cleaning buss connections
cleaning buss connections
(OP)
We have a rectifier where I work that produces 100,000 amps DC at about 330V. It has copper splice plates that mate to aluminum buss off the load side of the rectifier. Last week, we found one of these connections in excess of 520 degrees F. After about 12 hrs of finding the problem, management finally decided to shut down the plant to repair the problem. When we disconnected the splice plates they were very black on the mating surfaces. We ended up using scotchbrite pads, fine sandpaper, and HP Cleaner/Degreaser, which took some time to get them clean. We were about 75% done with the cleaning, when the Maintenance Manager stopped by. He wanted to know what was taking so long and said we should be using grinders with wire wheels or the wire cups to clean them. I told him I didn't think this was a good idea because of the grooves and valleys this would create and that it is important to have a flat smooth surface to make the best connection. He scoffed and made comments to other employees that I was f-ing him to death by taking so long. Any thoughts about using a wire wheel to prep the surface.






RE: cleaning buss connections
RE: cleaning buss connections
Keith Cress
kcress - http://www.flaminsystems.com
RE: cleaning buss connections
RE: cleaning buss connections
I hope you used some type of electrical joint compound suitable for copper to aluminum connections. Also, take a good look at the hardware holding the joint together. Not having enough bolts will lead to a connection problem.
RE: cleaning buss connections
RE: cleaning buss connections
This seems kind of small for 100kA. U.L. for switchboards is 200 amps per square inch of contact area. I realize this is not a U.L. switchboard.
RE: cleaning buss connections
64 sq. inch for 100 KA looks to be small. Is the bus force cooled ?
RE: cleaning buss connections
RE: cleaning buss connections
RE: cleaning buss connections
BTW, you see the copper blackening on the mating surfaces or on the exposed surfaces ? If it is latter, it is probably due to the chemical environment and nothing to worry about (unless it was eating away the copper)
RE: cleaning buss connections
That can develop into whiskers that can cause a fault.
RE: cleaning buss connections
RE: cleaning buss connections
sparky - 100 KA Al bus and the "management" decides to MIG weld that ? Aluminum is notoriously hard to weld properly due to porosity.
Wouldn't it have been better to replace that Al bus with copper and get rid of the root cause of overheating and failures ?
RE: cleaning buss connections
Are you using the correct size of Bellville washer? They should be thick heavy things and not about the same thickness as a standard washer. You may also need to stack a few to get the right spring force. More then once I've seen bellville washers specified and then these thin washers supplied that are wrongly speced and basically useless in the application. The bellville basically needs to be capable of the same spring force as the tension on the bolt when torqued.
You may also want to look for a different joint compound that can better protect in that application.
RE: cleaning buss connections
A large contractor may have dozens or hundreds of good steel welders available. Only the very best will be chosen to take the factory aluminum welding courses.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: cleaning buss connections
Make sure you use non-gritted anti-oxidant.
Agree, make sure you spec the Bellvilles. Simply ask for a Bellville and you will get a washer that flattens out after you torque it, and stays flat.
RE: cleaning buss connections
Where's jghrist when you need him? I thought it's always a mess to connect copper to aluminum unless you have some sort of bimetallic connector as a transition plate. jghrist had a good article on that.
Bottom line aluminum and copper don't go together! use transition.
RE: cleaning buss connections
RE: cleaning buss connections
RE: cleaning buss connections
http://ne
RE: cleaning buss connections
RE: cleaning buss connections
So silver whiskers are caused by a chemical reaction in the air where H2S is in the air? So you can not prevent this by air filters, this is the switch gear in a bad enviroment?
Or is this the reason not to use silver plating or silver oxide on bus connections?
RE: cleaning buss connections
Nickel plating will also prevent this, that is what we do for remanufacturing breakers that will be in this environment.