Guide:  In order to reduce the hazard of the shaft current, according to the quality of the power supply of the variable frequency power supply, the size of the motor, the type of the bearing, and the shaft voltage of the variable frequency motor, the corresponding measures are taken to prolong the service life of the bearing and improve the reliability of the operation of the variable frequency motor.

        AC shaft motor generates shaft voltage, which is a serious equipment hazard. The shaft current formed by the shaft voltage seriously threatens the safe operation of the equipment. With the use of high-power, high-switching frequency components, the variable-frequency power supply generates a relatively large high-frequency shaft current on the rotating shaft, which exacerbates bearing damage.

In order to reduce the hazard of the shaft current, according to the quality of the power supply of the variable frequency power supply, the size of the motor, the type of the bearing, and the shaft voltage of the variable frequency motor, the corresponding measures are taken to prolong the service life of the bearing and improve the reliability of the operation of the variable frequency motor.

There are many precautions for shaft current, such as the insulation of the shaft, the insulation of the bearing, the insulation of the bearing sleeve, the adjustment of the grounding voltage, and the use of necessary auxiliary measures. Regardless of the measure, the basic principle can be attributed to these two types, one is to cut off the circuit, and the other is to eliminate the shaft voltage.

In the specific implementation process, it has a certain relationship with the production and processing technology of the motor production plant and the actual working conditions of the motor. The method of shaft insulation, bearing insulation and bearing sleeve insulation is relatively straightforward, but it is more complicated. The balanced grounding voltage is simple to operate, but the latter maintenance is troublesome.

Axis current precautions

● The motor shaft is insulated. Insulation measures are taken on the shaft of the motor to take insulation measures on the front and rear bearing tables of the motor shaft using the rolling bearing structure and its shoulders, such as plasma uniform spraying of high-performance heat-resistant ceramic insulation. In order to cut off the shaft of the motor and the load machine, the shaft auxiliary device such as the tachometer and the encoder to form a shaft current path, special measures must be taken, such as insulating the coupling directly connected to the motor shaft.

●Insulated bearings are used. Insulated bearings should be used for motors with rolling bearing construction. The easiest way is to uniformly spray high-performance insulation on the inner surface and end faces of the inner ring of the bearing by plasma spraying. If an insulating layer is sprayed on the outer surface and both end faces of the outer ring of the bearing, it is easy to scratch when the end cap is removed, thereby losing the insulating ability. With the structure of the sliding bearing, the conventional method is to pad the epoxy glass cloth plate at the fixed bearing portion. Inlet and outlet pipes and insulated pipe joints. It can also be sleeved in the end cap bearing chamber, the insulating layer between the sleeve and the end cap, the bolts of the inner and outer cover and the insulating sleeve and the insulating mat are tightened. This structure and process are relatively complicated.

● Balance the ground voltage. Due to the presence of stray capacitance, the ground voltage across the shield of the same cable is not exactly equal, so there is a voltage drop across the cable and current is present. By balancing the ground voltage and reducing the voltage drop across the cable shield, the current through the bearing can be reduced.

● Grounded carbon brush. The shaft current is drawn out by a grounded carbon brush to avoid damage to the bearing. At present, there is a soft carbon brush that can be mounted on the shaft, which is sealed and fixed with the bearing, and can simultaneously eliminate the shaft current and the shaft but seal.

● Other measures. Add a high-frequency filter to the speed control system of the inverter power supply, or add a common-mode filter circuit to the frequency conversion speed control device.