Harm and prevention of the hottest shaft current

Generation, harm and prevention of shaft current

1 generation of shaft current

due to the high insulation requirements of high-voltage motor, when the slot insulation of the motor is damaged, the winding will contact with the iron core, resulting in shaft current

during the actual operation of the motor, there are many reasons for the shaft current, mainly including the following points:

(1) during the maintenance of the motor, the position of the stator and rotor of the motor is relatively moved, and the rotor is eccentric during the reset and installation, resulting in uneven air gap and shaft current during the operation of the motor

(2) axial current is generated by asymmetric pneumatic magnetic field

(3) there is shaft current generated by high-order harmonics in the power supply

(4) due to poor on-site maintenance, a path is formed between the motor shaft and the base and housing, resulting in shaft current

2 harm of shaft current

during the operation of the motor, if there is shaft current at the two bearing ends or between the motor shaft and the bearing, the service life of the motor bearing will be greatly shortened. If the over-axis current is serious, the motor may only run for a few hours, which will have a great impact on the safety belt of on-site production. At the same time, the direct economic losses caused by bearing damage and replacement are also large

large and medium-sized AC motors adopt thin oil lubrication system, and the motor shaft and bearing are insulated by oil film. If the oil quality of the lubricating oil is poor and there are small particles in the oil, the rotating shaft and the bearing seat will form a calling path, and the shaft current will pass through the metal contact points of the bearing and the rotating shaft. Because the metal contact points are very small, the current density of these points is large, and high temperature will be generated in an instant, causing the bearing to be locally burned. The burned bearing alloy will splash under the action of grinding pressure, and then dot shaped micropores will appear on the inner surface of the bearing bush, Or there are strip scratches, which can damage the bearing bush in serious cases

3 prevention of shaft current

in view of the root cause of shaft current formation, the following preventive measures are generally adopted on site:

(1) maintenance personnel are required to crank 90 when installing the motor. Measure the air gap between the stator and rotor of the motor respectively, and reposition it if necessary to ensure that the air gap of the motor is uniform

(2) in order to prevent shaft current from being generated due to magnetic imbalance and other reasons, it is often necessary to clarify the experimental purpose at the bearing seat and bearing support and add insulating diaphragms or insulating sleeves at each oil pipeline to cut off the calling path of shaft current. At the same time, it is necessary to ensure that the surrounding of insulating diaphragms is clean and free of dirt

(3) in order to avoid ground wire lapping of other temporary equipment (electric welding machine, etc.), or replace the shaft current caused by damaged tissue wire insulation with healthy tissue, the maintenance and operation personnel are often required to carefully check and strengthen the insulation of the wire, so as to eliminate unnecessary hidden dangers of shaft current

(4) monitor the quality of lubricating oil, take samples regularly for testing, maintain the purity of lubricating insulating oil, and filter or replace qualified lubricating oil in time if water and impurities in the oil exceed the standard

generally, through the above treatment, the shaft current of most motor raw materials to be imported from the United States will be limited to a very small range, which basically cannot pose a substantial harm to the motor