vacuum circuit breaker arm overheating
- Thread starter panthripu
- Start date
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SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
If current is normal & no harmonics I would supect that an increase in resistance is causing the heat.
How was the heat detected ? ( just curious )
How hot is it with how much current ?
Have you measured the resistance across the closed de-energized ( removed from service ) breakers contacts with a micro-ohm meter ?
Have you measured the stroke & wear gap ?
Is the breaker a drawout type ?
Do the primary disconnects have sufficient penetration ?
If possible measure resistance across that connection if nothing was found above.
How was the heat detected ? ( just curious )
How hot is it with how much current ?
Have you measured the resistance across the closed de-energized ( removed from service ) breakers contacts with a micro-ohm meter ?
Have you measured the stroke & wear gap ?
Is the breaker a drawout type ?
Do the primary disconnects have sufficient penetration ?
If possible measure resistance across that connection if nothing was found above.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The next step is to measure for voltage drop across the breaker, called 'fall of potential'. This will tell you if there is a restance where there shouldn't ought to be.
Larry, my guess is that this is a medium-voltage breaker and that a FOP measurement would not be possible or safe.
zog will know what to do about this one for sure.
overheating of breaker arm
overheating of breaker arm
hello guys
thanks for your comments.
Its a draw out type breaker and operates at around 2000A current.Every 15 days we rack it out during plant shutdown and check visually.
We found the copper arm was over heated which can be seen by the colour of the copper due to heating up.
overheating of breaker arm
hello guys
thanks for your comments.
Its a draw out type breaker and operates at around 2000A current.Every 15 days we rack it out during plant shutdown and check visually.
We found the copper arm was over heated which can be seen by the colour of the copper due to heating up.
brian john
Senior Member
- Location
- Leesburg, VA
No matter what type of CB this is (most likely MV) it is in need of inspection, Arrange a shut down, and perform inspection and maintenance on the CB.
zog
Senior Member
- Location
- Charlotte, NC
What do you mean by "phase arm"? Can you post a photo?
You either have a bad connection along the current path or a failing vacuum bottle. After S/D and removal use a microhmeter to check the current path and check the contact erosion indicators on the bottles.
Coould also be improper spring pressures on the finger clusters but you need special tools to check those. I could help a lot more if we had some more info on the breaker, nameplate info and photos or better description of the area where the heating is.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
If the heat was enough to discolour the copper I would have a concern that it may have effected the temper in the spring material, making them weak.
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
Back up a minute.
Back up a minute.
Lot of good suggestions here but let's not jump to conclusions. First of all,
2000A on a 2500A rated breaker is right at the NEMA standard of 80% maximum allowed loading unless it is a 100% rated breaker (which I doubt.) This would mean that all of the above mentioned conditions would have to be perfect (main contact resistance, contact wipe, erosion, pressure, finger cluster condition, spring pressure, etc.) for it not to be overloaded.
Second ( which I think is more likely the wrong assumption) how do you know it is overheated by the visual " color of the copper?" Most all switchgear and breaker conductors use silver plated copper bus bar and over time (how old is the gear?) the silver tarnishes into a black-gold color that can look exactly like overheated (annealed) copper. This has fooled many customers of mine and myself! So my guess is that there is no overheating taking place. To prove my argument take an IR gun or camera and measure the temperature of each phase and compare it to the load current in each phase to determine if overheating is actually occuring. If not, hire a reputable testing co to do an IR scan and provide you with a detailed report. Also, see if switching can be done to reduce the load below 2000A on this circuit, otherwise you are just asking for trouble.
Good luck!
Tony
Back up a minute.
Lot of good suggestions here but let's not jump to conclusions. First of all,
2000A on a 2500A rated breaker is right at the NEMA standard of 80% maximum allowed loading unless it is a 100% rated breaker (which I doubt.) This would mean that all of the above mentioned conditions would have to be perfect (main contact resistance, contact wipe, erosion, pressure, finger cluster condition, spring pressure, etc.) for it not to be overloaded.
Second ( which I think is more likely the wrong assumption) how do you know it is overheated by the visual " color of the copper?" Most all switchgear and breaker conductors use silver plated copper bus bar and over time (how old is the gear?) the silver tarnishes into a black-gold color that can look exactly like overheated (annealed) copper. This has fooled many customers of mine and myself! So my guess is that there is no overheating taking place. To prove my argument take an IR gun or camera and measure the temperature of each phase and compare it to the load current in each phase to determine if overheating is actually occuring. If not, hire a reputable testing co to do an IR scan and provide you with a detailed report. Also, see if switching can be done to reduce the load below 2000A on this circuit, otherwise you are just asking for trouble.
Good luck!
Tony
zog
Senior Member
- Location
- Charlotte, NC
Yep, springs have a pretty limited lifespan anyways, standard rebuild kit part, adding heat can make them fail much sooner than usual.
zog
Senior Member
- Location
- Charlotte, NC
To prove my argument take an IR gun or camera and measure the temperature of each phase and compare it to the load current in each phase to determine if overheating is actually occuring. If not, hire a reputable testing co to do an IR scan and provide you with a detailed report. Also, see if switching can be done to reduce the load below 2000A on this circuit, otherwise you are just asking for trouble.
Good luck!
Tony
Being a VCB this is MV gear, and being new enough to be VCB's the gear will have panels gaurding the terminals so a IR inspection is nearly imposible, let alone dangerous unless IR windows are installed. Shutting down the gear and testing the breaker is a much better option, and much safer too, in fact I think one would have a hard time justifing an EEWP for an IR scan on this type of gear.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Siemens breakers are notorious for bad finger assemblies, i.e. the part that actually connects the breaker to the bus when you rack it in. it is sometimes caused by the racking mechanism not aligning properly.
This can be a serious issue, and safety is paramount. My recommendation would be to de-energize the bus, then rack the breaker out, remove from cell, and have the Siemens engineer/tech there to look everything over.
Error on the safe side.
This can be a serious issue, and safety is paramount. My recommendation would be to de-energize the bus, then rack the breaker out, remove from cell, and have the Siemens engineer/tech there to look everything over.
Error on the safe side.
zog
Senior Member
- Location
- Charlotte, NC
Those sure help. Your fingers have all of the silver plating worn off the contact points, they also appear dry (No lubricants) which is likely causing the problem. It also looks like the plating on those is low quality, should never see flaking like that.
The exposed copper where your silver plating has worn off will form copper oxide, which has a high resistance, that is likely your problem. You should also check the pressures on those finger clusters, imporper pressure will also cause issues, too light and you get a high resistance connection, too high and you damage the plating.
Replace the finger clusters, or have them blasted and replated by a certified plating facility. And be sure to use the proper lubricant on the contact points of the clusters.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
"The Great and Powerful Zog has spoken!"
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
Did this breaker interrupt a fault prior to the heat problem ?
zog
Senior Member
- Location
- Charlotte, NC
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
Have you found the cause for the extra heat yet ?
overheating
overheating
No , i could not make any final reason, otherthan the fact that the silver plating over the contact fingres and the fix part inside breaker is missing.
We changed the arm now and since that day it is ok.
But i remember i observed this problem in past also in some other same breaker and we used to change the arm.
overheating
No , i could not make any final reason, otherthan the fact that the silver plating over the contact fingres and the fix part inside breaker is missing.
We changed the arm now and since that day it is ok.
But i remember i observed this problem in past also in some other same breaker and we used to change the arm.
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