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Joined: Oct 2000
Posts: 2,721
Scott35 Offline OP
Broom Pusher and
Member
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---

[Linked Image]

Image #1: Distant Overview shot of Transposition Pole

[Linked Image]

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

[Linked Image]

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

[Linked Image]

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).]


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Oct 2000
Posts: 2,721
Scott35 Offline OP
Broom Pusher and
Member
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" [Linked Image] [Linked Image] ...)

[Linked Image]


[Linked Image]


[Linked Image]

Any comments??? [Linked Image]

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Apr 2002
Posts: 2,527
B
Moderator
 
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…

[Linked Image from 6l6.net]


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).]

Joined: Oct 2000
Posts: 2,721
Scott35 Offline OP
Broom Pusher and
Member
Scott (Bjarney);

Thanks for posting this information!!! [Linked Image]

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jun 2003
Posts: 1,143
D
Member
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.

Joined: Jul 2002
Posts: 8,407
Member
Bjarney,
That's a really cool explanation!. [Linked Image]
BTW, is the top set of two wires on the pylon, to shield the pylon from lightning?.

Joined: Apr 2002
Posts: 2,527
B
Moderator
 
Here is a modified sketch to illustrate coupling between each phase and “ground” and shield wires {added fat and skinny green lines.}

[Linked Image from 6l6.net]

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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