Motor shaft currents arise due to “asymmetry” in the magnetic paths in the rotor and stator iron. As the rotor rotates through the stator and once the stator's magnetic field moves, small differences in the magnetic “reluctance” of the main components generate small voltages between sections of the shaft.

As you can understand from the above discussions, the circulating currents are the results of the electrical modeling of an electric motor. This is why some the constructor will design the motors with an insulated bearing housing; Bearing, or enable.

These special designs are produced in bearings to impede closed paths for transmitting currents in the grounded motor structure. These currents will jump through the ball-bearing space or break intermittently into sleeve-bearing oil films. This results in a race in ball bearings or electrocution on the very polished surface of the balls, which causes initial failure and fatigue.

It must be recognized that motor shaft circulating currents may also be caused by external supplies such as welding, etc., to magnetize the shaft (i.e., magnet). There are also static charges which can result in shaft transmitting current problems.

As the shaft is electrically charged, it then discharges into the bearings causing damage. It is also worth considering that shafts circulating currents are becoming more common in small horsepower electrical equipment due to the popularity of variable frequency controllers.

A variety of devices are now being employed, such as the AEGIS shaft grounding ring, which is manufactured and modeled to help the motor protect itself and divert circulating currents.

Ningbo Shitai Precision Machinery Co., Ltd. is not only a motor shaft manufacturer but also a spline shaft manufacturer, welcome to visit our official website.