cleaning buss connections

[twoelk]

I'm not sure if this is the right place for this post, but here it goes.
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.

 

[Buck Parrish]

It has copper splice plates that mate to aluminum buss





thoughts about using a wire wheel to prep the surface.

Is this metal to metal, what method is being used to inhibit oxidation?
The wire wheel should be okay.

 

[jim dungar]

Do not ever use a wire wheel, or any other coarse abrasive, on plated bus bars. Do not clean bus bars with any material, like true sandpaper, that will leave a residue or particles behind. The rougher the contact surface, the more likely the joint is to fail.

 

[twoelk]

We used Penetrox for the copper to aluminum connection.

 

[zbang]

A very fine brass wire wheel might be OK, but never steel. Since steel is harder than copper or AL, it will gouge the busbar surface, whether you can see it or now. Did you use a block to back the sandpaper/scotchbright? Just using a finger can lead to uneven removal; you loose the flatness. I'd even be inclined to check the flatness with some machinists dye and a good straight-edge or plate.

BTW, what's the application? Plating? That's a LOT of DC.

 

[LarryFine]

He scoffed and made comments to other employees that I was f-ing him to death by taking so long.

Tell him that using his suggestions would create a self-fulfillling prophesy. :wink:

 

[ironman3452]

first off, have you tried to contact the manufacture, to see what they use to clean, and they may have the correct way to clean this buss.

 

[twoelk]

We operate a chlor-alkali facility with 66 electrolyzer cells. This equates to thousands of additional copper to copper connections onour cell line which are all cleaned in the same manner, but not by me. Management has consistantly ignored my recommedations eventhough none of them are electrical engineers and claim to not know alot about electricity, so they rely on me to solve their issues and provide advice. The problem is they pick and choose which information they want to utilize. This is also not the first time we have had this problem. The last time, which was on entirely different connections, it actually melted chunks of the aluminum buss. They had a mechanical contractor come in with a MIG welder and build the aluminum up and re-surface it. I feel it is only a matter of time before we have major failures.