What is the sequence for powering down the transformer?
The sequence for shutting down a main transformer is as follows: when de-energizing, the load side should be shut down first, followed by the power supply side. For energizing operations, the reverse order applies: the power supply side is energized first, then the load side. This is because:
Energizing from the power supply side to the load side makes it easier to identify the fault range and take prompt judgment and handling measures in case of a fault, preventing the fault from spreading or expanding.
In multi-power supply scenarios, shutting down the load side first can prevent reverse charging of the transformer. If the power supply side is shut down first, a fault may cause protection devices to malfunction or fail to operate, prolonging the fault clearance time and potentially expanding the fault scope.
When the load-side bus voltage transformer is equipped with an under-frequency load-shedding device without current blocking, shutting down the power supply side switch first may trigger false operation of the under-frequency load-shedding device due to feedback from large synchronous motors.
