How do you calculate kva for unbalanced loads?

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orr263

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Is there a formula for calculating kva on unbalanced 3 phase loads when amperage and voltage are known?
 
If you need a precise answer, the math is very long and involved. If you want an answer that is good enough for most real situations, then use the average of the three amp readings as though the system were balanced at that value.
 
charlie b said:
If you need a precise answer, the math is very long and involved. If you want an answer that is good enough for most real situations, then use the average of the three amp readings as though the system were balanced at that value.
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However, the highest amperage must be carried by less than the entire system, so must be considered.
 
Smart $ said:
...less than the entire system, or simply by the system?
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What I so poorly related is that the phase conductor with the highest load current controls the ampacity requirements. The closer to balance, the less overbuilding required for a given kva.

In more other words, the entire system does not equally share an imbalanced polyphase load. Part will see less than 1/3 of the total kva, and part will see more than 1/3 of the total kva.

Is that any better?
 
LarryFine said:
What I so poorly related is that the phase conductor with the highest load current controls the ampacity requirements. The closer to balance, the less overbuilding required for a given kva.

In more other words, the entire system does not equally share an imbalanced polyphase load. Part will see less than 1/3 of the total kva, and part will see more than 1/3 of the total kva.

Is that any better?
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Works for me ;)
 
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