Electrical induced bearing damage

The electric motor is by far the most applied drive for a large variety of machinery. The variable frequency drive or VFD is nowadays the most common drive for industrial electric motors. A disadvantage of the VFD in regard to the classic star-triangle circuits is the increased risk for electrical fluting trough the bearings of the motor.

Damaged outer rings

At a chemical factory, active with the production of raw materials for the cement and concrete industry, we perform a 3-monthly condition monitoring program on various fans, spiral conveyors, mixers and grinders. Already during the first measurements of this new condition monitoring program a large bearing damage was detected. Our recommendation was, regarding the very low operating hours, to exchange the bearing for a new electrically insulated bearing.

However due to a communication error between the customer and the contractor, the bearing was exchanged for a new normal bearing. Directly at the first commissioning measurements, 1 day after the installation of a new bearing, a bearing outer ring damage was detected again. Additional measurements in the following weeks showed a significant increase of this damage.

The immediate occurrence of the damage and the fast progress were a confirmation of the earlier suspicion that electrical fluting was the cause of the damaged bearing. The recommendation was once again to exchange the motor bearing for an electrically insulated one.

At the next opportunity the motor was completely exchanged for a new one which was equipped with insulated bearings.

A bearing damage analysis later on confirmed the suspicion of electrical fluting.

Linqing Nine Star Bearing Science & Technology Co., Ltd 

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

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