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Power calculations

Johno12345

I have confused myself again.

Some time ago, I had a consultant monitor my air compressor usage, and he gave me a fairly useless graph with one line for kWh, it averaged 12kW. Nice and simple

I also now have monitoring equipment on a different compressor, which is averaging 3kW, but its 3kW on each phase. 

These are both 3ph inverter driven compressors, am I correct to effectively merge the three lines on the graph and say the original compressor used 12kW and the new one uses 3kW?

Looking at my monitoring equipment, it looks like I'm right to do that, as the old compressor is showing something in the region of 12kW per phase when accounting for all the other loads (the monitoring monitors a sub main, not the compressor alone)

I'm sure I'm over thinking this!

Thanks as always

Parents
  • 0

    For 3-phase equipment it's conventional to measure amps per phase but power (kW or kVA) overall (rather than per phase)  - so 1A per phase gives 690W overall. But there's nothing really stopping anyone working with power per phase if they really want. If the graph is showing 3 separate power lines, it might well be per phase, in which case you'd add them together to get an overall power figure. Best check with whoever originated the graphs for a definitive answer.

       - Andy.

Reply
  • 0

    For 3-phase equipment it's conventional to measure amps per phase but power (kW or kVA) overall (rather than per phase)  - so 1A per phase gives 690W overall. But there's nothing really stopping anyone working with power per phase if they really want. If the graph is showing 3 separate power lines, it might well be per phase, in which case you'd add them together to get an overall power figure. Best check with whoever originated the graphs for a definitive answer.

       - Andy.

Children
  • 0 in reply to AJJewsbury

    I decided to just use the kWh section to calculate, since that is the ultimate unit that I use to calculate cost. 

    It worked out just about the same as my rough calculations based on the average of all three active power kW, rather than the sum of all three

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