Closed Delta 120/240V 3-phase service

[[email protected]]

| [email protected] writes:
|
|
|>|
|>| I would assume no effect, as long as the insulation was rated for 208VAC
|>| to ground vs. 120VAC to ground, and you don't overload the possibly small
|>| high leg transformer. The insulation won't be an issue for anything
|>| designed for European use where either leg may be hot, since either leg
|>| must handle 240V. One overload problem is when something is connected
|>| across the missing leg of an open delta system. The transformers have to
|>| deal with a higher VA per delivered watt, plus more copper losses.
|>| Combine this with a small high leg transformer and you may see voltage
|>| sag.
|
|>Would a computer overload it?
|
| What do you mean by "computer"? A PC or a big-assed old mainframe?
| I seriously doubt a PC with a 400W power supply will overload a high leg
| transformer of a few kVA.

PC. I didn't think so.

The old mainframe might want three phase (to run its 400 Hz motor-gen set).

 

[krw]

Are we not forgetting about the primary windings for such a scheme?

....and how does this "six phase" differ from a center-tapped three-
phase?

For three phase, the textbooks say that wye-wye is not used because
of undesirable harmonics in the neutral. Would that not apple also to
this six phase scheme?

How would the primaries be connected then?

Three phase delta?

Also, doesn't six phase distribution mean six phase transmission? Six
phase transmission for any distance is going to be horrorendously
expensive just to keep a few apartment buildings at 120/240 V.

No need for six-phase transmission to get six phases at the
"apartment building". Like you, I don't see the point though.

Dunno, I'm not a power jock...

 

[Beachcomber]

So that must mean that you know how to "Dip the plate and peak the
grid"...

The way it was...

I remember those days well. It was around 19 74 or 75 when I went
down to the Chicago Federal Building FCC offices. There was a big
classroom where they gave the tests. The tests were all multiple
choice and had a lot of trick questions.

If you were really a hot operator, you could also take the test for
Element 9 which was the "Radar Endorsement". That meant that you were
better than the guy who had a mere First Class Radio-Telephone License
without it. A lot of military and maritime guys would take the First
Class Radio-Telegraph License Test which was really cool, as well.

In later years, the FCC test stimulated the startup of a lot of
instant hack schools where they gave you the answers to actual FCC
tests. Anybody who could memorize the answers would get a "ticket".

Back then, even the disk jockeys needed at least a Third Class Radio
Telephone License if they were going to operate a low-to mid-power
radio station's transmitter.

Operation of a transmitter at a higher power station required the
First Class License.

If you got your license from going to such a school, you were often
considered a lowly "nine-week" wonder or whatever the length of the
school was by the people who had done it on their own.

There was a lot of pressure during those times to bring more women and
minorities into broadcasting and the broadcast station owners, among
others, lobbied to do away with the tests.

Before this, the government was limiting the supply of qualified
broadcast employees by requiring high standards and testing before
granting you your "ticket". From an employee standpoint, this was
good because the low supply kept wages high.

Beachcomber

 

[[email protected]]

| In article <[email protected]>, [email protected]
| says...
|>
|> >> B C
|> >> \ /
|> >> \ /
|> >>A----N----D
|> >> / \
|> >> / \
|> >> F E
|> >
|> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> >>on the second core. C-N and N-F are both wound on the third core. A third
|> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> >
|> >I always wondered if either any electric company offered such a service,
|> >or if there was any such thing as a breaker panel that would support it.
|>
|> Are we not forgetting about the primary windings for such a scheme?
|
| ...and how does this "six phase" differ from a center-tapped three-
| phase?

When most or all of the loads are single phase, the "6 star" can keep the
loading balanced over the 3 incoming phases, while also providing genuine
240 volts to those single phase loads. 240DCT or 240DVCT puts most of
the loading on one phase angle (which might be 2 incoming phase lines).
208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
on the L-N circuits. 220Y/127 is sometimes a compromise.


|> Also, doesn't six phase distribution mean six phase transmission? Six
|> phase transmission for any distance is going to be horrorendously
|> expensive just to keep a few apartment buildings at 120/240 V.
|
| No need for six-phase transmission to get six phases at the
| "apartment building". Like you, I don't see the point though.

Which would you be willing to give up? Having 240 volts (and instead you
settle for a wimpy 208 volts) or having the phases balanced (this is more
of a utility concern)?

 

[[email protected]]

|>If the big can is already 3 phase, why would anyone need to also have a
|>Scott-T? That doesn't make sense. It must be something else. How many
|>MV bushings on each can?
|
| 3 on the big can, 0 (yes, zero) on the small can.
|
| I called it Scott-T like because I'm guessing the small can is fed from
| the 240 delta high leg to neutral, which would be 90 degrees shifted from
| the 240VCT winding. Assuming my guess at what it is is correct at all.
|
|> How many secondary lugs?
|
| 4 on the big can, I believe 4 on the small can.

So the small can had 4 lugs and no MV bushings? Sounds like it might be
wired in as some kind of autotransformer. Maybe it is correcting the
voltage on the high leg or something.

 

[[email protected]]

| Stuart wrote:
|> In article <[email protected]>,
|>
|>> A Scott-T is used to get two phase from three phase. There are very few
|>> two phase requirements any more.
|>
|> Often used for the filament supplies in the modulator valves on large AM
|> transmitters. Two seperate filaments fed from the two different phases to
|> reduce hum caused by modulation of the anode current due to variation of
|> the emmision at mains frequency.
|
| Yep. That's one of the very few. I worked as a "broadcast engineer"
| whilst going to college. I still have my Radio Telephone First Class
| license.
|
| There used to be a few two phase motors, but they're almost extinct.

You could run that from your three phase power if you wire things up
to get the right phase angles AND the right voltages. If a motor is
wound so one phase is 240 and the other is 208, that should be happy
on either 240DCT or Scott-T. But such a motor would not be run very
easily on a Wye system without some additional winding tricks, and that
would negate any economics of 2 windings.

 

[krw]

| In article <[email protected]>, [email protected]
| says...
|>
|> >> B C
|> >> \ /
|> >> \ /
|> >>A----N----D
|> >> / \
|> >> / \
|> >> F E
|> >
|> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> >>on the second core. C-N and N-F are both wound on the third core. A third
|> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> >
|> >I always wondered if either any electric company offered such a service,
|> >or if there was any such thing as a breaker panel that would support it.
|>
|> Are we not forgetting about the primary windings for such a scheme?
|
| ...and how does this "six phase" differ from a center-tapped three-
| phase?

When most or all of the loads are single phase, the "6 star" can keep the
loading balanced over the 3 incoming phases, while also providing genuine
240 volts to those single phase loads. 240DCT or 240DVCT puts most of
the loading on one phase angle (which might be 2 incoming phase lines).
208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
on the L-N circuits. 220Y/127 is sometimes a compromise.

Maybe I'm dense, but I see *no* difference between the two schemes.
ELectrically, I don't see how you could tell one from the other.

|> Also, doesn't six phase distribution mean six phase transmission? Six
|> phase transmission for any distance is going to be horrorendously
|> expensive just to keep a few apartment buildings at 120/240 V.
|
| No need for six-phase transmission to get six phases at the
| "apartment building". Like you, I don't see the point though.

Which would you be willing to give up? Having 240 volts (and instead you
settle for a wimpy 208 volts) or having the phases balanced (this is more
of a utility concern)?

Before I can tell you my preference in donuts, I need to see the
difference between six and half a dozen. ;-)

 

[krw]

So that must mean that you know how to "Dip the plate and peak the
grid"...

The way it was...

I remember those days well. It was around 19 74 or 75 when I went
down to the Chicago Federal Building FCC offices. There was a big
classroom where they gave the tests. The tests were all multiple
choice and had a lot of trick questions.

If you were really a hot operator, you could also take the test for
Element 9 which was the "Radar Endorsement". That meant that you were
better than the guy who had a mere First Class Radio-Telephone License
without it. A lot of military and maritime guys would take the First
Class Radio-Telegraph License Test which was really cool, as well.

In later years, the FCC test stimulated the startup of a lot of
instant hack schools where they gave you the answers to actual FCC
tests. Anybody who could memorize the answers would get a "ticket".

Back then, even the disk jockeys needed at least a Third Class Radio
Telephone License if they were going to operate a low-to mid-power
radio station's transmitter.

Commercial transmitter operation also required a "transmitter
endorsement", IIRC. I don't remember the details, but I had one in
the early '70s (took the tests in Chicago).

Operation of a transmitter at a higher power station required the
First Class License.

Didn't think a first class was needed for radio, only TV.

If you got your license from going to such a school, you were often
considered a lowly "nine-week" wonder or whatever the length of the
school was by the people who had done it on their own.

There was a lot of pressure during those times to bring more women and
minorities into broadcasting and the broadcast station owners, among
others, lobbied to do away with the tests.

Before this, the government was limiting the supply of qualified
broadcast employees by requiring high standards and testing before
granting you your "ticket". From an employee standpoint, this was
good because the low supply kept wages high.

Artificial limitations never work for long. Unions have had their
day too.

 

[Don Kelly]

----------------------------

A Scott-T is used to get two phase from three phase. There are very few
two phase requirements any more.

Some erroneously call the 240/120V system "two phase" when it's really a
single phase with a center tap. (Or two 120V windings connected in
series.)

The last time I encountered a true Scott-T was in my exam for Professional
Engineer, back in 1952.

In a strictly technical viewpoint one can say that for an N phase star the
phase voltages are 360/N degrees apart so that the 3 wire "Edison system"
satisfies this criterion just as 3 phase, 4 phase,.... do. All with N hots
and a neutral -i.e. star connection. With balanced loads the neutral
current is 0 in all these cases. That is the justification for calling it 2
phase.

However,
in Europe the 2-phase designation is used rather than 3-wire single phase
because of the above viewpoint. (Of course they don't use it there). In
North America 2 phase implies two windings in quadrature (and for balanced
loads there is a neutral current). The system was started by Edison for DC
circuits and somehow, along with the "Edison" name, the alternative single
phase center tapped nomenclature came into use.

So, while not normally called that in North America, it is quite justifiably
called (without error) a 2 phase system -at least on the secondary of a
single phase transformer.

I remember the Scott T back in the 50's but never saw one that I can
remember.
I do remember the more common open delta transformers but usually the
transformers were equal in size.

 

[Tom Horne]

| The "6 phase " scheme wouldn't cost any more in terms of the transformers
| and could be done using a bank of 3 single phase pole pigs. However, it
| would appear that there would be additional costs involved with no net gain
| as well as a more complex system. Where possible one should avoid adding
| complexity (KISS). This doesn't mean that it can't be done but may mean
| that it shouldn't be done.

So what would you have instead, keeping to the requirement of genuine
240 volts at the single phase circuits?


| There has been some playing around in the past on the basis that 3 phase is
| good so maybe 6 or 12 phase is better- tain't so except in some special
| cases.
| Where 6 phase has been used is in some urban distribution where there is a
| savings in terms of space necessary at a given line to neutral voltage
| because the line to line voltage between adjacent phases is then the same as
| to neutral. Whether this is still being done is something that I don't know.
| It also has been used for rectifier supplies in order to reduce harmonics
| and ripple.

I've wondered if any of those 6-wire transmission lines might be phased
this way, even if the loads end up being split at the far end.


| Your scheme of 480Y and single phase transformers is far better.

So that's the way you would go? What if the utility says they don't want
to have the loss of an extra set of transformers with MV -> 480 -> 120/240
and insist on no more than one transformer per MV -> meter path?

The utility cannot insist on anything if the service you order is
tariffed by the state public utilities commission they must provide it
on demand. The tariff may allow them to surcharge you if the service
does not draw enough current to justify the additional expense. If the
type of service you want is not tariffed then the utility must apply for
a tariff for that new class of service and obtain it prior to connecting
the service. If they don't want to provide it then you would be faced
with the insurmountable cost of applying for the tariff against their
opposition.

Dairy farmers in several states have obtained tariffs for ungrounded
delta service to supply customer owned transformers in order to keep
utility neutral currents off of the farm and away from their livestock.
The utilities initially fought the tariffs very hard for reasons that
were not clear to me. Once the problem with dairy cows and stray Multi
Grounded Neutral (MGN) currents became well known some utilities began
offering special transformers that do not permit the MGN currents to
flow on the premise service wiring. I've yet to learn how they
accomplish that but if it were my livelihood I'd want the ungrounded
Delta supply that was tariffed in spite of the utilities opposition.

 

[[email protected]]

|> So that's the way you would go? What if the utility says they don't want
|> to have the loss of an extra set of transformers with MV -> 480 -> 120/240
|> and insist on no more than one transformer per MV -> meter path?
|>
|
| The utility cannot insist on anything if the service you order is
| tariffed by the state public utilities commission they must provide it
| on demand. The tariff may allow them to surcharge you if the service
| does not draw enough current to justify the additional expense. If the
| type of service you want is not tariffed then the utility must apply for
| a tariff for that new class of service and obtain it prior to connecting
| the service. If they don't want to provide it then you would be faced
| with the insurmountable cost of applying for the tariff against their
| opposition.

I've read many tariffs from various areas. Most have limits on the
maximum capacity a utility is required to provide as single phase,
and allows the utility to require three phase for higher capacity
services. They all seem to indicate that 240 delta services are no
longer required to be provided.

In some cases there was some specification of rate compensation when
the utility required providing the service at a higher voltage, to
account for the loss in the customer transformer. I presume that is
when the metering is at the higher voltage. In the example case I
described with a large apartment building, presumably metering would
be done at the 120/240 end, since there would not be individual
transformers for each unit.


| Dairy farmers in several states have obtained tariffs for ungrounded
| delta service to supply customer owned transformers in order to keep
| utility neutral currents off of the farm and away from their livestock.
| The utilities initially fought the tariffs very hard for reasons that
| were not clear to me. Once the problem with dairy cows and stray Multi
| Grounded Neutral (MGN) currents became well known some utilities began
| offering special transformers that do not permit the MGN currents to
| flow on the premise service wiring. I've yet to learn how they
| accomplish that but if it were my livelihood I'd want the ungrounded
| Delta supply that was tariffed in spite of the utilities opposition.

One possible reason they fought those tariffs was because they believed
that the ungrounded transformers would be subject to damage caused by a
lightning strike involving an arc between primary and secondary when the
secondary is not grounded. This could damage the winding insulation.

The special transformers are probably ones that do have an ungrounded
secondary, but have a special arc gap device to allow a lightning strike
or surge to jump across between primary and secondary, reducing the risk
of damage to the winding insulation.

 

[[email protected]]

| In article <[email protected]>, [email protected]
| says...
|> | In article <[email protected]>, [email protected]
|> | says...
|> |>
|> |> >> B C
|> |> >> \ /
|> |> >> \ /
|> |> >>A----N----D
|> |> >> / \
|> |> >> / \
|> |> >> F E
|> |> >
|> |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> |> >>on the second core. C-N and N-F are both wound on the third core. A third
|> |> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> |> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> |> >
|> |> >I always wondered if either any electric company offered such a service,
|> |> >or if there was any such thing as a breaker panel that would support it.
|> |>
|> |> Are we not forgetting about the primary windings for such a scheme?
|> |
|> | ...and how does this "six phase" differ from a center-tapped three-
|> | phase?
|>
|> When most or all of the loads are single phase, the "6 star" can keep the
|> loading balanced over the 3 incoming phases, while also providing genuine
|> 240 volts to those single phase loads. 240DCT or 240DVCT puts most of
|> the loading on one phase angle (which might be 2 incoming phase lines).
|> 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
|> on the L-N circuits. 220Y/127 is sometimes a compromise.
|
| Maybe I'm dense, but I see *no* difference between the two schemes.
| ELectrically, I don't see how you could tell one from the other.

A saw a bunch of different schemes in this thread. Maybe you can list
the specific schemes you think are alike but treated as different.


|> |> Also, doesn't six phase distribution mean six phase transmission? Six
|> |> phase transmission for any distance is going to be horrorendously
|> |> expensive just to keep a few apartment buildings at 120/240 V.
|> |
|> | No need for six-phase transmission to get six phases at the
|> | "apartment building". Like you, I don't see the point though.
|>
|> Which would you be willing to give up? Having 240 volts (and instead you
|> settle for a wimpy 208 volts) or having the phases balanced (this is more
|> of a utility concern)?
|
| Before I can tell you my preference in donuts, I need to see the
| difference between six and half a dozen. ;-)

Can you describe an electrical system configuration which is capable of:

1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
single phase loads.

2. Divides up the single phase load in three equal groups in order to
maintain a balance on each of the three phases of the utility supply.

.... that is not the "6 star" I described?

 

[Beachcomber]

Calling the 240/120V common system "two phase" may not be technically in
error but it confuses common usage in the United States.

I don't know if it is official, but a lot of utilities, engineers, and
electricians call it "split-phase" in the USA. The term seems to
eliminate some of the ambiguity of "two-phase".

Someone could claim that the 208V coming into an apartment is "two
phase" since by one definition, you have two of the three phases
available at the panel, but electrically it just resolves into single
phase.

Then there is this interesting circuit.

H N H

| | |
| |- switch |
| | |
|____120V lamp____|______120V lamp_____|


If the two hots are connected to a single phase 120/240 split phase
circuit, the behavior of the lamps is different when the switch is
closed, then when the two hots are connected to a 120/208 V. supply
from a 3 phase service (such as for a large condo or apartment
building).

Beachcomber

 

[Beachcomber]

Then there is this interesting circuit.

H N H

| | |
| |- switch |
| | |
|____120V lamp____|______120V lamp_____|


If the two hots are connected to a single phase 120/240 split phase
circuit, the behavior of the lamps is different when the switch is
closed, then when the two hots are connected to a 120/208 V. supply
from a 3 phase service (such as for a large condo or apartment
building).

Beachcomber

CORRECTION - That should say, the behavior of the lamps is different
on the two different types of service when the switch is "OPEN".

Sorry, my bad...

Beachcomber

 

[[email protected]]

|
|>Calling the 240/120V common system "two phase" may not be technically in
|>error but it confuses common usage in the United States.
|>>
|
| I don't know if it is official, but a lot of utilities, engineers, and
| electricians call it "split-phase" in the USA. The term seems to
| eliminate some of the ambiguity of "two-phase".

So I could call the setup I described earlier as "three split-phase"?


| Someone could claim that the 208V coming into an apartment is "two
| phase" since by one definition, you have two of the three phases
| available at the panel, but electrically it just resolves into single
| phase.

You could derive three phase from it with 2 transformers that have
a 120 volt primary and an isolated 120 volt secondary. Wire up one
transformer primary to one 120 volt supply L-N. Wire up the other
to the other 120 volt supply L-N. Now wire the secondaries in series
with one of them having a reversed phase. Connect the end of the
other one to neutral, and you end up with 120 volts at a phase angle
120 degrees away from the two supply phases. The resultant diagram
would look like:

A *
\ / \
\ / \
N C
/
/
B

A-N and B-N are original supply connections, so wiring things this way
is ultimately an autotransformer. C-N is the newly derived phase that
completes the three phase system. The power factor on the two supply
phases will be awful, depending on how much that derived phase is used.

It could also be done NOT as an autotransformer with transformers that
have 2 120 volt secondaries. Many step-up/down transformers might have
dual 120 volt primaries and secondaries allowing them to be wired as
120 and/or 240 volt isolation transformers. Wire primaries in parallel
for 120 volts, and wire secondaries arranged as above to do the same
trick as an isolation transformer.


| Then there is this interesting circuit.
|
| H N H
|
| | | |
| | |- switch |
| | | |
| |____120V lamp____|______120V lamp_____|
|
|
| If the two hots are connected to a single phase 120/240 split phase
| circuit, the behavior of the lamps is different when the switch is
| closed, then when the two hots are connected to a 120/208 V. supply
| from a 3 phase service (such as for a large condo or apartment
| building).

Yes, that is true. This is also why the NEC has rules like 310.15(B)(4)(b).

 

[[email protected]]

|
|>Then there is this interesting circuit.
|>
|>H N H
|>
|>| | |
|>| |- switch |
|>| | |
|>|____120V lamp____|______120V lamp_____|
|>
|>
|>If the two hots are connected to a single phase 120/240 split phase
|>circuit, the behavior of the lamps is different when the switch is
|>closed, then when the two hots are connected to a 120/208 V. supply
|>from a 3 phase service (such as for a large condo or apartment
|>building).
|>
|>Beachcomber
|>
| CORRECTION - That should say, the behavior of the lamps is different
| on the two different types of service when the switch is "OPEN".
|
| Sorry, my bad...

Actually, I misread your diagram. I have a normal fixed space font and
you apparently have a variable space font. You can never reliably draw
a diagram in text with such a font because there is no standard for the
spacing of such fonts. Only someone using exactly the same font can see
exactly what you drew.

If you have any way to switch to a fixed space font like "Courier" when
editing a posting, that would be best because it will display as you
create it with any fixed space font (all characters are the same width
and the spacing you create is maintained the same).

So it seems what you drew is a "switched open neutral". Well, what can
I say but: you're not supposed to allow having an open neutral. Clearly
the exact behaviour of an open neutral varies by system configuration.

Try a 120 volt delta-vee system

 

[krw]

| In article <[email protected]>, [email protected]
| says...
|> | In article <[email protected]>, [email protected]
|> | says...
|> |>
|> |> >> B C
|> |> >> \ /
|> |> >> \ /
|> |> >>A----N----D
|> |> >> / \
|> |> >> / \
|> |> >> F E
|> |> >
|> |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> |> >>on the second core. C-N and N-F are both wound on the third core. A third
|> |> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> |> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> |> >
|> |> >I always wondered if either any electric company offered such a service,
|> |> >or if there was any such thing as a breaker panel that would support it.
|> |>
|> |> Are we not forgetting about the primary windings for such a scheme?
|> |
|> | ...and how does this "six phase" differ from a center-tapped three-
|> | phase?
|>
|> When most or all of the loads are single phase, the "6 star" can keep the
|> loading balanced over the 3 incoming phases, while also providing genuine
|> 240 volts to those single phase loads. 240DCT or 240DVCT puts most of
|> the loading on one phase angle (which might be 2 incoming phase lines).
|> 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
|> on the L-N circuits. 220Y/127 is sometimes a compromise.
|
| Maybe I'm dense, but I see *no* difference between the two schemes.
| ELectrically, I don't see how you could tell one from the other.

A saw a bunch of different schemes in this thread. Maybe you can list
the specific schemes you think are alike but treated as different.

Specifically, the six-phase "star" and three-phase center-tapped
wye. With any two phases any number of others is a few transformers
away.

|> |> Also, doesn't six phase distribution mean six phase transmission? Six
|> |> phase transmission for any distance is going to be horrorendously
|> |> expensive just to keep a few apartment buildings at 120/240 V.
|> |
|> | No need for six-phase transmission to get six phases at the
|> | "apartment building". Like you, I don't see the point though.
|>
|> Which would you be willing to give up? Having 240 volts (and instead you
|> settle for a wimpy 208 volts) or having the phases balanced (this is more
|> of a utility concern)?
|
| Before I can tell you my preference in donuts, I need to see the
| difference between six and half a dozen. ;-)

Can you describe an electrical system configuration which is capable of:

1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
single phase loads.

Look harder at a center-tapped wye. There is only 60degrees between
the "negative" of phase-A and Phase-B.

2. Divides up the single phase load in three equal groups in order to
maintain a balance on each of the three phases of the utility supply.

How does it divide anything? An imbalance can still be placed on
any one (or two).

... that is not the "6 star" I described?

I still don't see the difference between that and a center-tapped
wye. Again, I'm not a power jock, so may be missing something
subtile.

 

[krw]

A second could work under a first, who took responsibility.

Sure. I meant as the primary transmitter operator. A first-class
wasn't necessary 24/7. The guy that maintained the indian didn't
need a first. ;-)

 

[krw]

I remember the sample tests. They remind me of "Who Wants To Be A
Millionaire" with their stupid choices.

I remember one, to this day;

As the licensed transmitter operator, if the antenna lights fail, do
you:

A) Climb the tower and replace the light bulb
B) Cut down the tower
C) Dismantle the transmitter
D) Call the FAA and advise them of the danger

My choice at the time was E) laugh my ass off.

 

[[email protected]]

| In article <[email protected]>, phil-news-
| [email protected] says...
|> | In article <[email protected]>, [email protected]
|> | says...
|> |> | In article <[email protected]>, [email protected]
|> |> | says...
|> |> |>
|> |> |> >> B C
|> |> |> >> \ /
|> |> |> >> \ /
|> |> |> >>A----N----D
|> |> |> >> / \
|> |> |> >> / \
|> |> |> >> F E
|> |> |> >
|> |> |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> |> |> >>on the second core. C-N and N-F are both wound on the third core. A third
|> |> |> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> |> |> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> |> |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> |> |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> |> |> >
|> |> |> >I always wondered if either any electric company offered such a service,
|> |> |> >or if there was any such thing as a breaker panel that would support it.
|> |> |>
|> |> |> Are we not forgetting about the primary windings for such a scheme?
|> |> |
|> |> | ...and how does this "six phase" differ from a center-tapped three-
|> |> | phase?
|> |>
|> |> When most or all of the loads are single phase, the "6 star" can keep the
|> |> loading balanced over the 3 incoming phases, while also providing genuine
|> |> 240 volts to those single phase loads. 240DCT or 240DVCT puts most of
|> |> the loading on one phase angle (which might be 2 incoming phase lines).
|> |> 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
|> |> on the L-N circuits. 220Y/127 is sometimes a compromise.
|> |
|> | Maybe I'm dense, but I see *no* difference between the two schemes.
|> | ELectrically, I don't see how you could tell one from the other.
|>
|> A saw a bunch of different schemes in this thread. Maybe you can list
|> the specific schemes you think are alike but treated as different.
|
| Specifically, the six-phase "star" and three-phase center-tapped
| wye. With any two phases any number of others is a few transformers
| away.

I don't know which you mean by "three-phase center-tapped wye". Maybe you
can pick it out from this police lineup:

* * * * * *
\ \ / * * * | \ / \
\ \ / / \ / | | \ / \
N---* *---N---* / \ / | *---N---* N *
/ / \ / \ / | | /
/ / \ *---N---* *---N---* *---N---* | /
* * * * *

1 2 3 4 5 6 7

If you don't see the guilty party, maybe you can draw a picture

Note that drawings are NOT to scale (relative to voltage).


|> |> |> Also, doesn't six phase distribution mean six phase transmission? Six
|> |> |> phase transmission for any distance is going to be horrorendously
|> |> |> expensive just to keep a few apartment buildings at 120/240 V.
|> |> |
|> |> | No need for six-phase transmission to get six phases at the
|> |> | "apartment building". Like you, I don't see the point though.
|> |>
|> |> Which would you be willing to give up? Having 240 volts (and instead you
|> |> settle for a wimpy 208 volts) or having the phases balanced (this is more
|> |> of a utility concern)?
|> |
|> | Before I can tell you my preference in donuts, I need to see the
|> | difference between six and half a dozen. ;-)
|>
|> Can you describe an electrical system configuration which is capable of:
|>
|> 1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
|> single phase loads.
|
| Look harder at a center-tapped wye. There is only 60degrees between
| the "negative" of phase-A and Phase-B.

I don't know which I need to look at.


|> 2. Divides up the single phase load in three equal groups in order to
|> maintain a balance on each of the three phases of the utility supply.
|
| How does it divide anything? An imbalance can still be placed on
| any one (or two).

Of course an imbalance can always happen, and likely will. But it is a
statistical thing. If a building has 54 apartments, connecting 18 of them
to phase A, 18 to phase B, and 18 to phase C, would be "balanced" enough
for utility purposes. If the supply were coming in as 120/240DCT, then
all of the apartments would be on just one of the phases and the phase
loading would be as lopsided as if the entire building were supplied with
single phase power. If the utility insists on balancing the phases and
rejects single phase service for this reason, they will reject 120/240DCT.
If the supply is 208Y/120, that would satisfy the utility (18 apartments
supplied with phases A and B, 18 suppleid with B and C, and 18 supplied
with C and A). But it would not satisfied the need to have 240 volts.


|> ... that is not the "6 star" I described?
|
| I still don't see the difference between that and a center-tapped
| wye. Again, I'm not a power jock, so may be missing something
| subtile.

Maybe you saw something I didn't see. Check the above police lineup.