Insulated Bearing Sleeves for Three Phase Asynchronous Motors Prevent Shaft Current

Large three phase asynchronous motors have more complex bearing systems than small motors. Discussing motor bearings in isolation is not very valuable. A discussion of motor bearings should begin with the associated components, such as the shaft, bearing sleeve, end cap, inner and outer bearing caps. The coordination between these components is merely mechanical. Shandong Langrui, one of China's most professional large three phase asynchronous motor manufacturers, believes that external factors, such as the motor's operating conditions, should also be considered.

Bearing noise is a common problem during the actual operation and use of asynchronous motors. This problem may be related to both bearing quality issues and bearing selection. Most problems arise from bearing problems caused by inappropriate or unreasonable manufacturing processes.

We know that noise originates from vibration. To address bearing noise, the first thing to do is to address vibration. Compared to small and standard motors, high power motors, high voltage motors, and inverter duty motors also face the issue of shaft current. To address this, insulated bearings can be used, but these are relatively expensive to purchase, and some insulated bearings are not yet widely available. Alternatively, grounded carbon brushes can be used, but these are more difficult to maintain. In response to this, many Chinese three-phase motor manufacturers have developed insulated bearing sleeves. While these sleeves are complex to manufacture, their basic principle is to divide the bearing sleeve into two parts, isolating the bearing housing through insulation. This effectively eliminates the shaft current loop caused by shaft voltage, providing a permanent solution. The figure below shows a partial view of an insulated bearing sleeve.

This type of insulated bearing sleeve consists of an inner sleeve and an outer sleeve, with an insulating filler layer between the two. The thickness of the insulating filler layer is 2-4mm. This insulating bearing sleeve, separated by the insulating filler layer, blocks shaft current, thereby protecting the bearing and extending its service life.

Some three phase asynchronous motor manufacturers use insulating plates to achieve this effect. However, the insulating properties of these plates degrade when exposed to moisture. Furthermore, air gaps may form between the two cylindrical surfaces due to uneven thickness of the insulating plate or non-compliant roundness of the cylindrical surfaces. This can affect the performance of the bearing sleeve to a certain extent, and necessary remedial measures are recommended.