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What are the causes of motor shaft pressure and motor shaft current


The so-called motor bearing burnt out refers to the ind […]

The so-called motor bearing burnt out refers to the induced electromotive force (ie, shaft voltage) generated during the operation of the engine bearing, which in turn generates shaft current, which leads to electrical corrosion and damages the bearing.

1. Causes of motor shaft pressure

The shaft voltage of a three-phase AC motor is usually caused by the unbalanced magnetic circuit of the motor, which mainly includes the following situations:

(1) In the production process of the motor, the poor stacking process of the stator iron core magnetic steel sheets of the motor leads to uneven reluctance of the stator and rotor along the circumferential direction of the iron core, generating magnetic flux interlinked with the rotating shaft, thereby generating induced electromotive force.

(2) During the use of the motor, due to the use environment and the manufacturing (rigidity) problems of the motor itself, the air gap between the stator and rotor of the motor changes, resulting in changes in reluctance, uneven leakage flux, and electromotive force induced by the shaft.

(3) Electrostatic induction can also cause the motor to generate shaft voltage. If there are a lot of high-voltage equipment around the motor, the motor shaft may generate induced voltage. Or when the various signal devices used in conjunction with the motor are charged, if the device has weak insulation and comes into contact with the shaft, it will cause the shaft of the motor to generate shaft voltage.

2. Causes of motor shaft current

Although the motor shaft voltage is very low, only 0.5~2 V, it will form a voltage path between the motor shaft, the frame and the housing. Since the current loop impedance is very small, a large shaft current P will be generated.

Under normal circumstances, there is a lubricating oil film between the shaft and the bearing, which can play a role in insulation. For lower shaft voltages, the oil film can play a role of insulation and protection, and no shaft current will be generated. However, when the shaft voltage increases to a certain value, especially when the motor starts, because the lubricating oil film in the bearing has not been stably established, the shaft voltage will break down the oil film and discharge to form a charged circuit.

When the oil film of the motor bearing breaks down, as the bearing temperature increases, the number of bearing breakdown points increases, and the equivalent resistance of the bearing decreases. The shaft current conducts the metal contact points of the bearing and the rotating shaft, because the contact points are very small. , The current density is very large, and high temperature is generated instantaneously, causing the bearing to burn ficus locally. The sintered bearing alloy flies away under the action of rolling pressure, so small pits are formed on the inner surface of the bearing. Generally, the hardness and mechanical strength of the rotating shaft is higher than that of the bearing alloy, so it is manifested as a washboard-like dent in the raceway of the bearing inner ring.


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