The motor has a current-carrying wire and magnetic loop structure, which usually results in magnetization of the shaft or pulsating flux. Pulsating magnetic flux induces voltage in the loop formed by shaft, bearing and housing, so shaft current flows through the loop, and the surface of shaft and sliding bearing bush, or the surface of rolling bearing and bearing sleeve is damaged. The appearance is increased friction and heat, and the operation performance of rolling bearing deteriorates.

1, add insulation partition

In order to prevent the shaft current caused by magnetic unbalance and other reasons, insulation partitions can be added to the non-shaft end bearing seat and bearing support to cut off the loop of the shaft current.

For the shaft voltage caused by static charge, a grounding carbon brush can be added to the shaft on the load side of the motor. The grounding of the carbon brush must be reliable. In this way, we can always direct the static charge on the motor shaft to the earth, so that it cannot form the shaft voltage, and avoid the instantaneous shaft current caused by the charge discharge.

2, strengthen insulation protection

In order to avoid shaft current caused by wire insulation damage of other motor accessories, it is necessary to check and strengthen wire or gasket insulation regularly to eliminate unnecessary shaft current hidden danger.

For lubricating insulating medium oil between shaft and bearing bush, it is necessary to check the purity of lubricating oil in time, and it is found that water in oil must be filtered, otherwise the insulation strength of oil film cannot meet the requirements, and it is easy to be broken down by low voltage. In addition, we should also keep the insulation pad clean and dry, and effectively make the insulation pad play the role of insulation.

Sometimes the shaft current acting on the motor bearing causes the bearing burning accident will not attract people’s attention. In the bearing burning accident, only attention is often paid to mechanical coordination. After the replacement of the new bearing, because the shaft current of the motor is not eliminated, it causes the bearing burning accident, resulting in unnecessary losses.

In fact, it is inevitable for large ac motors to produce shaft voltage, and the shaft current formed by shaft voltage will do serious harm to equipment. Therefore, feasible measures must be taken to prevent the formation of shaft current and reduce the damage of shaft current to equipment to the greatest extent. Generally through the above treatment, most of the motor shaft current is very small, has no substantial harm to the electric mechanism.

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