Load Calculation for Transformer Secondary (Delta) with unbalanced single phase loads

[Smart $]

I have always seen that for a balanced 3-phase delta load the current in the delta windings were always 1.73 times less then the line currents (example of 3-phase motor) Would this multiplier apply to balanced single phase loads as well or just for 3-phase loads, and you always have to do the vector addition for single phase loads?

Yes, the multiplier works for balanced single phase loads.

 

[Smart $]

I used a formula based on the law of cosines for the calculation and came up with the same values...

I1 = (480^2+48^2 - 2*480*48*Cos(120))^-2

I1 = 505.7
I2 = 50.6
I3 = 482.4

I have to admit when I originally looked at gar and your equations I "felt" something was odd. It didn't really dawn on me what the oddity was until now, because previously I was only concerned with the accuracy of the results. Anyway, just so you (and gar) know, the notation x^-2 is not acceptable for indicating √x. A number to a minus (-) power indicates the power of the reciprocal. For example: x^-1 = 1/x and x^-2 = (1/x)?. The square root of a number in power form would be x^? or x^.5.

BTW, if current phase angles are referenced to "RA", then your line current phase angles appear to be off by about 30?.

Assuming the load currents to be the following:

RA= 480A @ 0deg
RB= 48A @ -120deg
RC= 4.8A @ -240deg

I come up with the following line current for L1,L2,L3. These currents are assuming unity power factor:

L1 = 506A @ -26deg should be -355?
L2 = 50.6A @ -145deg should be -115?
L3 = 486A @ -210deg should be -180?

 

[gar]

090101-1022 EST

Smart $:

Thanks for correcting my mind vs function disassociation. Strange things that the mind does at times. Also how fingers operate relative to what is being thought can be quite unconnected. Sometimes I type whole words that I have no idea how they got into the text. Even double and triple checking does not catch many mistakes. That is the value of independent checkers.

Just typing this post I had "for for" for "for", and "tripple" for "triple".

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