Three phase Measurament

Hi everyone,
I'm trying to measure the phase and the power factor for a three-phase motor. The problemn is that the motor is running with 480V and the SCXI module that I have can only handles until 300Vrms. I'm thinking about using some voltage transformers to step down the voltage and then connect it to the SCXI module. If I do that, will it affect my phase angle and power factor?
Assuming that this configuration works, how can I find the phase in each wire? Is it possible to run all samples at the same time and then make some comparisson between their plots to measure that?
Thank you!
Kenny Caldas
Solved!
Go to Solution.

Just want to emphasise Lynn's point about 480 nominal volts and what you might actually have.
Get your design and wiring checked by someone certified to do so before connecting.
Some further points:
How is the motor being fed?
a. If fed by a Direct On-Line starter or a Star-Delta starter, there will be a big spike when the contacts open to turn the motor off, or during the star-delta transition.
b. If fed by a PWM inverter, then the inverter synthesises the AC 50 or 60 Hz wave form by chopping DC very fast, and relying on the motor windings to act as the low pass filter. Good luck trying to instrument that.
Fault Level: You must have fuses as close to the instrumentation pick-off point as possible. That way, if there is a fault in your wiring the instrumentation fuse pops, and you do not have the full fault current flowing through your instrumentation wiring. Fault current will probably be about 4 times motor start current if the motor is fused correctly, and if it is an induction motor.
I would use isolation amplifiers on the voltage inputs. That way you can use a simple potential divider on the input to scale to the voltage you want, but make sure that the isolation amplifier has a suitable frequency range.
So it would go something like:
Line voltage->Fuse(or other protection device)->Potential divider->Isolation Amplifier->SCXI module.
IF you sample each channel fast, e.g. 10,000 samples per sec., then the time difference between samples and hence sampling induced phase error will be small.
Also look at the safety issues with Current Transformers here:
http://en.wikipedia.org/wiki/Current_transformer

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Hi All,
I'm not sure if this is the right board for this question, or if I should ask it on one of the hardware boards. Let me know if I should move it, please.
I need to set up a LabVIEW-based system to monitor the following:
1. Output from three-phase power analyzer (480VAC, 0-100AAC) - this could involved monitoring formatted power-quality data from a power analyzer OR monitoring voltage and current on all phases, then doing the power quality calcs in LabVIEW
2. DC output current (0-200ADC) - This needs to be relatively fast (2000 samples/sec), but not very precise (0.1A resolution would be fine).
3. DC output voltage (0-600VDC) - Again, this needs to be fast but not very precise. See current specs, above.
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Many thanks in advance.

diarmaede wrote:
Hi All,
I'm not sure if this is the right board for this question, or if I should ask it on one of the hardware boards. Let me know if I should move it, please.
I need to set up a LabVIEW-based system to monitor the following:
1. Output from three-phase power analyzer (480VAC, 0-100AAC) - this could involved monitoring formatted power-quality data from a power analyzer OR monitoring voltage and current on all phases, then doing the power quality calcs in LabVIEW
2. DC output current (0-200ADC) - This needs to be relatively fast (2000 samples/sec), but not very precise (0.1A resolution would be fine).
3. DC output voltage (0-600VDC) - Again, this needs to be fast but not very precise. See current specs, above.
4. CAN bus - I'll be monitoring a CAN bus and processing CAN data, probably using an NI USB-8473. I have much of the CAN code written already.
Any suggestions on how I should proceed? Has anyone had good results with specific power analyzers tied into an NI-based system? What about current probes? High voltage meters? Is there any pre-written LabVIEW code for three-phase power analysis?
Many thanks in advance.
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DC current and voltage that high will require a current shunt and some scaling for your voltage. Then you could measure it with any decent DAQ device, maybe a cheap as a NI-USB6009. We like to use the Agilent 34970A with a 34901A multiplexer card for this application. The 34970A/34901A is our Engineering Lab workhouse it has the benefit of ISOLATED CHANNELS direct measurement of 300VAC/DC and it can read thermocouples.

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Greetings
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figure 2.jpg ‏70 KB
figure 4.jpg ‏72 KB
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Duplicate Post
Cory K

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lock-in testmod.vi ‏36 KB

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RC Circuit Test Multiple AI.vi ‏265 KB

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http://zone.ni.com/devzone/cda/epd/p/id/5601
The example about will need to be modified for simulating the device. The NI-FGEN driver allows you to simulate a device so that you can run your application without the hardware present. Details of how to simulate this are available on -
http://digital.ni.com/public.nsf/allkb/07A1DC2A64B4F0A38625729A00065771
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Three phase Measurament

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