How to detect and control the shaft current of motor products?

Release Time：

2024-10-07

Most bearing systems for high-voltage motors and variable frequency motors have taken necessary measures for shaft current, but this does not affect the detection of shaft voltage.

Shaft current is a hacker in the bearing system of motor products. Once shaft current is generated, it can cause the motor bearing system to collapse in a short period of time. According to the necessary conditions for current generation, voltage, and circuit, this circuit is different from simple circuits in that it does not have a relatively clear circuit, making it difficult to measure current. Therefore, a more objective and feasible detection is the detection of shaft voltage.

For different motor products and bearing system structures, the difference in resistance in the circuit formed is relatively small, while the most significant impact is the magnitude of the shaft voltage corresponding to different motors. When the shaft voltage reaches a certain value (usually 300-500mV), it will cause the oil film of the bearing system to be broken down and generate a large shaft current.

Shaft voltage refers to the voltage generated between the two ends of the motor shaft or between the shaft and the bearing seat. It is caused by an unbalanced magnetic circuit around the motor shaft, which cuts the shaft and induces shaft voltage at both ends of the shaft.

Under normal circumstances, the lubricating oil film between the shaft and the bearing serves as insulation. When the shaft voltage increases to a certain value, especially when the ground motor is started, the lubricating oil film has not yet stabilized, and the shaft voltage will break through the oil film to form a circuit, generating a considerable shaft current, sometimes up to several hundred to several thousand amperes.

According to the magnitude of the shaft voltage, a millivoltmeter (also known as a high resistance voltmeter) can be used for measurement. From the analysis of the physical distribution of components, the insulation between the motor shaft and the casing is achieved through the lubricating grease inside the bearing. When there is a shaft voltage in the motor, there is a potential difference between the two ends of the motor shaft. After the motor is powered on, it can be directly measured through the measuring probe of the voltmeter, that is, one of the probes is in dynamic contact with the shaft (because the shaft is in a rotating state), but the keyway position should be avoided to prevent danger; The other probe of the voltmeter should be in good contact with the motor casing, avoiding areas with surface paint and ensuring good grounding of the motor casing.

Most bearing systems for high-voltage motors and variable frequency motors have taken necessary measures for shaft current, but this does not affect the detection of shaft voltage.