Pylons

[hannahs radios]

Also don't forget the original 132 Kv grid was actually run as seven separate areas with tie lines joining one area to another.

[Synchrodyne]

Presumably the CEGB choice of 275 kV for its mid-1950s “supergrid” was, apart from its being in the “multiple-of-eleven” sequence, a “fit-for-pupose” number given that higher voltages were already in use elsewhere. 220 kV had been used from about 1923, and 287 kV from the mid-1930s (Hoover Dam project, I think). Sweden had adopted 380 kV in 1952, and 345 kV was used in the USA from circa 1953. By then it looks as if the US had moved from multiples of eleven to multiples of 23 voltages. 330 kV was used in Australia (Snowy River project) from the later 1950s.

380 kV looks to be out of sequence, in that the nearest multiple-of-eleven would be 385 kV, halfway between 330 and 440 kV. But then one thinks of 380/220 volt 3-phase, 4-wire distribution systems, so perhaps that’s where the “380” number came from. Sweden already had a 220 kV grid, as far as I know. Anyway, it would seem that the multiple-of-eleven principle could apply – arbitrarily - to either the line-to-line voltage of the line-to-neutral/earth voltage of a 3-phase system.

287 kV fits neither the “eleven” or “23” sequence, but its line-to-earth voltage would be 165 kV, which is in the “eleven” sequence, halfway between 110 and 220 kV.

Of course, this retrospective searching for patterns could be a red herring, in that the voltage numbers wer chosen for completely different reasons, and if they can be fitted into a pattern, that is purely incidental and accidental.

The Swedish 380 kV number was sometimes rounded up to 400 kV. Way back when, I had an early 1960s ASEA brochure that inter alia featured the first 380 kV transmisison line, for which ASEA supplied much of the equipment. Whilst the article itself referred to 380 kV, the overview elsewhere in the brochure mentioned 400 kV. So maybe that’s why 400 kV became a common number.

Cheers,

[russell_w_b]

Originally Posted by Synchrodyne

The Swedish 380 kV number was sometimes rounded up to 400 kV...

Interesting that when the UK 275kV 'Supergrid' was under construction (1954, although the first section between Staythorpe and West Melton was commissioned in July 1953), some of the lines were only to run at 132kV, but '...certain lines were designed for later operation of 380kV, if required...'

No mention of 400kV back then, apart from an allusion to it in the Blaw Knox pylon advert!

[russell_w_b]

I found the following text in the British Engineering Standards Association Report No. 77—'British Standard Electrical Pressures for New Systems and Installations'.

23. British Standard Pressures. In Report No. 77, 1921, the British Engineering Standards Association specifies British standard electrical pressures for new systems and installations as follows:

(a) Direct Current Systems and Installations.
(i) Consumer's pressures.* 220, 440 V.
(ii) Station pressures.242, 484 V.
(b) Alternating Current (B-phase} Systems and Installations.
(i) Consumer's pressures.* 240 V between neutral and principal conductors; 416 V between phases.

*Consumer's pressure' denotes the pressure at the consumer's terminals
declared by the supplier.
Station pressure' denotes the normal pressure applied to the terminals of
the transmission line at the generating station or substation.

EXPLANATION OF ELECTRO-TECHNICAL TERMS
(ii) Station pressures *264 V between neutral and principal conductors ; 457 V between phases.
(c) Extra High Pressures.
(i) Delivered pressures.3 000, 6 000, 10 000, 30 000,
60 000, 100 000, 120 000 V.
(ii) Station pressures *3 300 6 600, 11 000, 33 000,
66 000, 110 000, 132 000 V.

The consumer's or declared pressures are the standard pres-
sures, the station pressure being derived in each case by adding
to the declared pressure the pressure lost (24) in the line when
carrying its full load; unless otherwise specified, this loss shall
be assumed to be such as to give the station pressures shown
above.

Earlier standards of pressure for D.C. and A.C. systems (given
in the third edition of this book, p. 10) will necessarily be repre-
sented in existing installations for many years to come. The
actual consumer's voltages in different supply areas are given in
various annual publications.

Going back to the development of the 275kV 'Supergrid' in the 1950s, it was first considered to use 264kV as a transmission voltage, being twice the existing 132kV. But 275kV was adopted later. I understand the factors (of which there'd be several) in deciding voltages chosen for transmission would be worked out economically on 'Volts per Mile'.

[Synchrodyne]

Thanks very much, that is most interesting.

That set of 1921 numbers consistently shows “station pressures” that are 10% above “consumer’s pressures”. In turn that adds quite a bit of weight to the theory that Edison chose 110 volts for his Pearl Street system in order to provide 100 volts at the customers’ premises, and that that was the origin of the “multiples of eleven” sequence.

Re 275 kV, it is conceivable then that CEGB modelled its initial 264 kV idea and concluded that a slight increase in voltage would be desirable, so went up by 11 kV. But also, it might have been something of a “numbers game”. I imagine that 132 kV originated as a doubling of 66 kV, which in turn was a doubling of 33 kV. But meanwhile a separate sequence had started, with 110 kV followed by 220 kV. Allowing for the 10% “overage”, this put the net voltages in round 100 kV increments. So there may have been an inclination to work in round numbers, if only to maintain a sense of “neatness”. Where required, 50 kV (net) intermediate increments could be used, and for example, 165 kV, although not common, does exist. 275 kV (nominally 250 kV net) is such a number, and it was also close enough to the 264 kV proposal.

I also took another look at the American 287 kV number, as used for the Hoover Dam project. Allowing for very minor rounding, It does actually fit the “multiple-of-23” pattern, as 287.5 kV is in that sequence and halfway between 230 and 345 kV. With 275 kV being halfway between 220 and 330 kV, one might say that the CEGB had an eminent precedent for its choice.

I haven’t found a definitive reason for the American move from multiples-of-eleven to multiples-of-23, though. I assume that it had something to do with greater losses at 60 Hz as compared to 50 Hz, but that remains unconfirmed. On the other hand an American friend who once worked in the utility industry suggested that it was just a case of “pushing the envelope” and taking advantages of the upwards tolerances in insulation capability. On the frequency issue, there is a precedent of railway electrification. The 25 kV voltage common for 50 Hz single-phase systems was arrived at to equalize the percentage voltage drop in feeders with that obtained in 15 kV, 16⅔ Hz systems. This required sqrt3 times the voltage, namely 26 kV, and this was rounded down to 25 kV, either for “neatness” or as suggested earlier, because 25 kV was the line-to-neutral voltage of a 44 kV three-phase system. Still, the fact that 25 kV is also used for 60 Hz railway systems suggests that the feeder loss difference between 50 and 60 Hz was not a big issue.

Re 400 kV, the CEGB case, with some 275 kV lines planned as being upgradable to 380 kV, but Blaw-Knox mentioning 400 kV, coupled with the ASEA example, suggests that 400 kV was in fact arrived at simply by upward rounding of 380 kV. And that by this time, the 10% overage was no longer factored into “new” voltages.

Cheers,

[russell_w_b]

Would this notion of 'rounding' and 'neatness' explain why European harmonisation of UK voltages changed a hitherto decent 415 / 240V LV system into a 400 / 230V one, with its increased I^2R losses inherent in lower distribution voltage?

To be fair, some 1950s electrical textbooks I have also refer to 230V, so there has been some tinkering since then. But I notice *they* didn't adopt *our* voltages! In reality, the supply tolerances mean nothing much has changed. I'm still on 239/240V here, out in the sticks, a half-mile from the 33kV / 11kV local substation to which I am connected by around a mile of open-wire pole-mounted conductors.

[russell_w_b]

You mention 16 2/3 Hz as a working frequency (early electric railways used this frequency, I believe). Would this, perchance, be the origin of the frequency of telephone magneto ringing voltage: on the railway, powered by such a supply?

I can't believe a conscious decision was ever made to wantonly separate an a.c. telephone signalling frequency from an electrical power frequency for the hell of it?

[Synchrodyne]

Well, I don’t know.

The 16⅔ Hz number came about because it made for easy conversion from 50 Hz, using directly-coupled motor-alternators. Originally Behn-Eschenburg, who had done the essential development work on the single-phase series traction motor, chose 15 Hz as the optimum frequency. I imagine that it was seen as low enough to minimize transformer EMF effects in the motors but not so low that stepdown transformers became impossibly big and heavy for use on-board locomotives. There was some initial electrification at 15 kV, 15 Hz in Switzerland, but 15 kV, 16⅔ Hz soon became the standard. But there was prior use of 16⅔ Hz for early three-phase railway electrifications.

In the telephone case, would 16⅔ Hz have been used because it was a submultiple of 50 Hz, and so convenient to generate where 50 Hz supplies were available? I have a vague notion that in the USA, 20 Hz was used for telephone ringers, this being a subharmonic of 60 Hz.

I don’t think that 16⅔ Hz was ever used for railway electrification in the UK. There were a couple of 6.6 kV, 25 Hz single-phase systems, one in the south and the other in the northwest, I suspect inspired by American practice, where, because 25 Hz was an established industrial frequency (dating from Niagara Falls hydro), and also used to supply the rotary converters of DC traction systems, it was also used out of convenience for single-phase railways, even though it was higher than preferable for single-phase series motors.

So maybe the telephone folks arrived at 16⅔ Hz independently of railway practice, but for the same subharmonic reason.

Cheers,

[Hampus]

Sweden and several other european countries still use 15KV 2/3 hertz for their railways. In sweden this power is obtained with rotary converters but e.g. norway have dedicated powerplants that generate this.

To not drift away too much of topic I here post a picture of the railways power line alongside the ordinary 50hz lines.

[cheerfulcharlie]

Originally Posted by russell_w_b

Here are a couple of adverts from 1954, ahead of the construction of the new 275kV 'Super Grid'.

Wonderful stuff! thank you.

I suppose the ones I used to see in the woods as a boy with a rusty 'warning 132KV' sign on were perhaps some of the oldest ones predating the super grid construction?
Another surprise to me was the weight of an insulator- apparently over a 1000 ibs - blimey! that is around the weight of two 6 cylinder car engines.

Blaw Knox seemed to be one of those "what do you want and we will make it for you" type companies....whatever the years have proved the quality of their 'widgets'.

[russell_w_b]

Originally Posted by cheerfulcharlie

Blaw Knox seemed to be one of those "what do you want and we will make it for you" type companies....whatever the years have proved the quality of their 'widgets'.

Blaw-Knox made radio towers too, including the MF European Service aerial at Droitwich (later used as a reserve aerial) and the beautifully-styled MF mast at BBC Lisnagarvey.

They seemed to have fingers in quite a few pies!

[pmmunro]

On a walk taking in a hydro-electric dam just upstream on the Donau (Danube) from Ingolsadt last year, I noticed that the power lines leaving the transformer compound didn't look right. There were two pairs of overhead lines rather than groups of three. The generating station was out of use at the time and the dam was spilling spectacularly causing widespread foaming still clearly visible in the town about a kilometre downstream - investigating the cause was one reason for the walk.

Only afterwards did it occur to me that it was a 16 2/3 Hz system. On a return visit last month, the station was back in action and there are signs posted by Eon stating that the power is for DB. I didn't hear the characteristic transformer hum, so perhaps there is much less, or it is inaudible at such a low frequency.

This article https://en.m.wikipedia.org/wiki/15_k...lectrification explains that the frequency was originally chosen to minimise inductive reactive effects and pole piece eddy currents in traction motors.

PMM

[Tim]

It's a shame about 'pylon of the month'

Cor, look at the insulators on that!

[glowinganode]

Originally Posted by russell_w_b

I found the following text in the British Engineering Standards Association Report No. 77—'British Standard Electrical Pressures for New Systems and Installations'.

Hi Russell, very interesting, thanks for sharing this supporting evidence. Would it be possible to scan and publish the whole article?

Many thanks, Rob.

[russell_w_b]

It's on t'internet, Rob. I should've put the link in, but auntie Google will know.

[glowinganode]

Ok, thanks.

[russell_w_b]

Originally Posted by Hampus

Sweden and several other european countries still use 15KV 2/3 hertz for their railways.

When I was there last September I noticed the railway alongside the E20 had what looked like a 3-phase supply 'piggy-backed' on top of the railway catenary infrastructure. I wished I'd been mindful of the low frequency stuff, though.

Attached is a photo of the aforementioned structure, and three other pylon shots along the E22, two of which look like 275kV transmission lines. Nice towers!

[broadgage]

Originally Posted by hannahs radios

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.

To be strictly correct, I am not aware of the National grid being at "breaking point".
Whilst the popular press regularly make such statements, it would be more accurate to state that concerns exist regarding potentially insufficient generating capacity to meet peak demands.
There is no general problem regarding TRANSMISSION capacity, but there are undoubtedly concerns about GENERATING capacity.

I would agree that an HV transmission route would not be taken out of use without good reason.
As has already been suggested, it is likely that the dismantled route served a now closed power station, or it might perhaps have been superseded by an alternative route.
Replacement by underground cable is possible but less likely, due to the vast cost of buried HV cables.

[hannahs radios]

Hi broadgage you are correct. It's a lack of generating capacity at peak times that's the major problem. However I understand that certain sections of the grid are running at full amperage with little headroom to spare. As you say sometimes the lay press get it wrong.

[Radio Wrangler]

Someone posted this link a year or so ago and I've found it fascinating to keep it on the favourites bar of my computers:

http://www.gridwatch.templar.co.uk

It surprised me how little hydro contributes.

David