Why does the transformer core need to be grounded?

Why should the iron core of the transformer be grounded? What should be paid attention to when grounding? When the transformer is running or during high-voltage testing, the iron core and its metal parts are in different positions in the strong electric field, and the potentials induced by static electricity are also different. The result is a potential difference between the iron core and each metal part or the ground body, forming intermittent spark discharges between metal parts with different potentials. This discharge will cause the transformer oil to break down and damage the solid insulation. In order to avoid the above situation, the iron core and its metal parts (except the core screw) must be reliably grounded. Due to the shielding effect of the iron core, the potential of the core-through screw is similar to that of the iron core, so it does not need to be grounded. Since the insulation resistance between the silicon steel sheets of the iron core is very small, only one piece of the iron core needs to be grounded, and all the laminations of the iron core can be considered to be grounded.

The core is only allowed to be grounded at one point, and only single-wire connections are allowed between components that need to be grounded. If there are more than two points of grounding in the iron core, a closed loop may be formed between the grounding points. When a large magnet passes through this closed loop, an electromotive force will be induced in the loop and cause a current. The size of the current determines Depends on the magnitude of the induced electromotive force and the impedance value of the closed loop. When the current is large, it will cause local overheating failure or even burn out the iron core. The grounding piece should have a certain strength and cross-sectional area, and is generally made of 0.3mm×20mm, 0.3mm×30mm or 0.3mm×40mmr tin-plated copper sheet. The depth of the ground plate inserted into the iron core should be no less than 30mm for distribution transformers, no less than 70mm for main transformers, and 140mm for transformers. The grounding piece should be close to the clamp and must not collide with the end face of the iron yoke to prevent the silicon steel piece of the iron yoke from short circuiting. All other metal accessories on the instrument body should be grounded. The iron core contact should generally be set on the low voltage side. The above is the content shared with you. I hope it will be helpful to everyone.