Aerial Ground vs. Lightning Arresters 2

[enggines]

Hello guys.
I would like get your comment or suggestion on the following method of protection.
Which is a better method of protecting a distribution circuit, aerial ground or lightning arresters? The circuit is 13.8 KV, around 6 Km long, #4/0 ACSR conductor and right of way is along main road. It will be utilized to serve a neighboring town (6 Km away from substation).
Thanks a lot in advance.

 

[IRstuff]

It would seem like an aerial ground would provide better protection than arrestors, since it's got to be better to not get the transient started at all than to try an dissipate it afterwards.

Since the arrestor is an after-the-fact device with a certain threshold, wouldn't you still get some sort of surge in your lines from a strike?

I would guess that the prudent thing would be to do both, since the aerial ground may not be suffficient to cover all the lines.

TTFN

 

[kinneyj]

There was an article in T&D Magazine back in April 1991 that performs a comparison of both. Published by an engineer with Oklahoma Gas & Electric...

The conclusion is that arresters on all phases is the best method for both cost and switching surge protection. The static or aerial grounding does not provide switching surge protection.

The study covered both 34.5kV and 12.5kV.

 

[busbar]

The general concern is protecting components connected to the line, with a given that statistically there will always be potential damage from lightning or switching transients. Of critical importance is how and where the system is grounded.

There are several grades of surge arresters available, from station class to distribution class. Use of station-class arresters “on the crossarm” is not unheard of. Basic references are IEEE Std. C62.92.4 {description at

http://standards.ieee.org/reading/ieee/std_public/description/surge/C62.92.4-1991_desc.html

} and IEEE Std. C62.22 {description at

http://standards.ieee.org/reading/ieee/std_public/description/surge/C62.22-1997_desc.html

}

 

[joan271273]

Kinneyj:

Would you have a copy of this article. I was trying to search for it with no luck

 

[jghrist]

Aerial grounds (shield wires) are not very effective for distribution lines because the BIL is not high enough to prevent backflashes caused by voltage buildup on the downlead when lightning surges flow to ground. Also, many lightning flashovers on distribution lines are caused by voltages induced by nearby strokes. Shield wires give little protection against induced voltages.

 

[cuky2000]

The ground wire only provide shielding protection to mitigate direct lightning strike over the phase conductors.

The surge arrester will provide overvoltage protection.

Some utility located in moderated ligning areas use their distribution system in delta configuration with one phase conductor on top protected by surge arrester.

They claim that their reliability index are as good as this arrangement provides shielding and surge protection with the benefit of saving on ground wire, extra cross arm space, hardware, etc.

 

[RRaghunath]

Cuky2000,
You mean the utility doesn't provide surge arrestors for all three phase conductors. Just a clarification, otherwise the info is very interesting. Thanks.
I understand that in populated areas, the probability of direct lightning strike is negligible and hence the ground conductor on top is not necessary. However, the surge arrestors are provided in all the three phases to protect transformers etc. from induced lightning surges travelling along the distribution line. Raghunath

 

[hknair]

Hi,
Aerial ground no doubt.Given the length of the line and the voltage level you are telling lightning arrestors are overkill.Also you have not mentioned the termination at the other end or that whether any interconnection or tie feeding is their or not.But any how go for aerial ground only.

 

[cuky2000]

Hi faulty:

The line mentioned above operate with one surge arrester every other pole connected to the top delta configuration conductor. As usual, transformers or transition from OH to UG cable, are protected with one surge arrester in each phase.

The local region isokeraunic level is about 30 thunderstome / day. This translate in one stroke per mile of line per year thunderstome per day. Some region in FL could get more than 100 thunderstome/day).

 

[cuky2000]

Enclose is an interesting article of unshielded lines protected by surge arresters

http://www.hubbellpowersystems.com/powertest/tips_news/pdfs_best/EU1494_Brazilian.pdf

 

[jbartos]

Suggestion: There seems to be the cost of protection involved, which has not been addressed above yet. Visit

http://grouper.ieee.org/groups/spd/Working_Groups/3-4-14/Spring2000/Spring_2000Min.pdf

(in Attachment 4)
etc. for more info.