Calculating kWh with one phase no voltage reading

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Robert Croghan

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Toronto, Canada
If someone could help me - I installed an energy monitor on a transformer, one voltage clamp came off thus reading 6V's the entire recording cycle (one month) - I have amps for this phase. The other two phases recorded properly except for the fact that the voltage was recorded at 259V not 480V. I am trying to clarify can I do the calculations manually to calculate kWh as I have the amperage and know the "typical" voltage (expected voltage).

Thanks
 
When you say that 'one' voltage clamp came off but the other to phases recorded properly, did you get _two_ measurements of about 259V and one measurement of 6V?

Were your voltage measurements supposed to be line-line, did you have a clamp on neutral so that you were supposed to have line-neutral measurements?

Does your energy monitor report (and log) power factor per individual phase?

Does your energy monitor report (and log) power consumption by the individual phase?

As Smart $ says, you need power factor information in one form or another. If you continuously measure voltage and current and continuously integrate power, then the power factor is automagically dealt with in that calculation. If your logging system _separately_ logs power for each phase, and if your phase current log looks balanced, then 3/2*(sum of power for the two good phases) would be a reasonable approximation.

If all you have to go by is a log of RMS current (per phase) and RMS voltage (line to neutral), then you will need to multiply voltage*current*power factor to get the power being delivered to that phase.

So being able to do the calculation all boils down to what information was actually logged and how approximate you are willing to be.

-Jon
 
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