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#143137 - 05/15/05 02:54 PM A very basic question
chipmunk Offline
Registered: 07/20/04
Posts: 144
Loc: Southampton, UK
This may sound silly to people in the know, but... in the UK, when they rate a distribution voltage as "11kv" or "33kv" and so on, seeing how the UK only connects phase-phase loads, is this the phase to phase voltage? I believe the low voltage side of the distribution transformers is Wye connected, with delta connected loads.

I once asked my boss when I was being trained as an electrician "what is the phase to earth voltage?". He replied "it's the same as phase to phase at that kind of voltage". It is now my understanding that this could only be true if it was a corner grounded delta system, which aren't used here. So does anyone know?
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#143138 - 05/15/05 04:16 PM Re: A very basic question
pauluk Offline
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
Yes, the specified voltages are phase-to-phase. If you find a pair of binoculars and a pole in a suitably accessible location, that's the voltage you'll see listed on the rating plate of the transformers.

So far as I'm aware, the U.K. system either feeds into the HV lines with a wye secondary as you say, or there might be some delta connections with associated balancing windings to keep the system referenced and symmetrical to earth. Thus the phase-to-ground voltage will be at the usual Vph-ph./ SQRT(3).

At least that's how I understand the network to be arranged.
#143139 - 05/15/05 05:34 PM Re: A very basic question
chipmunk Offline
Registered: 07/20/04
Posts: 144
Loc: Southampton, UK
That's what I thought, thanks for clearing it up though, it was one of those great unanswered questions of life the universe and everything, at least for me

It makes sense to quote ph/ph here because of the use of delta primaries on the transformers here.

Now, 11,000 divided by (sqrt 3) is close to 6350v, which is within tapchanging range of 6.6kv. Am I totally wrong in thinking maybe they can (or did at some stage) use the 6.6kv windings in wye for 11kv and delta for 6.6? (I am thinking again, bad sign )
#143140 - 05/16/05 01:21 PM Re: A very basic question
Alan Belson Offline
Registered: 03/23/05
Posts: 1803
Loc: Mayenne N. France
Volts and Frequencies (UK).
Between 1908 and 1912, the Board of Trade adopted (both for ac and dc) -
115v, 230v, 460v and 525v as standard 'low pressures', at the generator terminals.
At the consumer's terminals this reduced to
110v 220v 440v and 500v, with 3 phase at 380v across principal 220v conductors to neutral.
For high pressure, the Board adopted
2200v, 3300v, 6600v and 11000v at the generator terminals, and at the transformer terminals 2000v, 3000v, 6000v and 10000v
Tramway voltages were set at 500v
Frequency was set at 50hz as standard, with exceptional use of 25hz permitted.
A variation of plus or minus 10% was permitted (then) on voltage supplied.
So it looks like they allowed for losses in arriving at what appears at first to be illogical voltages.
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#143141 - 05/17/05 05:19 AM Re: A very basic question
djk Offline
Registered: 12/26/02
Posts: 1237
Loc: Ireland
The Irish version:

220/380V (230/400V rated appliances)

(occasionally 110kV)

Industrial supplies are available at all of the above voltages.

(and a 275kV line - interconnector to Northern Ireland... there are 2 more smaller interconnectors that operate at 110kV)

Gives you all of the stats of the Irish network.

(remember it's quite a small country, 3.9 million people and almost 2 million of those are concentrated around the Dublin area, so outside of a few population centre's it's mostly a rural network)
#143142 - 05/18/05 05:47 AM Re: A very basic question
Trumpy Offline

Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
Good explanation Paul,
This is one area as an Apprentice that took me ages to get a grasp of, at the start of my Electrical career.
I've never liked 3 Phase AC theory, we had a tutor on my First Qualifying Block course that was more like a Mathematician than any sort of an Electrical worker.
All he seemed to do at the time was write endless screeds of algebraic equations on the blackboard, we were told to write down what he was writing in our folders and then read it at home that night.
But it was never actually explained to us young fella's in the lab, as to why Star and Delta is like it is.
I was one of only a few Apprentices that actually passed the exam at the end of the course (and I only just scraped through).
Strange how poor teaching methods rub off on you, eh?.
Once you learn something one way, it's rather hard to un-learn it.

[This message has been edited by Trumpy (edited 05-18-2005).]
Let's face it, these days if you're not young, you're old - Red Green grin

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