Rowbotth said:
We have a few GE Generators (all under 80 MW) about 30 years old, and
we've been having more problems than normal with brushes arcing.
We think some of the problems may have to do with CBLF deviations, but
not all.
Is there a source for information on this sort of problem that I could
get access to, please?
Don't know what 'CBLF deviations' is supposed to mean.
If this is an AC unit (the brushes are for slip-rings), then I'd check....
Runout of the rings (if bad, check the vibration and tolerance of the shaft
bearings). Once the problem is fixed, you'll have to 'turn' the rings to
get them back into round. Even if round, roughness caused by contact with a
brush holder or other rigging can cause the brush to vibrate and spark.
Same hardness of brush as recommended by manufacturer? Extremely hard
brushes can sometimes spark under normal operation. When replacing, have
they been 'seated' to match the curvature of the rings? Is the face of the
brush all one smooth and shiny surface? If there seem to be two or more
'polished' areas, then it's shifting around. When only part of the brush
face contacts the ring, the current density is high and can cause sparking.
If the face has chips missing around the edges, it may be impacting the ring
and shattering the face.
Brush spring tension (can allow 'chatter') and bursh holder alignment. The
holder must hold the brush consistently and not allow the brush to wobble
back and forth. If the brush moves even slightly, then it never gets
completely 'seated' as it shifts position. Especially if the machine was
recently serviced.
Color of the slip ring face Absolutely bare brass/silver is *not* good, too
much friction. Should be a slight brown coating. But too dark can be bad
as well. This sort of thing can be oil contamination (too dark, 'sludge'
buildup on rings). Too shiny, look for atmosphere contaminants like some
paint thinners and solvents in the area. They will 'reduce' the 'brass'
surface and the bare brass does not have the best performance (higher
friction with the brush can cause chatter).
Do you swap the field leads periodically, or perhaps you can't do that with
this machine?
I could probably go on some more, but these are things that I remember
seeing on a variety of different machines.
daestrom