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#119212 - 12/10/04 09:28 PM Transposition Pole - Again...
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Transposition Pole - Again...

Hello all;

Here are a few shots of a Transmission Pole with Transpositions on it.

Two individual 3Ø Circuits, Voltage is like 138 KV (???).

Images shot in North Hollywood / Sun Valley, and these Circuits may be for City of Glendale DWP - if not, then would be LADWP's stuff.

These Circuits are "Rolling Away From Each Other" - whereas the previously posted image shows both Circuits "Rolling At Each Other" on the 66 KV Pole.

The Circuit on the Left-Hand side "Rolls" from "Top To Bottom" (Phase at the uppermost part is brought down to the lowermost position, and remaining two Phases move upwards in position).

The Circuit on the Right-Hand side "Rolls" the opposite way - from "Bottom To Top".

Images below---



Image #1: Distant Overview shot of Transposition Pole



Image #2: Cropped close-up from above Image (Image #1)



Image #3: Sort-Of in front of the Pole shot...



Image #4: Cropped close-up from above Image (Image #3)

I will try for better view(s) next week!

Scott35

Edited to fix UBB / HTML tagging "Suck Script" problem
(forgot a "/" slash in a tag - which resulted in "Suck-Script")

[This message has been edited by Scott35 (edited 12-11-2004).]
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#119213 - 12/15/04 03:40 PM Re: Transposition Pole - Again...
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Here are a few more shots of the same Transposition Pole, taken from the Fuel Station this time
(instead of doing a "Drive-By Shooting" ...)









Any comments???

Scott35
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Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#119214 - 12/16/04 03:45 PM Re: Transposition Pole - Again...
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
 
The need for line transpositions seems to be a bit subtle. First, HV circuits generally differ from LV circuits in that the source and load impedances are much closer together—there is less of a gap between the two. Ideally, the perfect electrical source will not result in lower voltage during a short circuit, and the perfect load will not cause voltage drop when connected.

Increased source impedance means that, comparatively, less current will flow when the source is shorted out. Decreased load impedance will cause greater voltage drop when connected or ‘switched on’.

[Positive- and negative-sequence components in power systems correspond to phase-to-phase balanced and unbalanced conditions, where zero-sequence components relate to phase-to-ground characteristics.]

The idea is that 3-phase systems work most efficiently when everything is most closely balanced or symmetrical—especially voltages, currents and impedances. That applies to phase-to-phase characteristics as well and phase-to-ground or circuit-to-adjacent-circuit in the case of side-by-side [2-circuit] lines.

Another very critical situation is for protective relaying to be able to differentiate between faulted and unfaulted conditions on 100-mile circuits. The further a fault gets from the breaker and relaying point, the more difficult it is to differentiate it from simple load imbalance. The interconnected everything in recent power systems does not help the issue at all—except make it all more interesting and get increasingly fun toys to fight the battle.

Schematically, line transpositions are illustrated as…




See http://www.gorge.org/pylons/faq.shtml#designer

   Scroll down to: “Transposition Tower”

”Each pylon carries lines in a multiple of three - usually 3 or 6 lines per pylon. In each set of three, one wire will be for each phase. Ideally, the capacitance of each line should be the same. However, the different heights at which each line is carried means there is a small difference in length between them. For short distances, the difference is tiny and can be discounted. However in areas where the lines run for hundreds of miles, such as across Africa or Continental Europe, these differences between the sets of wires can be enough to cause problems. So a transposition tower is used to swap the electricity from one line onto another, in order that over the entire line, the capacitance of each line will be more-or-less the same.”




[This message has been edited by Bjarney (edited 12-16-2004).]

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#119215 - 12/17/04 06:30 PM Re: Transposition Pole - Again...
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Scott (Bjarney);

Thanks for posting this information!!!

Scott35
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Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#119216 - 12/18/04 09:23 PM Re: Transposition Pole - Again...
DougW Offline
Member

Registered: 06/08/03
Posts: 1083
Loc: North Chicago, IL
Thanks for the explanation, bjarnery! I was getting confused...

It's things like these that make me realize that there's a big difference between linemen and electricians.

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#119217 - 12/19/04 09:03 PM Re: Transposition Pole - Again...
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Bjarney,
That's a really cool explanation!.
BTW, is the top set of two wires on the pylon, to shield the pylon from lightning?.
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#119218 - 12/20/04 08:25 AM Re: Transposition Pole - Again...
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
 
Here is a modified sketch to illustrate coupling between each phase and “ground” and shield wires {added fat and skinny green lines.}



It’s kind of convoluted in a 2-D drawing, for everything’s flattened out, but the idea behind line transposition is to ‘even out’ {mainly capacitive} coupling between each phase and ground/grounded-shield wires.

Trumpy, you are right about the grounded overhead shield wires, Their use and effectiveness tend to be localized based on expected lightning incidence.




[This message has been edited by Bjarney (edited 12-22-2004).]

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