Over head Line Design

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Electriman

Senior Member
Location
TX
Guys,

I am working on a project that It has a short run of over head line and I need to calculate the wire size and the number of poles that are required to feed the transformer. I was wondering if you know any guide that I can use for my calculation.

Thank you in advance.
 
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Electriman

Senior Member
Location
TX
Bugman1400 said:
Are you referring to an MV or LV application? If LV, you may be able to start with an UGLY's Handbook.
Click to expand...

Thank you for your response. My application is 12.47 kV. But I will look at ugly to see what differences are between MV and LV over head design beside the distance between the conductors.
 
kingpb

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Size conductors, then based on conductor's you'll have to do sag and tension calcs. Don't think this is something you just whip together unless local utility has some rule of thumb guildelines; which will be one-size fits all = overkill.
 
bob

bob

Senior Member
Location
Alabama
Electriman said:
Guys,

I am working on a project that It has a short run of over head line and I need to calculate the wire size and the number of poles that are required to feed the transformer. I was wondering if you know any guide that I can use for my calculation.

Thank you in advance.
Click to expand...

How long is the circuit?
 
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Electriman

Senior Member
Location
TX
bob said:
How long is the circuit?
Click to expand...

It is relatively short 500' to 1000'. Since it is short the company does not want to contract a transmission line engineering firm. I am think to put a pole every 300'. But I want to support it somehow.
 
bob

bob

Senior Member
Location
Alabama
The minimum conductor #4 ACSR. The area over which the conductor crossed is important. Crossing a parking lot requires a
greater minimum clearance that crossing an open field. Using a 40 ft class 6 pole would allow you to use a 300 ft span an have adequate clearance. This clearance depends on the size of the conductor. Bigger the conductor the more sag you have. Have you determined the
conductor size. There are plenty of pictures of construction techniques on Google.

http://electrical-engineering-portal.com/typical-constructions-of-overhead-lines
 
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E

Electriman

Senior Member
Location
TX
bob said:
The minimum conductor #4 ACSR. The area over which the conductor crossed is important. Crossing a parking lot requires a
greater minimum clearance that crossing an open field. Using a 40 ft class 6 pole would allow you to use a 300 ft span an have adequate clearance. This clearance depends on the size of the conductor. Bigger the conductor the more sag you have. Have you determined the
conductor size. There are plenty of pictures of construction techniques on Google.
Click to expand...

I am feeding a 4 MVA transformer So I have an app that calculates the wire size but it is asking about parameters like Azimuth, or wind speed latitude and so on. I know these are important. I Googled it but I was not able to find an engineering guide of how to design the over head line. Most of the is manufacturer catalog. I am going to use 2/0 ACSR.
 
bob

bob

Senior Member
Location
Alabama
Electriman said:
I am feeding a 4 MVA transformer So I have an app that calculates the wire size but it is asking about parameters like Azimuth, or wind speed latitude and so on. I know these are important. I Googled it but I was not able to find an engineering guide of how to design the over head line. Most of the is manufacturer catalog. I am going to use 2/0 ACSR.
Click to expand...
Different areas of the country have different requirements due to ice and wind loadings. You line is so short I would not be concerned.

power line.jpg
 
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Iron_Ben

Senior Member
Location
Lancaster, PA
Well, there is a lot more to it than meets the eye. You could get a copy of the NESC and study that for hours but you'd fall asleep many times before acquiring much practical knowledge. For something as seemingly straightforward as this, yes 300 foot spans sounds good. 40's would almost always work, but 45's would be unlikely to hurt. 2/0 ACSR is a size bigger than I'd have likely chosen, but no matter. All this advice is given freely and while I am a PE, it's just that, friendly advice. This is all pretty routine until some guy contacts the energized line somehow and they come after you. You would wish you had a stamped drawing in such a case.
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Electriman said:
It is relatively short 500' to 1000'. Since it is short the company does not want to contract a transmission line engineering firm. I am think to put a pole every 300'. But I want to support it somehow.
Click to expand...

It sounds like you are the project manager/engineer/chief-cook-and-bottle-washer for this gig. Do you feel you have adequate relevant experience to tackle this project? It sounds like a terrific project to show what you can do, but remember, "success has a thousand fathers, failure is an orphan". It sounds like you need soils engineering, foundation design, site planning, rights of way, erection planning, and service tie in, just off the top of my head and I don't do this for a living. I personally wouldn't feel comfortable trying to rely on catalog cut sheets to execute my design.
 
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Bugman1400

Senior Member
Location
Charlotte, NC
If the wire is tensioned, you'll need equal tension on the opposite side. For example, if you line makes a 90deg turn, you'll need to apply proper guying on the two opposite sides equal to the tension of the primary conductor. If it is clear underneath and clearance is not an issue, you may be able to slack span the conductor with minimum tension, however, you will be more susceptible to wind blow-out..
 
E

Electriman

Senior Member
Location
TX
Bugman1400 said:
If the wire is tensioned, you'll need equal tension on the opposite side. For example, if you line makes a 90deg turn, you'll need to apply proper guying on the two opposite sides equal to the tension of the primary conductor. If it is clear underneath and clearance is not an issue, you may be able to slack span the conductor with minimum tension, however, you will be more susceptible to wind blow-out..
Click to expand...

Thank you guys for all the advice. It is a straight run and we have engineering in place for Foundation ROW and so on. I am also a PE and I know NESC gets very confusing with no help when it gets designing overhead line. I am experienced in power distribution design but not overhead. Like what you guys said I have not been able to find a practical engineering guide to design over head line. If you know please tell me and I follow step by step to make sure I meet all the requirement. So I have selected everything very conservatively so I cover myself in case an audit take places.
 
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GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The two tension matches for a 90 can be combined into a single guy at 45 if the path is clear and the tensions are equal.
If unequal, still one guy at the appropriate angle.
 
B

Bugman1400

Senior Member
Location
Charlotte, NC
Do you have a supplier for poles, crossarms, insulators, cutouts, and the rest of the hardware?

Remember, for pole placement, 10% + 2 feet, and the big end goes in the hole.:D
 
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