480V 3ph Current Measurement?

[chuggins1434]

Hello LabVIEW Guru's,

I'll just preface this with that I'm not an EE.  🙂 

Todays challenge is that I'm measuring 480V-3ph and have a question about the current measurements.... specifically, I can measure each individual leg (I have a Fluke 435 Power Quality Analyzer to compare my readings to...)  ...but my question is how do you calculate the amp data to give a simple single reading?  ..is it just a simple average of all the legs, or is it like measuring the voltage and need to multiply by the sqrt(3)?

Hardware...

cDAQ-9185 (2.5k samples @ 1k Hz)

Voltage measurements with a NI-9225 (measuring each leg to ground/neutral)

...calculating voltage by taking RMS of each wave x sqrt(3) and averaging the three values... assuming that this is correct since it matches the voltage I'm reading on my DMM.

Current measurements are with a NI-9205 measuring the mV signals from Fluke i400s amp clamps (output = 10mV/A) and I'm matching what my Fluke 435 is telling me. (~1.2A/leg)

I've been measuring single phase for a long time and this is my first stab at 3phase...  a point in the right direction would be much appreciated!  

C

[santo_13]

Assuming you are able to capture the voltage and current (as mV/A and converted back to A) for all three phases synchronously (just put the channels in the same DAQmx task), computing the instantaneous power is

Power = Pr + Py + Pb

P = V * I

[chuggins1434]

Thank you for the response Santhosh... 

Turns out I had an error in my approach to this... I'm measuring the voltage/current going to a VFD/blower and I didn't have the VFD at a full 60Hz... this was generating a difference between the current I was seeing on my VFD readout and from my NI hardware... once I pushed the VFD up to 60Hz my current readings matched within a 0.1A and I'm good with that.

Thank you,

CHuggins