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Calculating current in 3-phase circuit 1

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PaulKraemer

PaulKraemer

Electrical
Jan 13, 2012
155
Hi,

I have a tank that is used to melt glue. It has six heaters, each with a resistance of 10 ohms. It is powered with 208 VAC three phase.

Originally, it was wired as shown below with two heaters in parallel across each possible pair of lines (L1-L2, L2-L3, and L1-L3)...

Parallel_rm2mkp.jpg


... with this wiring, I had a resistance of 5 ohms across each pair of lines. With this being the case, I used ohms law to calculate the expected current between L1 and L2 (through heaters R1 and R2 wired in parallel) as 41.6 amps. Then I calculated the expected current between L1 and L3 (through heaters R5 and R6 wired in parallel) as 41.6 amps as well. I'd like to determine the expected total current through L1. Being the current through L1-L2 is not in phase with the current through L1-L3, I don't think it is correct to simply add 41.6 + 41.6 = 83.2.

If anyone here can tell me the correct way to calculate the expected current through L1 (and through L2 and L3 for that matter), I would greatly appreciate it.

Thanks and best regards,
Paul
 
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√3*(41.6 A) = 72.1 A

You should see that on L1, on L2, and on L3.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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Thanks xnuke,

I appreciate your help!

Best regards,
Paul
 
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If L1-L2 angle will be 0 L23=-120 degrees and L31 angle -240 degrees then:
Absolute: 72.05331 I1= -62.4+36.0266567974326i
Absolute: 72.05331 I2= 62.4+36.0266567974326i
Absolute: 72.05331 I3= -72.0533135948652i
72.05331/sqrt(3)=41.6 indeed.
 
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OP just wants to check his math for his desire for a magical connection scheme that gets him the same heat at a lower current from the breaker, and that ain't going to happen

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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