Delta-Wye Question

kwired said:
I think your real question was probably about running a motor only rated for 230 volts on a 208 supply.

It will work. It will draw roughly 10% more current for same output as it does when supplied from 240 volt supply. Closer you are to loading it to it's rated output the more likely it will be operating beyond it's designed current rating. If it runs for short periods of time, or is seldom to never fully loaded you may never really have any trouble with it. If it runs rather continuously and at/near rated load you may have shorter motor life due to extra heat in the windings.

Motors marked 208-230 volts were intentionally designed to handle the extra current when used on a 208 supply. Also if your 208 supply tends to run a little on the high end of acceptable tolerance - say around 215 volts, you are kind of near the lower acceptable tolerance range of 230 volts and that does help you out a little with how much impact you will have from operating it at a low voltage.
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This 4HP, 230 volt motor powers an airless sprayer. The 480v primary is actually only 458, so the best I'm getting out of the Delta-Wye xfmr is 220V on the secondary. I have a 13KW generator that I will use if the commercial supply proves to be inadequate. It has a fairly sophisticated control circuit that includes over and under-voltage protection and temperature monitoring. I bought it (used) for one job using donated funds and must be able to sell it after the work for the project to stay in budget (a submarine memorial). Maybe I'm being overly cautious, but I do appreciate everyone's input.
 
OldSparks said:
It has a fairly sophisticated control circuit that includes over and under-voltage protection and temperature monitoring. I bought it (used) for one job using donated funds and must be able to sell it after the work for the project to stay in budget (a submarine memorial). Maybe I'm being overly cautious, but I do appreciate everyone's input.
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As I said, the motor coils only see the L-L voltage and can't see the phase angles because the necessary reference is not connected to the motor.

But if the control circuit is monitoring L-N or L-G voltage it will see the phase angles or the strange L-N voltage. If the control circuit expects 120V L-N, it will instead be getting 139V
 
OldSparks said:
I'm getting my you-know-what kicked while trying to post the photo. What's the trick?
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Where is the pic?

If you can see it, try right-clicking, select Copy Image, then in the forum window, right-click and select Paste Image.

If you have a URL, you can copy and paste the link in the button that looks like a dot above the mountains in By URL.
 
LarryFine said:
Where is the pic?

If you can see it, try right-clicking, select Copy Image, then in the forum window, right-click and select Paste Image.

If you have a URL, you can copy and paste the link in the button that looks like a dot above the mountains in By URL.
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I have a photo on my phone (and on my Mac computer).
 
I know, let's forget about voltage. Let's consider "potential difference." After all, voltage is the measurement unit of potential difference:

So, in a 240V 3-phase system, what is the potential difference between any two legs? 240 volts. Wait! What if it is corner ground? 240 volts. Huh? what if it is a Wye-system? 240 volts. How about in an ungrounded system? 240 volts. Hmmmm, ok smarty-pants, what if it is a split phase system with the center tap grounded? 240 volts. Ah, I think I gotcha! How about if one of the end taps is grounded? (I've seen it, although it was electronic, not a transformer) 240 volts. (Damn!!!)
 
TwoBlocked said:
...what if it is a split phase system with the center tap grounded? 240 volts. Ah, I think I gotcha! How about if one of the end taps is grounded? (I've seen it, although it was electronic, not a transformer) 240 volts. (Damn!!!)
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As long as the center tap is not also grounded, yes.
 
TwoBlocked said:
I know, let's forget about voltage. Let's consider "potential difference." After all, voltage is the measurement unit of potential difference:

So, in a 240V 3-phase system, what is the potential difference between any two legs? 240 volts. Wait! What if it is corner ground? 240 volts. Huh? what if it is a Wye-system? 240 volts. How about in an ungrounded system? 240 volts. Hmmmm, ok smarty-pants, what if it is a split phase system with the center tap grounded? 240 volts. Ah, I think I gotcha! How about if one of the end taps is grounded? (I've seen it, although it was electronic, not a transformer) 240 volts. (Damn!!!)
Click to expand...
The issue is that the motor in this case is single-phase 230 volt. NOT 3-phase, although the PRIMARY to the xfmr is 3-phase. I'm starting to think that slippage may not be such an issue in a single-phase motor (compared to 3-phase motors). But my concern remains that the two hot legs to the motor will be only 120 degrees apart, not the 180 degrees the motor is expecting. Possible RPM issue? I'm no motor expert, hence my concerns.
 
Hi OldSparks.

I believe you are thinking that the 2 hot legs you are bringing to the single phase motor are 120 degrees apart.

Long story short, they are not. I know it's a bit hard to sometimes wrap your head around, but if your circuit has only 2 "wires" (L-L or L-N) they are 180 degrees apart. The 120 degree phase angle you have in your head requires 3 wires, so that you can measure an angle between any 2 of them from the 3rd point.

This is often a source of confusion. Bear with me for a minute for a simple story that might help you visualize.

Imagine you are on a flat 2 dimensional sea. Picture an X-Y graph paper if that helps. There is nothing on any horizon, just endless ocean as far as you can see.

Now imagine that a point pops up on this sea, lets call it L1. There are no other points on this sea, just Line1. So there is nothing yet to measure to or measure from.

Now, suddenly, another point pops up, some distance away. We will call this L2. We measure distance on this sea in volts, and L2 is 208 volts away from L1.

If you draw a straight line to measure the distance between Line1 and Line2, that's all it will be. A straight narrow line. Standing on the point at L1, L2 is 208 volts away, straight down that line (180 degrees). And conversely, somebody standing on L2 would measure L1 also as 208 volts away, but directly the other way, straight down the line. These 2 points will always simply be directly "opposite" each other, straight down the line, the only shape you can draw between 2 points. And that's all the single phase motor cares about... 2 points that have some potential distance (voltage) between them.

When you want to think about 120 degree phase angles in 3 phase systems, it means you want to start drawing triangles (like for a Delta), or maybe a Y shape (for a Wye). But all those shapes require at least 3 points (like needing an L3). If you bring only 2 points onto your big flat sea, you can only draw (and measure) one shape between them... a straight 180 degree line.

I know you want to think that L1 and L2 are 120 degrees apart... and they are... but ONLY if you bring a 3rd point onto that sea to create a shape you can measure angles with. If all you take out of the transformer is 2 wires, then in the motor's little universe it only knows those 2 points.

There is no 3rd point to measure angles from, just the 2 points and the straight (180 degree) line between them.

Apologies in advance if you knew all this already. Hope any of it helps.
 
MD Automation said:
Hi OldSparks.

I believe you are thinking that the 2 hot legs you are bringing to the single phase motor are 120 degrees apart.

Long story short, they are not. I know it's a bit hard to sometimes wrap your head around, but if your circuit has only 2 "wires" (L-L or L-N) they are 180 degrees apart. The 120 degree phase angle you have in your head requires 3 wires, so that you can measure an angle between any 2 of them from the 3rd point.

This is often a source of confusion. Bear with me for a minute for a simple story that might help you visualize.

Imagine you are on a flat 2 dimensional sea. Picture an X-Y graph paper if that helps. There is nothing on any horizon, just endless ocean as far as you can see.

Now imagine that a point pops up on this sea, lets call it L1. There are no other points on this sea, just Line1. So there is nothing yet to measure to or measure from.

Now, suddenly, another point pops up, some distance away. We will call this L2. We measure distance on this sea in volts, and L2 is 208 volts away from L1.

If you draw a straight line to measure the distance between Line1 and Line2, that's all it will be. A straight narrow line. Standing on the point at L1, L2 is 208 volts away, straight down that line (180 degrees). And conversely, somebody standing on L2 would measure L1 also as 208 volts away, but directly the other way, straight down the line. These 2 points will always simply be directly "opposite" each other, straight down the line, the only shape you can draw between 2 points. And that's all the single phase motor cares about... 2 points that have some potential distance (voltage) between them.

When you want to think about 120 degree phase angles in 3 phase systems, it means you want to start drawing triangles (like for a Delta), or maybe a Y shape (for a Wye). But all those shapes require at least 3 points (like needing an L3). If you bring only 2 points onto your big flat sea, you can only draw (and measure) one shape between them... a straight 180 degree line.

I know you want to think that L1 and L2 are 120 degrees apart... and they are... but ONLY if you bring a 3rd point onto that sea to create a shape you can measure angles with. If all you take out of the transformer is 2 wires, then in the motor's little universe it only knows those 2 points.

There is no 3rd point to measure angles from, just the 2 points and the straight (180 degree) line between them.

Apologies in advance if you knew all this already. Hope any of it helps.
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I appreciate your thoughtful response. I will move forward with the project. Thank you!
 
OldSparks said:
The xfmr involved.
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Glad you posted the photo we can see that it is a 208/120 volt 9kVA transformer not a 240/139 volt, so you have just 25 amps on the 208 side.
So since your feeling cautious make sure the sprayer is rated 208-240V.
If the sprayer manufacturer says its good on 208 then 4HP load would be about ~14 - 15 amps on the 208 side. You may want to check what the other loads are on that transformer if its the only load your fine.
 
tortuga said:
Glad you posted the photo we can see that it is a 208/120 volt 9kVA transformer not a 240/139 volt, so you have just 25 amps on the 208 side.
So since your feeling cautious make sure the sprayer is rated 208-240V.
If the sprayer manufacturer says its good on 208 then 4HP load would be about ~14 - 15 amps on the 208 side. You may want to check what the other loads are on that transformer if its the only load your fine.
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It is a straight 230 volt motor, and I've adjusted the xfmr taps to produce 220 at the secondary. Sprayer nameplate amps is 16. I have a 13KW generator as a backup source if the commercial power arrangement proves inadequate. The only other load is some LED PAR-38's that I can (and probably will) deenergize while I'm spraying.
 
OldSparks said:
... But my concern remains that the two hot legs to the motor will be only 120 degrees apart, not the 180 degrees the motor is expecting. ...
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The motor is "expecting" a potential difference of 230 vac, and that is what it will get. Just the same as if the a 460/230 single phase transformer transformer is "expecting" 460 on the primary, it does not mater if the legs are 120 degrees or 180 degrees apart. It is the potential difference between the legs that is important, not the phase angle between them when referenced to ground or even some arbitrary reference.

It really will be ok. :)
 
OldSparks said:
The issue is that the motor in this case is single-phase 230 volt. NOT 3-phase, although the PRIMARY to the xfmr is 3-phase. I'm starting to think that slippage may not be such an issue in a single-phase motor (compared to 3-phase motors). But my concern remains that the two hot legs to the motor will be only 120 degrees apart, not the 180 degrees the motor is expecting. Possible RPM issue? I'm no motor expert, hence my concerns.
Click to expand...
It took me a while to wrap my head around this as well when I first started dealing with three phase, but the voltage waveform between any two conductors in a three phase system is a simple 60Hz sine wave. As long as a neutral from the center of the wye is not involved the 120 degree separation between phase conductors is irrelevant.
 
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