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.
