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Odd Substation Corrosion

Odd Substation Corrosion

Odd Substation Corrosion

(OP)
At one substation we've noticed that on multiple two-legged three-phase stands for the 115kV equipment there is the appearance of corrosion between B- and C-phases. Nothing apparent between A- and B-phases.


As can be seen, it isn't just one support structure, and it has a hard edge at B-phase. Interestingly it is just the space between B-phase and C-phase. It doesn't seem to build up across the mounts, it just starts on the C side of B and on the B side of C.

Bad galvanizing seems a bit of a stretch given how it's the same on both supports visible and that it has such sharp edges.

The possibility of only the leg nearer to C-phase being grounded (can't tell in the photos, hasn't been field verified) contributing has been raised. Can't totally refute that, but if so, wouldn't there be at least some corrosion between A- and B-phases? And wouldn't there also be some corrosion between the cross arm and the ground connection?

Thoughts, opinions, questions welcome. Questions that require field observation to answer may take a few days.

Thanks.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

RE: Odd Substation Corrosion

In the world of galvanic protection, if you maintain an excessively positive charge it can cause an accumulation or deposits on the surface. Is there their any type of DC offset between the phases?

RE: Odd Substation Corrosion

Is the dark material definitely corrosion rather than a buildup of particulates or mildew? Is the effect on the other same on the other three faces of the beam.

The hard vertical lines seem to correspond to overhanging switch mounting brackets. The switch mounting plates might provide protection from rain. It seems like the dark coloration continues for a bit on the left side of the middle phase.

Any chance that the bus turning 90 degrees results in different amounts of induced losses in different part of the beam, resulting in the left portion being slightly warmer than the right portion, leading to the right portion staying damp more often?

RE: Odd Substation Corrosion

Could the isolator between those two poles cause some sort of galvanic corrosion in that section?

Muthu
www.edison.co.in

RE: Odd Substation Corrosion

We've had a representative from a galvanizer visit an industrial substation that has lots of rust colored surface. The verdict was the galvanizing is intact and the steel is still being protected. No pattern quite like this, it looks that way station wide. I also find this curious, but it might not be a problem.

RE: Odd Substation Corrosion

(OP)
I will try to find out about the other surfaces of the beam. I haven't personally seen it, but the Substation Engineer that provided the photo said it was corrosion so I went with that term and don't know if this goes beyond the galvanizing.

Thanks for responses.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

RE: Odd Substation Corrosion

A screenshot enlargement does not help much with the detail needed to diagnose, results are too coarse. This does look more like environmental or iron oxide stain than rust. If corrosion is present it will appear on the flat top surface first.
If there is a way to take some zoomed in pictures of the top surface you will get better answers.
An examination using binoculars may also be helpful.

RE: Odd Substation Corrosion

A thought:
Possibly a combination of prevailing winds shielded by the control room and a nearby plant with deleterious emissions.
I don't feel strongly about this and I admit that there are some contra-indications.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Odd Substation Corrosion

Well that strange pole thing in that bay compared to the other looks like it's worth investigating?

What is it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Odd Substation Corrosion

(OP)
“Strange pole thing” - please describe, nothing appears odd or out of place, but it’s one of our substations and looks perfectly normal to me other than the discoloration. There is a wood pole beyond the fence where the line drops in but otherwise nothing appears pole like to me.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

RE: Odd Substation Corrosion

The column supporting the insulator on the right-hand bus looks as if may have the same condition, David.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Odd Substation Corrosion

This strange pole thing. Its the only thing that immediately seems different between the two halves of the support.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Odd Substation Corrosion

Quote (LittleInch)

This strange pole thing. Its the only thing that immediately seems different between the two halves of the support.
This is the switch operating rod. It rotates to operate the switch.

RE: Odd Substation Corrosion

(OP)
The face of the tube seen in the photo is the south face, so I don't think that shading would be an issue.

The substation from Google Earth. This is a transfer station between taps from two different lines so the only current on the 115kV is what's feeding the transformer at this location. The photo posted above is from the west bay, the east bay has similar discoloration.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

RE: Odd Substation Corrosion

Thank you for your courtesy in responding to my suggestion of shielding/shading.
Part of effective trouble shooting is eliminating possibilities.

I wonder if the cause was some factor during the manufacture, storage or transport before the parts arrived on site or something that happened after the station was constructed and put in service.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Odd Substation Corrosion

(OP)
I'm told that similar discoloration has been observed on beams oriented north-south as well.

No idea how we'd measure any standing DC between B- and C-phases, and no idea why it would show up here but not elsewhere on the 115kV system.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

RE: Odd Substation Corrosion

Still grasping at straws:
Acid rain?
I notice that the areas of the member that are somewhat shielded by the insulator bases from the rain are free from discoloration.

Anecdote alert; Surface conditions.
Years ago the fuel gauge failed in a one ton truck.
The sender was replaced with no joy.
A second sender did not resolve the problem.
The truck model was available with either a gas or a diesel engine.
The same sender was used for either truck.
The word from the factory support was that the slider resistor was coated with a protective film.
When installed, the gasoline dissolved the protective film.
Diesel fuel did not rapidly dissolve the film.
Solution:
Was the new sender in gasoline before installing in a diesel truck.
/anecdote alert off.

The point is, what could have made part of the supports more or less susceptible to acid rain?
Possibly delivery?
I visualize the long pieces loaded onto a truck and the shorter pieces loaded on top at one end so as to somewhat protect part of the longer pieces.
Then a long road trip on a mild winter day with a lot of brackish road spray on the unprotected parts of the load.

Again acid rain;
Something has caused an insulating coating on part of the supports.
Acid rain on bare zinc, little or no effect.
Acid rain on a thin insulating coating on the zinc, a very low capacitive voltage between the rain and the metal.

I strongly suspect acid rain.
The question is what has caused one part to be more or less susceptible to acid rain.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Odd Substation Corrosion

For the DC offset, it might happen because of anodes used to protect for corrosion. Such anodes do make a Dc offset for the intent of preventing corrosion.
This seems unlikely to me, but that is not my specialty.
These appear to maybe be manufactured switch structures. If so who manufactured them? (I don't need to know). A look at there manufacturing process maybe of value. The reason is some galvanizers have limits, and may unevenly coated the steel. (seems unlikely also, but not impossible).
Then again, it might be a leakage of some of the insulating parts, or some misalignment of the switch.

RE: Odd Substation Corrosion

Here's a photo I took yesterday. Less industrial acid rain here, more ocean salt. It's definitely directional, this is the windward side. Lee side is just dull grey. I was interested to see that the less visible leg has a galvanizing defect where the zinc is peeling away. Even with the defect, the steel is still full thickness due to the cathodic protection from the intact galvanizing nearby.

RE: Odd Substation Corrosion

Thank you for sharing, stevenal.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

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