Delta amperage

[mbrooke]

How does one calculate unbalanced amperage on single phase loads connected in delta (phase to phase)?

 

[GoldDigger]

You do the vector sums for each phase wire, unless all of the loads have the same displacement power factor.
If the power factors all match, then there is a formula which was recently posted here. (By iwire?)


Tapatalk!

 

[Smart $]

You do the vector sums for each phase wire, unless all of the loads have the same displacement power factor.
If the power factors all match, then there is a formula which was recently posted here. (By iwire?)

Even if the power factors match, you still have to do it by vector sum... except if they have the same magnitude. Then it's simply arithmetic sum of magnitudes times 0.866 (or one magnitude times square root of three). This arithmetic method will yield a decent approximation for unbalanced loads.

 

[GoldDigger]

Actually, if the displacements match but magnitudes are not equal, the fact that the relative angles are all fixed at 120 degrees allows a closed form formula involving just the three magnitudes.
Similar to the formula for the neutral current in an unbalanced wye, I think.
But the vector math will always work.

Tapatalk!

 

[mbrooke]

You do the vector sums for each phase wire, unless all of the loads have the same displacement power factor.
If the power factors all match, then there is a formula which was recently posted here. (By iwire?)


Tapatalk!

That would be helpful

The way I see it if all loads are purely resistive and all even such as electric heat (25kw L1-L2 25kw L2-L3 25kw L3-L1) you just multiply the current by the square root of the to give you the phase current. 25kw/240 volts= 104 amps multiplied by srt3 (104x1.73) giving you 180. 180 amps per phase and 75 kw of load. Correct?

However iffy on non balanced loads such as 20kw/25kw/32kw or power factors outside of unity.

 

[Smart $]

Actually, if the displacements match but magnitudes are not equal, the fact that the relative angles are all fixed at 120 degrees allows a closed form formula involving just the three magnitudes.
Similar to the formula for the neutral current in an unbalanced wye, I think.

Nope. I could explain, but I'm sure you'll figure it out for yourself.

 

[GoldDigger]

The way I see it if all loads are purely resistive and all even such as electric heat (25kw L1-L2 25kw L2-L3 25kw L3-L1) you just multiply the current by the square root of the to give you the phase current. 25kw/240 volts= 104 amps multiplied by srt3 (104x1.73) giving you 180. 180 amps per phase and 75 kw of load. Corrrect?

Well, you got the right answer, but technically instead of multiplying by sqrt3, you should have multiplied by (sqrt3)/2 and than multiplied by 2. :angel:

More to follow after dinner...



Tapatalk!

 

[iceworm]

Well, you got the right answer, but technically instead of multiplying by sqrt3, you should have multiplied by (sqrt3)/2 and than multiplied by 2. :angel:

nah - Balanced 3ph. Add the three loads: 25k +25k +25k = 75k. Divide by 240, divide by sqrt(3) =

That's okay, you still got the right answer (show body language of "tongue - ahhh - fingers in cheek")

ice

 

[GoldDigger]

The forum needs to implement an emoticon for that. I would use it a lot.

Tapatalk!

 

[iceworm]

... However iffy on non balanced loads such as 20kw/25kw/32kw or power factors outside of unity.

Yes. It is vector algebra.

Here is an example for delta leg currents of 1A, 2A, 3A, resistive loads, leg currents in-phase with leg voltages. So the leg currents are 3A<0, 2A<120, 1A<-120. ("<" means angle)

It looks messy, but if your calculator can do polar-rectangular swaps (and complex math) it is pretty easy. Otherwise you got to do some trig

Each one of the calcs involves:
1. swap each current vector from polar to rectangular.
2. subtract
3.swap result back to polar

If the loads are not resistive it isn't really more messy - just have to have the leg voltage to leg current displacement so you can get the current phase angle

Hope I helped and didn't just muddle

ice

 

[kwired]

How does one calculate unbalanced amperage on single phase loads connected in delta (phase to phase)?

Easiest way - present all your data here and let the math geeks find the answer for you :happyyes:

 

[mbrooke]

Yes. It is vector algebra.

Here is an example for delta leg currents of 1A, 2A, 3A, resistive loads, leg currents in-phase with leg voltages. So the leg currents are 3A<0, 2A<120, 1A<-120. ("<" means angle)

It looks messy, but if your calculator can do polar-rectangular swaps (and complex math) it is pretty easy. Otherwise you got to do some trig

Each one of the calcs involves:
1. swap each current vector from polar to rectangular.
2. subtract
3.swap result back to polar

If the loads are not resistive it isn't really more messy - just have to have the leg voltage to leg current displacement so you can get the current phase angle

Hope I helped and didn't just muddle

ice

Need more info. Example would help to. Ok Ill admit Im a bit addled. But your way is starting to make sense.

Easiest way - present all your data here and let the math geeks find the answer for you :happyyes:

:lol: I might do that. Anyone know of any online software that calculate unbalanced 3 phase power?

 

[iceworm]

.... Anyone know of any online software that calculate unbalanced 3 phase power?

That is a completely different question than the phase currents. If you are looking at straight resistive loads, it is pretty simple. Figure out the load in each delta leg, add them together - no vectors involved. The number you get is the kw the power company will charge for, or the power required from an engine to turn a generator - but not a number that you could use to size a transformer, nor use to size a generator.

If you are looking for complex power - I don't know what to tell you. I've never even seen an application where unbalanced 3ph power was used to do any design calculations. For example, I don't know how one would use the number for power factor.

Interesting idea - certainly something one could calculate. But I don't know what it would mean.

ice

 

[mbrooke]

That is a completely different question than the phase currents. If you are looking at straight resistive loads, it is pretty simple. Figure out the load in each delta leg, add them together - no vectors involved. The number you get is the kw the power company will charge for, or the power required from an engine to turn a generator - but not a number that you could use to size a transformer, nor use to size a generator.

If you are looking for complex power - I don't know what to tell you. I've never even seen an application where unbalanced 3ph power was used to do any design calculations. For example, I don't know how one would use the number for power factor.

Interesting idea - certainly something one could calculate. But I don't know what it would mean.

ice

By unbalanced 3 phase I mean single phase loads that are not equal to each other in kw (current draw) connected across each leg. That would result in each leg having a different current when measured with an amp clamp or current measuring CT.

If say load connected across phase A to phase B draws 40 amps, load connected across Phase B and Phase C draws 30 amps and Load between phase C and Phase A draws 20 amps how does one mathematically calculate the current that would appear on each phase leg? This is what I meant by unbalanced, since the loads on each leg relative to one another are not equal.

 

[iceworm]

By unbalanced 3 phase current (added by ice) I mean single phase loads that are not equal to each other in kw (current draw) connected across each leg. That would result in each leg having a different current when measured with an amp clamp or current measuring CT.

If say load connected across phase A to phase B draws 40 amps, load connected across Phase B and Phase C draws 30 amps and Load between phase C and Phase A draws 20 amps how does one mathematically calculate the current that would appear on each phase leg? This is what I meant by unbalanced current (added by ice), since the loads on each leg relative to one another are not equal.

Two issues mentioned in this thread:
Post 1
Calculate curent in each phase when each delta leg has a different load. I gave you an example of how to calculate this in post 10. It is a complex math (vector algebra) calculation even if the loads are resistive.

Post 12
You asked for calculation of unbalanced 3phase power - way different thing than the current. I gave the best answer I could. This one is difficult because I don't know where one would or could use the number.

I was (and still am) pretty sure the one you want is the un-balanced current - the current in each phase as noted in post 1. If the attachment I gave in post 10 didn't make any sense, that's because I didn't explain it very well. Sometimes I'm prone to that. If that is the one you are after, I should be able to do better.


ice

 

[mbrooke]

Two issues mentioned in this thread:
Post 1
Calculate curent in each phase when each delta leg has a different load. I gave you an example of how to calculate this in post 10. It is a complex math (vector algebra) calculation even if the loads are resistive.

This is the part I need help with. Just a guided explanation.

I found this online, supposedly it does the computations automatically for current but I question its accuracy. Try it out and you'll see what I mean, but if its accurate it will help. http://www.google.com/url?sa=t&rct=...74GgDg&usg=AFQjCNGWd_ggmFPrgM7X-DSeeNlpdhvH1A




Post 12
You asked for calculation of unbalanced 3phase power - way different thing than the current. I gave the best answer I could. This one is difficult because I don't know where one would or could use the number.

I was (and still am) pretty sure the one you want is the un-balanced current - the current in each phase as noted in post 1. If the attachment I gave in post 10 didn't make any sense, that's because I didn't explain it very well. Sometimes I'm prone to that. If that is the one you are after, I should be able to do better.


ice

By 3 phase power I meant the system as a to be analyzed for current. Im still referring to the first post. I didn't know you would get caught up over a single word. It wasn't my intention. I used power not so much because it was my literal intention of the meaning but rather that's what most software is called slang wise "ie 3 phase power system analyzation, "computing 3 phase power" regardless if its computing vectors, load flow, phase currents, harmonics, temperature ect ect. I just need a way to compute line currents in a 3 phase delta.

 

[Smart $]

I found this online, supposedly it does the computations automatically for current but I question its accuracy. Try it out and you'll see what I mean, but if its accurate it will help. http://www.google.com/url?sa=t&rct=j...-DSeeNlpdhvH1A

Couldn't get it to function. Get message about protection doesn't allow changes.

Currently working on new computer. Installing programs, updating, and customizing. I may put together an Excel calculator... but no promises at this point, as other issues have priority.

 

[iceworm]

By 3 phase power I meant the system as a to be analyzed for current. Im still referring to the first post. I didn't know you would get caught up over a single word.

Yeah - that happens to me sometimes in power analysis. (color me minorly embarassed)

I found this online, supposedly it does the computations automatically for current but I question its accuracy. Try it out and you'll see what I mean, but if its accurate it will help.

[URL="http://www.google.com/url?sa=t&rct=j...-DSeeNlpdhvH1A"]http://www.google.com/url?sa=t&rct=j...-DSeeNlpdhvH1A[/URL]

I think you picked a good one. The shortcomings don't look important. The sheet is protected so I can't see the algolrithm. I tried three different delta currents. The line currents came up fine. The sheet assumes the loads are resistive - no phase angle information.

The calculated power not so good. For the 480D selection, the power is not correct. I didn't look at the other selections - there is no 240D.

Since your main concern is the line currents, it should work for what you want. I think you got it.

ice

 

[Smart $]

Couldn't get it to function. Get message about protection doesn't allow changes.

...

... (color me minorly embarassed) ...

... I tried three different delta currents. The line currents came up fine. ...

My turn.

I was trying to input load currents in the Line Current column...

:ashamed1:

 

[david luchini]

I think you picked a good one. The shortcomings don't look important. The sheet is protected so I can't see the algolrithm. I tried three different delta currents. The line currents came up fine. The sheet assumes the loads are resistive - no phase angle information.

It seems line some of the line current calculations come up wrong as well...Try entering 10, 0, 0 for L-L load currents...You get 8.66, 8.66 and 0 for line currents...On "split phase," two 10a l-n loads give a 20A neutral current.

It's a real nice interface though. Be great if the errors were corrected. I'd be nice to see the hidden part of the sheet.