Need to measure harmonic distortion

[kyle_vi]

I need to measure the harmonic distortion of voltage.    What equipment might I consider for this?  I need to measure this over 60 minutes.

[johnsold]

You do not provide very much information.

What are the magnitude and frequency ranges of the voltage you will be measuring? How much and how fast can the fundamental frequency change during a measurement? What levels of harmonic distortion do you expect? What accuaracy and resolution is required? How many harmonics need to be considered? 

Will the result(s) be displayed to a user, stored in a file, or used to control something? Do you want one value which represents the distortion for the hour or do you want multiple measurements? If multiple, what interval between measurements and what duration of signal will be included in each?

Lynn

[Bob_Schor]

Find a competent Electrical Engineer (a smart undergraduate would do).  She should know how to help you answer Lynn's questions, and can help you decide what hardware is appropriate to take the measurements.  If you are planning to use LabVIEW to acquire the data needed for this determination, she may want to ask a colleague who knows LabVIEW for help with the data acquisition step(s), but should be competent to at least describe the analysis steps that need to be taken.  It's a Bonus if she is also a LabVIEW Guru herself, of course ...

Bob Schor

[kyle_vi]

I just need something where I can certify our lab power quality is good every year or when needed.  My voltages are 120V 60Hz, 230V 50Hz, 240V 60 Hz.   Our voltage should be 5% or below.   I just need to display the THD % at start and then at 1 hr.  I think this would just be two readings.

On a separate issue I could use a set up to measure THD and flicker of a unit under test. 

[Bob_Schor]

This is definitely not a LabVIEW issue.  I don't know where you work, but someone in Facilities should be able to locate someone who can do these measurements for you.  You can also contact your local Utility Company ...

BS

[johnsold]

OK. 

1. You need a protection interface to the power line(s). This should protect your equpment from transients and faults. It is possible that the lab power already is protecteed from external events such as lightning, but you still need to be careful about internal problems.

2. You need transformers or tranducers to reduce the line voltages to the 5-10 V range which is typical of most data acquisition equipment. The devices need to have enough bandwidth to get all the harmonics required.

3. You need a data acquisition device which can sample fast enough, with enough resolution, and with enough accuracy to make the THD measurement.

4. You need a calibration procedure and standards to allow you to verify the performance of the system.

Is there a particular standard to which your lab must comply? If so, that standard will specify the bandwidth and accuracy requirements.

If this is a once per year requirement, you might be better off renting a power quality analyzer instrument as needed.  The calibration and certification issues are meanaged by the rental company so you do not have to worry about that.

Lynn

[johnsold]

Bob,

I once worked for an electrical utility and later worked with a different utility on a similar power quality issue. While the utilities want their power to be "nice," they are not in a position to certify the quality. The power quality standards utilities are required to meet are usually significantly less stringent than what might be required in a lab.

Lynn

[Bob_Schor]

I definitely defer to your Wisdom and Experience.  I think your previous post should have Solved this Problem and should be Marked as the Solution!

BS