When the power transformer operates normally, the bakal ubod must be reliably pinagbabatayan at one point. If there is no grounding, the suspension voltage of the iron ubod to the ground will cause intermittent breakdown discharge of the iron core to the ground.

The possibility of forming the suspension potential of the iron core is eliminated after the iron core is pinagbabatayan one point. However, when the iron core is grounded at more than two points, the non-uniform potential between the iron cores will form a circulating current between the grounding points, and cause multi-point grounding heating fault of the iron core.

The iron core grounding fault of the transformer will cause local overheating of the iron core. In serious cases, the local temperature rise of the iron core will increase, the light gas will act, and even the heavy gas will act and trip. The short circuit fault between iron chips is caused by the local iron cores melted, which increases the iron loss and seriously affects the performance and normal operation of the transformer, so that the silicon steel sheet of the iron core must be replaced for repair. Therefore, the transformer is not allowed to be grounded at multiple points, and only one point can be grounded.