This paper investigates the abnormal system behaviour under conditions of transformer faults. A power sub-system configuration has been employed for the simulations using dedicated electromagnetic transient simulation package PSCAD/EMTDC. The events in the power system encompass many scenarios, including various faults and normal operating states, and correspond to specific time scales. The diversity of the cases has been achieved by changing the type of fault (single line-to-ground fault, double line-to-ground fault) and time to apply the fault. In the event of a fault it is important to be able to reconstruct and have evidence of the surrounding circumstances and the timing of the disturbance as well as the faults` modes, or ways in which the circuit breaker fails. This study presents the simulation techniques for the currents that may occur in the network under different fault conditions. These short circuit currents determine the rating of circuit breakers that must be able to clear the fault in order to avoid permanent damage to the equipment. Using different transformer models available in PSCAD/EMTDC software package the results obtained are different.
