The cast aluminum rotor of a conventional motor is a relatively sturdy whole, while the wound rotor motor is different. Whether it is a hard winding or a soft winding, the stability of the winding ends is relatively weaker.
To avoid this problem, in addition to impregnating and curing the windings, another measure is to add a support ring at the end of the winding to ensure that the spatial distance between the end and the shaft meets the requirements. Then, heat-shrinkable binding tape is tied around the outer ring of the rotor winding end to control the radial outward deformation of the rotor winding. Ms. Can demonstrates the process of tying heat-shrinkable tape around the outer ring of the rotor winding end through a video.
The binding tape is tied to the rotor end after the rotor winding is inserted and before impregnation. Through the subsequent impregnation and drying processes, the binding tape shrinks and fits tightly with the winding in the radial direction. It can form a whole with the winding through the insulating varnish, thus enhancing the reliability of the rotor.
For wound rotor motors, the motor speed must be strictly controlled, because overspeed operation may cause the rotor winding ends to deform outward and rub against the rotor windings, resulting in a catastrophic electrical failure of the motor.
What is a rotor slippage fault in a motor?
The runaway rotor is a fault unique to wound rotor motors. It occurs when the motor runs at overspeed. This type of fault often occurs during winch or crane operation when the rotor runs over. The fault manifests as deformation of the rotor winding ends, which protrude above the outer diameter of the rotor core. This problem can also lead to damage and burnout of the stator windings.
A slippage fault is fatal to a motor, but it can be effectively avoided by using a speed limiting protection device. During motor manufacturing, necessary fixing measures should be taken at the ends of the motor rotor windings to prevent deformation.
Measures taken during the production process
To enhance end rigidity and reliability during production and processing, necessary measures include the following:
● Support and clamping. Add supports and end clamps to the rotor ends to overcome the radial centrifugal force of the rotor windings and prevent the windings from deforming due to heat during motor operation.
● Elastic cable ties for fixation. PST elastic cable ties are used to fix the winding ends to ensure the windings are securely fixed as a whole. During the motor impregnation and baking process, the PST shrinks due to heat, which better ensures the reliability of the curing at the rotor ends.
● Impregnation and curing. Similar to the stator winding process, the VPI impregnation process is used, which significantly improves the mechanical strength and insulation reliability of the winding.
●Rotor dynamic balancing. Strictly control the dynamic balancing accuracy of the rotor to reduce and eliminate damage to the rotor windings caused by alternating excitation forces.
It is important to note that during the motor manufacturing process, the manufacturer will conduct an overspeed test of 1.2 times the rated speed to verify the robustness of the rotor end, and there will be specific regulations in the motor's technical specifications; however, the most effective approach is for customers to be aware of these requirements and take the necessary measures.
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