Flicker measurement using Electrical Power Suite

[Vikingyong90]

I try to use DAQ to obtain voltage and current from the grid voltage, around 240 V, 50 Hz as attached in the file attached.

Then, the flickermeter is used to obtain the instanteneous flicker, P inst to calculate the short term flicker, P st and long term flicker, Plt.

Usually, the value obtain for the P st is around 1.0, but the value obtain as shown in the picture attached is far greater.

Hope for guidance. Thank you

[Yifan.Liu]

Pst VI and Plt VI have output valid indicators, and you should obtain Pst and Plt values when output valid is TRUE.

[Vikingyong90]

Thanks for the advice.

By the way, for short term flicker measuremnt, Pst duration is 10 minutes while the long term flicker measurement, Plt duration is 2 hours according to the international standards.

The result I obtained from the attached picture show that there is Pst and Plt over few minutes.

Is there any way that I can change to obtain result according to the standards?

Hope for your guidance. Thank you.

[Yifan.Liu]

You still have to use the output valid to make your test compliant with standards.

The Pst output valid? becomes TRUE every 10 minutes and the Plt output valid? becomes TRUE every 2 hours, which is compliant with IEC standard.

[Vikingyong90]

Hi,

I try to improve the program, as shown in the attached file.

But, the measurement time value for the Pst seems not to be 10 minutes. 

As I not too sure whether there is error using case structure in such way to check the timestamp.

Did I make wrong selection for the initialize VI? I am not sure what value should I insert for the sample per cycle parameter.

Other than that, is the initialize VI will affect by the DAQ assistant setting on no. of sample and rate?

[Yifan.Liu]

1. About measurement period of Pst

   The Pst output valid? becomes TRUE after the VI running for 10 minutes, and will return TRUE every 1 minute after that (because of using 10 minutes sliding window). As a result, the value of Pst becomes valid after the VI running for 10 minutes and the value will update every 1 minute after that.

2. To measure Flicker correctly using EPS 2013 on DAQ platform, please refer to the example provided at the filepath below:

    ...\Program Files\National Instruments\LabVIEW 2013\examples\Electrical Power\Power Quality\Applications (DAQmx)\Flicker Measurement (DAQmx).vi

[Vikingyong90]

Hi all,

I try to remove the unused part and left only the flicker measurement part.

I try to configure the DAQ Assisstant with continuous acquisition mode and not using the N sample.

After around 20 mins, I encounterd problem error 200279 as shown.

Since I required 2 hours to obtain long term flicker, therefore, I reall hope someone can help me on this.

Thank you.

[Vikingyong90]

When I using N sample in the acquisition, the value I obtain for the flicker is way larger than 1.0,

However, when i change the acquisition mode to continuious, the flicker I get is around 0.2, something i wish to get perhaps.

But seems that the error -200279 pop up around 20 mins time and stop the whole program and I cant proceed further.

I try several run with different sample to read and rate value in the properties of DAQ assistant.

But the error remains there.

Can anyone help me on this. Thank you.

[Vikingyong90]

Here attached the VI file. 

Hope for guidance.

[Yifan.Liu]

You need to preprocess(resampling) the signal acquired from DAQmx before performing measurement and analysis on it.

The sample rate after resampling will be different from the original sample rate set in DAQmx. For example, if you set samples per cycle as 192 and the frequency of input signal is 50 Hz, the sample rate after resampling will be 192*50 HZ = 9600 Hz.

In your VI, without resampling, the actual sample rate is set in DAQmx, however the following flicker measurement VIs are using the sample rate of samples per cycle(hard coded as 500 in your VI) * input signal frequency, this difference will finally make the measurement invalid.

Following picture captured from DAQmx flicker example shows the preprocessing part which is necessary for your application:

Again, please DO refier to the example to customize your VIs.

Thanks.