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240V 3-Phase Measurement


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#1 Guy

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Posted 21 September 2011 - 06:33 AM

I am working with a 3kW 3-phase 240VAC generator and want to measure the voltage and current on all 3-phases. How would you recommend I do this with a U3-LV?

#2 LabJack Support

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Posted 21 September 2011 - 08:39 AM

What sort of information do you want about the voltage/current signals? Do you just want the RMS of each? Or perhaps the true-RMS? True-RMS with phase relationships between voltage and current and also phase-to-phase? Or if you are trying to do accurate power/energy measurements, you probably just want all the waveforms so you can process in software to get all the information you want.

Here is another topic with related info:

https://forums.labja...?showtopic=4263

#3 Guy

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Posted 26 September 2011 - 02:28 AM

Thanks, I want as much information as possible to calculate the power factor and system energy etc. I want to find out how much power is being produced by a 3-phase alternator and how it is being delivered. Would a resistor network and a current shunt work? Guy

#4 LabJack Support

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Posted 26 September 2011 - 08:21 AM

It is possible, but you need to know what you are doing. You will want to use 3 single-ended voltage dividers and low-side shunts and thus will wind up with a bunch of signals referenced to the same ground. It is very easy to make a mistake and wind up with something referenced to the high-side rather than ground, and the result could be damage. I recommend that for the current measurements you use current transformers or hall-effect sensors. Both are available cheap and much better suited for this type of measurement. Both are isolated so you don't have the common-mode issues. For voltage, I recommend you put each through a cheap step-down transformer (which also provides isolation), and then you can use resistors to divide further as needed. Depending on what exactly you wind up with, you might need to consider how to handle bipolar signals. Once you have the hardware decided, you can stream the 6 signals and in your software calculate everything you want about them.


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