Manual for Induction Motors and Generators
86 -
Maintenance
3BFP 000 050 R0101 REV E
7.7.2.1 Brush pressure
The brush pressure should be evenly distributed over the whole contact surface, i.e. the brush
should conform to the slip ring curvature. Brush pressure is one of the most important single
factors in brush operation. The pressure should be 18-20 mN/mm
2
(180-200 g/cm
2
). Use a
spring-balance to measure the brush pressure. Attach a spring balance to the tip of the lever
pressing the brush and pull in a radial direction until the pressure is just relieved from the brush.
Use a piece of paper between brush and press lever to detect when pressure is relieved, see
Figure 7-9 Checking brush pressure with spring balance
.
Figure 7-9 Checking brush pressure with spring balance
***Following chapters for cooling type: Open air, Air-to-water and Air-to-air
7.8 Maintenance of cooling units
The cooling units normally require little maintenance but it is advisable to regularly check their
condition in order to ensure trouble-free operation.
***Following chapter for cooling type: Open air
7.8.1 Maintenance instructions for machines with open air cooling
The cooling air is normally circulated by a fan and/or by the rotor. The fan may be mounted on
the shaft or driven by a separate motor. A connection to external air pressure is also possible.
Depending on the machine design, the circulation may be axially symmetrical or asymmetrical.
The cooling air should be as clean as possible, because any dirt, which drifts into the machine,
causes contamination and reduces the efficiency of the cooling.
The upper covers of the standard weather protected machines are delivered with or without
filters according to the specification. By special order, the upper cover is equipped with a
differential pressure switch for monitoring the condition of the filters.
