Corroded Aluminum Bus

[cinderblue]

Trying to determine the source of corrosion of aluminum rigid bus in a substation. There isn't any galvanic corrosion going on. The air isn't caustic but there is a lot of humidity. The bus doesn't have weep holes drilled along it's length and the ends are capped. I'm thinking moisture is building up in the bus, but unsure of how this would cause corrosion. Does anybody have any ideas?

 

[waross]

If you are in a high humidity area and if the bus is lightly loaded and running cool you may have condensation issues. Are you losing a significant amount of mass or is this more of a visual issue?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cinderblue]

As far as I can tell, it's visual. I'm wondering how much it's reduced the ampacity of the bus. I'm still at a loss for why condensation inside the bus would produce corrosion on the surface. This is in an environment that is at 70 degrees F or higher all year round.

 

[waross]

When the temperature is rising in high humidity areas, the dew point may rise faster than the temperature of the bus. When dew point rises higher than the temperature of the bus you will get surface condensation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[oldfieldguy]

surface condensation plus CO2 equals carbonic acid. Mildly corrosive. If there are industries in the area that release other chemicals, they may add other reactions.

Dust is another factor, often introducing dry salts that interact with dew and rain to give some corrosive products.

One of my substations was adjacent to a chlor-alkali/chlorinated hydrocarbon manufacturer on one side and a calcium chloride producer on another. Had some really interesting corrosion.

old field guy

 

[cinderblue]

Thanks old field guy, that answer makes sense. I will recommend the utility drill weep holes in their bus (like most utilities already do) to allow the drainage of moisture and increase the longevity of the bus.

By the way, do you have pictures of that bus that corroded in an "interesting way"?

 

[oldfieldguy]

CB-

I no longer work for that company, a rather large electric utility with a number of substations feeding industrial facilities. I can tell you that over the life of one substation, we had tracking across the glass pots at the tops of oil-filled bushings. The tracking paths were deep enough to detect by dragging a fingernail across the surface.

old field guy