Grounding of Painted Towers

It is surprising that someone might order the painting of 380kV towers if the towers were not already painted, and if they are energised, they will be earthed already.

Provided the existing earth bonds are not disturbed, there shouldn't be any issue with the earthing arrangements.

We have ordered galavanized steel towers and then we have painted them before erection... i got confused in that if all parts are painted it menas they all are isolated from eachother. as you know that current has to pass from OPGW to tower earthing conductor (From peak to foundation stub).

Well, if they are galvanised, why the hell is anyone messing around with paint?

As per our standards, we have to paint all towers within 25kM of coastal area.

Then ask the individual that approved the standards for use. Why ask CR4?

It is standard practice for some items that will be in a salt spray area. One of the big oil companies did it on a refinery on the design of which, I worked. Apparently, the salt is bad for the galvanizing.

that was my exact 1st thought

Yes, I can see where 0.01" of paint will be able to stop 380,000 volts and God knows how much current dead in its tracks.

No way to tell.

Probably not, since current takes the path of least resistance.

so in case of painted towers there is no problem in flow of current from peak to bottom? because i read some where that tower painting should be done after erection so that each part should not be isolated

<...read some where...> To what published standard are these towers being erected and painted, then?

Why not scrape off the paint where the connections are made and afterwards just paint that area? You must have some paint left?

After reading through the responses, I am wondering if this basic concept is somehow not understood.

Does the OP think that just by painting the towers that they will no longer conduct electrical current?

That cannot be the case...that would be ludicrous...right?

I guess we are all just miffed that an industry expert has not been consulted and governing regulations not utilized/followed in the construction of something so safety critical.

Then, an ad-hoc engineering forum is consulted instead. It's like a surgeon calling up Car Talk to get advise on a stroke victim.

Then again, maybe this is actually a cleverly disguised homework problem?

They certainly will, but perhaps in first instance not through the straps to the ground, but maybe through the foundation structure - with a chance to compromise it.

Paint thickness for such constructions is somewhat "rhetorical". Once I made a magnetic robot to climb these constructions and the paint turned out to be a few millimeters thick at certain places. While the specs were microns too. They were probably painted with a push broom? We also do not know what paint he is using, but in case of epoxy, 1 mm paint needs to convert to carbon before a "real" smaller current passes. When the straps are around the elements, they might need to be re-tightened after?

The galvanized structure could have problems with salt. Here my question: some galvanized steel lasts long close to salt and others don't. I suppose the process is also important and perhaps the composition.

A thin fence pole last about 15 years here, a epicore panel 5 years (when on the grond, after 3 weeks the zinc is gone, and some heavy constructions seem to last for ever?

Are these Lyndoor 'hover towers' ? or are they firmy bedded into deep solid foundations... in the ground... earth?
Del

(just askin')

Yes, my thoughts exactly. Can you imagine trying to maintain the insulation resistance of painted parts that are bolted together? I believe this is a complete non-issue.

Exactly. Even with rather low voltages like when I am MIG welding at 20 - 30 volts DC open circuit I rarely ever have come across prepainted bolted together joints that would cause conduction problems.

Now rust and corrosion building up between two joints and their fasteners is a whole other issue and yes that can, if given the right conditions, easily make a joint non conductive to surprisingly moderate voltage differentials.

Any body know any international standard describing in favour of your replies.

that thing i wanted to know.... thanks ....

passingtongreen has already expressed similar experience of painting GI structure in coastal area where there is possibility of salt spray as Galvanizing is not resistance to salt + moisture.

He is right as NaCl + H2O = HCL +NaOH. Both hydrochloric acid and Sodium Hydroxide reacts with Zink. Dilute Acid + Zn is famous preparation of H2 gas in laboratory and Sodium Hydroxide based Etching Primer is applied on galvanized surface before painting.

Therefore the Galvanized structure is painted with Epoxy based paint system of 250 micron thickness.

Epoxies are bad conductor of electricity hence each bolted joint is like a capacitor and all joints together are capacitors connected in series, connected between top cross arm and ground.

There is always leakage current whatever small (dry condition) or moderate (wet or dirty condition of insulators) between 380kV conductor and earth through the structure of the tower to earth. This leakage current will result in voltage drop across each bolted joint. Total sum of Voltage drop between insulator string and joints = 380kV (line voltage). This can result in dangerous touch potential to earth. Therefore I suggested:

1. Not to disturb the paint considering environment.

2. Lay bare earth wire along the structure height binding it with the structure as well as to supporting bolts of Insulators on cross arm at one end and tower safety earth at other end.

No standards in the world disallow using safety earth. By doing this:

1. We are providing low resistance path to normal leakage current avoiding any build of Statics.

2. Keeping entire structure at earth potential thus avoiding risk of touch potentials.

3. Providing low path for fault current to ensure fast isolation under fault.

Comments of IQ, Quote, "Text book techs should stay in libraries and stay off transmission lines. We will all be safer." Unquote, surprised me. He should understand that various safe practices and Standards are also written in Books not by persons like him but by those who have sound fundamentals. Further he shall know that what we apply in field is from what have learnt in Schools.

Ok, painting the galvanized towers to add furthur protection from high salt concentrations in the air. No problem, fine idea.

You stated:

i read some where that tower painting should be done after erection so that each part should not be isolated

Did you read this in the tower installation manual?

What assembly method have you employed, section assembly, ground build, or Build Up?

It seems like it would make sense to paint it before assembly for the sake of cost.

It is a lot more time consuming (costly) to paint when the tower is erect in whatever method you use to assemble the tower.

IMHO and in my experience I never left the bonding of anything up to mother nature or an ignoramus with a paint brush.

clean the area's with metal to metal contact and you bolt them together, then paint over joint, bolt and all.

seems to me it would have been easy to know where the tower pieces bolted together (oh maybe the big hole stamped in the end) and painted everything leaving a small area for metal to metal contact. followed up with painting over the bolted locations. Perhaps whilst bolting them together!

Well, no use crying over spilt milk. Hopefully it was a govt. project and there was no need to do it right and make a profit.

Do not paint the sections where you want to put the grounding clamps, eyes, lugs, etc. Be sure to use a metal which is compatible with galvanizing. Install these on the tower (on, thru. etc.) whichever way you want too.

Then, paint the tower, grounding wire stubs and the clamps, eyes, etc. as one unit. It would probably be beneficial to give them several extra coats of paint in that area so that any minor gaps between the two surfaces are sealed.

Good Luck, Old Salt

One way is to scrap the paint at the joints but this defies basic purpose of painting.

Solution has to be developed in this case because if a fault develops it will result in high touch potential along the height of tower and will be fettle.

Even surface leakage can result in risky touch potential and kill a person when the line insulators are dirty and wet.

One option in my opinion is to take earth conductor up along the height of tower and earth the Cross Arm(s) on which insulator is supported. This will ensure:

1. Effective earthing in case of fault, subsequent tripping and isolation of fault.

2. Tower and footing at same potential during normal leakage hence no risk of any accident due to dangerous touch potentials.

Stunned by the question. Galvanized steel towers! OPGW! Is this one tower? Is this a route length of more than one tower? Is the OPGW connected all the way from end to end? Is the tower securely connected to earth (ground)? Is this a magically isolated and insulated tower? Have you done a dielectric test on the new paint thickness? Do you know the fault currents that could appear on the towers? Have you measured a bolted connection on any tower. Have you done a earthing test at the tower? Do you know what OPGW stand for? Have you thought this question through?

Text book techs should stay in libraries and stay off transmission lines. We will all be safer.

OPGW..FiberOptic Ground Wire... its not as much complicated as you are questioning.. simple question ... what will be the effect if we paint all parts seperately, then assembly them and erect them ... will there be any electrical conductivity between tower parts or not? i asked from paint manufacturer they replied paint after curing is non conductive for electricity... thats why i questioned

Just as I knew: OPGW = Optical POWER Ground Wire. Specifically designed to carry earth fault currents at a certain rating.

If the paint is not conductive, then why are you using an inferior paint on transmission towers? See above comments about cleaning contact surfaces. Clearly cost is involved here and tower safety is not valued. Bad practise indeed. Clean all contact surfaces, properly, bolt up and paint over the joint. (ground build). Get an IEC standard, read it and digest the information. Speak to your client and get him to stipulate the paint to be used, that is his asset and he knows better than you, or should do. Speak to the consultant who issued the work and get him to state the paint to be used. (It will be in the spec/tender for the work). The consultant gets paid for the signing off of the work and design and specifications. They have insurance just for in cases of screw ups. There is some good info here and advice, if you don't know these simple solutions you are in the wrong work field.

Grind the paint,weld a grounding lug,re-paint.

I have to agree with PWSlack! why the hell are you gonna paint hundred´s of High Voltage towers (as everybody know´s, they are very small) with a high precision coating, when they´r cable´s are insolated.

save the do!

Why not drill and tap the location of the ground attachment.

I suggest bonding the major tower components to each other using conventional methods such as the thermite weld bonding used in steel structures.

Does Any body know international standard describing in favour of your replies.

There are many standards and work methods for painting towers and painting towers is world wide. And each utility will have a standard and work method/procedures. You need to speak to your consultant or utilities/assets owner as they will have the standard they work to. No point in asking here as no one knows where you are, (country). Do yourself a favour and rather than hope for all your wishes to be granted here, use the internet and look up standards. I assure you there are enough documents on the web to fill you head with knowledge, and try subscribing to a Standards Institute. All your questions have been answered very well, (in some cases). So do your research and confirm your findings with the answers. Alternately, I am happy to quote for the works, and I am sure we will all arrive over to paint your towers for you.

Send us details of the works, how many towers, heights, locations, span lengths, voltage and I shall happily quote the works!!! Anyone else want to join me in this adventure? Put you name here!