Insulated Bearings prevents bearing discharge

When current is induced into the motor shaft inductively, current flows axially along the length of the shaft causing a voltage drop along the length of the shaft. If there are bearings at eanch end of the shaft, and the voltage along the shaft length (between the bearings) is high enough to cause the insulating lubricant to break down, we will have electrical discharges through the bearings.

If a shaft brush is fitted at one end, then the voltage to cause a breakdown is halved as there is only one bearing in the circuit. Without the shaft brush, we have two bearings in series.

To prevent a bearing discharge, we need to break the circuit through the shaft, round vvia the shaft brush, through the stator and back via the non drive end bearing. The way to break the circuit, is to replace the non drive end bearing with an insulated bearing, but there are several variations in the insulated bearing that can be used.

1. External coated. The outer surface of the bearing is coated with a ceramic film to provide an insulation barrier.

2. Internal caoated. The inner surface of the bearing is ceramic coated.

3. Hybrid Bearing. The bearing is assembled using ceramic insulated balls.

The insulated bearing with the outer surface coated is the easiest bearing to fit and is least prone to damage, but it has the highest surface area so offers the greatest capacitance in series with the circuit path. This will allow high frequency currents to flow and of course, the induced currents are all high frequency and have been either capacitively or inductively coupled. A high capacitance bearing may only reduce the current flow by a small margin.

The insulated bearing with the coating on the inner surface offers a much reduced capacitance and therfore a much improved EDM reduction. This bearing is much harder to fit without causing damage because the ceramic coating has to be driven over a long length of motor shaft.
The lowest capacitance is offered by the hybrid insulated bearing and while it is the more expensive bearing, it is the best at reducing the EDM problems.

Linqing Nine Star Bearing Science & Technology Co., Ltd 

( Insulated bearing, Hybrid ceramic bearing and  Brass cage DGBB)

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