When the power transformer is operating normally, the iron core must be reliably grounded at one point. If there is no grounding, the floating voltage of the iron core to the ground will cause intermittent breakdown discharge of the iron core to the ground. After the iron core is grounded at one point, the possibility of forming a floating potential of the iron core is eliminated.
However, when the iron core is grounded at more than two points, the uneven potential between the iron cores will form a circulating current between the grounding points and cause a multi-point grounding heating failure in the iron core.
A ground fault in the core of the transformer will cause local overheating of the core. In severe cases, the local temperature rise of the core will increase, causing light gas operation, or even causing a tripping accident due to heavy gas operation.
The melted partial iron core causes a short-circuit fault between the iron sheets, which increases the iron loss and seriously affects the performance and normal operation of the transformer so the iron core silicon steel sheets must be replaced for repair.
Therefore, the transformer does not allow multiple points of grounding and can only have one and only one point of grounding.