Will the motor winding burn out in the no-load state?

A netizen asked why the winding of the shaded-pole motor would burn out when it is running at no load? To answer this question, we analyze the reasons why the winding of the motor is burned out when it is running at no load.

Compared with the load, the no-load state of the motor is an operating state without any load. Theoretically, for electric motor products, there is a pure no-load state only when the motor is running alone. For the motor of the traction equipment, even if the towed equipment is not loaded, the equipment connected to the motor is also a load relative to the motor. It’s just that different equipment has different corresponding load sizes, that is, the motor is in a light-load state.

Let’s take a three-phase asynchronous motor as an example. When the rated voltage is applied to the motor and the motor is not carrying any load, the current of the motor is only in the range of 1/3 to 1/2 of the rated current. The motor with fewer poles and higher speed will be smaller, while the motor with more poles and lower speed will be slightly larger. In the no-load state under the rated voltage, there will be no problem of winding burning. However, low voltage that is not enough to start the motor, and no-load operation exceeding the rated voltage may cause the winding to burn out because the current exceeds the rated current.

In addition to three-phase motors, we have also talked about the characteristic of old-style washing machines that cannot run at no-load in previous articles. The main reason is that in the no-load state, the characteristics of the non-circular magnetic field of this type of motor cause the motor no-load current to be greater than the rated current in most cases.

For single-phase shaded-pole motors, the starting and running characteristics of such motors are relatively poor because the motor’s spatial magnetic field contains many harmonic components, the axis of the motor’s main winding and auxiliary winding is less than 90 degrees apart in electrical angle, and the leakage magnetic field caused by the shaded-pole coil and magnetic shunt plate. The shaded-pole coil increases the current and loss in the motor winding. The no-load current of such motors is already very large, and the motor current does not change significantly when the load increases. Therefore, such motors are not suitable for no-load or light-load operation, but the motor is not prone to winding burnout when it is overloaded and decelerated.