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This topic comprises 6 pages: 1 2 3 4 5 6
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Topic: Who has had a fire somewhere in their projector? -> OT: Voltage around the world
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-14-2005 05:38 AM
quote: Gordon McLeod
"Is there such a thing as a 480 volt rectifer, or is everything in the normal projection booth 208?"
Yes in Europe and any other country that the pahse to neutal is 240 the phase to phase is in the 480 range depending on other factors
Gordon, three phase in Europe is always Star (wye). There is no normal 480V supply, until a few years ago the nominal voltages were 220/380 in most countries except Britain, where it was 240/415. As part of the European harmonisation thing this was changed to 230/400 throughout the continent. This change was just in the declared Voltage, the allowed tolerances were changed to bring both of the previous Voltages within the allowed range. Here in Britain it used to be 240/415 +/- 6%, this was changed to 230/400 +10/-6%. I think there may have been another small change in tolerance since then, but I'm not certain. Nothing has really changed, my home Voltage is usually about 239V, and is pretty stable. Three phase at home is unusual, but not unknown. All distribution is however three phase, all three phases are taken down each street, usually underground, but sometimes on poles in rural areas, and houses are connected to each phase in turn. We don't normally have small transformers up a pole feeding one, or a few houses, except for isolatted buildings in remote areas, but large substation transformers feeding at least several streets. This has the disadvantage that there is a greater Voltage drop to buildings furthest from the substation, but the Voltage tends to be more stable; we don't see lights dimming if we switch on a washing machine, or something similar. Just about all industrial, and most commercial buildings have three phase.
We do not normally (with one exception) use a centre-tapped supply as is done in the US and, I think, Canada. Our single phase supply consists of one live (hot) wire and one neutral, which should be at, or very close to, earth (ground) potential unless something is seriously wrong. The live conductor is 230V from earth whichever phase it is on, there is no 'high leg' as there is with a delta system with one phase centre tapped. Between any two live conductors on different phases there is 400V. The one exception which I mentioned is in certain industrial situations, e.g. building sites, where small portable power tools have to be rated at 110V, and are operated from a small local isolating transformer with a 110V centre-tapped secondary, giving 55-0-55V. This has to be used as 110V across the whole of the secondary, the use of 55V from one sive is not allowed. The transformer is contained in a small yellow box, close to where the tool is being used.
We also do not have the odd Voltages, 277, 480 etc. that America does. Unless you are operating something very large, like a steelworks, electric railway or power station, you will be supplied with 230/400V, 50Hz. If a customer needs some other sort of supply then they install there own conversion equipment to provide it from the standard supply.
Our single phase sockets are rated at 13A, and are wired in a ring main, which is protected by a 30A fuse of breaker. This is the reason why British plugs have to be fitted with an internal fuse, usually rated at 3 or 13A; connecting something like a table lamp, with a thin flex to a circuit protected by a 30A fuse would not be a good idea. The standard for these plugs is BS1363, and they were introduced in 1947. The sockets are required to have a shutter which is opened when the correct plug is inserted, and the part of the live and neutral pins closest to the plug body has for some years now, had to be shrouded to prevent them being touched when the plus is partly inserted in a socket.
There are various other types of plugs for industrial use; but by far the most common are what used to be known as the BS4343 range, now BS EN 60309 and also known as IEC 60309, CEE 17 ceeform and various other names, which are available for various Voltages, in 3,4 and 5 pin versions and in 16,32,63 and 125A ratings. The same things in the US are rated at 20, 30, 50 and 100A for some reason.
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John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 07-14-2005 01:33 PM
In the US, 277/480V is used for heavy machinery, like huge air conditioners in reasonably-sized buildings, etc. That's 277V phase-to-neutral and 480V phase-to-phase.
It's hard for me to believe that the UK doesn't use higher voltages for applications that draw a lot of power -- the goal is to avoid loss over longer distances. EDIT: Mostly because I wasn't paying attention to the fact there was 400V power. Sure, 400V seems a reasonable analog to 480V in the US.
While 277/480V exists all over the US, and probably exists for, say, HVAC equipment in large multiplexes, it is not at all common for rectifiers. This is not to say that 277/480V rectifiers don't exist, but I think few projectionists would have the opportunity to get killed by them.
(Also, as a point of trivia, many buildings on our campus run their fluorescent lighting ballasts off of 277V phase-to-neutral).
And while it's a rare US residence that has 120/208V Wye 3-phase, it's pretty-much a nonexistant residence that has 277/480V. I suppose a large apartment building with central air might.
--jhawk
[ 07-14-2005, 07:12 PM: Message edited by: John Hawkinson ]
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-14-2005 03:47 PM
quote: John Hawkinson
It's hard for me to believe that the UK doesn't use higher voltages for applications that draw a lot of power -- the goal is to avoid loss over longer distances.
Large buildings, factories, office blocks and the College where I work for example, would have their own substation, stepping down from a medium Voltage, usually 11 kV, though I think my college is 6.6 kV, which is not common. The substation equipment belongs to the electricity company; the customer is supplied at 400/230V. Even large equipment operates on 400V. It's not until you get to the realy big stuff, usually thousands of kW, that you tend to find motors running on higher Voltages, then it's typically a few kV. Examples which I've seen include a large steel rolling mill, and the primary air fans and condenser cooling water circulating pumps in a large (2000 MW) coal-fired power station.
For residental supply the distance from the substation can be considerable, typically hundreds of metres, but the current is fairly small.
For industrial use the current is large, but the distance from the substation is small. In my College the substation is in the basement of the main building, and I believe it is rated at 12,000A per phase. It's overloaded at peak times, and we have a 500 kW generator in the car park at the moment feeding some large extraction/air conditioning plant serving some additinal new-build added last Summer, and two wings of the bulding which were refurbished at the same time, until the substation can be upgraded. Given that the current substation installation dates from the '50s, it must have been way over spec'ed when it was put in. Most of the building is not air conditioned. All of this, and other heavy loads, the boiler house plant and lift motors for example, runs on 400V three phase 50Hz.
Transmission Voltages here are 132, 275 and 400kV. Distribution usually at 11, 33 and 66 kV, though 6.6 and 22kV can also be found. Supply is almost always 400/230V.
What's the smallest size of motor over there that you would normally find running on anything greater than 240V?
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