During the operation of the motor, if there is a shaft current between the two bearing ends or between the motor shaft and the bearing, the service life of the motor bearing will be greatly shortened. The following Dalan motor small series takes the three-phase asynchronous motor as an example to discuss the cause of the shaft current and the measures to prevent the shaft current.
First, the cause of the shaft voltage and shaft current
1. Magnetic imbalance produces shaft voltage
When an AC asynchronous motor is operated with a sinusoidal alternating voltage, its rotor is in a sinusoidal alternating magnetic field. Due to the stacking factors of the motor stator and rotor fan-shaped punching piece, silicon steel sheet, etc., together with the existence of the iron core groove and the vent hole, an unbalanced magnetic yin is caused in the magnetic circuit. An alternating magnetic flux intersecting the axis is generated, thereby generating an alternating potential.
2. Inverter power supply produces shaft voltage
When the motor is operated by inverter power supply, the power supply voltage contains high-order harmonic components, which cause electromagnetic induction between the end of the stator winding coil, the wiring part and the rotating shaft to generate the shaft voltage.
3, static induction generates shaft voltage
At the motor running site, the shaft voltage is induced at both ends of the rotating shaft due to the strong electric field of the high voltage equipment.
4, static charge
During the operation of the motor, the fluid in the load is rubbed against the rotating body to generate an electrostatic charge on the rotating body, and the electric charge gradually accumulates to generate the shaft voltage.
5, external reasons
The intervention of an external power source produces a shaft voltage. Due to the complicated wiring on the operation site, especially the large motor protection and measuring component wiring, which one has the wire head overlapped on the rotating shaft, the shaft voltage is generated.
Second, measures to prevent the generation of shaft current
1. Install a grounding carbon brush on the shaft end to make the grounding carbon brush reliably ground, and make reliable contact with the rotating shaft to ensure that the potential of the rotating shaft is zero potential, and the static electric charge on the motor shaft is led to the earth at any time, thereby eliminating the shaft current.
2. In order to prevent the shaft current from being generated due to magnetic imbalance, an insulating spacer is added to the bearing housing and the bearing bracket of the non-shaft end to cut off the circuit of the shaft current.
3. Require inspection and operation personnel to carefully inspect and strengthen the insulation of wires or gaskets.
4. In addition to a bearing seat in the machine base, the remaining bearing housings and all metal parts including the instrument housing and other metal parts mounted on them shall be grounded and the non-insulated bearings shall be grounded with anti-static charging.
5. For the shaft voltage generated by the cross-linking flux of the shaft, an insulating pad can be added under the bearing seat on the motor side to cut the circuit formed between the shaft and the bearing bush, so that the shaft current cannot be generated. And always check the insulation strength of the bearing housing, measured with a 500V shaker, the insulation should not be less than 0.5MΩ
6. Maintain the purity of the insulating medium oil between the shaft and the bearing bush. It is found that the water in the oil must be filtered into the ground. Otherwise, the insulation strength of the oil film cannot meet the requirements and is easily broken down by low voltage.
----- Editor-in-Chief: Dalan Oil Pump Motor 02-Procurement Consultant
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