Sea contamination upon a distribution circuit in Honduras 2

[cpinedai]

Hello,

I am from Honduras and would like some help in regards as to having problems with a distribution circuit that runs along the coastal part of this city. The sea contamination(Salt and other deposits) upon the insulation of arresters, cutouts and insulators is really bad. All of this distribution equipment get ruined after some moderate contamination upon them and followed by rain. The voltage used is 34.5 Kv and as you may see that in other coastal areas in Honduras they have a voltage of 13.8 Kv and they don't have such a problem as we do here. Of course, some years ago it was a bad design in buying a power transformer of such voltage but I am stuck with the problem and the company (Government owned) is broke, but I need to improve the customer service. Every three months we do cleaning and changing distribution operation equipment replacement(cutouts, arresters, etc) but unfortunately when a big, long, and windy storm comes along then I have problems because the sea contamination deposits really fast in matter of days than it usually does in two or three months.

Right now, I am in the middle of buying cutouts, arresters and insulators made of polymers but I would like to know what other tecnologies I may use or are using in other countries to improve the circuit confiability? Also trying to buy a small power transformer 34.5/13.8 Kv would not be a good idea because we are in financial problems. Any ideas or suggestions made need to consider our financial problems. Thank you and Allah'u'abha!

 

[jtkirb]

One suggestion would be switching to higher voltage insulators- that would help with the tracking to ground and flashover (I assume this is the main problem). Can you isolate the problems to just insulators, arrestors, or the like?

I have heard of an anti-tracking, self healing, gel that can be put on the insulators, but I have no idea on the product or how it works.

I would call an inuslator mfg for suggestions- Lapp or someone like that. You are not the only one with sea-side installations. They may have a solution.

A government owned utility that is broke...imagine that.

JTK

 

[stevenal]

Over-insulate, specify extra creepage, use polymer insulation (the more the silicone the better), use stainless steel cutouts and distribution transformers, avoid fiberglass, and avoid cycloaliphatic and any other type of epoxy.

 

[cpinedai]

JTK:

I have tried that. The life expectansy of this porcelain insulators are a little longer but still great amounts of salt deposits upon the insulators and we have to do the maintance until six months instead of three to four months.

One of the solutions I may do is relocating the distribution circuit not near the ocean and just have circuit feeder branches of one to two phases in the coastal part of the city. Along this line of thought I may put polymer cutouts, arresters, etc, and get the gel you are suggesting.

Too bad you don't have any name or way to find out more info about it.

As to the company's bankruptancy it's a long story to tell... but you're right.

 

[cuky2000]

Insulator with standard creepage distance may be one of the possible problems. Insulator with extra creepage distance rated for 31mm/kV or higher may be better choice for this environment.
_{[blue] I understand that Honduras is a very active lightning zone. This combined that the site is very close to the coast and exposed to sea-spray or to very strong and polluting winds from the sea, may me believe that this site may qualify for insulator rated for very-heavy pollution level of category IV or greater.[/blue]}

Before star expending money and guessing solutions, it is strongly recommended perform an insulation coordination study to find the actual cause of the problem and be able to implement the best options for your organization to take in account budget constrains and other limiting factors.

Here are some suggestions to consider in the insulation coordination study:

a) Replace existing standard insulators and devices with larger creepage distance. This could be achieved using porcelain or composite insulators.
b) Because of budget constrains, local supplier in LA could be cost effective. [blue] i.e. Brazil and Colombia among others may be potential source to supply insulators and other distribution products. See the enclose site for reference:

http://www.gamma.com.co/boletinestecnicos.php

[/blue]
c) For apparatus bushing and expensive component, creepage extender may be a suitable option. [blue]See the enclose reference.

http://www.raychemrpg.com/electrical/hvce.html

[/blue]

d) Washing program and periodical cleaning may help but is not a permanent solution and the maintenance cost and planned outages will increase as well reducing the overall system availability.
e) Silicon grease application may work as temporarily solution.
f) If you have shield wire in the distribution system, check the angle of protection is adequate. Typically, 30 degrees is OK to protect the OH phase conductors and underbuild. _{[blue](NOTE: Sometime extending the high of the shield wire is an economical solution to provide additional flashover protection) [/blue]}
g) Add surge arresters in unprotected area if shield wire is impractical to be installed.

 

[RalphChristie]

Insulator Maintenance normally takes one or more of the following forms:

Periodic hand wiping on the de-energized installation,
Periodic coating with grease compounds,
Periodic washing while either energised or de-energised,
Application of a hydrophobic coating.

Greasing
Grease compounds used for coating insulators are mainly silicone or hydrocarbon products. The action of the grease is to provide the insulator with a hydrophobic surface film and to surround the individual contaminating particles with grease. In this way, wetting of the particles are prevented and a conducting path is not formed along the insulator surface. This action will continue until the grease is saturated with contaminant. The thickness of the layer depends on the type of grease and on the degree of pollution. Generally, a thickness of 1mm is adequate for silicone products, whereas for hydrocarbon grease a thickness of 2 to 3mm may be necessary.
Once grease has been applied, it is necessary to clean and re-grease the insulators at intervals which depend on the degree of contamination and weather conditions. Intervals between cleaning and re-greasing will range from some months to some years. Greasing is an expensive procedure and should only be done if other remedies prove to be uneconomical.

Washing
Insulators can be washed with fixed or hand-held equipment. The hand-held equipment can be operated from the ground, from a platform or from a helicopter. For effective washing, care should be taken with the design of the spray nozzles and in the case of live washing, the conductivity of the water is also extremely important. Manual washing requires a sharply-focused jet, and cleaning is commenced at the bottom of the insulator or string. With automatic systems the spray must be such that the full length of the insulator is uniformly wetted. Water conductivity must be very low. The maximum conductivity which can be tolerated will depend on nozzle design and the water flow rate.
Washing as an anti-pollution measure requires a high capital investment, but generally the annual cost is less than the cost of greasing.

Application of a tough hydrophobic coating
The performance of glass or porcelain insulator can be significantly improved by applying a coating which bonds with the insulator surface and has hydrophobic properties. These coatings are usually silicone based and can be applied by brush or spray-gun. It gives a remarkable improvement in performance. Long time experience of these coatings is very limited and while it is expected that they will have a long live, inspections at intervals of two to three years are recommended.

Increase creepage distance: if the clearances allow, additional discs may be added to increase the reliability of a line. This solution is not always possible and will be expensive.

Replace hydrophilic with hydrophobic insulators: one possibility by replacing the hydrophilic insulators with hydrophobic insulators of the same lenght and creepage distance. Solution is expensive.

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[jtkirb]

This may seem like a long way to go to solve your problem, but a product like this:

http://www.hendrix-wc.com/hendrix/home.htm

Might help reduce your outage intervals. The wire is insulated along with the hangers. Allows for tighter spacing around congested areas, but may also allow for better contamination resistance. They even list your problem.

JTK

 

[stevenal]

One brand of coating goes by the name of Silguard. I'm not sure that's the correct spelling. More like a paint than a grease, and lasts for years without reapplication. It provides better hydrophobicity than the uncoated porcelain.

 

[MikeHalloran]

I've never been involved in high- voltage distribution, except when screwing around with car distributors. Based on that highly limited expertise, I have this to say about greases:

Hydrocarbon grease decomposes, e.g. after a flashover or exposure to intense heat, into ... carbon. Which pretty much guarantees more flashovers.

Dow Corning Silicone High Vacuum Grease, and other silicones, decompose into ... nonconductive, fine white sand.

When cars still had distributors, a thin coat of silicone grease inside the distributor cap made them run a lot better, especially in the rain.



Mike Halloran
Pembroke Pines, FL, USA

 

[mc5w]

The electrical utility in Los Angeles, California washes their distribution insulators more like once per month.

Florida Power and Light uses 2 types of construction on 7,620Y13,200 volts lines:

1. In rural areas frequently 13,200 volt construction but with an overhead ground wire to stop lightning. During a rainstorm there is a lot in the way of silent and invisible lightning.

2. In urban and suburban areas 34,500 volt construction derated down to 7,620Y13,200 volts. All 3 phases have lightning arrestors once every 3 poles and at both ends of a section switch.

Also keep in mind that lightning protection is only as good as the ground and that you might need to use 17 foot or 18 foot ground rods using rod couplings. In a coastal area sandy soil would be normal and you might need a perforated plastic pipe buried vertically next to the rods so that you can periodically pour in water. Erico also has Ground Enhancement Material that you can use a backfill and also chemically enhanced ground rods.

First Energy here in Ohio has also built 34,500 volt lines with 69 KV insulators and 69 KV lines with 138 KV insulators. This has the advantages of eliminating crossarms and reducing poletop fires.

You might be better just to bite the bullet and put in 13,800 volt underbuild and switching most customers to that.

 

[itsmoked]

How about pressure washing the insulators frequently like task someone just to wash insulators. When they're done start back at the beginning. Would seem cheaper than lots of capital equipment replacement. If the contamination is really bad as it sounds you would probably still have the problems just at a lower frequency whereas regular frequent washing might prevent all occurrences.

In N.Amer this would be prohibitively expensive but I would imagine in Honduras it would be very workable.

 

[RalphChristie]

Sorry - little off the thread:

mc5w - nice to see you back again.