The no-load current of a transformer is determined by its impedance. Poor performance and quality of the silicon steel sheets, or inadequate manufacturing process of the iron core, such as uneven lamination, excessive seams, insufficient or excessive clamping force, can all lead to an increase in no-load current. Another scenario is when the number of coil turns is designed to be too few, or the cross-sectional area of the iron core is too small, resulting in excessively high magnetic flux density and an increase in no-load current. Generally speaking, the no-load current of a low-frequency transformer ranges from 3% to 10%, depending on the material and model of the transformer.
After being used for a period of time, the no-load current of the transformer increases, indicating the need to check for short circuits in the windings or control feedback circuits. Whether it is a control transformer, an autotransformer, or an isolation transformer, all are composed of silicon steel sheets, primary windings, secondary windings, insulating varnish, etc. All transformers experience no-load losses and an increase in no-load current.
What are the main reasons for the increase in no-load loss and no-load current of transformers? Let's analyze them together:
1. The insulation effect between silicon steel sheets is poor
2. Short circuit between some silicon steel sheets in the magnetic circuit
3. Loosening of silicon steel sheets in the magnetic circuit leads to the formation of air gaps, which increases magnetic reluctance
4. The through-bolt or pressing plate, upper yoke, and other parts are damaged, leading to insulation damage and forming a short circuit
5. The number of wire turns in each parallel branch is different
6. The coil has a short circuit between turns or in parallel branches
7. The ampere-turns of the winding are incorrect
Therefore, in the manufacturing process of transformers, the quality of the product is determined by the raw materials, but at the same time, each process step is also extremely important.
