Cars, as the most common means of transportation, have changed people's lives, but have also led to an imbalance in people's physical health. Every weekend, groups of hikers get together to go hiking and enjoy the scenery, which has become an important activity to relieve work pressure and improve their lives. Ms. S, who has extensive experience in market services, belongs to a relatively fixed group of veteran hikers.
Life and work are often difficult to separate. S was talking about his work again: he encountered several very similar embarrassing incidents in a row. The high-voltage motor, which had a good reputation in the market, had a strange problem with the bearings lacking oil!
Based on past experience, the problem should have been a loss of control during the parts manufacturing process. However, it turned out to be far more complex than anticipated. The complete process log shattered what should have been an accurate and reliable prediction. What truths were overlooked in this seemingly inexplicable and embarrassing incident? Could it be shaft current again?
In recent years, there have been frequent incidents of damaged bearings, especially bearing electrical erosion, which occurs every now and then. After disassembly, most of these incidents are found to be typical shaft current faults.
1. Shaft current and its prevention measures
Due to the specific requirements of equipment applications, variable frequency power supplies and frequency converters have become a product of the times. For three-phase AC motors, at the customer end, when using frequency converters to power the motors, frequency converters are mostly used instead of variable frequency power supplies.
Abundant harmonic components cause shaft magnetization, inducing shaft voltage and generating shaft current. To prevent shaft current from flowing through the bearing, three options are available: first, install a grounded carbon brush; second, use an insulated bearing; and third, use an insulated bearing sleeve structure. Today, we will only discuss one topic—insulated bearings, also known as anti-electro-erosion bearings.
2. Regarding insulated bearings
Insulated bearings include all rolling bearings that prevent current from flowing through the "outer ring-rolling element-inner ring" path. These include hybrid ceramic bearings and electrically insulated bearings.
Hybrid ceramic bearings
The inner and outer rings of the bearing are made of bearing steel, and the rolling elements are made of silicon nitride to form an insulated bearing. In addition to having good electrical insulation properties, it can operate at higher speeds.
Insulated bearings
The outer or inner ring has a 100μm layer of aluminum oxide on its outer surface, which can withstand a DC voltage of 1000V.
Insulated bearing applications
Whether it is an electrically insulating bearing with a ceramic coating on the inner or outer ring, or a hybrid ceramic bearing with silicon nitride as the rolling element, it can prevent current from passing through and has insulation capabilities.
3. Disconnect the shaft current circuit
Generally speaking, completely eliminating the potential difference inside a bearing is very difficult. However, if we can block or significantly reduce the current flowing through the bearing, we can prevent electrolytic corrosion.
Currently, all types of insulated bearings are designed for this purpose. The insulation method of the bearing is selected according to the type of voltage generated.
4. Convenience of on-site replacement
Compared to using carbon brushes to shunt shaft current, insulated bearings can solve the shaft current problem in the field. However, because insulated bearings are relatively expensive, carbon brush shunt shaft current solutions or insulated bearing sleeve structures should be used for mass production whenever possible.
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
