Running a 4 kW motor

[JohnW2]

This is 220V 3-phase ....

I'm not sure I would say so. For a start, the Y-axis is labelled "VRMS", which is nonsense. RMS voltage only has a meaning in relation to voltage over whole numbers of half-cycles, and has no meaning as an instantaneous value at a point in time. If it were a 220V RMS supply,, the instantaneous voltages (relative to an actual or hypothesised neutral) would have a peak of around 311V.

Kind Regards, John

 

[ban-all-sheds]

Thank you, John, for that extremely useful, worthwhile, important and helpful point, without which, of course, my question would have made no sense whatsoever, and could not possibly have been answered.

This is 220V 3-phase - what do you connect between to get 220V single-phase?

 

[JohnW2]

Thank you, John, for that extremely useful, worthwhile, important and helpful point, without which, of course, my question would have made no sense whatsoever, and could not possibly have been answered.

This is 220V 3-phase ...

But it's not (in terms of normal terminology), is it? Just as a "400V (RMS) 3-phase supply" has each phase being ~230V RMS (about 325V peak) relative to the 'neutral reference', a "220V (RMS) 3-phase supply" would have each phase being about 127V RMS (about 180V peak), not 311V peak, relative to that reference, wouldn't it?

KInd Regards, John

 

[SimonH2]

Thank you, John, for that extremely useful, worthwhile, important and helpful point, without which, of course, my question would have made no sense whatsoever, and could not possibly have been answered.

Oooh, in a sarcastic mode now eh

This is 220V 3-phase - what do you connect between to get 220V single-phase?

View attachment 133597

You don't, because what you have drawn is NOT a 220V 3 phase supply. But had you not got the Y axis scale wrong, the simple answer is that you connect between ANY two of the phases. Literally, pick ANY two phases and plot the difference between them - what do you get ?

Ah, John beat me to it on the scale

As to the rest of your previous diatribe, IIRC (and no I'm not going back to look for it) you were told that such supplies exist long before you continued to argue their non-existence and the pointlessness of making motors that would run on them.
You have been given some pointers to relevant information which you ignored.
And most importantly, you could have just gone off and ... well there are these things on the internet called search engines. I'm sure someone of your knowledge and skills could have found the information without demanding that it be spoon fed to you.

 

[JohnW2]

You don't, because what you have drawn is NOT a 220V 3 phase supply. But had you not got the Y axis scale wrong, the simple answer is that you connect between ANY two of the phases. Literally, pick ANY two phases and plot the difference between them - what do you get ? ... Ah, John beat me to it on the scale

As we knew would be the case, with a 220V RMS 3-phase supply, thus ~127V RMS (~180V peak) per phase, what one would get, between any two phases, would be ~311V peak (~220V RMS) ...

Kind Regards, John

 

[ban-all-sheds]

But it's not (in terms of normal terminology), is it?

No, it's not.

I screwed up in the original diagram, and then carried that through to the second one as I was distracted by my reaction to your pettifogging comment about RMS.

 

[JohnW2]

No, it's not. .... I screwed up in the original diagram, and then carried that through to the second one as I was distracted by my reaction to your pettifogging comment about RMS.

It wasn't so much the mislabelling of the axis as "VRMS" which concerned me, since it was obvious that, despite what it said, you were showing plots of instantaneous voltages against time.

My real concern was that, regardless of the axis label, you had plotted incorrect values for the individual phases of a 220V (RMS) 3-phase supply - as you say, a "screw up"

Happy New Year to you and all.

Kind Regards, John

 

[ban-all-sheds]

As to the rest of your previous diatribe, IIRC (and no I'm not going back to look for it) you were told that such supplies exist

Oh, you should go back to look for it.

You really, really should go back to look for the post where my question "Where in the world do they have 230V 3-phase supplies, such that there would be motors made for it?" was answered.

long before you continued to argue their non-existence and the pointlessness of making motors that would run on them.

I have not continued to argue their non-existence.

I have continued to say that I've never heard of anywhere with 3-phase supplies, 230V phase-to-phase, and continued to point out that that was why I asked the question "Where in the world do they have 230V 3-phase supplies, such that there would be motors made for it?". That is not arguing against their existence.

You have been given some pointers to relevant information which you ignored.

I've ignored nothing.

And most importantly, you could have just gone off and ... well there are these things on the internet called search engines. I'm sure someone of your knowledge and skills could have found the information without demanding that it be spoon fed to you.

I have tried to find the information.

I did not find anything which indicated that there are places in the world where they do have 230V 3-phase supplies, such that there would be motors made for it.

But I did not imagine that I would necessarily have searched properly, nor that even if I had that the material would be there to find.

If you would care to pay attention, you'll see that what I wrote was not

"I've searched on the internet, and there is nowhere where they have 230V 3-phase supplies, such that there would be motors made for it."​

It was, in fact

"Where in the world do they have 230V 3-phase supplies, such that there would be motors made for it?"​

 

[ban-all-sheds]

My real concern was that, regardless of the axis label, you had plotted incorrect values for the individual phases of a 220V (RMS) 3-phase supply - as you say, a "screw up"

But no worse, I suggest, than your screw-up - as you realised I was meaning to show a 220V 3-phase supply, you should have pointed out that my peak Y values should have been +/- 180, not 311.

 

[JohnW2]

But no worse, I suggest, than your screw-up - as you realised I was meaning to show a 220V 3-phase supply, you should have pointed out that my peak Y values should have been +/- 180, not 311.

Two wrongs don't make a right. I fairly rapidly corrected my mistake. Without prompting from Simon and myself, you may eventually have also corrected yours, but who knows?

In fact, it's hard to see how this suggestion ever arose. We all know that the meaning of a "400V (RMS) 3-phase supply" is that there is 400V between phases (and 230V between each phase and the real, or notional, 'neutral'), so I don't see why it was ever doubted that there would be 220V (RMS) between phases in a "220V (RMS) 3-phase supply".

Kind Regards, John

 

[Jackrae]

Think it's time the moderator decided that this nit picking should end at 23:59:59,12/12/17 now that the OP has been suitably 'advised'

 

[JohnW2]

Think it's time the moderator decided that this nit picking should end at 23:59:59,12/12/17 now that the OP has been suitably 'advised'

I think you may wish to edit that, given that this thread did not start until 19/12/17

It's certainly of no use or interest to the OP, but if that were a criterion for truncating threads, this would be a very quiet place, and a good few 'regulars' might well lose interest in participating!

Speaking personally, I kept well and truly out of the endless, but irrelevant, discussion about why a certain type of motor should exist - but I did feel it appropriate to make some comments when I saw some incorrect statements being made about phase-phase voltages in a 3-phase supply (because I thought that may have misled some readers).

As far as I am concerned, even though I don't see the point, BAS is welcome to continue repeating himself as many more times as he wishes in his quest to get someone to give him what he would regard as a satisfactory answer to his question as to 'why such motors exist', but I will continue to keep out of that.

Happy New Year!

Kind Regards, John

 

[bixter]

"Where in the world do they have 230V 3-phase supplies, such that there would be motors made for it?"

Norway, possibly other scandinavian countries and many ships

Read more: https://www.diynot.com/diy/threads/running-a-4-kw-motor.494586/page-4#ixzz52sxKYZUz

 

[ban-all-sheds]

Two wrongs don't make a right. I fairly rapidly corrected my mistake. Without prompting from Simon and myself, you may eventually have also corrected yours, but who knows?

Indeed, who knows.

If my mistake had not been pointed out to me, correcting it would have involved me going back to an old post to look for a mistake, or looking at an old post and happening to notice one.

In fact, it's hard to see how this suggestion ever arose. We all know that the meaning of a "400V (RMS) 3-phase supply" is that there is 400V between phases (and 230V between each phase and the real, or notional, 'neutral'), so I don't see why it was ever doubted that there would be 220V (RMS) between phases in a "220V (RMS) 3-phase supply".

What "suggestion"?

My copy of the post contains a question, not a suggestion:

This is 220V 3-phase - what do you connect between to get 220V single-phase?

One which I asked Simon to confirm that when he uses the term "X volts 3-phase" he does mean the voltage between phases, because there was a time, earlier on, when I wondered if sometimes he meant something else:

So, take a motor that's 240V wired Delta, re-connect it in star, what's it's operating voltage now ?

because how you wire a motor - to which ends of which windings you connect which wires from your supply does nothing to change the voltage of the supply. To be sure you may change the voltage seen across each winding by having them in series, but to my mind the operating voltage of the motor has not changed - it is still connected to a, e.g., 400V 3-phase supply.

Since all along Simon seemed unable to distinguish between an asked question about where there were 230V 3-phase supplies and an unasked question about how motors are/can be connected I just wanted to make absolutely sure what he meant.

 

[JohnW2]

What "suggestion"? ... My copy of the post contains a question, not a suggestion:

This is 220V 3-phase - what do you connect between to get 220V single-phase?

It was one of your many questions (rhetorical and/or socratic) which does, indeed, imply a suggestion. If you had (somewhat more characteristically) written something like ".... what on earth do you connect between to get 220V single-phase?" that would have been even more obvious. The implication of your question was surely that you did not believe that one could get 220V by 'connecting between' anything?

In any event, as you know, the answer to your question was/is very simple/obvious ... IF what you had shown actually had been "220V 3-phase" (which it wasn't), then you could connect between any two of the phases to get 220V, since that is the accepted meaning of "220V 3-phase".

Kind Regards, John