Varying the energisation condition to mitigate sympathetic inrush current

Transformers are generally easy to access and can contribute significantly to entire power system. When a transformer is turned on for the first time, it produces a magnetising inrush current which acts as a starting current. Energisation of transformer has a substantial impact on inrush current and transformer that are connected in parallel. Sympathetic inrush current is a phenomenon that appears when a transformer is switched-on in network whereas the other transformers that was earlier energised. Besides, when sympathetic inrush phenomena occur, the peak and period fluctuate significantly. In this paper, the transformers will be energised in three different ways and each condition will be explored in depth. The operation time of the transformer’s energisation whether it is energised simultaneously or at different times are tested and analysed in terms of their characteristics. It is performed using power system computer aided design (PSCAD) software, starting with a develop model of the energisation and then generate the outcomes. The results of the simulation demonstrate that energising the transformer in different ways can give different effect on the sympathetic inrush current, as well as the variables that affect it and methods for reducing it

IMPACT OF INRUSH CURRENTS AND GEOMAGNETICALLY INDUCED CURRENTS ON TRANSFORMER BEHAVIOR

Transformers are the tie-points of electrical power systems. Their protection from power system faults and other innate issues is of prime importance. A few of the issues that are studied in this report are magnetic inrush currents, geomagnetically induced currents in power transformers and Over-excitation. This project develops a novel way of initializing and visualizing the flux linkage in the transformer core for studies on energization inrush currents. In addition, a quasi-DC source for GIC has been developed in order to study the GIC effects on power transformers and a sensitivity analysis has been carried out to understand effects of GIC amplitudes and frequencies on the transformer core. Lastly, a study has been carried out in order to understand Over-excitation effects on transformers. The cases have been simulated in ATP (Alternative Transients Program) using the hybrid transformer model available in the program. The simulation results suggest the models developed are capable of providing an in depth analysis of GIC, inrush currents and over-excitation. Future recommendations include studies on relationship of var absorption and GIC amplitude as well as developing a model for studying controlled switching with residual flux linkage monitoring for minimizing inrush currents