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Solucore Inc. | A Professional Elevator and Escalator Consulting Firm
Solucore Inc. | A Professional Elevator and Escalator Consulting Firm

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DC Motor and Generator Maintenance

One of the most basic aspect of the elevator maintenance in the elevator machine room is looking after the motor and generators. Therefore, it should not surprise you when I say that I am shocked to see: 1. Brush rivets on the commutator; and 2. Arcing and sparking brushes and commutators.

The commutators are the segmented copper bars on the motor’s or generator’s DC side that are connected to the coils of the armature. The segmented copper bars are fixed around the circumference of the rotor (the rotating part of the generator located in the core) and their number can vary between 100 or more depending on the size of the generator or motor. Riding on the brass bars are spring-tensioned brushes fixed to the endbell (stationary side of the machine). The outside supply of current (for a motor) or electrical load (for a generator) is connected to the brushes. The copper segments are isolated from one another with mica (an insulating resin that keeps the segments from touching each other). It is extremely important to ensure that the commutator has a thin uniform film to assist with the commutation of the brushes and conductivity.

It is also as important to ensure that the wear on the copper segment is monitored for wear. When the copper bars wear, they create peaks and valleys on the commutator surface. This can be contributed to many things but mostly due to environmental issues like dust and other particles embedded on the brushes and then acting like sandpaper on the elevator motor or generator commutator surface or brush grade hardness or tension on the brush gear. As mentioned before, the brush gear holds the brushes to the elevator commutator surface at the ideal tension and hence over tensioning or under tensioning will create problems.

What is also as important is the brushes themselves as well. The brushes cannot be replaced at the same time across all poles. The ideal way to replace the brushes is one pole at a time over a long period of time to ensure that the brushes are properly seated on the commutator surface. Imagine if more than one set of brushes is replaced on the motor or generator – the poor commutation between the brushes and commutator will likely cause poor motor/generator performance which can manifest itself as poor leveling or harsh ride quality.

In this photo, you can see that the commutator surfacr has some issues with respect to burn mark on the edges of the commutator bars. The brushes are also burnt (look at the side in contact with the commutator) and in need of replacing. In this case, you want to replace the brushes (once burnt, they should not be used as the surface of the brushes is hardened and the commutation becomes poor), sand the commutator surface, then check the brush grade, tension and the nutrality of the ring.

In the second photo you can see a close up of the burnt brushes and the hardened and discoloured edges.

As you can see, that's a poor way to maintain the generator commutator.


In the photo above, you can see that the brush on the left is so worn, that it is cutting into the cummutator surface. The brush at this point is actually damaging the surface of the generator commutator. This is the thing that gives elevator consultants goose bumps. How can someone maintain an elevator equipment on a monthly basis leave the elevators in this condition. The brush rivet is half damaged and it is my guess that this has been in the works for at least 6 months because of the hard brush grade.

Take a look at this video and the affect of bad generator maintenance.


by Farid in Maintenance - Back to Posts




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