phases

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LarryFine said:
Two-phase is just as appropriate as single-phase is for 120/240v.
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No.

Put an isolated scope on the two "phases" and you will see ONE trace. A single phase.

Of course I use terms like "put the meter from a phase to ground, now try the other phase". But never call it two phase. ;)

Just a center tapped transformer, like in high quality tube rectifier radios to make B+.:unsure:
 
AdrianWint said:
If a 'device' is powered from two hots (phases?) & does not have a neutral connection.......is that device single phase?
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Yes, as are all devices in 99% of American homes. The exception is houses with elevators that got 3 phase service, or some really old houses with air conditioning that had 3 phase compressors.
 
Frank DuVal said:
No.

Put an isolated scope on the two "phases" and you will see ONE trace. A single phase.

Of course I use terms like "put the meter from a phase to ground, now try the other phase". But never call it two phase. ;)

Just a center tapped transformer, like in high quality tube rectifier radios to make B+.:unsure:
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I was referring to the comment that genuine two-phase could be called "four-phase".

That's no more appropriate than calling a center-tapped one-phase source "two-phase".
 
jaggedben said:
Incomplete. You count phases by counting each combination of non-neutral conductors, (unless you've only got one, then it's single phase).
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Sounds like that count would give you 6 for a 4-wire or 5-wire 2-phase system. So that's a bit too general.

If we restrict the count to pairs of circuit conductors whose voltage difference is maximal (up to small differences), then that works for 2-wire (obviously), 3-wire 120/240V, 3-wire 120/208V (assuming you want to call it single phase), 3-wire delta, 4-wire wye, 4-wire high leg delta, 4-wire 2-phase, and 5-wire 2-phase. It doesn't work for 3-wire 2-phase, though, it identifies that as single phase, just like 3-wire 120/208V.

Also, a complete way of defining the number of phases should be able to handle something oddball, such as: Take a 4-wire wye, add center taps to the 3 coils to produce a 7-wire system, and then just bring out the 3 center taps and 1 other non-neutral conductor.

So given an arbitrary collection of wires with the voltage between any two AC of a fixed frequency, I don't have a good general definition for the number of phases present.

Cheers, Wayne
 
wwhitney said:
Sounds like that count would give you 6 for a 4-wire or 5-wire 2-phase system. So that's a bit too general.
If we restrict the count to pairs of circuit conductors whose voltage difference is maximal (up to small differences), then that works for 2-wire (obviously), 3-wire 120/240V, 3-wire 120/208V (assuming you want to call it single phase), 3-wire delta, 4-wire wye, 4-wire high leg delta, 4-wire 2-phase, and 5-wire 2-phase.
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Sorry for not accounting for two phase. It's very rare. You're correct that the definition would need to include something like 'pairs intended to be used together in a circuit'.

wwhitney said:
It doesn't work for 3-wire 2-phase, though, it identifies that as single phase, just like 3-wire 120/208V.
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Wrong, because the common wire in a 2 phase system isn't a neutral. ;-) Without the additional qualification it identifies it the same as 3-wire delta.

wwhitney said:
Also, a complete way of defining the number of phases should be able to handle something oddball, such as: Take a 4-wire wye, add center taps to the 3 coils to produce a 7-wire system, and then just bring out the 3 center taps and 1 other non-neutral conductor.

So given an arbitrary collection of wires with the voltage between any two AC of a fixed frequency, I don't have a good general definition for the number of phases present.

Cheers, Wayne
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True as far as it goes. But for electricians, having to consider hypothetical oddballs isn't needed or helpful.
 
jaggedben said:
Wrong, because the common wire in a 2 phase system isn't a neutral. ;-) Without the additional qualification it identifies it the same as 3-wire delta.
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My statement was based on the rule "count pairs of conductors at maximum voltage difference," which doesn't rely on treating any possible neutral conductor specially. For 3-wire 120/170V 2-phase, the pairwise voltages are 120V, 120V, and 170V, so that algorithm calls it single phase.

Cheers, Wayne
 
wwhitney said:
My statement was based on the rule "count pairs of conductors at maximum voltage difference," which doesn't rely on treating any possible neutral conductor specially. For 3-wire 120/170V 2-phase, the pairwise voltages are 120V, 120V, and 170V, so that algorithm calls it single phase.

Cheers, Wayne
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Okay. That proves that thowing 'non-neutral' out of the defintion wasn't optional, if you want to talk to the folks in Philly who still use two-phase.
 
In the 'high phase order' motor world (thinks like 5 or 9 or 18 phase machines) the term 'hemi-phase' is used to differentiate between systems where you have 180° and those where you do not.

A common three phase motor has slot conductors for each phase and its inverse, since coils wrap around. In other words with 3 phases you have 6 different phase angles to work with on the stator. So a common 3 phase machine is a 6 hemiphase machine.

I've been working with motors that use 18 hemiphase machines driven with 'full bridge' inverters. These same inverters could be configured to run a true 18 phase (36 hemiphase) machine.

-Jon
 
jaggedben said:
Okay. That proves that thowing 'non-neutral' out of the defintion wasn't optional, if you want to talk to the folks in Philly who still use two-phase.
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I don't quite follow. Do you have a pairwise counting definition that covers all the cases I listed in post #45, paragraph 2?

Cheers, Wayne
 
winnie said:
A common three phase motor has slot conductors for each phase and its inverse, since coils wrap around. In other words with 3 phases you have 6 different phase angles to work with on the stator. So a common 3 phase machine is a 6 hemiphase machine.
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By "common" you mean an everyday 3 phase motor supplied by 3 wires in a delta? How do you get all 6 hemiphases out of that?

Cheers, Wayne
 
OK, here's a counting method that works for all the standard systems below, although it calls 120/208V 3-wire 2 phase (which is plausible in my book, although it's a system only ever used for single phase loads).

Namely, write down all pairwise voltages between conductors. For the voltage with the highest count (up to small differences, and choosing the larger voltage in the case of ties, to be unambiguous), choose any pair to be phase angle zero, and plot the phase angles of all those pairs. The number of phases is the number of lines through the origin spanned by those vectors. I.e. the number of different phase angles up to sign.

2-wire: 1 phase
120/240V 3-wire: 1 phase
120/208V 3-wire: 2 phases
120/170V 3-wire: 2 phases
Delta 3-wire: 3 phases
Wye 4-wire: 3 phases
Hi Leg Delta 4-wire: 3 phases
2 phase 4-wire: 2 phases
2 phase 5-wire: 2 phases

Cheers, Wayne
 
wwhitney said:
I don't quite follow. Do you have a pairwise counting definition that covers all the cases I listed in post #45, paragraph 2?

Cheers, Wayne
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No, I don't have a complete definition that would satisfy you, not really. However I would note that the two problem cases have something in common, which is that the conductor that doesn't share the maximal voltage isn't neutral to the other conductors present. Those are 3-wire two phase and 3-wire 120/208. (The latter has a conductor that's a neutral to the entire system but not to the two hots present.) 3-wire 120/208 is single phase in some senses and not in others.

In other words, you probably can't come up with a sensible definition matches traditional nomenclature, because arbitrary convention has been imposed in those cases. But if you leave two-phase out of it, you've got a good enough definition for every electrician who doesn't have to work with two-phase. And the latter need special training anyway.
 
wwhitney said:
OK, here's a counting method that works for all the standard systems below, although it calls 120/208V 3-wire 2 phase (which is plausible in my book, although it's a system only ever used for single phase loads).

Namely, write down all pairwise voltages between conductors. For the voltage with the highest count (up to small differences, and choosing the larger voltage in the case of ties, to be unambiguous), choose any pair to be phase angle zero, and plot the phase angles of all those pairs. The number of phases is the number of lines through the origin spanned by those vectors. I.e. the number of different phase angles up to sign.

2-wire: 1 phase
120/240V 3-wire: 1 phase
120/208V 3-wire: 2 phases
120/170V 3-wire: 2 phases
Delta 3-wire: 3 phases
Wye 4-wire: 3 phases
Hi Leg Delta 4-wire: 3 phases
2 phase 4-wire: 2 phases
2 phase 5-wire: 2 phases

Cheers, Wayne
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I guess that works for engineers.
 
wwhitney said:
By "common" you mean an everyday 3 phase motor supplied by 3 wires in a delta? How do you get all 6 hemiphases out of that?

Cheers, Wayne
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On the stator itself you have coils of wire sitting in slots. If the 'left' side of the coil is sitting in a slot is phase A, then the 'right' side of the coil is sitting in a different slot with the opposite current flow. When a winding is described you need to identify both the phase and the direction that wires are going in the slot.

So going around the stator your phase bands are A C' B A' C B' A C' .... 6 different phase angles of current flowing in slots, 3 phases and their inverse. Thus 6 'semiphases'.

-Jon
 
Trust us to have three pages of arguments (so far) over what to call something that every one of us knows what is. :D
 
wwhitney said:
OK, here's a counting method that works for all the standard systems below, although it calls 120/208V 3-wire 2 phase (which is plausible in my book, although it's a system only ever used for single phase loads).

Namely, write down all pairwise voltages between conductors. For the voltage with the highest count (up to small differences, and choosing the larger voltage in the case of ties, to be unambiguous), choose any pair to be phase angle zero, and plot the phase angles of all those pairs. The number of phases is the number of lines through the origin spanned by those vectors. I.e. the number of different phase angles up to sign.

2-wire: 1 phase
120/240V 3-wire: 1 phase
120/208V 3-wire: 2 phases
120/170V 3-wire: 2 phases
Delta 3-wire: 3 phases
Wye 4-wire: 3 phases
Hi Leg Delta 4-wire: 3 phases
2 phase 4-wire: 2 phases
2 phase 5-wire: 2 phases

Cheers, Wayne
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Corner grounded?
 
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