switching to mitigate power transformers inrush current phenomenon

Abstract

During energisation of a power transformer, inrush current phenomenon happens which is able to be ended up with a collection of undesirable consequences. This inrush current could lead to mal-operation of protection system, considerable stresses over transformer (electrical, mechanical and thermal stresses) and electrical transient tension on the power system network. Accordingly, transformer energisation and inrush current phenomenon has to be studied in order to find a solution for mitigating these effects. This paper highlights a real case study that shows the inrush current phenomenon for a 400kV network. Energisation of two super grid transformers, which are in a banked arrangement, will be demonstrated using EMTP. The paper will highlight different switching scenarios and analyses the results to show the effects of the inrush currents. The Point-on-wave switching (POW) device will be proposed as a method of controlled switching to mitigate the inrush currents' effects. In addition, the effect of inaccuracies in the POW timing will be assessed. Conclusion shows Point-On-Wave switching with consideration of tolerance in CB (Circuit Breaker) timing is still a good means for inrush current reduction.