How ph shift 120* works

[Besoeker3]

Beacause apparently the OP doesn’t have a great grasp or electrical theory.
its not as easy as you think to fully explain.
saying “Single phase is just single phase“ doesn’t makes sense to those that don’t understand it. You explained nothing with that statement.

180-0-180
That's it. What else is there to explain?

 

[Seven-Delta-FortyOne]

Oh no!!!

Not sure what that means.

Obviously I was talking about 3 phase 120/208Y.

Yes there is single phase 208. 2 phases of the aforementioned. Stinger legs.

I just wired up a commercial facility from 120/208Y 3 Phase and there are no 3 phase loads in the whole facility.

Just trying to keep it simple for the OP. He’s asking a very basic question.

 

[Besoeker3]

You explained nothing with that statement.

So what's to explain?
180-0-180 degrees.
That's it.

 

[Besoeker3]

Deleted.

 

[Besoeker3]

Sorry - again...................

 

[electrofelon]

Not sure what that means.

Obviously I was talking about 3 phase 120/208Y.

Yes there is single phase 208. 2 phases of the aforementioned. Stinger legs.

I just wired up a commercial facility from 120/208Y 3 Phase and there are no 3 phase loads in the whole facility.

Just trying to keep it simple for the OP. He’s asking a very basic question.

I just meant that it seemed like we were on the precipice of the phase/phases/line debate

 

[Seven-Delta-FortyOne]

My bad. I’m new here.

 

[synchro]

One important thing about common 3 phase electricity is that power delivered to a load is constant. One of our engineers here who can explain that power being a "voltage squared" or "current squared" thing can perhaps explain what I could have 50 years ago. At any instant in time, the sum of squared voltage or current is constant ...

...
That is true. The sum of the squares of three equal sine waves that are 120 degrees apart is a constant, and it's equal to 1.5 times the peak value of each sine wave. I've scaled the coefficients below so that the x-axis is in degrees instead of radians.
You could also prove this using trig identities (known equations) if you wanted.

 

[Carultch]

...
That is true. The sum of the squares of three equal sine waves that are 120 degrees apart is a constant, and it's equal to 1.5 times the peak value of each sine wave. I've scaled the coefficients below so that the x-axis is in degrees instead of radians.
You could also prove this using trig identities (known equations) if you wanted.

I tried your equations myself and I stand corrected with my earlier post. I was thinking of 3-phase rectifiers, where it is a lot closer to constant than a single phase rectifier, but not quite constant.

 

[synchro]

I tried your equations myself and I stand corrected with my earlier post. I was thinking of 3-phase rectifiers, where it is a lot closer to constant than a single phase rectifier, but not quite constant.

I understand, since waveforms for rectifiers (which just affect the polarity) are much more commonly used than the squaring of a sinusoidal waveform. I think the easiest thing to see that is different with squaring is that it results in a zero slope when the AC voltage or current is zero, while the AC waveforms themselves have the maximum slope at the zero crossing.

 

[GoldDigger]

Subtle.

 

[junkhound]

And now, moving on to negative sequence and zero sequence <G>

Can something that is an analytical tool be called 'real'.

 

[GoldDigger]

Vector math (which works pretty well with phasors too) tells us that if you have any two non-parallel phases (which rules out 180-0-180) you can construct any arbitrary phasing you want by using transformers to modify the voltage and a series connection to add the two results.

So you can produce 90 degree four-phase from 120 degree three phase and vice versa with purely passive components.

You can even produce a single phase output from three phase such that the power loading on all three original phases is equal. For those situations where putting all of the load on one phase is not acceptable.

 

[winnie]

You can even produce a single phase output from three phase such that the power loading on all three original phases is equal. For those situations where putting all of the load on one phase is not acceptable.

Please show me this one. The closest I've seen put equal kVA on each leg of the supply transformer but the phasing was such that the load was still single phase upstream of that transformer.

Thanks
Jon

 

[winnie]

Back to the OP's question:

A transformer coil does not change phase angle; the phase of its output matches that of its input.

If you have multiple transformer coils supplied by _different_ phase angle voltages, by connecting them appropriately you can create new phase angle voltages.

A common example would be a delta:wye transformer where the output phase angles are 'rotated' by 30 degrees from the input. If you look at the individual single phase components that make up the three phase transformer you see no phase angle difference, but the connection puts the input one-line phase angle on the output line-neutral voltage thus changing the line-neutral phase angle.

With more complicated transformer connections you can create other phase angle differences, but you have to start with an existing phase angle difference. If you want to go from true single phase power and create phase angle differences then you need more than a transformer. You need something that stores energy for later delivery such as a rotating phase converter.

Jon

 

[GoldDigger]

Please show me this one. The closest I've seen put equal kVA on each leg of the supply transformer but the phasing was such that the load was still single phase upstream of that transformer.

Thanks
Jon

I was referring to the so-called Leyton 3-2 circuit, which was discussed in some depth here: https://forums.mikeholt.com/threads/leyton-transformer-connections.133711/
You noted the same objection there. Unfortunately the original Leyton post with wiring diagram seems to be gone now and the links to earlier threads in the Forum got broken by the last software upgrade.
<sigh>

 

[roger]

I am having a hard time understanding exactly what your question is. Are you talking about the phase shift that results from certain transformer configurations, such as a Delta -> wye? Or are you talking about the 120 degree difference between phases on a 3-phase system?

The way the question was asked I thought he was talking about phase shift too, but the conversation seems to be about the winding configurations.

Roger

 

[oldsparky52]

I don't like the term "single phase" for this kind of grid, but that is the industry term we have for it. I prefer the term "open wye".

I really like that, open wye.

 

[wwhitney]

I was referring to the so-called Leyton 3-2 circuit, which was discussed in some depth here: https://forums.mikeholt.com/threads/leyton-transformer-connections.133711/

I don't think my instantaneous power flow accounting question in that thread was ever addressed: can a transformer arrangement do the necessary power unsmoothing to change the constant power delivery of 3 phase to the sinusoidal twice frequency power delivery of single phase?

Cheers, Wayne

 

[Hv&Lv]

The way the question was asked I thought he was talking about phase shift too, but the conversation seems to be about the winding configurations.

Roger

I just thought he was trying to figure out why they are at 120 degrees to start with.
Either way, it seems this thread has lost him In complexity.