The conditions for the formation of shaft current: first, there is a shaft voltage, and second, a loop is formed. For a motor with normal design and operating conditions, there is only a small voltage difference across the rotating shaft, and this is not enough to cause damage due to oil film processing or bearing insulation.
If there is a problem in a certain link and the shaft voltage exceeds the limit, it may break the original insulation, forming a loop between the rotating shaft, the inner ring of the bearing, outer ring of the bearing and bearing chamber, thus the bearing position of the rotating shaft. The surface of the inner ring of the bearing will produce small and deep circular corrosion spots or band arc scars due to arc discharge, which may be enough to burn the journal and bushing in severe cases. .
According to the structureture and working principle of the synchronous generator, due to the joints of the stator core assembly, the joints of the stator silicon steel sheets, the uneven air gap between the stator and the rotor, the center of the 'incoherent shaft and magnetic field center, etc., the main shaft of the unit is inevitable. The earth rotates in a magnetic field that is not completely symmetrical. In this way, an alternating voltage is generated across the shaft.
Detailed information
Based on the principle of shaft current generation, the following measures are generally taken to solve it:
1. Bypass: A grounding carbon brush is installed at the extension end of the shaft so that the grounding carbon brush is reliably grounded and in reliable contact with the rotating shaft to ensure that the potential of the rotating shaft is zero. It can drive the electrostaticthat. Charge the motor shaft to ground at any time to remove current from the shaft. This method is typically used on generators and is sometimes used on large AC motors.
2. Blockage: One of the important conditions for the formation of shaft current is the formation of a loop. Installing an insulating pad or using an insulating bearing between the bearing seat and the bearing at the non-extension end of the shaft to cut off the current loop of the shaft is a measure adopted by most engine manufacturers.
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