The main reasons are as follows:
1. Poor insulation between silicon steel sheets;
2. Short circuit between some silicon steel sheets in the magnetic circuit;
3. Insulation damage of the through-core bolts or clamps, the upper yoke iron and other parts, resulting in short circuit;
4. Loose silicon steel sheets in the magnetic circuit creating air gaps, increasing magnetic resistance;
5. Short circuit in the coil due to inter-turn or parallel branch shorting;
6. Different number of turns in each parallel branch;
7. Incorrect calculation of the ampere-turns of the winding.