Why does the transformer core need to be grounded?

1.Why does the transformer core need to be grounded?

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

In addition, when the transformer is in operation, there is a strong magnetic field around the winding. The iron core, metal structure, parts, components, etc. are all in a non-uniform magnetic field. The distance between them and the winding is not equal. Therefore, each The magnitude of the electromotive force induced by the magnetic field of metal structures, parts, components, etc. are also not equal, and there are also potential differences between each other. Although the potential difference is not large, it can also break down a small insulation gap, which may also cause continuous micro-discharge.

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

The effective solution is to reliably ground the iron core, fixed iron core, and winding metal structures, parts, components, etc., so that they are at the same earth potential as the fuel tank. The core of the transformer is grounded at one point, and it can only be grounded at one point. 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, large eddy currents will be caused. The core is severely hot.

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

It should be noted that the iron core of the transformer must be grounded at one point, not at two points, and more than at multiple points, because multi-point grounding is one of the common faults of the transformer.2.Why can’t the transformer core be grounded at multiple points?

The reason why the transformer core laminations can only be grounded at one point is that if there are more than two grounding points, a loop may be formed between the grounding points. When the main track passes through this closed loop, circulating current will be generated in it, causing an accident due to internal overheating. The molten local iron core will form a short-circuit fault between the iron chips, which will increase the iron loss, which will seriously affect the performance and normal operation of the transformer. Only the iron core silicon steel sheet can be replaced for repair. Therefore, the transformer is not allowed to be grounded at multiple points. There is one and only one ground.

3. Multi-point grounding is easy to form a circulating current and easy to generate heat.

During the operation of the transformer, the metal parts such as the iron core and clamps are all in a strong electric field, because electrostatic induction will produce a floating potential on the iron core and metal parts, and this potential will discharge to the ground, which of course is not acceptable Therefore, the iron core and its clips must be grounded correctly and reliably (except for the core bolts only). The iron core is only allowed to be grounded at one point. If two or more points are grounded, the iron core will form a closed loop with the grounding point and the ground. When the transformer is running, magnetic flux will pass through this closed loop, which will generate a so-called circulating current, causing local overheating of the iron core, and even burning metal parts and insulating layers.

To sum up: the iron core of the transformer can only be grounded at one point, and cannot be grounded at two or more points.