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Old 19th Oct 2015, 8:13 pm   #61
ms660
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Default Re: Pylons

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Originally Posted by Radio Wrangler View Post
The process of wrapping a wire back around itself, I think, is called 'serving' for thread, it's called 'whipping'
Slightly off topic so I'll keep it short.

In a past life I was the sawyer at one of our local tin mines, in the tool box in the sawmill was a serving mallett and a marlin spike, it was for the winch rope that pulled the logs into the saw blade, the saw being of the drag feed type, I never did get to use them.

Lawrence.
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Old 19th Oct 2015, 8:16 pm   #62
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Default Re: Pylons

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Originally Posted by russell_w_b View Post
Are you sure that's not a cable repair? The procedure is to wrap overound spirals of wire onto the conductors to strengthen chafing and damage, using a thing called a 'Parrot's Beak'.
No - these are separate free and non-current-carrying overwinds of around 10 turns of cable placed round the actual conductors - each overwind is fitted around a metre from the insulators on the poles.

[Photos will follow to illustrate: it's night here now!]
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Old 19th Oct 2015, 8:29 pm   #63
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Default Re: Pylons

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No - these are separate free and non-current-carrying overwinds of around 10 turns of cable placed round the actual conductors - each overwind is fitted around a metre from the insulators on the poles.
I've got you... I had a google. It'll be good to see a pic though: never seen one of those!
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Old 20th Oct 2015, 10:26 am   #64
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Default Re: Pylons

Here's a photo taken on this morning's dog-walk showing the kind of spiral overwinds I was describing.

They seem tightly wound to the cables (which are plastic-sheathed) at the ends closes t to the insulators, but loosely wound at theor outer ends.

Note also the *very* small insulators they are using - this is a 11Kv line! Concerned about the possibility of leakage across the insulators causing RF interference I asked the riggers nabout the smallness of the insulators when they were doing the replacement a couple of years back - seems these modern insulators have a higher creep-resistance than the old ceramic type.

The line photographed is a feed to a healthcare residential/assessment centre from my local substation. The transformer on the end is rather impressively rated!
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Old 20th Oct 2015, 10:36 am   #65
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Default Re: Pylons

On a hot summer's day that's a lot of near boiling oil
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Old 20th Oct 2015, 10:44 am   #66
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Default Re: Pylons

Indeed! I just hope the fans on the cooling radiators don't fail.

Here's a photo of one of the 33Kv 3-phase pylons that feeds the substation. This is the line that heads off towards Avebury. This one uses the more-traditional big brown ceramic insulators.
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Old 20th Oct 2015, 5:06 pm   #67
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Default Re: Pylons

I've seen those wire wraps on lines near here I never really thought about them too much just assumed they were to do with holding the conductor to the insulator ah well you learn something new every day. I rememberseing what looked like a large tape joint in the neutral on a 3 phase 415 volt line and something similar on an 11Kv line could these be repairs to damaged lines?
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Old 20th Oct 2015, 5:19 pm   #68
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Default Re: Pylons

Hi Gents, the spirals look like "Stocksbridge dampers" that are fitted near the insulators to stop the conductors galloping in a wind and possibly clashing. On higher voltage lines these are dumbbell shaped.
Modern insulators are often resin types with much improved properties inclusing reduced weight.

On the earlier topic of multiple conductors, it was usual on 275KV (2 conductors) and 400Kv (4 conductors). These both reduced the wind resistance and corona loss as the "bundle" had a larger effective diameter than each wire. Very common now to see the trefoil arrangement.
The spacers were usually fitted by the apprentice being dragged along on a sledge on the conductors.

Surprising the number of interesting things that can be seen associated with HV lines.
You will also see lines with big insulator strings but long arc horns fitted over them. These are usually towers strung for 400KV, but run at 275KV

There are some strange towers on the continent, these appear to be wired for 4 phase. It is not an insulated neutral, but separate insulated supplies (no neutral) for traction supplies.
This is derived from a special transformer so that the normal single phase 25kv traction supply draws power from all 3 phases and does not unbalance the supply. It is normally derived from a transformer that appears to have too many porcelains!

Ed
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Old 20th Oct 2015, 7:53 pm   #69
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Default Re: Pylons

Hi Ed is that what they call a Scott transformer?? Also at the Austrian Italian border I saw pylons with 2 wires perhaps HV DC??
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Old 20th Oct 2015, 8:52 pm   #70
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Default Re: Pylons

For amusement, here's a shot of another "business end" of the 33Kv line previously mentioned - this is at a point where the line takes a slight [15 degree, though not obvious in the photo] deviation-from-straight, so each side is tensioned to the pole separately and there's a lateral strainer-wire [complete with two insulators which are house-brick-sized versions of the 'egg' insulators as used on long-wire receiving aerials in times past] off to one side to take the asymmetric load on the poles.

Again, it has traditional big ceramic insulators.

One thing that seems spectacularly inconsistent with these kind of poles is whether the bridge-wire between the two sides is underslung or runs above with a separate supporting insulator. Here we see two underslung and one over-the-top! is there a standard for this, or does it depend on what the riggers happened to have in the back of their truck at the time??
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Old 20th Oct 2015, 9:07 pm   #71
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Default Re: Pylons

The over slung cable is there to keep the cable away from the tensioner wire so that it does not short out if the wind blows it about in a storm.
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Old 20th Oct 2015, 10:57 pm   #72
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Default Re: Pylons

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Originally Posted by hannahs radios View Post
Hi Ed is that what they call a Scott transformer??
It might be. The first attachment shows an example as to how Scott transformers were used for single-phase railway feeding.

Quote:
Originally Posted by hannahs radios View Post
Also at the Austrian Italian border I saw pylons with 2 wires perhaps HV DC??
At a border, HVDC seems likely. The 2nd and 3rd attachments show examples of HVDC towers.

But two-line towers could also indicate low-frequency single-phase railway supplies. Austria, Germany and Switzerland all use 15 kV, 16⅔ Hz single-phase, and Switzerland at least has an extensive supply grid using I think 132, 66 and 33 kV single-phase lines, some single-circuit and some multiple-circuit. I think that it has a single-phase grid link with Germany, and also takes (or at least in the past took) single-phase power from a generating station across the border in Italy. Unfortunately I can’t find a picture of a single-phase tower.

Pertinent in this forum, back in the mid-1970s I visited Mangahao power station, a very old (1924) and very small (19 MW) hydro station in the Manawatu, near Shannon, and tied into the 110 kV grid network. The engineers there told me that they used the 110 kV lines as their (AM) radio aerial, and got very good reception. No details of the connection were provided, though – “proprietary” information. The location was nominally within the 66 dBV contour for the Wellington regional radio transmitters, but in a poor earth conductivity area that degraded reception (the same was evidently true for Palmerston North city). So some ingenuity was needed to improve reception of these, and also to be able to receive the Wellington locals. Power station engineers and operators often had interesting stories to tell. In the early 1970s, the guys at Tuai (part of the Waikaremoana hydro scheme) told me that the 110 kV lines through the Urewera back country were often tripped out because large shags rested at the ends of the tower cross-arms, and often jettisoned directly on to the insulators as they took off, causing flashovers.

Cheers,
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Old 20th Oct 2015, 11:45 pm   #73
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Default Re: Pylons

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Originally Posted by hannahs radios View Post
Hi Ed is that what they call a Scott transformer?? Also at the Austrian Italian border I saw pylons with 2 wires perhaps HV DC??
Scott does 3-phase 120deg to 2-phase 90deg not single phase. However, those odd transformers may still be Scott types. There's some discussion about traction supplies in this Wiki entry:

https://en.m.wikipedia.org/wiki/Scott-T_transformer
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Old 21st Oct 2015, 12:37 am   #74
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Default Re: Pylons

The rationale for the use of Scott (three phase-to-two-phase) transformers to feed single-phase railway systems was that the two phases on the output side could be used respectively to supply adjacent sections of line. Imbalance of current demand between the two sections would still result in imbalance on the three-phase system, but less so than in the case of V-connected feeders.

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Old 21st Oct 2015, 12:49 am   #75
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Default Re: Pylons

It would appear from the attached excerpt that the term “pylon” was a rather grandiose name for transmission towers, adopted by the UK CEB in the 1920s. It is used here in NZ, although I think less so today than back in the 1950s and 1960s, and I also heard it used in Australia and South Africa, but not in the USA, where “pylon” would likely be interpreted as something that supports a bridge or perhaps something that old airplanes race around. In NZ usage, it seemed to be applied to steel lattice towers and not to the wooden poles that were often used for single-circuit 110 kV and 50 kV lines.

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Old 21st Oct 2015, 1:12 am   #76
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That picture looks like what I saw in Italy Austria border area there was also 2 or3 conventional AC lines probably 110 and 220 Kv though not sure about the voltages used. Interesting about NZ engineers using power lines as an aerial I'm surprised the QRM from them did t ruin reception
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Old 21st Oct 2015, 1:27 am   #77
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Default Re: Pylons

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In NZ usage, it seemed to be applied to steel lattice towers and not to the wooden poles that were often used for single-circuit 110 kV and 50 kV lines.
Pylon here generally refers to the big steel things used for the national grid. The wooden structures are generally referred to as 'poles' even if they have several vertical components. The terminology within the supply industry may well be different of course.
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Old 21st Oct 2015, 8:13 am   #78
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Default Re: Pylons

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The terminology within the supply industry may well be different of course.
I've heard 'towers' being bandied about quite a bit, as well as pylons. But poles are poles.
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Old 21st Oct 2015, 5:33 pm   #79
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Default Re: Pylons

Hi Folks, Scott connection is a 3 to 2 phase conversion system as has been said. Often used by test houses to get phase and quadrature signals to drive test bridges.

One of the problems with traction supplies is that they often wind up driving DC motors, implying rectification. This is now not liked by supply authorities as it distorts the power factor of the supply and can introduce harmonics.

Simplistically speaking the rectifier takes a "bite" out of the current waveform near the peak of the voltage wave and not at lower phase angles. this leads to waveform distortion which manifests itself as a poor power factor.

In modern industrial power supplies, on a 3 phase network, there is often conversion to 18 phase or more by a transformer. If the current "bites" are then evenly spaced on the 18 phases it produces a much better "power factor" on the basic 3 phase supply.

I believe this is being used in traction supplies these days. They are often in the 10 to 25KV range at the railway, but as large power users they have their own distribution network at up to 132kv. The conversion to single phase is done at various voltage levels and is normally a both poles insulated supply (which may have a centre point earthed for system insulation level purposes). This only becomes a single phase earthed supply when it reaches traction supply voltage levels.

The maths for this lot gets quite interesting!!!


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Old 21st Oct 2015, 6:44 pm   #80
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Default Re: Pylons

The Marconi B6122 / BD272 HF 250kW transmitters used Scott transformers to get two phases in quadrature from the 3-phase supply, for the valve filaments. This minimised noise. There was an autotransformer configuration or an isolation transformer configuration. √(3/2) comes to mind somewhere...

12-phase rectification was also employed for the main 11kV HT d.c. supply, with two rectifier transformers and staggered phasing.

Nomenclature: The structures upon which high-voltage cables are suspended are referred to as 'towers' in the NWEB (now ENWL) HV Rules.
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