Measuring reactive power
Measuring reactive power
(OP)
How can you measure reactive power in a 3 phase system using a single anologue watt meter?
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RE: Measuring reactive power
If you know what the magnitude of the voltage and current, and you know the power, you can calculate the reactive component by subtraction.
Knowing the power, and the VA calculation, you can also determine the power factor, which will give you the relative phase angle between the voltage and current.
RE: Measuring reactive power
The kH factor may be used to read the average Watts or Vars over a short period of time on revenue meters. (5, 10, or more seconds.)
To measure single phase VARs, connect "A" phase current to the meter and connect "B" to "C" phase voltage to the meter.
You have a 90 degree voltage shift so the meter will respond to VARs. Divide the reading by 1.73 to adjust for the ratio between line to neutral and line to line.
I will leave it to you to expand this to three phase. I don't have the time just now.
Bill
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RE: Measuring reactive power
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As Bill said, we used Phase shifting transformers for this, back in the day. They could be external or built into the varmeter.
Dave