Discussion on grounding reasons of Transformer Iron Core

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


In addition, during the operation of transformers, there is a strong magnetic field around the windings. The iron core, metal structure, parts, components, etc. are all in a non-uniform magnetic field, and their distances from the windings are not equal. Therefore, the magnitude of the electromotive force generated by the magnetic field induction of each metal structure, part, component, etc. is also different, and there is also a potential difference between them. Although the potential difference is not significant, it can also break through very small insulation gaps, which may cause sustained micro discharge phenomena.

 

Whether it is the intermittent discharge phenomenon that may occur due to the 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 these intermittent discharge parts.

 

The effective solution is to reliably ground the metal structures, parts, and components of the iron core, fixed iron core, and winding, so that they are at the same ground potential as the oil tank. The grounding of the transformer's iron core is one point grounding, and can only be one point grounding. Because the silicon steel sheets of the iron core are insulated from each other, this is to prevent the generation of large eddy currents. Therefore, all silicon steel sheets must not be grounded or grounded at multiple points, otherwise it will cause large eddy currents and cause serious heating of the iron core.

Silicon steel coil

The grounding of the iron core of a transformer usually involves grounding any piece of silicon steel sheet of the iron core. Although silicon steel sheets are insulated, their insulation resistance values are very small. The uneven strong electric and magnetic fields can cause the induced high-voltage charges in the silicon steel sheets to flow from the grounding point to the ground through the silicon steel sheets, but they can prevent eddy currents from flowing from one sheet to another. So, as long as any piece of silicon steel in the iron core is grounded, it is equivalent to grounding the entire iron core.

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