Are you talking about the secondary winding of a VT?
It is usual to earth the yellow phase in the UK. although I don't know
why.
I have copied this to sci.engr.electrical.sys-protection, maybe
somebody there will be able to answer your question.
Barry wrote:
> Hi Guys,
>
> Thanx for your responses. A little about me then!! I am 55 years old
OUCH ,
> and have always been an electronics engineer. I have been in the
> "electrical" industry for a little over fourteen years now. I am
Technical
> Manager for my company and part of my job is sorting out customers
problems
> when everything else fails, the buck stops here.
>
> This goes back a few years now and I have seen the yellow phase earthed
a
> couple of times. I remember that on one occasion it was down in a valley
at
> a sub station in Scotland serving a distillery (no samples were given
> unfortunately). The problem was with a power factor transducer which was
> connected between the red and yellow phases for reference, it didn't
work !!
> It transpired that the yellow phase was pulled to ground. Connecting
between
> the blue and red phases restored normal operation.
>
> It was then I was told of the earth fault impedence but I'm still not
sure
> of the logic of this? Its not really im****tant I suppose but its just
one
> of those things that come to mind from time to time as unsolved.
>
> Cheers,
>
> Barry
> <furles@[EMAIL PROTECTED]
> wrote in message
> news:1160732930.472987.268860@[EMAIL PROTECTED]
> >
> > Barry wrote:
> >> Hi John,
> >>
> >> Thanks for your reply. I have seen this a couple of times when I've
been
> >> out
> >> troubleshooting and told that its something to do with earth fault
> >> impedances? L2 (yellow as it was) is the star point. By the way the
> >> colours
> >> I am reffering to are not the wire colours but the "old" phase
rotation
> >> colours ie (R) L1 (Y) L2 and (B) L3.
> >> "John McLean" <jaymack12@[EMAIL PROTECTED]
> wrote in message
> >> news:avadnXil0KflILPYRVnyig@[EMAIL PROTECTED]
> >
> > I've been thinking more about this on the bus going to work. There
> > seem to be three possibilities:
> >
> > 1) You are mistaken, and you weren't seeing what you think you were
> > seeing.
> >
> > 2) You were seeing some strange long obsolete system.
> >
> > 3) You were seing something unusual, which was done for some specific
> > reason.
> >
> > Taking these in order, I don't know how experienced you are, you could
> > be an electrical engineer with many years experience, or a total
novice
> > - or anywhere in between. This would of course greatly affect the
> > possibility that you were mistaken. You say that you've seen this
when
> > you've been 'out troubleshooting'. You also say that you were told
> > that 'its something to do with earth fault impedances' The fact that
> > you were somebody who would be doing troubleshooting, and that you
> > asked the reason, and were given one, albeit not a very clear one,
> > rather than being told that you were mistaken, and that it was not
> > connected that way does seem to make this possibility less likely.
> >
> > Until after the War there were still various odd systems in use in the
> > UK; there were a few places on odd frequencies like 40Hz., I think a
> > few were even still on d.c. Odd Voltages lasted even longer, I just
> > remember being converted from 200 to 240V, in about 1961. Things have
> > however been standardised for a long time. When did you see this, if
> > it was less than about 50 years ago then I think we can rule out the
> > second possibility.
> >
> > The third possibility would be the most interesting, and if this is
the
> > case, then I would like to know the reason too. I doubt that the fact
> > that you saw it in the North of the UK is technically significant.
> > There aren't really many technical differences from the rest of the
UK;
> > there are more hydro-electric stations in Scotland than there in the
> > South, but I doubt that has anything to do with it. As for
'political'
> > differences, things really have been standardised for a long time. Do
> > you simply spend more time looking at installations in the North than
> > elsewhere, and therefore if odd systems exist then you are more likely
> > to see them there.
> >
> > Where did you see this; was it a low Voltage supply system, or a
medium
> > Voltage distribution one? Was it in an industrial situation; if so,
> > what sort of industry? Was there some sort of specialised equipment
> > installed nearby?
> >
> > I think it's very unlikely that any normal customer would be supplied
> > with this system; in this country people expect neutral to be close to
> > earth potential, which it obviously wouldn't be with this system.
This
> > suggests that either the costomer produces this themselves via their
> > own isolation transformer, or that it is a distribution system, with
> > the final low Voltage supply having conventional earthing
arrangements,
> > and the customer knowing nothing about the odd distribution system.
> >
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