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Old 21st Oct 2015, 11:35 pm   #81
hannahs radios
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Default Re: Pylons

With regards to names, to most I think metal towers are pylons regardless of their use. In my day we used to call our local TV relay a pylon. I called it the TV tower. Older people call any wooden pole a telegraph pole regardless of what's on it.
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Old 11th Nov 2015, 12:52 am   #82
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Sad to report that in my now frequent trips down the M1 I have come across several dead pylons lying in a field next to the new 11- A?? junction which is being constructed....I think. Although you can now see they were very old and weathered these poor beasts retained their dignity when they were brought down as they remained in one piece with just a little distortion at the top as that hit the deck first with the weight behind it.
There does not appear to be a new route for the cable,,or perhaps that will come later?..fascinating then if they can just take this route out of service and think about another one later.
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Old 11th Nov 2015, 12:09 pm   #83
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Default Re: Pylons

Perhaps they have fitted an underground cable across the new junction.
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Old 11th Nov 2015, 3:45 pm   #84
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I wish I could find a photo of a rather nice piece of machinery I used to regularly see when I worked for the CEGB. It was an all-wheel-drive HGV sized vehicle for planting poles (power line) with drill, crane and room for half a dozen or so poles - known, IIRC, as the "pole cat". Never did see it in action and was not allowed to take it for a spin

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Old 11th Nov 2015, 8:53 pm   #85
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I would think they've already got an alternative circuit in place I can't imagine they would just be able to take an HV line out of commission and not have something to take its place. After all we are told the grid's at breaking point as it is.
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Old 13th Nov 2015, 1:37 am   #86
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Underground cables carrying a 100K volts and more -another fascinating subject- I mean crikey the insulation involved, the fields that might be produced and of course the prevention of something like a digger breaking into them.
I can only really observe when the traffic grinds to a halt but cannot see any new overhead alternative circuit running parallel to the construction.

I suppose they will need some sort of huge powered reel to pick up the cable?....unless the travellers get there first
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Old 13th Nov 2015, 1:50 am   #87
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Default Re: Pylons

Probably just an old redundant route, or a power station closure. There must have been many changes to the grid since it's construction.
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Old 13th Nov 2015, 2:52 am   #88
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Interesting about HV and EHV transmission line voltages is that many are in multiples of eleven, e.g. 11, 33, 66, 110, 132, 220 and 330 kV. This seems to go back to the very early days. I imagine that it could have derived from Edison’s original 110-volt DC distribution system, which number was apparently chosen so that allowing for line losses, it delivered around 100 volts at destination, considered to be the optimum number for the incandescent light bulbs of the time.

Those multiples of eleven largely have been retained in 50 Hz systems, but in the USA and elsewhere, 60 Hz systems have moved to somewhat higher voltages that are multiples of 23, such as 13.8, 69, 138, 230 and 345 kV.

Above the 330/345 kV level, though, multiples of 11/23 seem to have been abandoned, with “round” numbers adopted such as 400 and 500 kV.

Quote:
Originally Posted by Ed_Dinning View Post
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.
Autotransformer feeding for single-phase railway systems appears to have become quite common in the last several decades, overshadowing the booster transformer system used in older European electrifications. In this the catenary is one “line” of a three-wire system, say 25-0-25 kV, arranged so that most of the “return” current goes via the other “line”, and not by earth. That said, I was surprised to see that the recent Auckland suburban electrification uses a simple feeding system with earth return; there is very heavy earth bonding of all nearby conducting structures, such as safety fences.

The 25 kV that is the worldwide norm for industrial frequency single-phase railway electrifications does actually fit the multiple of eleven scheme. It is the line-to-neutral voltage of a 44 kV (line-to-line) three-phase system. Hence the common use of 3-bell and 4-bell insulators.

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Old 13th Nov 2015, 8:07 am   #89
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Default Re: Pylons

Maybe it's all just evidence of a preference for integer turns ratios in transformers?

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Old 14th Nov 2015, 10:16 am   #90
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Our young son was fascinated by the pylons on the continent in the '70s, in Belgium and Holland they were all painted in two or more colours, didn't stop talking about them for weeks.

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Old 14th Nov 2015, 12:16 pm   #91
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Re #88, the "Odd Voltages" question, and some explanations, were discussed in the pages of "Wireless World" in 1943. Page 274 of the Sept 1943 attached. Sept 1943 is the earliest issue I have, so I don't know what was mentioned in the previous discussion by "Diallist" that is referred to.
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Old 14th Nov 2015, 12:49 pm   #92
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What a fascinating piece, and a plausible explanation of the 240V standard as well as the multiples of 11.
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Old 14th Nov 2015, 8:58 pm   #93
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Speaking of standard voltages can someone please tell me what is the phase to earth voltage for 275 Kv and 132 Kv lines? I can't work it out.

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Old 15th Nov 2015, 11:42 am   #94
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158.77kV and 76.21kV. 1/sqrt3 x line voltage if there is a centre-connected star point.
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Old 15th Nov 2015, 8:55 pm   #95
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Thank you Russell. I find maths really hard, it's easier to just ask.
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Old 15th Nov 2015, 11:57 pm   #96
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Default Re: Pylons

The line running to the east of the M1 around junction 10 has been subject to re-routing for the last few years due to widening of the carriage way and junction alterations.
For a long time local earths and were applied and gaps left every km or so, so obviously not in service for a good while. The northern end goes to the large OLE sub-station at Toddington. At the southern end two circuits were split and terminated to 2 (very tall!) wooden posts.
I too spend a long time on the M1 sitting in traffic.

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Old 15th Nov 2015, 11:58 pm   #97
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Default Re: Pylons

You're welcome. It's just the same as 415V / 240V 3-phase / single phase relationship. Because the three phases are 120 degrees apart, the addition of two of them form a triangle that itself consists of two right-angle triangles back-to-back. From then it's a bit of trigonometry to find the resultant value. 2 x the cosine of 30 degrees happens to equal the square root of three.

It's easier to visualise if you draw a phasor diagram. If you want to study further, get hold of a copy of Hughes' 'Electrical Technology' or the 1938 Admiralty Handbook of Wireless Telegraphy (often found in charity shops) or similar. They give a good, straightforward grounding in polyphase circuits, both mathematically and vectorially.
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Old 18th Nov 2015, 6:46 am   #98
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Default Re: Pylons

Quote:
Originally Posted by emeritus View Post
Re #88, the "Odd Voltages" question, and some explanations, were discussed in the pages of "Wireless World" in 1943. Page 274 of the Sept 1943 attached. Sept 1943 is the earliest issue I have, so I don't know what was mentioned in the previous discussion by "Diallist" that is referred to.
That explanation is certainly plausible, but I think not yet definitive.

The era of commercial electricity reticulation is generally viewed as having begun in 1882 September with the opening of Edison’s Pearl Street generating station in New York. That was about the time that the volt was defined. So did Edison choose 110 volts per se, or had he based his voltage on 100 Daniell cells. I imagine that the answer would be buried somewhere in whatever papers Edison left behind.

I doubt that Edison would have had any voltage tolerance regulations to contend with at that time. The ±2 percent number mentioned in the WW article, appears to be of UK origin, and might not have had any connection with or any bearing on events in the USA. On the other hand, Edison would have been concerned with providing his customers with satisfactory lighting that did all that was claimed for it and was generally better than gas lighting. So the voltage drop at the end of the reticulation system would have been of concern. A voltage 10% below nominal meant an energy output drop of close to 20%. And the resultant lower filament temperature would result in red shift that moved some of the energy out of the visible spectrum and into the infrared, so perceptually the difference might have been more than the numbers suggest. So the 10% overvoltage theory still has some traction.

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Old 18th Nov 2015, 11:55 am   #99
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As a matter of interest regarding the National Grid, its existence goes back the thirties in this country, it was then at 132kv, in the mid fifties the 275kv was introduced, this usually has two conductors per phase and then in the late sixties the 400kv system came along and usually had four conductors per phase.
Because the 400kv system was relatively lightly loaded in its early existence we had to carry out MVAR absorbstion and run our generators at about 10Mw during the night when the system was lightly loaded this was due to the high capacitance which existed on the lines at the time.
Hope this is of interest?
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Old 18th Nov 2015, 4:57 pm   #100
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Here are a couple of adverts from 1954, ahead of the construction of the new 275kV 'Super Grid'.
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