Why the transformer can only be grounded at one point
Writer： Hengfeng you electric Time：2023-05-09 views：times
During the operation of the transformer, the iron core, fixed iron core, winding and other metal structures and parts are all in a strong electric field, which has a high potential to the ground. If the iron core is not grounded, there will be potential difference between it and the grounding clamp and the oil tank. Intermittent discharge may occur under the action of potential difference.
In addition, when the transformer is running, there is a strong magnetic field around the winding. The iron core, metal structure and parts are all in an uneven magnetic field, and the distance between them and the winding is different. Therefore, the magnetic field induced electromotive force of each metal structure and component is different, and there is potential difference between them. Although the potential difference is small, it can also break through small insulation gaps and may cause continuous micro discharge.
Intermittent discharge caused by potential difference or continuous micro discharge that may break through a small insulation gap is not allowed, and it is very difficult to check these intermittent discharge parts.
The effective solution is to reliably ground the iron core, fixed iron core, winding metal structure and parts to make them equal to the ground potential of the oil tank. The iron core of the transformer is grounded at one point, and only one point is grounded. Because the silicon steel sheets of the iron core are insulated from each other, this is to prevent large eddy currents. Therefore, all silicon steel sheets must not be grounded or grounded at multiple points, otherwise large eddy currents will occur and the iron core will heat seriously.
The iron core of the transformer is usually grounded by any silicon steel sheet of the iron core. Although silicon steel sheets are insulated, their insulation resistance is very small. The non-uniform strong electric and magnetic fields can make the high-voltage charges induced in the silicon steel sheets flow from the ground to the earth through the silicon steel sheets, but can prevent the eddy currents from flowing from one sheet to another. Therefore, as long as any silicon steel sheet of the iron core is grounded, the whole iron core is grounded.
It should be noted that the iron core of the transformer must be grounded at one point, neither at two points nor at many points, because multi-point grounding is one of the common faults of the transformer.
1. Why can't the transformer core be grounded at multiple points?
The reason that the transformer core lamination can only be grounded in a small amount is that if more than two points are grounded, a loop may be formed between the grounding points. When the main track passes through this closed loop, circulation will be generated in it, causing internal overheating and accidents. The melted local iron core will form a short circuit fault between iron sheets, increase the iron loss, and seriously affect the performance and normal operation of the transformer. It can only be repaired by replacing the silicon steel sheet of the iron core. Therefore, the transformer is not allowed to be grounded at multiple points, but only at one point.
2. Multipoint grounding is easy to form circulating current and heating.
During the operation of the transformer, the iron core, its clamps and other metal parts are in a strong electric field, because electrostatic induction will generate a floating potential on the iron core and metal parts, which will discharge to the ground, which is of course not allowed. Therefore, the iron core and its clamp must be correctly and reliably grounded (except for the threaded bolt). Only one point of the iron core is allowed to be grounded. If two or more points are grounded, the iron core will form a closed circuit with the grounding point and the ground. When the transformer is running, the magnetic flux will pass through this closed circuit and generate the so-called circulating current, causing local overheating of the iron core, and even burning the metal parts and insulation layer.
To sum up, the iron core of the transformer can only be grounded at one point, not at two or more points. Qingdao Hengfengyou Electric belongs to Hengfengshuai Group, which is a professional electrical company focusing on the production, manufacturing and sales of electrical distribution products. Thirty years of production experience in the global power market. It is mainly engaged in the manufacturing and sales of distribution transformers, medium and low voltage switchgear, distribution boxes, American box type transformers and box type substations. It has been successfully sold to more than 50 countries worldwide. The product certification is complete. Hengfengyou Electric will provide you with the best electrical product solutions. https://www.hengfengyou.com ； info@hengfengyou.com ；
