The no-load current of transformer is determined by impedance. If the performance and quality of silicon steel sheet itself are poor, or the manufacturing process of iron core is poor, the lamination is uneven, the joint is too large, and the clamping force is too small or too large, the no-load current will become larger. Another situation is that the number of turns of the design coil is too small, or the cross-sectional area of the iron core is too small, resulting in too high magnetic flux density and large no-load current. Generally speaking, the no-load current of low-frequency transformer is between 3 ~ 10%, which shall be considered according to different materials and models of transformer.

After using for a period of time, the no-load current of the transformer increases. Check the winding short circuit or control feedback circuit short circuit. Whether control transformer, autotransformer or isolation transformer, they are composed of silicon steel sheet, primary winding, secondary winding, insulating paint, etc., and all transformers will have no-load loss and increase of no-load current.

What are the main reasons for the increase of transformer no-load loss and no-load current? Let's make a joint analysis:

1. Poor insulation effect between silicon steel sheets

2. Short circuit between some silicon steel sheets in the magnetic circuit

3. The silicon steel sheet in the magnetic circuit is loose, resulting in air gap and increasing magnetic resistance

4. The insulation of threaded bolt or pressing plate, upper yoke and other parts is damaged to form a short circuit

5. The number of wire turns in each parallel branch is different

6. The coil has inter turn or parallel branch short circuit

7. Incorrect winding ampere turns

Therefore, in the manufacturing process of transformer, raw materials determine the quality of products, but at the same time, each process is also very important.