Shaft current is a major mass killer of variable frequency motors, large motors, high voltage motors and generators, and it is extremely harmful to the motor bearing system. There are many cases of bearing system failures due to insufficient shaft current precautions.

The shaft current is characterized by low voltage and high current, and the damage to the bearing system can be said to be unavoidable. The generation of shaft current is due to shaft voltage and closed loop. To solve the problem of shaft current, it can be solved by eliminating the shaft voltage or cutting off the loop.

Unbalanced magnetic circuit, inverter power supply, electrostatic induction, electrostatic charge and external power supply interference may all generate shaft voltage. Faced with a closed loop, the large shaft current will cause the bearing to ablate due to heat in a very short time. Bearings burned by shaft current will leave washboard-like marks on the outer surface of the bearing inner ring.

To avoid the problem of shaft current, necessary measures must be taken in the design and manufacturing process of the motor, such as adding necessary insulation measures to the end cover and bearing sleeve. The link increases the leakage carbon brush. From the point of view of use, it is a once-and-for-all measure to take circuit breaker measures on components, while the use of diversion methods may lead to the replacement of carbon brush devices, at least during the maintenance cycle of the motor, the carbon brush system should not have problems.

The size and bearing capacity of the insulated bearing and the ordinary bearing are the same. The difference is that the insulated bearing can prevent the passage of current very well, and the insulated bearing can avoid the damage caused by electrical corrosion. The operation is more reliable, and the insulated bearing can avoid the electric corrosion effect of the induced current on the bearing, and prevent the current from causing damage to the grease, rolling elements and raceways.

When the motor is operated with inverter power supply, the power supply voltage contains high-order harmonic components, which causes electromagnetic induction between the ends of the stator winding coils, the wiring parts, and the rotating shaft, thereby generating the shaft voltage.

The stator winding of the asynchronous motor is embedded in the stator core slot, and there are distributed capacitances between the turns of the stator winding and between the stator winding and the motor frame. The common mode voltage changes sharply, and the leakage current is formed from the motor casing to the ground terminal through the distributed capacitance of the motor winding. This leakage current may form two types of electromagnetic interference, radioactive and conductive. Due to the unbalance of the magnetic circuit of the motor, electrostatic induction and common mode voltage are the causes of shaft voltage and shaft current.