Discussion on inspection and test of motor stator and rotor windings

Winding is the most critical part of the motor and can cause fatal electrical and mechanical failures if not handled properly. For the standard motor manufacturer, the necessary inspections will be carried out on the relevant links through the necessary instruments and tooling.

For the inspection of the windings, on the one hand, the inspection of its appearance, on the other hand, the electrical quality compliance; for these two inspections, before the motor assembly and after the assembly of the complete machine. The pre-assembly inspection is carried out before the winding is completed after the wiring is finished. The motor manufacturer is used to call it the electric semi-finished product test. There is not much difference in the appearance inspection, but for the inspection of the electrical performance, different manufacturers have different ones. Ways, such as: some use integrated tester, some use bridge + day meter + pressure gauge, and some use low voltage current measurement. We will discuss and share with you in this category. Today we only cover appearance and electrical inspection projects.

1. appearance inspection of the winding

After the windings are bulk, the elongation of the ends shall be the same. The height of the end extension shall comply with the requirements of the drawings. The highest point of the end of the rotor winding and the outer tie must be 2~5 mm lower than the outer circumference of the rotor core. The windings shall be on the base, the shaft and the wind. Parts such as plates must maintain a certain insulation distance. The connecting line and the lead wire shall be tied firmly. There shall be no blockage on the cooling air passage. The insulation of each part shall be lining according to the regulations. The wedge should be loose or not high. The slot insulation should be wrapped in the wedge. Under the insulation, there is no crack at the slot, and all the insulating materials should be free from loose and convex images, so as not to be blown by the wind when the motor is running. This kind of problem is more common in the production process of the motor, especially for manual operation. The windings, the human factor is more, if there is no effective testing and control tools, only found in the motor test).
After dipping, the paint film is smooth and flat, without wrinkles, blistering and bulging paint. The paint is elastic with fingers, but there are no fine cracks, and no dry insulating paint emerges from the crack of the paint film. The problem mainly involves the process of dipping and drying, and Ms. has also encountered it. When the end is sprayed with the paint, it should be covered and the color should be the same.

2. three-phase winding current balance test

After the three-phase AC winding is connected, a three-phase current balance test should be performed before immersion. To check the symmetry of the three-phase winding. This test makes it easier to find winding turns or wiring errors compared to measuring the winding DC resistance. For example, the test winding is connected to a low voltage of three-phase symmetrical power frequency (usually taking 3~10% of the rated voltage). If the maximum or minimum value of the three-phase current is different from the average value, the upper and lower deviations do not exceed the average value. 3%, and the value is close to the motor of the same model, it is qualified. If the three-phase current is unbalanced, it is advisable to change the power supply connector to re-test once, analyze whether there is a problem with the power supply wiring, and then record the values of the three-phase current and the three-phase voltage. Pay attention to whether the winding has a serious inter-turn short circuit (the coil is partially overheated, or even Smoke) and check that the winding wiring meets the drawing requirements.


When testing in this way, the judgment is made according to the following criteria:

(1) During the test, magnetic objects are not allowed to be placed on the windings of the test and its core, so as to avoid an increase in the reactance of some coils and artificially cause three-phase current imbalance.

(2) If the three-phase current of the tested winding is balanced, but the current under the same applied voltage is more than 3% of the same type, it may be the number of parallel windings, the number of pole pairs connected, or the star or delta connection. Error (this type of error is much larger than 3%), or the number of turns and pitch used are not consistent with the drawing.

(3) In order to determine the cause of the three-phase current imbalance of the stator winding, usually check the wiring of the winding, whether the first and last ends of each phase winding are connected incorrectly, whether the polarity of each coil or pole phase group is reversed, and the number of slots per phase per pole. Whether they are equal or grouped according to certain rules; whether the coil has leakage, wire breakage or poor soldering, and the case where one phase winding is connected to another phase. Then check whether the windings have a phase-to-phase short circuit or two insulation breakdowns to ground.

(4) In order to judge the reason that the rotor is unbalanced by the three-phase current of the winding, it is usually checked whether the headgear is short-circuited; then it is checked whether the connection of the three-phase winding is connected (whether the outlet position is correct and the pitch is wrong), Finally, open the connection line of the neutral point of the three-phase winding to check whether there is a phase-to-phase short circuit or two ground-to-ground breakdowns.

(5) If the rotor winding has been untied, it is not easy to check the winding pitch by appearance. The neutral point connection in the three-phase winding can be loosened, and then the headlights of each phase winding can be ascertained by the calibration lamp (or multimeter). If the number of parallel heads per phase is equal to the number of slots per phase per winding of the winding, and the pole groups are evenly distributed on the circumference, the connection is correct.

Reprinted from the network