distribution transformer

i just want to know why is it important to ground the nuetral of a 3- phase delta-y connnected transformer

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What do you think would happen if the transformer shorted from primary to secondary?
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or even just capacitive coupling from primary to secondary?
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As distribution system carries unbalanced current, neutral is used in a distribution transformer to carry this unbalanced current. As this unbalance and hence neutral current is not maintain constant, star point or neutral potential continuously varies, as a result to bring neutral to some constant value, neutral is grounded so that neutral is always maintain at or near ground potential. Also neutral is grounded for a safety purpose. As unbalanced current is flowing through neutral, some potential drop occurs in the neutral. To avoid this neutral is grounded at several point as well so that through constant potential maintained . In olden system, three phase five wire system was used in which three phase, neutral and protecting earth conductor was used. but these includes extra cost to distribution system, so they have eliminated protective earth conductor and instead start grounding neutral. hence most of the system uses three phase four wire with neutral grounded.
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----------------------------
wrote:

As distribution system carries unbalanced current, neutral is used in a distribution transformer to carry this unbalanced current. As this unbalance and hence neutral current is not maintain constant, star point or neutral potential continuously varies, as a result to bring neutral to some constant value, neutral is grounded so that neutral is always maintain at or near ground potential. Also neutral is grounded for a safety purpose. As unbalanced current is flowing through neutral, some potential drop occurs in the neutral. To avoid this neutral is grounded at several point as well so that through constant potential maintained . In olden system, three phase five wire system was used in which three phase, neutral and protecting earth conductor was used. but these includes extra cost to distribution system, so they have eliminated protective earth conductor and instead start grounding neutral. hence most of the system uses three phase four wire with neutral grounded. -------------- That is clear and succinct as well as being correct.
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| ----------------------------
| wrote: |> i just want to know why is it important to ground the nuetral of a 3- |> phase delta-y connnected transformer | | As distribution system carries unbalanced current, neutral is used in | a distribution transformer to carry this unbalanced current. As this | unbalance and hence neutral current is not maintain constant, star | point or neutral potential continuously varies, as a result to bring | neutral to some constant value, neutral is grounded so that neutral is | always maintain at or near ground potential. Also neutral is grounded | for a safety purpose. As unbalanced current is flowing through | neutral, some potential drop occurs in the neutral. To avoid this | neutral is grounded at several point as well so that through constant | potential maintained . In olden system, three phase five wire system | was used in which three phase, neutral and protecting earth conductor | was used. but these includes extra cost to distribution system, so | they have eliminated protective earth conductor and instead start | grounding neutral. hence most of the system uses three phase four wire | with neutral grounded. | -------------- | That is clear and succinct as well as being correct.
If you grounded one leg of a wye/star system, instead of the center, then you would still have a stable system relative to ground. So why is it the center point that is grounded? Is it just because that makes it symmetrical? Or is it because that minimizes the highest voltage in the system? I point to "center tapped delta" as an example of a non-symmetrical system where one leg is a higher voltage than the others. But is that relevant? I doubt it.
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wrote:

---------------- Symmetry is relevant. It is relevant in the "Edison" single phase 3 wire system and just as relevant for polyphase systems. You refer to a center tapped delta. Fine- but single phase 120V loads on a 240V delta are only available on two legs to the center tap. The line currents are then unbalanced and there is no hope of getting a balance between all 3 phases. You'd be better of with 3 single phase 120V transformers which have no secondary interconnections except a common ground -which reduces to a Y system. With, say, a 208/120 Y system, the single phase loads can be balanced between the phases. Look at the current distributions -both primary and secondary with a mix of single and 3 phase loads. ) . Now if you ground one leg of a Y, then you would have one leg at 120V to ground and two legs at 208 to ground. Now, what are the chances of someone connecting, in error, a 120V load to 208V? Consider that wiring in a new commercial situation is done before any connection is made to the supply so prior checking of voltages is not possible. It can be done (with good electricians and good supervision) but is it practical to do so? Given a general balance between phases, the normal neutral to ground voltage is naturally near 0. Thus a connection between neutral and ground results in a minimum insulation stress to ground. This might not be important at 120V but becomes more so at higher voltages.
Also consider fault protection which would have to be tailored to the phase but then might be incorrect for 3 phase situations.
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|
| wrote: |> |> i just want to know why is it important to ground the nuetral of a 3- |> |> phase delta-y connnected transformer |> | |> | As distribution system carries unbalanced current, neutral is used in |> | a distribution transformer to carry this unbalanced current. As this |> | unbalance and hence neutral current is not maintain constant, star |> | point or neutral potential continuously varies, as a result to bring |> | neutral to some constant value, neutral is grounded so that neutral is |> | always maintain at or near ground potential. Also neutral is grounded |> | for a safety purpose. As unbalanced current is flowing through |> | neutral, some potential drop occurs in the neutral. To avoid this |> | neutral is grounded at several point as well so that through constant |> | potential maintained . In olden system, three phase five wire system |> | was used in which three phase, neutral and protecting earth conductor |> | was used. but these includes extra cost to distribution system, so |> | they have eliminated protective earth conductor and instead start |> | grounding neutral. hence most of the system uses three phase four wire |> | with neutral grounded. |> | -------------- |> | That is clear and succinct as well as being correct. |> |> If you grounded one leg of a wye/star system, instead of the center, then |> you would still have a stable system relative to ground. So why is it the |> center point that is grounded? Is it just because that makes it |> symmetrical? |> Or is it because that minimizes the highest voltage in the system? I |> point |> to "center tapped delta" as an example of a non-symmetrical system where |> one |> leg is a higher voltage than the others. But is that relevant? I doubt |> it. |> |> -- |> |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to |> ignorance | |> | by the abuse department, bellsouth.net is blocked. If you post |> to | |> | Usenet from these places, find another Usenet provider ASAP. |> | |> | Phil Howard KA9WGN (email for humans: first name in lower case at |> ipal.net) | | | | ---------------- | Symmetry is relevant. It is relevant in the "Edison" single phase 3 wire | system and just as relevant for polyphase systems. You refer to a center | tapped delta. Fine- but single phase 120V loads on a 240V delta are only | available on two legs to the center tap. The line currents are then | unbalanced and there is no hope of getting a balance between all 3 phases. | You'd be better of with 3 single phase 120V transformers which have no | secondary interconnections except a common ground -which reduces to a Y | system. With, say, a 208/120 Y system, the single phase loads can be | balanced between the phases. | Look at the current distributions -both primary and secondary with a mix of | single and 3 phase loads. ) . | Now if you ground one leg of a Y, then you would have one leg at 120V to | ground and two legs at 208 to ground. Now, what are the chances of someone | connecting, in error, a 120V load to 208V? | Consider that wiring in a new commercial situation is done before any | connection is made to the supply so prior checking of voltages is not | possible. It can be done (with good electricians and good supervision) but | is it practical to do so? Given a general balance between phases, the | normal neutral to ground voltage is naturally near 0. Thus a connection | between neutral and ground results in a minimum insulation stress to ground. | This might not be important at 120V but becomes more so at higher voltages. | | Also consider fault protection which would have to be tailored to the phase | but then might be incorrect for 3 phase situations.
There seems to be a misunderstanding of what I said. I questioned and doubted that "NON-symmetry" was relevant.
Of course in a wye/star system, where the center is grounded to make the system symmetrical around the ground reference, it lets you use 3 balanced groups of line-to-neutral connections and keep the system balanced.
OTOH, I have yet to see a good reason why we have to have one of the _utilized_ conductors be grounded. The _system_ needs to be grounded. Consider the center-tapped-grounded 240 volt delta system ... used to power ONLY 240 volt loads that can handle either or both conductors being as much as 240 volts above ground reference. That can be in balance.
We have LEGACY appliances which assume a grounded conductor, so we can't just change. But in theory, we could use a system where the ground reference is somewhere else in the system rather than the center. I would NOT want to in part because the costs are a bit higher than if we did ground in the center.
Consider a 240/139 volt star/wye system. The center is grounded. All loads are 240 volts. All breakers will be 2-pole. All switches will be 2-pole. The insulation systems can assume no voltage is more than 139 volts above ground reference (as the nominal reference value).
Now consider grounding that system at one end instead of the center. What changes? The voltage relative to ground changes. Now the highest is 240 instead of 139. It will cost a bit more to insulate for that. But 2/3 of the loads will have a grounded conductor. Breakers and switches can be of the single pole type for these only. Of course this can make for confusion and/or imbalance. It's also about the same as corner grounded delta.
In single phase, those 240 volt loads would be supplied with each end of a 240/120 Edison style split just like we have now in North American. If we only had 240 volt single phase utilization everywhere like this, we could supply these loads with either 240/120 single phase or 240/139 three phase systems.
I'd rather have the grounding at the center of the system so I can keep the system in balance with like loads all around. But my point is, there is no fundamental _electrical_ reason we can't have an unbalanced relative to ground system design. There are good _costs_ reasons to avoid that.
And for the most part we also have line-to-grounded-conductor utilization which can be powered in North America by either 240/120 single phase or by 208/120 three phase systems.
Still, I would prefer a line-to-line system (always center grounded, though), because of the reduced copper wiring requirements, and the decreased power lossage, of the higher voltage that can be had at a lower relative ground voltage. While breaker costs and switch costs are higher due to the 2-pole needs, the branch circuit wiring costs will be lower for a given voltage relative to ground.
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The only such "legacy" appliances I can think of were the cheap tube radios and TVs.
Electric Clothes Dryers and Electric Stoves for many years have been shipped so that the installer can connect it to a "legacy" 3 wire outlet (with ground and neutral combined) or a "modern code compliant" 4 wire outlet (with ground and neutral separate.)
Of course most "Edison" socket lamps like to have the base which occasionally can come in contact with the users skin connected to the neutral conductor.

Well, most folks would "consider" this to be a PITA.

It's not the insulation (which is typically good for 600 volts) but the risk of death or serious injury if some poor idiot ends up getting shocked.
That said, the air handler in our home is designed for 240 volt operation and has a warning that no conductor can be over 150 volts from ground. So my HVAC system would be perfectly happy with your 139?/240 system.

The 120/208 system is downright silly. If local distribution MUST be 3 phase, it might make sense to have a 7 wire system with the 3 phases on 3 separate 120/240 system. Folks who NEED 3 phase can get 120/208 AND 120/240 with 2 extra wires.

The "service" conductors are almost all Al today. Inside the building most electricians perfer sticking to Cu with the possible excepts of stove, water heater, and HVAC circuits.
Cu is dirt cheap compared to Cu.
But the cost (including panel capacity) of 2 pole breakers for all loads is a "deal breaker."

Not compared to 120/240 basic service.

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Actually, it seems just about everything has a polarized plug (if not using a 3 prong plug) with the wide blade attached to the nonswitched side. Even things that make little sense have them now.
"Back in the day" the only things that had polarized plugs were the "hot chassis" transformerless tube radios and TVs. Not any more.

Question: Why don't power companies do something like this for their HV power lines? It would seem to me that it would be rather cheaper if they could run power lines with two insulated conductors on the towers and one uninsulated grounded conductor low on the towers rather than 3 insulated conductors high up. The system with the grounded conductor would be either a wye with a grounded phase (rather than grounded neutral) or a corner grounded delta.
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----------------------------
writes:

--------------- The insulation cost for 120 or 240V service is not affected by the configuration as the insulation is typically rated for 600V and with a humungous safety factor. That is not so for HV lines.
Consider the insulation requirements for this situation. At 500KV you would have two conductors at 500KV to ground vs 3 at 289KV to ground. The insulation cost would be at least 15% higher for the 2 conductors at 500KV vs 3 at 289KV to ground (2*500/(3*289) roughly. This is not a negligable part of the line cost. Considerable effort goes into optimization of the insulation design. Conductor costs won't change so there is no gain there. Tower costs would likely increase due to the need for larger clearances.
You would also find that the total charging MVA would double with the one line grounded situation. (as well as being unbalanced). This can be appreciable for long HV lines.
In addition, there would be higher ground level electric fields (or higher towers) . For magnetic fields at ground level the use of a grounded phase low to the ground would result in higher fields.
There are a few other problems but that's enough for now.
Now you come to the terminal apparatus and the insulation costs in transformers as well as other equipment factors would push the costs even higher.
It could be done but the cost factors as well as technical factors don't favour it.
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Thanks for the info. My question was actually semi-rhetorical, since I knew such factors were involved but didn't know details. It was partially pointing out a case where an unbalanced system likely wouldn't work (the rhetorical part), and partially trying to ferret out details.
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| Of course most "Edison" socket lamps like to have the base which | occasionally can come in contact with the users skin connected to the | neutral conductor.
We need to get rid of those. I know, maybe we can ban light bulbs :-)
|> Consider a 240/139 volt star/wye system. The center is grounded. All |> loads |> are 240 volts. All breakers will be 2-pole. All switches will be 2-pole. |> The insulation systems can assume no voltage is more than 139 volts above |> ground reference (as the nominal reference value). | | Well, most folks would "consider" this to be a PITA.
I consider the added cost of larger/more branch circuit conductors to be a PITA.
|> Now consider grounding that system at one end instead of the center. What |> changes? The voltage relative to ground changes. Now the highest is 240 |> instead of 139. It will cost a bit more to insulate for that. But 2/3 of |> the loads will have a grounded conductor. Breakers and switches can be of |> the single pole type for these only. Of course this can make for |> confusion |> and/or imbalance. It's also about the same as corner grounded delta. | | It's not the insulation (which is typically good for 600 volts) but the risk | of death or serious injury if some poor idiot ends up getting shocked. | | That said, the air handler in our home is designed for 240 volt operation | and has a warning that no conductor can be over 150 volts from ground. So | my HVAC system would be perfectly happy with your 139?/240 system.
And about everything else designed that way could be happy. And most of the appliances used in Germany would work, given they cannot depend on one conductor or the other always being the grounded one given the Schuko is not polarized.
|> In single phase, those 240 volt loads would be supplied with each end of a |> 240/120 Edison style split just like we have now in North American. If we |> only had 240 volt single phase utilization everywhere like this, we could |> supply these loads with either 240/120 single phase or 240/139 three phase |> systems. |> |> I'd rather have the grounding at the center of the system so I can keep |> the |> system in balance with like loads all around. But my point is, there is |> no |> fundamental _electrical_ reason we can't have an unbalanced relative to |> ground |> system design. There are good _costs_ reasons to avoid that. |> |> And for the most part we also have line-to-grounded-conductor utilization |> which can be powered in North America by either 240/120 single phase or by |> 208/120 three phase systems. | | The 120/208 system is downright silly. If local distribution MUST be 3 | phase, it might make sense to have a 7 wire system with the 3 phases on 3 | separate 120/240 system. Folks who NEED 3 phase can get 120/208 AND | 120/240 with 2 extra wires.
If I had a home so large that it needed so much power that I had to have three phase, that would be the way I would want to go. But it might be done by having 480/277 coming in and 3 gray humming boxes in the electrical room (a house that big means electrical gets its own room). Of course if I had that, I'd want to use that 480 somewhere :-)
Likewise, if I build an apartment building bigh enough to require three phase, I'd want that to supply each apartment with genuine 120/240.
I had previously posted my preference for line-to-line systems so we can use the higher voltage across the build to avoid crazy voltage mixes between single phase and three phase systems, while keeping line-to-ground lower for reduced shock risk in the mode most humans get zapped. I had also proposed that if I got to go back in time and decide the system, I'd have chosen to go with 288 volts line-to-line for everything, which could be had with 144 volts on single phase and 166 volts on three phase.
|> Still, I would prefer a line-to-line system (always center grounded, |> though), |> because of the reduced copper wiring requirements, and the decreased power |> lossage, of the higher voltage that can be had at a lower relative ground |> voltage. | | The "service" conductors are almost all Al today. Inside the building most | electricians perfer sticking to Cu with the possible excepts of stove, water | heater, and HVAC circuits.
The service conductors are mostly irrelevant. With a 120/240 system, the loads will be "mostly" in near balance, and the effect on the conductors is equivalent to 240 volt loads.
It's the branch circuit conductors I'm concerned with. There are a lot of them and they tend to have more amps on them in the 120 volt parts of the world.
| Cu is dirt cheap compared to Cu.
?
| But the cost (including panel capacity) of 2 pole breakers for all loads is | a "deal breaker."
Is it? Compared to the cost of wiring the circuit?
With a 240 volt circuit, you can put more on it. That means fewer circuits. So you can approach maybe half as many circuits. So the total number of circuit breaker poles would be only slightly increased, not doubled.
|>While breaker costs and switch costs are higher due to the 2-pole |> needs, the branch circuit wiring costs will be lower for a given voltage |> relative to ground. | | Not compared to 120/240 basic service.
You can put a lot more watts on smaller wires with 240 volts, compared to with 120 volts. So either you have circuits with smaller wires, or you have fewer circuits, or some combination.
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----------------------------
wrote:

----------- And doesn't this ground a utilized conductor? ---------------------------

---------- Now, you are proposing a different system which is actually more complex. You now have 120/240 to ground on 2 phases and 240 /173 to ground on the other. Which of the 3 neutrals is which? Note that some of your 120 V loads will require two pole breakers. Sure it is electrically possible- no fundamental reason otherwise but a good engineering practice called KISS comes into play. >

-------------------------- Now I don't quite see what you are getting at. If loads are balanced then there is no difference in line currents and copper needs between a delta and star system. If you want all single phase loads at 240V- fair enough. In that case forget about center tapping or "Edison" type setups on each leg. It isn't going to save anything. You could also take 3 240V/120V windings and tie the center taps together to get a 6 phase star 120V to ground, 120V, 208V, and 240V available between phases. This could be a nightmare in practice as KISS is kissed off. Such a system has been applied in distribution in some places but even there it is not widespread.
Lots of different schemes can be tried but if you did an analysis on them, you would still likely end up with the present grounded neutral Wye. One can quibble about the proper choice of voltage and the advantage of 240V over 120V but, in general the choice has been made, differently in different parts of the world, already.
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|> Consider a 240/139 volt star/wye system. The center is grounded. All |> loads |> are 240 volts. All breakers will be 2-pole. All switches will be 2-pole. |> The insulation systems can assume no voltage is more than 139 volts above |> ground reference (as the nominal reference value). | ----------- | And doesn't this ground a utilized conductor? | ---------------------------
No. The idea referenced here is that the system originates with a WYE but all the utilizing loads are connected line-to-line.
|> Now consider grounding that system at one end instead of the center. What |> changes? The voltage relative to ground changes. Now the highest is 240 |> instead of 139. It will cost a bit more to insulate for that. But 2/3 of |> the loads will have a grounded conductor. Breakers and switches can be of |> the single pole type for these only. Of course this can make for |> confusion |> and/or imbalance. It's also about the same as corner grounded delta. |> |> In single phase, those 240 volt loads would be supplied with each end of a |> 240/120 Edison style split just like we have now in North American. If we |> only had 240 volt single phase utilization everywhere like this, we could |> supply these loads with either 240/120 single phase or 240/139 three phase |> systems. | ---------- | Now, you are proposing a different system which is actually more complex. | You now have 120/240 to ground on 2 phases and 240 /173 to ground on the | other. Which of the 3 neutrals is which? Note that some of your 120 V loads | will require two pole breakers. Sure it is electrically possible- no | fundamental reason otherwise but a good engineering practice called KISS | comes into play.
Yes, grounding at one END of a WYE is more complex. It can be confusing and opens exposure to more errors.
The change to referring to single phase did not involve 3 neutral unless you want to have 3 instances of that. In that case I'd bond them all together. In any event, if all loads are line-to-line, then you don't need to run the neutrals to the loads.
Just to be clear, each of those paragraphs was describing different systems.
|> I'd rather have the grounding at the center of the system so I can keep |> the |> system in balance with like loads all around. But my point is, there is |> no |> fundamental _electrical_ reason we can't have an unbalanced relative to |> ground |> system design. There are good _costs_ reasons to avoid that. |> |> And for the most part we also have line-to-grounded-conductor utilization |> which can be powered in North America by either 240/120 single phase or by |> 208/120 three phase systems. |> |> Still, I would prefer a line-to-line system (always center grounded, |> though), |> because of the reduced copper wiring requirements, and the decreased power |> lossage, of the higher voltage that can be had at a lower relative ground |> voltage. While breaker costs and switch costs are higher due to the |> 2-pole |> needs, the branch circuit wiring costs will be lower for a given voltage |> relative to ground. | -------------------------- | Now I don't quite see what you are getting at. If loads are balanced then | there is no difference in line currents and copper needs between a delta and | star system. If you want all single phase loads at 240V- fair enough. In | that case forget about center tapping or "Edison" type setups on each leg. | It isn't going to save anything. You could also take 3 240V/120V windings | and tie the center taps together to get a 6 phase star 120V to ground, 120V, | 208V, and 240V available between phases. This could be a nightmare in | practice as KISS is kissed off. Such a system has been applied in | distribution in some places but even there it is not widespread.
In a single phase scenario, with only one transformer with with a 120/240 winding, you can deliver the just 2-conductors to the line-to-line loads. The neutral isn't needed. It just gets bonded to ground at the source and a ground wire is carried along with the 2 line wires. The service drop to a house would still _look_ the same (2 black wires wrapping around a silver one). But it would be connected _logically_ different, as it would be treated as ground only, and is not supposed to be a current carrying conductor.
| Lots of different schemes can be tried but if you did an analysis on them, | you would still likely end up with the present grounded neutral Wye. One can | quibble about the proper choice of voltage and the advantage of 240V over | 120V but, in general the choice has been made, differently in different | parts of the world, already.
I agree that the best system is to have a center point grounded, whether it is a three phase wye system, or a single phase split system.
Yes, the choice has been made. But I believe I am right that if we had made the choice another way (always line-to-line utilization), in the end, costs would be slightly lower when accounting for everything including cost of Cu and power loss. But since the choice has already been made, that adds in the cost of conversion, which would be a lot higher than the savings. But we can do SOME of this by using more things on 240 volts (line-to-line). Computers and many other things can do it.
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snipped-for-privacy@ipal.net wrote:

<snip>
Well, I have heard tell that in distribution lines (neighborhoods), it is desirable to have the three phases symetrical to avoid too much interference with telephone lines on the same poles. This may be a hold-over from older telephone days, I don't know. And I can't really vouch for it personally, just something I ran across somewhere.
For transmission lines, I wonder if the radiant losses would be the same if one phase was grounded along the line (every tower). Seems like with an unbalanced E-M field on the other two lines, you might have a sort of increased radiator.
daestrom P.S. And of course, symmetrical just sort of 'feels' better from a psychological standpoint :-)
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wrote:

------------- Even if the phases are symmetrically placed (in an equilateral triangle) as often done, there can be some interference with open condctor telephone and telegraph lines. The solution to this is to transpose the wires -essentially each phase takes up each line position for a third of the line length. Telephone pairs were transposed more often but it is easier to do it and. it also reduces cross talk between lines (this transposition also takes place inside telephone cables). Transposition also helps balance the impedances of the lines. In some EHV lines transposition has been omitted as it is somewhat awkward and expensive to cross over the phase positions while still maintaining adequate clearances. ------------

---------------- I should think so. Certainly the capacitances to ground and the line inductances would be unbalanced and I would expect less cancellation of fields. It seems to me that I still have an old program that I wrote to do the field calculations. I should dig it out and try it.
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| Even if the phases are symmetrically placed (in an equilateral triangle) as | often done, there can be some interference with open condctor telephone and | telegraph lines. The solution to this is to transpose the | wires -essentially each phase takes up each line position for a third of the | line length. Telephone pairs were transposed more often but it is easier to | do it and. it also reduces cross talk between lines (this transposition | also takes place inside telephone cables). | Transposition also helps balance the impedances of the lines. In some EHV | lines transposition has been omitted as it is somewhat awkward and expensive | to cross over the phase positions while still maintaining adequate | clearances.
I have seen three phase distribution in rural West Virginia (Roane and Calhoun counties) using a "Y" shaped crossbar turned 90 degrees. It alternated left and right, and the three phases made 1/6 of a rotation between each pole.
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----------------------------
wrote:

------------ Was this done continuously as usually it is done, at most, every few miles? Actually it sounds like a neat approach.
--

Don Kelly snipped-for-privacy@shawcross.ca
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| ----------------------------
| wrote: |> |> | Even if the phases are symmetrically placed (in an equilateral triangle) |> as |> | often done, there can be some interference with open condctor telephone |> and |> | telegraph lines. The solution to this is to transpose the |> | wires -essentially each phase takes up each line position for a third of |> the |> | line length. Telephone pairs were transposed more often but it is |> easier to |> | do it and. it also reduces cross talk between lines (this transposition |> | also takes place inside telephone cables). |> | Transposition also helps balance the impedances of the lines. In some |> EHV |> | lines transposition has been omitted as it is somewhat awkward and |> expensive |> | to cross over the phase positions while still maintaining adequate |> | clearances. |> |> I have seen three phase distribution in rural West Virginia (Roane and |> Calhoun |> counties) using a "Y" shaped crossbar turned 90 degrees. It alternated |> left |> and right, and the three phases made 1/6 of a rotation between each pole. |> |> -- |> |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to |> ignorance | |> | by the abuse department, bellsouth.net is blocked. If you post |> to | |> | Usenet from these places, find another Usenet provider ASAP. |> | |> | Phil Howard KA9WGN (email for humans: first name in lower case at |> ipal.net) | | | | ------------ | Was this done continuously as usually it is done, at most, every few miles? | Actually it sounds like a neat approach.
There were some places where it went through several complete rotations in a continuous stretch. But in others it would rotate 1/6 turn then stay that way a few poles before rotating again. There might have been partial rotations of more than 1/6 turn. I saw this in the 1960's. I haven't been back there in that part since then. I was young, then, and it was when we traveled to visit relatives. I just sat in the back seat watching these out the side window, watching the wires occaisionally rotate, until they shifted to the other side of the road where I could not see. I always took the left side back seat so I could watch those. There were about 20 miles worth. It was almost trance-like in some places.
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