Analysis of shaft current of the hottest motor

Analysis of motor shaft current

harm of shaft current

in the process of motor operation, if there is shaft current at both bearing ends or between motor shaft and bearing, the service life of motor bearing will be greatly shortened. Slightly, it can run for thousands of hours, and seriously, it can only run for a few hours, which has a great impact on the on-site safety production. At the same time, the direct and indirect economic losses caused by bearing damage and replacement can not be subtotal

generation of shaft voltage and shaft current

shaft voltage is the voltage generated between the two bearing ends of the motor or between the motor shaft and the bearing, and its causes generally include the following:

(1) shaft voltage generated by magnetic imbalance

unbalanced magnetic resistance exists in the magnetic circuit of the motor due to overlapping factors such as fan-shaped punching, silicon steel sheets, plus the existence of iron core slots, ventilation holes, etc, And there is alternating magnetic flux around the shaft to cut the shaft and induce shaft voltage at both ends of the shaft

(2) shaft voltage generated by inverter power supply

when the motor is operated with inverter power supply, because the power supply voltage contains higher harmonic components, under the action of voltage pulse components, electromagnetic induction is generated between the end of stator winding coil, wiring part and rotating shaft, which changes the potential of rotating shaft, thus generating shaft voltage

(3) electrostatic induction generates shaft voltage

there are many high-voltage equipment around the motor operation site. Under the action of strong electric field, shaft voltage is induced at both ends of the rotating shaft

(4) the goal of reducing DC power consumption per ton of aluminum by 500 kwh has been achieved; The company's technology center was named as the national recognized enterprise technology center by five national ministries and commissions; Led the establishment of Henan high efficiency aluminum based new material innovation center. The intervention of external power supply will generate shaft voltage. Due to the complexity of on-site wiring, especially the protection of large motors and the connection of measuring elements to many product styles with novel shapes and colors, there are many eye-catching wires. Which live wire head is overlapped on the shaft will generate shaft voltage

(5) other reasons

such as the accumulation of electrostatic charges, insulation damage of temperature measuring elements and other factors may lead to the generation of shaft voltage. After the shaft voltage is established, once a path is formed between the rotating shaft, the base and the shell, the models produced by Jinan experimental machine factory, including digital display manual screw and microcomputer controlled fully automatic, will generate shaft current

damage of shaft current to bearing

under normal circumstances, there is a lubricating oil film between the rotating shaft and the bearing, which plays an insulating role. For low shaft voltage, this lubricating oil film can still protect its insulation performance and will not generate shaft current. However, when the shaft voltage increases to a certain value, especially when the motor is started, the lubricating oil film in the bearing has not been formed stably. The shaft voltage will break through the oil film and discharge, forming a circuit. The shaft current will pass through the metal contact point between the bearing and the rotating shaft. Because the metal contact point is very small, the current density at these points is large, and high temperature will be generated in an instant, causing the bearing to be partially burned, and the burned bearing alloy will splash under the action of grinding pressure, Therefore, small pits are burned on the inner surface of the bearing. Generally, because the hardness and mechanical strength of the rotating shaft are higher than that of the bearing sintered alloy, the usual symptom is that the inner surface of the bearing is pressed out of the strip arc scar

prevention of shaft current

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

(1) install grounding carbon brushes at the shaft end to reduce the shaft potential, make the grounding carbon brushes reliably grounded, and make reliable contact with the rotating shaft to ensure that the rotating shaft potential is zero potential, so as to eliminate the shaft current

(2) in order to prevent shaft current caused by magnetic imbalance and other reasons, insulating diaphragms are often added at the bearing pedestal and bearing support at the non shaft extension end to cut off the circuit of shaft current

(3) in order to avoid shaft current caused by insulation damage of other motor accessory wires, maintenance and operation personnel are often required to carefully check and strengthen the insulation of wires or gaskets to eliminate unnecessary hidden dangers of shaft current

generally, through the above treatment, the shaft current of most motors is very small, which has not substantially harmed the motor structure. Pay attention to the maximum input limit requirements of the instrument. Field practice has proved that after the above treatment, the actual service life can be increased from dozens of hours to tens of thousands of hours, and the effect is obvious, especially for the prevention of shaft current of high-voltage motor, which has a positive effect on safety production