SECTION 3 - BRUSH THEORY AND CHARACTERISTICS
Question 3:15 Do SCR Drives Cause Problems For Brushes?
As a general rule pure DC supply from a DC generator in a Ward Leonard type system is the easiest supply for brushes to handle.
SCR drives, which produce a highly rippled form of DC, can make commutation more difficult.
In older solid iron frame machines it is sometimes necessary to incorporate some smoothing chokes in the supply.
Modern DC machines with laminated frames and field poles perform much better and brushes can operate quite normally with the correct grade fitted.
If
a machine has been working well for some time and suddenly exhibits excessive
arcing then a fault in the SCR drive system should be considered. If there is no
obvious armature fault and the brushes and holders appear normal the output from
the drive should be investigated.
Question 3:16 Why Do Some Sliprings And Commutators Have Spiral Grooves?
The information has been drawn from experience of Morganite Taiwan Limited Application Specialists combined with a wide range of published information from major carbon supplier and motor manufacture. However, the material can not be downloaded, copied or used without written permission.
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