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"SQLit" <(E-Mail Removed)> wrote in message
news:tW%Qe.1443$(E-Mail Removed)...
>
> "magic" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) oups.com...
>> Hi,
>>
>> Would you please find me why in overhead transmission line (HT)system
>> there is no earthing line provided instead of Red, Yellow, Blue,
>> Neutral lines.
>>
>> Appreciate if everybody give your opinion.
>>
>> Tks
>>
>> magic
>
> I can not discuss every part of the world or the US for that matter.
> Medium
> and High voltage transmission lines do not have an neutral, the small wire
> that goes along is a ground/static line, in my experience. The static wire
> may or may not be grounded to the pole or tower ground. I have seen it
> done
> both ways. Most of the time the static line is there for lightning and it
> is
> grounded to each tower/pole ground.
> Earthing is only required on the transmission lines at the transformers.
> The transmission lines are not in a wye configuration they are in delta.
> No
> neutral.
>
> Distribution lines/short distances are generally under 35 kv, considered
> medium voltage in my neck of the woods. Transmission lines are generally
> long distances and begin at 69 kv and go up from there.
>
> Colors mean nothing. They are just a means of identification that the
> guys
> installing it used.
> When I was working on transmission lines we never used colors. Just id
> numbers or names.
>
In general medium to high voltage overhead lines are supplied from a Y
source where the Y point is grounded,either directly or through impedance.
The "neutral" is the ground.
The use of delta for the supply of such lines is restricted to low voltage
and/ or short lines. A long line is capacitively coupled to ground and back
around 1920 or earlier, there arose the problem of ground faults which were
effectively undetectable but caused severe damage due to arcing. In
addition, passing charged clouds could and sometimes did, induce excessive
voltages on floating lines. Technically there are other advantages to
using a Y connected HV connection to overhead lines- these include cheaper
transformers, CT's, PT's insulation requirements, protective relaying needs.
In some distribution systems, delta was/is used, but in many places a
cheap way to handle increased load was to retain the lines and reconnect to
Y with existing distribution transformers switched from line to line to
line to ground.
Overhead static lines are grounded- in fact they are rather useless
otherwise. This may not be at every pole but the more ground connections,
the better.
--
Don Kelly @shawcross.ca
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