Overhead Transmission Line System

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
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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.
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Not exactly 100% true. There are many wye-delta and delta-wye transformer connections in transmission lines. I believe the wye-wye configuration is verboten due to harmonics, plus utility companies don't like to send huge current through the earth as would be the case with a grounded wye-wye with a significant imbalance in phase currents.
Most transmission transformers have just one insulated bushing insulator for economy. A delta connection would require two bushings. Autotransformers (with no secordary) are also used.
Beachcomber
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----------------------------

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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Yes, it really does help to say which country poster is interested in.

Red, Yellow, Blue, are the 3 phase identification colours in the UK (and some other countries which copy our scheme).
--
Andrew Gabriel


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