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Why does a motor produce axial current?
The current in the circuit of the shaft – bearing – base of the motor is called shaft current.
Causes of axial current generation:
Magnetic field asymmetry;
There are harmonics in the power supply current;
Manufacture, installation is not good, due to the rotor eccentricity caused by uneven air gap;
There is a gap between the two semicircles of the detachable stator core;
The number of pieces of stator cores with fan-shaped laminated cores is not suitable.
Hazard:
The motor bearing surface or ball is eroded, forming point-like microholes, which worsens the bearing performance, increases the friction loss and heat, and eventually causes the bearing to burn out.
Prevention:
Eliminate pulsating flux and power harmonics (such as installing AC reactor on the output side of the frequency converter);

One solution is to add insulation to cut off the shaft’s current path. That is, when the motor is designed, the bearing seat and base of the sliding bearing are insulated, and the outer ring and end cover of the rolling bearing are insulated, for example, using expensive ceramic bearings.Another scheme is to dredge: such as using conductive brush (most schemes), conductive bearing (Model3), conductive ring (ETRON), conductive oil seal (ZOE), conductive carbon ring (Leaf) and so on to export the shaft current to the grounding end of the shell, to eliminate the destructive effect of shaft current on bearing grease.

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