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Old 20th Sep 2018, 2:47 pm   #61
broadgage
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Default Re: Last public DC mains supply in the UK?

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Originally Posted by Richard_FM View Post
It's always interesting to learn about non-standard electricity supplies.
Yes, and they are getting less common "every opportunity should be taken to replace legacy systems with standard 3 phase, 4 wire, at 230/400 volts"

"no significant expansion of legacy systems is permitted"

The main drawbacks of such systems is the risk of a relatively prolonged outage in the event of a transformer failure.
The failure of a "conventional" substation transformer is normally handled by backfeeding at LV from adjacent mains on different transformers.
This can be done within an hour by two men in a van inserting fuses or links into street link boxes.
If this can't be done, then a large transportable generator may be connected to the LV busbars in the substation. This can usually be done within three hours.

The odd legacy systems can't be paralleled, nor supplied from a large generator. The supply would remain off until the new transformer was delivered. A small stock is kept of both reverse polarity and diametric transformers. But transport from a distant stores department and crane hire is unlikely to be achieved in less than 12 hours.
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Old 20th Sep 2018, 6:19 pm   #62
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Default Re: Last public DC mains supply in the UK?

A bit off topic. When I worked for BR in 1950's they had a large warehouse with 3 wire DC. 460 volts for the motors and for the lighting 230 volts positive to neutral or negative to neutral. All supplied from two transformers and two large mercury arc rectifiers. The line shafting motors were open brush gear type with oil rings for lubrication and I think made by Siemens dated about 1910.I can't ever remember the commutators needing skimming, the motors just purred away.Originally the local power station supplied the DC. Oh, I forgot the Face plate starters. I didn't know about the reverse connected transformer, very interesting. Ted
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Old 20th Sep 2018, 8:58 pm   #63
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Default Re: Last public DC mains supply in the UK?

broadgage thanks for the explanation of the system used, as I said I couldn't remember the details but did remember about the two transformers used. My mate told me that in summer the voltage can be up to 260 volts and in the winter down to 220. I think the voltage regulation's not too good.
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Old 21st Sep 2018, 3:44 am   #64
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Default Re: Last public DC mains supply in the UK?

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Thanks for informative post and supporting literature Steve! So basically with the series-wound DC motors, auxiliary coils were completely necessary for regenerative braking. Makes sense!
No problem, but I suspect that in what I said I sacrificed precision for concision. In the railway case, separate excitation of series-wound motors for electric braking purposes was achieved by using the existing series field for this purpose, power-brake changeover switches (somewhat like reverser switches) being used to separate the field circuits from the armature circuits. Additional field coils were rare in railway DC traction motors.

More generally, re the use of existent DC three-wire distribution systems for AC, I imagine that this could explain the origins of the standard American three-wire system of single-phase AC distribution. I suppose that one probably inadvertent benefit of the three-wire system would be that, assuming a statistical distribution of appliances on each side, there would be much reduced net DC on the transformers secondaries from the use of AC-DC radio and TV receivers.

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Old 21st Sep 2018, 4:44 am   #65
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Default Re: Last public DC mains supply in the UK?

The list of UK electrical supply voltages, etc., at the rear of the Electrical Engineer’s Reference Book ninth edition, 1958 shows some locations as also having some two-phase distribution. Exeter was one example. Possibly this came about through re-use of existing three-wire DC distribution systems. In that case the neutral (common) would have been nominally undersized, although perhaps considered satisfactory for typical loads. Conversion from 3- to 2-phase was easily done with Scott tee-connected transformers.

By way of broad comparison , here in New Zealand, standardization of electrical distribution came quite early, with most conversions (from DC and non-standard AC) done in the 1920s and 1930s. But some DC systems lasted until after WWII.

The decision to standardize on 50 Hz, 3-phase, 4-wire, multiple-earth-neutral (MEN) type distribution was made in 1920. Part of the MEN system was that at each consumer switchbox, the neutral was bonded to local earth by the MEN link, so I think we avoided some of the earthing issues that have cropped up elsewhere about differences between local earth and supply earth. Shortly after that decision, the voltage was standardized at 230/400 volts. There was also early use of 11 kV for primary distribution; for example Christchurch started building a city-wide underground 11 kV network in 1913. There was also early use of direct transformation from 11 kV to 230/400 volts, without an intermediate 3.3 or 6.6 kV step. A very early such installation by Lloyd Mandeno (later of SWER fame) would have run fairly close by to where this is being written.

Even so, special-purpose DC systems were retained in Christchurch and Wellington additional to the standard AC systems until the later 1950s. These were said to be for applications such as elevators and dentist drills. Auckland though had a fairly extensive inner city DC system, 3-wire 230/460 volts. Conversion had not been completed before WWII, and something around 100 route miles still remained, with slow progress resumed after WWII. The work was finally completed in the late 1950s. Whether the three-wire distribution system was re-used for AC I don’t know. (This kind of information is not so easy to find.) There were some cases of 230/460 volt three-wire single-phase distribution in rural areas, but these were at the end of two-wire 11 kV single-phase or SWER spurs.

Notwithstanding the survival of the Auckland DC system into the 1950s, I have not found any evidence that the local setmakers offered AC-DC type radio receivers for use in the DC area in this period. Their products of this period seem to have been AC-only, and were fitted with 3-core power leads, i.e. true Class I by later terminology. Perhaps those living in the DC area used battery receivers. Post-WWII, the DC system had a known limited life, with progressive diminution, so production of special appliances was probably seen as something best avoided. Whether live chassis AC-DC equipment would have met the safety regulations of the time is debatable, and the supply authorities didn’t like them anyway, so they would not have been keen on any such receivers being retained in use after conversion to AC.


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Old 21st Sep 2018, 1:18 pm   #66
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Default Re: Last public DC mains supply in the UK?

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According to the Ian Allan "British Rail Handbook" for 1981, the Class 76 locos for the 1500VDC Manchester - Sheffield - Wath services had regenerative braking. It says " These locomotives were fitted from the first for regenerative braking, and the driver had to balance the regenerated voltage with the voltage in the overhead line before allowing regeneration to begin." Rheostatic braking was added later, integrated with the normal braking operation, and only required the operation of a switch to activate it. No other technical details given.
The Woodhead railway is relevant to this topic on two counts.
The regenerative braking was meant to help power trains uphill, unfortunately there was often not enough traffic for that and the re-generated power had to be dissipated in load banks (the right term?) at Hadfield substation. There were problems of excessive voltage on the overhead lines causing circuit breakers to trip as well as some burning out of resistances on the locos themselves.
Secondly, when the electrification was done in the early 50's a few houses for railway staff were built at Woodhead Tunnel itself. These houses were powered from the 1500v dc traction supply via a rotary converter, don't know its output voltage, perhaps 200v? The line closed in 1981 so I assume the houses got connected to the National Grid then.Ironically , the " new" Woodhead tunnel built 1954, now carries HV cables (132KV?) instead of railway.
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Old 21st Sep 2018, 2:17 pm   #67
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Default Re: Last public DC mains supply in the UK?

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Ironically , the " new" Woodhead tunnel built 1954, now carries HV cables (132KV?) instead of railway.
Technology and economics (and perhaps a bit of politics, but let's avoid that!) dictate that it's now cheaper to transport energy across the Pennines as electricity than as lumps of coal.
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Old 21st Sep 2018, 3:11 pm   #68
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Default Re: Last public DC mains supply in the UK?

One of the original reasons for building the national grid was to facilitate the burning of coal in large modern, high efficiency power stations situated in the coal fields.

It was indeed cheaper to transmit electricity by high voltage grid lines, than to transport coal to power stations nearer the load.
Electrical losses were said to be 1%.
Coal losses in extra handling, and the coal burnt by steam locomotives to haul the coal were said to be 2%.
A well built grid line was less vulnerable to bad weather than a railway.
OTOH, a railway built primarily to transport coal was also useful for other traffic.

All a bit academic these days as coal is much less used.
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Old 21st Sep 2018, 3:19 pm   #69
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Default Re: Last public DC mains supply in the UK?

Re post #66.
The railway houses built near Woodhead tunnel were I suspect supplied with 240 volts AC. By the 1950s, DC was on the way out for new installations, as distinct from continued use of existing infrastructure.

A rotary converter run "inverted" from the 1500VDC traction current would have supplied this.
An AC supply, probably from the same rotary would also have been desirable for signalling.
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Old 16th Feb 2019, 10:13 pm   #70
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Default Re: Last public DC mains supply in the UK?

When I did my 17th edition wiring regs about 10 years ago, there was a Engineer on the course from London Underground, who informed me, their system still used a fair bit DC power, and not just for the locomotive traction either.
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Old 17th Feb 2019, 12:34 am   #71
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Default Re: Last public DC mains supply in the UK?

I presume the signalling systems might still use DC.

There are some Walsall sockets at some Underground stations for a DC supply, I presume for maintenance equipment.
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Old 17th Feb 2019, 12:47 am   #72
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Default Re: Last public DC mains supply in the UK?

The signalling on London Underground would be mainly AC.
In general, signalling on DC electric railways tends to use AC, whilst AC electric railways favour either DC or sometimes AC of a different frequency to the traction supply.
This reduces the risks of interference.

London underground used to have, and may still have, an AC power supply at 33 2/3 cycles for signalling on those parts of the network close to or shared with main line railways, again to avoid interference.

This supply was also used for some station lighting, so as to avoid being reliant on one supply.
33 cycles is a bit too low for lighting and the line frequency flicker is noticeable on low current lamps.
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Old 17th Feb 2019, 1:33 am   #73
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Default Re: Last public DC mains supply in the UK?

According to one of my books on the London Underground (published in 1967), 33 1/3 Hz at 11kV was originally used by the Underground's central power stations for distribution to local rotary converters that supplied the 600V DC traction current, but that the old generators were replaced by 50Hz 22kV machines.

Never mind DC, until circa 1964, three of my local District Line stations (Upton Park, East Ham and Barking) were still lit by gas!
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Old 17th Feb 2019, 12:14 pm   #74
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Default Re: Last public DC mains supply in the UK?

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Never mind DC, until circa 1964, three of my local District Line stations (Upton Park, East Ham and Barking) were still lit by gas!
I think that happened with some railway stations too - they'd signed a very advantageous contract for gas supply back in the year dot and it had become ridiculously cheap compared to electricity.
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Old 17th Feb 2019, 3:36 pm   #75
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Default Re: Last public DC mains supply in the UK?

I heard some shops & other public buildings still had gas lighting even later, which must have been useful during the early mid 1970s.

Some branches of Woolworths had gas for emergency lighting into the 1980s.
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Old 17th Feb 2019, 8:24 pm   #76
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Default Re: Last public DC mains supply in the UK?

Woolworths in Barmouth, North Wales had gas lighting in the 1970's till it was demolished and a new store built.

Ten miles away, Dr Williams girls school had two electricity supplies in the very late 1950's. I don't know the details, but they were certainly incompatible and staff had to be careful. My parents worked there (met there). Whether one was a private supply, or whether they were two separate public supplies, I don't know either, and I'd be interested!

Last edited by kalee20; 17th Feb 2019 at 8:25 pm. Reason: Clarified
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Old 18th Feb 2019, 3:14 pm   #77
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Default Re: Last public DC mains supply in the UK?

I remember the gaslights in a couple of Wales/Shropshire-borders Woolworths back in the 60s/early-70s: they had a downward-facing mantle about the size of a pudding-bowl, and two dangling chains with rings on the ends, at about 10 feet off the ground, to control the gas-valve. I remember them being used during the 1973/74 pit-strike and ensuing 3-day-week powercuts.

There were 'public' DC mains in some parts of the Nottingham coalfield (where I had relatives) until the mid-1960s; miners got free electricity in the same way as they got a coal-allowance. There was much muttering when the houses were switched to grid-provided AC - along with electricity-meters and subsequent bills!
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