Elementary Question on Electrical Power 3

[Aishah]

Hi Electrical Gurus,

I have an elementary question on calculating the electrical energy consumed by an air-conditioner. That is, one of my technicians reports his measurements that goes like this: Current R/S/T = 12.9/10.3/11.6 Amps and Voltage R/S/T = 216/231/225 Volts. I know that to calculate the power (in W) is an easy thing using P = sqrt(3) * V * I * PF.

But in my case, which current and voltage do I need to plug in the P-equation? Can I use the average current and voltage in that formula?

Thank you for your answer(s)

Regards,
Aishah

 

[wareagle]

Yes you can use the average to get an approximate answer.
You can also take each amperage x the voltage and add the 3 up. How close do you need to be? I am not familar with the terms R/S/T. Is the the phase readings? We usually use
A,B and C to designate the phase voltage and current.

 

[NewfieSparky]

I never heard of the R/S/T thing either put my guess would be that these mean that the unit can run at either of these voltages. Is this a 3-phase unit? If you are running at 225V, use the 11.6A. If you are running at 231V, use the 10.3A. Maybe I am wrong, but without more info this is what I'd say.

 

[ScottyUK]

R/S/T is European terminology. It probably originates at the same time as the U/V/W notation.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[rcw retired EE]

Multiply R amps x R volts = R volt amps.

Do the same for S & T phase and add the VA up to get total VA (Volt Amps) consumed. The root 3 factor does not apply since these are single phase voltages (line to neutral).

Watts = Volt amps x power factor.

You will have to take a guess on the power factor of the AC unit. It is probably about 0.85 - 0.9. If any electric heating elements are operating, they will be at 1.0 power factor and pull the total power factor higher (0.9-0.95).