The Chinese language is very interesting. The same word can have different effects when used in different situations. For example, the word "shui bao" means being irresponsible and abandoning others. It can also be extended to mean that a couple quarrels and breaks up due to disagreements. This word is more often used in motors.
Bag dumping is a fault description for wound rotor motors, which refers to the consequence of radial outward deformation of the rotor winding end due to overspeed. If we know something about wound rotor motors, we can find that there are some restrictions on the speed of this type of motor. From the number of poles, there are more motors with 6 poles or more, which means that their rated speed is relatively small; some motor manufacturers will make 4-pole wound rotor motors, but the manufacturing process is relatively complicated, and the rotor winding must be evaluated for overspeed reliability.
Actual production and verification show that the hard winding rotor has a stronger ability to prevent the package from being thrown away than the soft winding rotor; in addition, the necessary fixing, binding, varnishing and curing measures for the winding ends are very critical factors. Of course, if an overspeed limiting device is added during the operation of the motor, this problem will be solved.
Knowledge expansion -
The fundamental reason for the package throwing is the centrifugal effect
An object doing circular motion, due to its own inertia, always has a tendency to fly along the tangent direction of the circle. When the combined external force suddenly disappears or is insufficient to provide the centripetal force required for circular motion, it will move gradually away from the center of the circle. This phenomenon is called centrifugal phenomenon.
During the operation of the motor, each particle of the rotor part moves in a circular motion around the center of the motor shaft. According to the relationship between speed and centrifugal force in circular motion, the greater the speed, the greater the centrifugal force.
Commonly seen in life are washing machine dehydration barrels, cotton candy making, etc. Centrifugal speed regulators, centrifugal testers, centrifugal dryers, centrifugal precipitators, washing machine dehydration barrels, cotton candy making, automatic coin sorting machines, discus and hammer throw competitions in competitive sports, etc. are all practical applications of the centrifugal principle.
Everything has its pros and cons. Due to the centrifugal force, some accidents may occur, causing harm to people's lives. For cars driving on horizontal roads, the centripetal force required for turning is provided by the static friction between the wheels and the road surface. If the speed is too high when turning, the required centripetal force F is greater than the maximum static friction, and the car will perform centrifugal motion and cause traffic accidents. Therefore, vehicles are not allowed to exceed the specified speed at the bends of the road. High-speed rotating grinding wheels, flywheels, etc. often break and shoot out at high speeds due to material strength and internal cracks.
Knowledge expansion-
What is centrifugal force?
Centrifugal force is a virtual force, a manifestation of inertia, which moves the rotating object away from its center of rotation. In Newtonian mechanics, centrifugal force has been used to express two different concepts: an inertial force observed in a non-inertial reference frame, and the balance of centripetal force. In Lagrangian mechanics, centrifugal force is sometimes used to describe generalized forces under a generalized coordinate system.
In the usual context, centrifugal force is not a real force. Its function is only to ensure that Newton's laws of motion can still be used in a rotating reference frame. There is no centrifugal force in an inertial reference frame, and inertial force is only needed in a non-inertial reference frame.
Imagine a disk rotating around its center with an angular velocity of ω. On the disk is a wooden block of mass m, connected by a rope, the other end of which is fixed to the center of the disk (also the center of rotation). The length of the rope is r. The wooden block rotates with the disk. Assuming there is no friction, the wooden block rotates due to the tension of the rope. To an observer rotating with the disk, the wooden block is stationary. According to Newton's law, the net force on the wooden block should be zero. However, the wooden block is only subject to one force, the tension of the rope, so the net force is not zero. Does this violate Newton's law? Newton's law is only valid in an inertial system, but the reference system of the observer rotating with the disk is a non-inertial system, so Newton's law does not hold here. In order for Newton's law to still hold in a non-inertial system, an inertial force, namely the centrifugal force, needs to be cited.
The magnitude of the centrifugal force is equal to the tension provided by the rope, but the direction is opposite. After the centrifugal force is introduced, from the perspective of an observer who is rotating with the disk, the wooden block is simultaneously subjected to the tension of the rope and the centrifugal force, which are equal in magnitude and opposite in direction, and the net force is zero. At this time, the wooden block is stationary, and Newton's law holds true.