Shaft current is one of the common problems in high-voltage motors, generators, variable frequency motors, and other types of motors. When the shaft current is high, it can cause the bearing system of the motor to collapse, even affecting the motor winding. Therefore, the control of shaft current is a common concern for motor manufacturers and even users.
A netizen suggested that he detected the shaft voltage and asked if it is possible to measure the shaft current? We will have a brief discussion on whether shaft voltage will harm the bearing system of the motor and other related issues.
From the analysis of the principle of current formation, shaft voltage and closed circuit are necessary conditions for generating shaft current. The measures to avoid shaft current are based on two ideas: cutting off the circuit or bypassing it.
If circuit breaking measures such as insulated bearings, insulated end caps, and insulated bearing sleeves are used in the design and manufacturing process of the motor, even if the shaft voltage exists, because no closed circuit can be formed, the shaft current will naturally not be generated.
If a bypass measure is adopted, that is, guiding the direction of shaft current through grounded carbon brushes, it can greatly reduce the magnitude of shaft current and naturally solve the problem of shaft current harm to bearings.
We are now discussing another issue, which is raised by the netizen. When the shaft voltage is high, it will pose a threat to the quality and performance of bearings. Therefore, necessary measures need to be taken when the shaft voltage is high! According to the accumulation and statistics of data from different motor manufacturers, when the shaft voltage generated by the motor does not exceed 350mV, it does not have a significant impact on the bearing system of the motor. Otherwise, corresponding avoidance measures must be taken.
Finally, let’s talk about the detection of shaft voltage and shaft current. Relatively speaking, the detection of shaft voltage is relatively simple, and can be detected using a millivolt meter with appropriate accuracy. However, due to the irregularity of the shaft current passing through the channel, the collection of shaft current is relatively difficult, and specialized detection equipment is needed for detection.
The shaft current monitoring device adopts a high-performance microcontroller as the core control component to form a controller, and a hollow ring transformer as the shaft current sensor to monitor the changes in motor shaft current. The microcontroller monitors the real-time change value of the shaft current sensor, which is linearly related to the large shaft current. After filtering and numerical transformation, it is confirmed that the shaft current exceeds the set value. The shaft current monitoring device outputs a second level alarm signal. The device displays the specific current size in real-time through parameter tuning.