2 Phases of a 3 Phase System

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GoldDigger said:
Restating the premise of the whole thread, on which there is still no consensus:

A pair of L conductors without a neutral, taken from a three phase delta or wye source, is single phase.
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Agreed without question. And directly answers the OP. Should be EOS.

GoldDigger said:
A pair of L conductors plus a neutral, taken from a three phase wye source is either single phase or "two out of three phases", (not two phase) depending on your personal preference and maybe the context in which it is being discussed.
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Yes, context matters but it isn't something I've done, seen done, or seen any single application where it would have any merit.
 
Besoeker said:
Agreed without question. And directly answers the OP. Should be EOS.


Yes, context matters but it isn't something I've done, seen done, or seen any single application where it would have any merit.
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The two out of three wye connection is actually quite common in the US.
It is seen, for example, in an apartment complex where the site feed is 208Y/120 and each individual apartment.
The apartment panels are the same ones used for 120/240 single phase 3 wire, and the heating appliances are the same ones used for 240.
There are no three phase loads and approximate balance comes from distributing units over the three pairs.
European standard usage of only one voltage for residential single phase makes this configuration less useful.
 
Besoeker said:
But not single phase as described in the OP.
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Yet the presence or absence of the neutral does not change the fact they are both single phase circuits supplied by a three phase system.

Neither circuit is described as 'two phase' which was the OPs question.
 
GoldDigger said:
European standard usage of only one voltage for residential single phase makes this configuration less useful.
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I don't know about residential use in countries but here the residential supply is single phase 230V (nominal) usually from the secondary of a Dyn0 11kV/400V phase to neutral with one transformer, typically 1000 - 1500kVA feeding a number of residences.
 
iwire said:
Yet the presence or absence of the neutral does not change the fact they are both single phase circuits supplied by a three phase system.

Neither circuit is described as 'two phase' which was the OPs question.
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The OP's question has been answered clearly several times.
 
GoldDigger said:
Restating the premise of the whole thread, on which there is still no consensus:

A pair of L conductors without a neutral, taken from a three phase delta or wye source, is single phase.

A pair of L conductors plus a neutral, taken from a three phase wye source is either single phase or "two out of three phases", (not two phase) depending on your personal preference and maybe the context in which it is being discussed.
Click to expand...
It seems to me that whether the neutral is a center tap between two phases (high leg) or the center neutral of a wye makes a difference. In the first case if you display the two line to neutral voltage waveforms they will be 180 degrees apart, but in the second case they will be 120 degrees apart, wouldn't they?
 
ggunn said:
It seems to me that whether the neutral is a center tap between two phases (high leg) or the center neutral of a wye makes a difference. In the first case if you display the two line to neutral voltage waveforms they will be 180 degrees apart, but in the second case they will be 120 degrees apart, wouldn't they?
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Open delta three phase secondaries are derived from two lines and the neutral conductor of the primary system all the time;)
 
ggunn said:
It seems to me that whether the neutral is a center tap between two phases (high leg) or the center neutral of a wye makes a difference. In the first case if you display the two line to neutral voltage waveforms they will be 180 degrees apart, but in the second case they will be 120 degrees apart, wouldn't they?
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ggunn said:
OK, but irrespective of that is what I posted correct?
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Yes, but other than what kwired pointed out, of what use is the phase displacement?
 
Smart $ said:
Yes, but other than what kwired pointed out, of what use is the phase displacement?
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Use of any two lines of the supply can only be used as single phase

Use of three of the four lines can supply single phase multiwire load or three phase load, probably two phase load as well though traditional 90 deg two phase system may be better suitable for equipment typically designed for two phase operation.
 
kwired said:
Use of three of the four lines can supply single phase multiwire load or three phase load, probably two phase load as well...
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Which three of four lines?

We are talking two of three lines and the neutral, are we not?

You cannot power three phase load or a two phase load with any combination of these conductors... i.e. without a transformer or some other form of conversion.
 
Smart $ said:
Which three of four lines?

We are talking two of three lines and the neutral, are we not?

You cannot power three phase load or a two phase load with any combination of these conductors... i.e. without a transformer or some other form of conversion.
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Correct, but you need more then just transformer(s) to do such conversion from a two wire supply.
 
Smart $ said:
Yes, but other than what kwired pointed out, of what use is the phase displacement?
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I'm just curious. Riddle me this: if it is, as I postulated, that in a high leg system if you display line to neutral A-N and C-N, the two waveforms would be 180 degrees out of phase, what would B-N look like relative to them? I know the amplitude will be higher (208V rather than 120V) but what would be the phase relationship?
 
ggunn said:
I'm just curious. Riddle me this: if it is, as I postulated, that in a high leg system if you display line to neutral A-N and C-N, the two waveforms would be 180 degrees out of phase, what would B-N look like relative to them? I know the amplitude will be higher (208V rather than 120V) but what would be the phase relationship?
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+/- 90 degrees.
 
ggunn said:
That's what I figured; would it be to the right or to the left (+ or - 90 degrees) of the A-N waveform?
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Depends on your reference and rotation.

With positive rotation starting with A, we have A at 0 degrees, B at 180 degrees and C at 270 degrees.

So, C lags A by 270d and C lags B by 90d. Also, C leads A by 90d and C leads B by 270d.
 
mivey said:
Depends on your reference and rotation.

With positive rotation starting with A, we have A at 0 degrees, B at 180 degrees and C at 270 degrees.

So, C lags A by 270d and C lags B by 90d. Also, C leads A by 90d and C leads B by 270d.
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Cool. Thanks!
 
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