Something is not right: If everything already done and checked, the cause of the problem would have been found out and remedy initiated.
Sparking on slip rings of generator
- Thread starter ansmehmood
- Start date
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zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
That doesn't make sense if a new brush starts out OK but then begins sparking. I'm still curious what happens if the pos and neg brush sets are swapped (it that's even possible).
How much of a problem is the sparking actually? There's a range between "it looks ugly" and "the machine will self-destruct in 20 minutes".
junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Not on anything as large as 150 MW (just a diesel 200 kW), but had sparking due to overheated spring having lost its temper resulting in some 'set' and thus lower brush pressure. Did re-look at past posts and you did not list brush force as having been checked.
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
I’ve had sparking on slipring motors due to the rings being slightly eccentric. It’s worth checking with a dial indicator.
JFletcher
Senior Member
- Location
- Williamsburg, VA
Beat me to it. Was going to suggest that the ring in question is slightly out of round.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Shouldn't a good spring be able to follow a little eccentricity? Could also be the brush holder is binding when the brush gets "close enough" but from the OPs description, this happens on all positive brushes.
Spring yes... but not the curvature of the brush.
JFletcher
Senior Member
- Location
- Williamsburg, VA
It should, and it's hard to imagine a 150MW generator coming with such a mfg defect, or wear issue. at 3600rpm tho, a little eccentricity could result in a large harmonic bounce that overrides spring tension (think valve float in a car at high rpm). It's also one of the things the OP didnt check; if that can be eliminated, then he can move onto troubleshooting elsewhere.
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
No. It happens only on positive brushes, but only on those brushes from 12 o'clock to 5 o'clock, so about 150° of arc.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
That really sounds characteristic of an out-of-round or off-center problem to me.
But that subset of the brushes cannot spark if any of the brushes in the other 210° arc are not making good contact. The brushes are all in parallel.
That would be why pushing any one brush into constant contact stops the sparking. There will be a significant voltage drop across one brush if it is the only one conducting, and so inefficient, but the voltage will still be low enough to avoid sparking on the rest of the brushes.
this is a good approach
check run out, concentricity, etc
if it is only doing it for 75 deg out of 360 my bet is on the rings (or lord forbid the shaft)
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Did "Everything already done and checked" include using a "stroboscope"!
Regards, Phil Corso
Regards, Phil Corso
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
Ahhh, yes. Rotating equipment and all. Very good point.
But it does not explain sparking recurrence every 24-48 hours. The other explanation that remains is positive brushes/brushgears in the sparking zone are all defective and sparking may cease on their replacement.
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
You seem to have missed the point that the sparking happens ONLY in the region of 12 o'clock to 5 o'clock.
I said positive brushes/brush gears in the sparking zone ie in the region of 12 to 5 o'clock are all defective.
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
Yes you did, my mistake. :slaphead:
jimo144
Member
- Location
- Western Grove, AR Newton County
Arcing Slip Rings
Arcing Slip Rings
If one set is not flashing / arcing and another set is, it is clear evidence of a Slip Ring condition. With that said, as others have said, make certain that the Brush Length is within wear limits because a short Brush has less Spring Tension and can start flashing / arcing. Lift each Brush away from the Slip Ring one at a time to make sure the Brushes are not stuck in the holders and that the Springs are working. If they are stuck, wiggle them free and lay flat on Fine Sandpaper to remove whatever has creating the sticking. Once reapplied, again pull test the Brush again to make sure your efforts have worked.
Use a (DC) Commutator "Seating Stone" which is essentially Pumice Stone that is very soft but abrasive enough to wear off Tarnishes, Oxidation, and shellacs created by environmental contaminants like Diesel Fuel, Exhaust Fumes, and Lubricating oils. A shellac buildup will insulate the Brushes and Slip Rings enough for them to flash or arc, consuming the Brushes and burning the Slip Rings.
Once you have cleaned the Slip Rings, apply compressed air under load if you have plastic or other non-conductive tubing. If you can't apply compressed air safely, do as best you can with the Generator shut down. Again lift each Brush and blast the Brush Tip with the compressed air to remove any Pumice Stone residue. The compressed air will also clear out Cob Webs and other debris common with Generators in Standby Service.
If this doesn't clear the flashing / arcing, the Slip Ring may have worn out of round and may be bouncing the Brush causing the arc.
JimO
Arcing Slip Rings
If one set is not flashing / arcing and another set is, it is clear evidence of a Slip Ring condition. With that said, as others have said, make certain that the Brush Length is within wear limits because a short Brush has less Spring Tension and can start flashing / arcing. Lift each Brush away from the Slip Ring one at a time to make sure the Brushes are not stuck in the holders and that the Springs are working. If they are stuck, wiggle them free and lay flat on Fine Sandpaper to remove whatever has creating the sticking. Once reapplied, again pull test the Brush again to make sure your efforts have worked.
Use a (DC) Commutator "Seating Stone" which is essentially Pumice Stone that is very soft but abrasive enough to wear off Tarnishes, Oxidation, and shellacs created by environmental contaminants like Diesel Fuel, Exhaust Fumes, and Lubricating oils. A shellac buildup will insulate the Brushes and Slip Rings enough for them to flash or arc, consuming the Brushes and burning the Slip Rings.
Once you have cleaned the Slip Rings, apply compressed air under load if you have plastic or other non-conductive tubing. If you can't apply compressed air safely, do as best you can with the Generator shut down. Again lift each Brush and blast the Brush Tip with the compressed air to remove any Pumice Stone residue. The compressed air will also clear out Cob Webs and other debris common with Generators in Standby Service.
If this doesn't clear the flashing / arcing, the Slip Ring may have worn out of round and may be bouncing the Brush causing the arc.
JimO
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Anyone interested in a very safe way to monitor brush current! Current measurement can reveal the cause of a host of problems!
BTW, in my day we called it "Brushgear Tribology!
Phil Corso
BTW, in my day we called it "Brushgear Tribology!
Phil Corso
big john
Senior Member
- Location
- Portland, ME
Can you safely see the brush rigging under load? Bouncing brushes due to ring misalignment are often visible to the naked eye.
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