As an important mechanical foundation part, insulated bearing is the leader in the bearing field due to its superior performance, high temperature resistance, super strength, corrosion resistance and other characteristics which are incomparable to metal bearing. The specific advantages of insulated bearing compared with ordinary bearing are as follows:
As the insulating bearing has the characteristics of corrosion resistance, it is suitable to work in the harsh conditions full of corrosive media. The special spraying process is adopted for the electrically insulated bearing. The outer surface of the bearing is sprayed with high-quality coating, which has strong binding force with the substrate and good insulation performance. It can avoid the electric erosion of the bearing caused by the induced current, prevent the damage caused by the current to the grease, rolling body and raceway, and greatly improve the service life of the bearing compared with the common bearing.
The process has been improved continuously. In the insulating bearing, there is a layer of 100 μ m thick coating on the outer or inner ring surface, which can withstand the voltage of up to 1000 V DC. The special spraying process can form a layer of coating with uniform thickness and strong adhesion. After further treatment, it can be free from the influence of moisture and humidity.
The electric insulated bearing can avoid the damage caused by the electric corrosion, so compared with the ordinary bearing, it can guarantee the operation more reliable. Compared with other insulation methods, such as shaft shell insulation, it is more cost-effective and reliable. The external dimensions and basic technical characteristics of insulated bearings are the same as those of uninsulated bearings, so they can be 100% interchanged.
Classification of electric insulated bearings, electric insulated deep groove ball bearings, electric insulated cylindrical roller bearings, electric insulated self-aligning roller bearings, hybrid ceramic ball bearings, etc
The causes and harms of the formation of the shaft voltage and the bearing current of the motor in the operation of the motor, in the stator and rotor magnetic circuit or the phase current around the shaft, any imbalance can produce the magnetic chain of the rotating system. When the shaft rotates, these flux chains can produce potential difference at both ends of the shaft, which is called shaft voltage. The shaft voltage can excite the circulating current in the loop (closed circuit) formed by the shaft and the casing through the bearings at both ends, which is called the shaft current. In addition, the residual magnetism of rotor core is more. For wound rotor motor, if there are two or more winding points and short circuit to rotor core or shaft, shaft voltage and shaft current will also be generated. The magnitude of bearing current is related to motor structure, motor power, driving voltage amplitude, pulse rise time, cable length and other factors. The higher the power of the motor, the higher the driving voltage and the steeper the rising edge of the driving voltage. The shorter the cable, the greater the bearing current.
Measures to block shaft current -- using insulated bearing
In order to avoid the damage of shaft current to the bearing, effective measures should be taken to isolate the shaft current. For large motors with independent bearing pedestals at both ends, a gasket made of insulating material can be placed between the bearing pedestals and the metal pedestals. For the motor with ordinary bearing and shell assembled as a whole, the insulating bearing is generally used at one end (usually arranged at the extension end of non main shaft). For the occasions with high requirements, the insulating bearing is installed at both ends. The insulating bearing used is generally the method of adding (coating) insulating layer to the outer ring, and the inner and outer rings will be added with insulating layer in some occasions.
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