Transformer in operation, iron core and fixed iron core, winding metal structure, parts, components, etc. are in a strong electric field, under the action of electric field, they have a high potential to the ground. If the iron core is not grounded, there will be a potential difference between it and the grounded clamp and the fuel tank, etc., under the action of the potential difference, intermittent discharge may occur.

In addition, in the operation of the transformer, the winding has a strong magnetic field around, the iron core, metal structure, parts, components, etc., are in a non-uniform magnetic field, their distance from the winding is not equal, so the metal structure, parts, components and other magnetic field induction generated by the electromotive force size is also not equal, there is a potential difference between each other. Although the potential difference is not large, it can also break down a small insulation gap, so it may also cause a persistent trace discharge phenomenon.

Whether it is the intermittent discharge phenomenon that may be caused by the role of potential difference, or the continuous micro-discharge phenomenon that may be caused by the breakdown of a small insulation gap, it is not allowed, and it is very difficult to check the location of these intermittent discharges.

The effective solution is to ground the iron core and the fixed iron core, the metal structure, parts and components of the winding reliably, so that they are equal to the fuel tank in the geodetic potential. The core grounding of the transformer is one point grounding, and only one point grounding. Because the electrical steel sheets of the iron core are insulated from each other, this is to prevent the production of large eddy currents, therefore, it is necessary not to ground all the electrical steel sheets or multi-point ground, otherwise, it will cause large eddy currents and serious heating of the iron core.

The iron core of a transformer is grounded, usually by grounding any piece of electrical steel in the iron core. Although the electrical steel sheet is insulated, its insulation resistance value is very small, and the uneven strong electric field and strong magnetic field can make the high voltage charge induced in the electrical steel sheet flow to the earth through the electrical steel sheet from the ground, but it can prevent the eddy current from flowing from one piece to another. Therefore, as long as any piece of the electrical steel sheet of the iron core is grounded, then it is equal to the entire iron core is grounded.