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Pulpmillguy
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Phase Position Change in HV Transmission Lines

01/08/2012 5:13 AM

Hey all of you Electrical Gurus...I have a question for you. Every time I travel between my home and Helsinki I pass under some high tension transmission lines that get me wondering about something.

Just next to the highway the phases change position...on one side of the tower they are arranged (left to right) A-B-C and then for some reason they swap the A and B phases so they now run B-A-C. I don't know how far they have run in either configuration but have wondered for some time now is this phase position swapping common practice or is there just some special case that is causing it here.

Thanks for satisfying the curiosity of a fellow engineer!
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JohnDG
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#1

Re: Phase position change in HV Transmission lines

01/08/2012 6:13 AM

It's to even out the line-ground capacitance of the phases. It's not used - because it doesn't make any significant difference - on short lines (I don't think it's used at all in the UK), but it's often used on long runs.

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madhu sudhan
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#2

Re: Phase Position Change in HV Transmission Lines

01/08/2012 7:59 AM

If you consider two HV conductors those are separated by air{di-electric medium} ,acting as a capacitor .the capacitance effect form between the conductors & between the conductor and ground

in order to equalize these capacitance and inductances effect ,the three transmission lines must be trasported in such a way that the three lines occupies a position relatively other wires for 1/3 of the total length..from these type of eraction will help to reduce the transmission losses due to line constants capacitance and inducatance
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TonyS
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#3

Re: Phase Position Change in HV Transmission Lines

01/08/2012 9:30 AM

Pulpmillguy, please don't wreck your car or yourself looking for the next transition point as you drive along. (Sorry)

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msamad
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#4

Re: Phase Position Change in HV Transmission Lines

01/08/2012 10:09 AM

This technique of balancing the transmission line impedance is called Transposition of the transmission line.

See this document: http://helios.acomp.usf.edu/~fehr/carson.pdf

- MS

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Pulpmillguy
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#5

Re: Phase Position Change in HV Transmission Lines

01/08/2012 11:24 AM

Thanks guys, I fugured it had to be something like that!

I have been driving past that point for 6 years now and have thought about it every time...I searched around on the web for an answer but never came across anything.

Don't worry Tony, I am usually looking out for the "other guy" as I am driving along...defensive driving is the only way to go!
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electricalexpert65
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#6
In reply to #5

Re: Phase Position Change in HV Transmission Lines

01/09/2012 7:05 AM

Hats off! Mr. Sherlock Holmes! I sincerely appreciate your observation. Even not many electrical engineers observe the phenomenon. I suppose you are not an electrical engineer, but you still have the curiosity to observe the "transposition" of the OH lines and seek clarification. CR4 becomes a better place to stay back, because of people like you inspite of the "king.faisals".

By the by, hope you got your answer from other experts here.
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Phaddy
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#7

Re: Phase Position Change in HV Transmission Lines

01/09/2012 4:42 PM

You see a lot of this in outback Australia, particularly I noticed it in SA, with runs of hundreds of miles.
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Users who posted comments:

electricalexpert65 (1); JohnDG (1); madhu sudhan (1); msamad (1); Phaddy (1); Pulpmillguy (1); TonyS (1)

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