Unbalanced Power Calculation

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bonding jumper

Senior Member
Hello, I am attempting to learn more about my worksite and the capacities of our systems. I have attained data but am having a hard time understanding exactly what is happening.

I am attempting to calculate efficiency of three seperate UPS Systems with real world data, one MGE, and two different Lieberts. The easiest way to acomplish this is to make an equation is to compare the kW in to the box to the kW out, or (kW IN)/(kW OUT)*100 = Percent efficiency

Data:
Module; Input A B C Voltage; Input A B C Amp; Output A B C Volts; Output A B C Amps; KW(displayed); KVA(displayed)
A1; 466, 469, 466; 259, 276, 260; 483, 480, 482; 168, 219, 183; 153; 157
A2; 468, 468, 467; 346, 361, 356; 482, 477, 480; 239, 282, 268; 215; 219
A3; 466, 468, 465; 299, 310, 294; 479, 481, 479; 225, 233, 187; 178; 178

B1; 474, 477, 473; 370, 318, 323; 486, 485, 487; 276, 309, 271; 235; 257
B2; 471, 474, 471; 373, 353, 361; 485, 485, 485; 311, 338, 314; 269; 282
B3; 473, 475, 474; 407, 390, 398; 480, 487, 491; 389, 352, 316; 295; 329

The forumula I was using to calculate Input Power was
(Phase A Power + Phase B Power + Phase C Power)/1.732 = 3 Phase Power
This was working somewhat reliable untill I discovered that unit B3 was displaying negative losses, or the input power was less than the output. So the formula isn't only wrong, but not even close. I also am confused about the difference between I (phase) and I (line). I am trying to find out what formula the UPS uses to calculate its power output, so I can do something similar to derive that power input by using an excel formula. Even if its complicated, excell will make it easy to calculate if I gather all the data.
Thanks in advace for your help.
I have attached a view of my spreadsheet for clarification.
http://img425.imageshack.us/my.php?image=untitledgj2.jpg
untitledgj2.jpg
 
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readings?

readings?

Do you trust the reading on B3? I am getting the same problem when I use B3's values. Maybe there is a problem with the meter... ...or something else is going on.
 
Well, if you think my methodology is correct, then i would agree that the display is off. But for some reason I feel that my power calculation is wrong.
 
I have calculated MVA with your data set, is this what you have calculated? If you just multiply that current and voltage, this is MVA. How have you been calculating (A power + B power + C power) ?

-Matt
 
mpross said:
I have calculated MVA with your data set, is this what you have calculated? If you just multiply that current and voltage, this is MVA. How have you been calculating (A power + B power + C power) ?

-Matt
Click to expand...
Basically, for module A1, I would calculate the A phase power by this formula,
A phase volts L-L* A phase current = a phase V*A; B phase volts L-L * B phase current = B phase V*A; C phase volts L-L * C phase current = C phase V*A. I added these together and divided by 1.732 to get 3 phase V*A. Then multiplied that value by the nameplate advertised input power factor of the UPS module and called that KW.
Thanks for the help.
 
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Mva

Mva

oops.

I am used to MVA values (working for the POCO) ! Disregard my MVA, which is wrong, should be kVA.

OK then, I follow your last post.

I would next make sure that I have the line/phase relationship completely ironed out. If you already do, I dont know what to do next.

-Matt
 
Thanks for the help. I figured the MVA was kVA. Yeah I agree about the different types of ways to measure current. The I Phase I mentioned was what was on the display of the unit. Its a delta input delta ouput so I imagine that is I phase not I line.
 
There are many different metering configurations, but the basic principle is, circuits can be connected to create dot products (multiplication), and cross products (for determining phase angles). These two vector products determine VA (multiplication) and kW (multiplication along with phase differential). All without the need for electronic circuitry.
 
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