# LabVIEW

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## pmu

Hi

I want to measure three phase voltages and cuurent using NI USB 6009 until now I have implemented  all the outside circuit and whene i transfer signals to labview i need to simulate  PMU(phasor measuremet unt)in order to get the voltages and currents phase an magnitude

so does any one has the simulation of pmu

thank you

Message 1 of 7
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## Re: pmu

Hello MATI19

Here you can find a full case study about an Open-Source Phasor Measurement Unit with LabVIEW.

Regards

Frank R.

Message 2 of 7
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## Re: pmu

Well, your problem specification is kind of vague.... so here comes a kind of vague answer.

Doesn't sound like too hard a problem to code. Measure the voltage and current at your required sampling rate, and perform whatever math is necessary to get the results in your required format. Use the Extract Single Tone vi from the Waveform Measurements palette to get phase information. I understand from your text that you have implemented the necessary circuitry (transformers, voltage dividers, shunts, etc.) in order to get your 3 phase down to levels that are measureable with the 6009?

When you say 'simulate PMU', are you trying to simulate a specific PMU, do you have a particular requirement for data rates and formats, etc?

What have you tried so far and what problems do you have?

Message 3 of 7
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## Re: pmu

HI
here is a photo  shows what I have done
i get the voltage from the signal conditioning circuit i enter it to labview by NI usb6009 then i get a constant frequency and magnitude but a variable phase
normaly i need to get constant phase when there is no fault
so what i need exactly is a simulation circuit that gives me the phase and magnitude of the measured three phase voltages and current
thank you again

Message 4 of 7
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## Re: pmu

For starters you don't need a SIMUALTION circuit, you need a measurement algorithm. Simulation is easy - you just make up the values 😉

Next, phase is a comparative measurement. You can only measure the phase of one signal in comparison to a reference point or another signal. The Extract Tone vi has no reference point other than the samples you give it, so (if you look at the formulas at the bottom of the documentation page for that vi) it measures at what phase angle on the waveform the first sample in the window is assuming a cosine signal.

When your DAQ samples the waveform, it starts its sampling at a random point on the waveform and measures a set number of samples. Each time it takes a new set of samples it will start at a different random point on the waveform unless you have somehow syncd the sampling to the source which it looks like you have not. Hence the measured phase will be random for each set of samples.

Real world PMUs use a reference time clock (usually a GPS clock) so that different PMUs in different locations all start their measurement windows at the same time and are synchronised to the generator.

Your phase signals might make more sense if you measured all six signals (3 voltage and 3 current) and picked one as your phase reference and subtracted that value from all the others - then you would have the phase of the other signals referenced to that one.

Otherwise you will need to ensure your measurement window is synchronised with the waveform source (the generator) - you can do this (kind of) by accurately timing your acquisition so that it starts at exact multiples of the waveform period - eg. if you put some timing in there so that the acquisition started at exactly one second intervals then the results should be somewhat more stable.

As a suggestion, you would do well to work out how to set up and acquire the signals using the DAQmx vis rather than the express vi as that gives you much more control over all aspects of your measurement. There are numerous examples in the Example Finder under Hardware Input and Output>DAQmxAnalog Input

Also check out Use VI Snippet to Store and Share Reusable Code Sections for a handy way to post your code snippets here (more useful than just pictures).

Good Luck.

Message 5 of 7
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## Re: pmu

Hi Sir,

How do you did the circuit to get the 3 phase voltages before you transfer it to labview.

Can you suggest me that circuit.?

Thanks,
Surya S

Message 6 of 7
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## Re: pmu

Hi Surya,

It may be helpful to look at the hardware discussion forums also, particularly the MultifunctionDAQ one if you are also using an NI DAQ device:

MultifunctionDAQ Discussion Forums

http://forums.ni.com/t5/Multifunction-DAQ/bd-p/250