Relation Between Voltage and Current Unbalance

This case was occurred in February 2021 during the commissioning of the power plant. Through three checks were carried out, It was confirmed the cause of the current unbalance is the voltage unbalance, vice versa. The two faults were occurred five hours apart and the first fault occurred when a large motor was activated. It tripped as soon as it started and the startup transformer lost power. Second fault occurred when another large motor was activated. Six large motors were shut down at the same time. The check points and analysis results are as follows. In the process of switching the load of 11 busbar, the ground current of the ① ㎸ startup transformer decreases as the unbalanced current of the main transformer decreases. In the process of shutdown of a large ② motor, the rate of the current unbalance affected the rate of the voltage unbalance by 5.3 times. In the process of blackout of ③ the startup transformer, the cause of voltage unbalance is the current unbalance.