phases

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junkhound

junkhound

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EE, power electronics specialty
On another non-electrical forum, lots of folks call 120/240 a 2 phase system.

How common is that?

Have always considered as 'uneducated' folks that talk about 120/240 being a 2 phase system or if one side of the 120/240 out calling it a 'lost phase'.
These folks insist that 120/240 is 2 phases - 180 out of phase.
Is htis a regional thing, some folks say their poco calls120/240 2 phase.

NOt talking about 120/208 which is obviously 2 of 3 phases.
 
It comes from people talking like a phase is a conductor - black phase, red phase, blue phase (or brown, orange, yellow), phase tape 🙄 and all sorts of bad lingo to perpetuate a huge misunderstanding.
 
120/240 is not from a two phase system and calling it that is incorrect. It's single phase, some call it a split-phase because of the center tapped neutral. In a 2 phase system the phases are 90° out of phase.
 
220707-2335 EDT

If I have two sine wave sources, this only requires a minimum of 3 wires, that are frequency synchronized, then I may very well want to call those two signals different phases, even if precisely synchronized with 0 phase difference you might want to call that a single phase. However, in most cases if the phase difference is 0, then most likely you want to call that single phase.

A resolver is a rotary electro-mechanical device that I can use to produce any phase angle between the input and output from 0 to 360 degrees based on the input angular position of the mechanical shaft.

Whether one wants to call a center tapped secondary 2 phases or something else is really dependent what you are trying to say.

.
 
OP: 208/120 is 3 phase.

Two phase is the original system invented by Tesla. His drawings show 4 coils, 90 degrees apart. This causes excessive torque pulsing and there are issues with efficiency. Eiffel improved it by going to 6 coils 60 degrees apart which is why we have 3 phase power today. 2 phase systems persisted for a little while by I’ve never personally seen one.
 
This is a 'ground up or down' discussion. Have fun with it, don't get angry or mean, you won't get to a resolution.

IMHO there are different ways that the word 'phase' gets used.

120/240 is a single phase system with two phase angles and two phase conductors. It cannot provide continuous power delivery.

A true polyphase system offers continuous power delivery.

Jon
 
winnie said:
120/240 is a single phase system with two phase angles and two phase conductors. It cannot provide continuous power delivery.
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Do you say that because of the simultaneous zero crossing?
 
ggunn said:
Do you say that because of the simultaneous zero crossing?
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If by simultaneous you mean the L1-N and L2-N voltages, yes. There are two points in time each cycle when all 3 circuit conductors are at the same voltage (0V difference), so at those points in time, no instantaneous power is being delivered.

Cheers, Wayne
 
Outside of some campfire chat topics, this one topic that has created a few very long threads in the past.

Really comes down to terminology and accurate usage.

I recently had service calls that ended up being POCO lost a "phase conductor". I think if I said "lost a phase" there that possibly is not totally accurate, but saying "lost a phase conductor" gives enough description that even if not totally accurate, is much more accurate on the surface anyway at informing someone of what happened.

The best definition I can give on this is for two AC currents to be "in phase" they must have voltage/frequency/current peaks occurring at the same time.

If they don't occur at same time, they are simply not in phase with one another.

Phase as a stand alone word kind of doesn't mean anything specific, it needs other context to go with it.

You can have a "single phase" supply but place a capacitor or inductor in a parallel segment of a circuit and create a current that is not in phase with other parallel segments of said circuit. This is big part of how any single phase AC induction motor works.
 
Outside of North America, two-out-of-three phases is referred to as “two phase”. We call that single phase. 120/240 single phase is called “split phase”.
 
Jraef said:
Outside of North America, two-out-of-three phases is referred to as “two phase”. We call that single phase. 120/240 single phase is called “split phase”.
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We call 208/120V single phase? I usually don't.
 

IEEE Std C57.12.80Ö-2002):​


single-phase circuit: An alternating-current circuit consisting of two or three intentionally interrelated conductors that enter (or leave) a delimited region at two or three terminals of entry. If the circuit consists of two conductors, it is intended to be so energized that, in the steady state, the voltage between the two terminals of entry is an alternating voltage. If the circuit consists of three conductors, it is intended to be so energized that, in steady state, the alternating voltages between any two terminals of entry have the same period and are in phase or in phase opposition.

two-phase circuit: A polyphase circuit of three, four, or five distinct conductors intended to be so energized that in the steady state the alternating voltages between two selected pairs of terminals of entry, other than the neutral terminal when one exists, have the same periods, are equal in amplitude, and have a phase difference of 90 degrees. When the circuit consists of five conductors, but not otherwise, one of them is a neutral conductor.

NOTEùA two-phase circuit as defined here does not conform to the general pattern of polyphase circuits. Actually, a two-phase, four-wire or five-wire circuit could more properly be called a four-phase circuit, but the term two-phase is in common usage. A two-phase three-wire circuit is essentially a special case, as it does not conform to the general pattern of other polyphase circuits.

three-phase circuit: A three-phase circuit is a combination of circuits energized by alternating electromotive forces that differ in phase by one third of a cycle, that is, 120 degrees.

NOTEùIn practice, the phases may vary several degrees from the specified angle.

six-phase circuit: A combination of circuits energized by alternating electromotive forces that differ in phase by one-sixth of a cycle, that is, 60 degrees.

NOTEùIn practice, the phases may vary several degrees from the specified angle.
 
Hv&Lv said:
Actually, a two-phase, four-wire or five-wire circuit could more properly be called a four-phase circuit, but the term two-phase is in common usage.
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I disagree with that opinion. Two-phase is just as appropriate as single-phase is for 120/240v.
 
Jraef said:
Outside of North America, two-out-of-three phases is referred to as “two phase”. We call that single phase. 120/240 single phase is called “split phase”.
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ggunn said:
We call 208/120V single phase? I usually don't.
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I think he meant we usually call it single phase if only two "hots" and the neutral is all that is present at a particular location. However other than maybe with the help of semiconductors, 208/120 is only possible from multiphase sources.
 
I'm glad it is simpler for us UKIPERs. Domestic is single phase 230V. Industrial is 3-phase 400V. Job done!
 
kwired said:
Outside of some campfire chat topics, this one topic that has created a few very long threads in the past.

Really comes down to terminology and accurate usage.

I recently had service calls that ended up being POCO lost a "phase conductor". I think if I said "lost a phase" there that possibly is not totally accurate, but saying "lost a phase conductor" gives enough description that even if not totally accurate, is much more accurate on the surface anyway at informing someone of what happened.

The best definition I can give on this is for two AC currents to be "in phase" they must have voltage/frequency/current peaks occurring at the same time.

If they don't occur at same time, they are simply not in phase with one another.

Phase as a stand alone word kind of doesn't mean anything specific, it needs other context to go with it.

You can have a "single phase" supply but place a capacitor or inductor in a parallel segment of a circuit and create a current that is not in phase with other parallel segments of said circuit. This is big part of how any single phase AC induction motor works.
Click to expand...

The neutral is a phase conductor. It is conducting amps. It is only “zero Volts” because we always measure Voltage with respect to another point. And guess what happens if the utility loses the neutral? Same as a phase conductor…some circuits are affected, some aren’t.
 
Besoeker3 said:
I'm glad it is simpler for us UKIPERs. Domestic is single phase 230V. Industrial is 3-phase 400V. Job done!
Click to expand...

Ok so what about motors over say 400 kW where you need to go to higher voltages?

And I wouldn’t say it’s that easy. RCDs aren’t used in many parts of the world and neither are loop tests,
 
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