Problem with power factor measurements (ADE7816)

Hi agarciaoteros

I understand that you have connected a reference meter and ADE7816 Evaluation board to a same load, in order to check the accuracy of PF. I would like to make sure if you have done phase calibration prior to this, because CTs can add a considerable phase shift and hence the PF measurement can be erroneous.

Also, the two methods that you have used to measure PF are a little different:

1.cos(arctg(AVARHR / AWATTHR))=0.985

     This method uses energy register readings and hence includes harmonic content as well (upto 2KHz).

2. directly reading ANGLE0 -->  cos(ANGLE0*(50-360)/25600)=0.995

     This method measures the angle using ZX circuitry which is filtered to 70 Hz and so, is a fundamental only measurement.

So if the phase calibration is done correctly, the difference between these two readings will correspond to the harmonics.

And can you let me know what is the bandwidth of the reference meter that you are using?

Regards

hmani

Hi himani,

thank you for your help,

I am using this reference meter:

http://www.ndmeter.co.uk/files/Rail_350_Meter_Leaflet_Jan2012.pdf

we use this meter before and I think it's accurate, up 30th armonic to 50Hz.

Today I have changed the load and now PF=0.87, as you see in the picture that I attach you.

I attach you other picture with the jumper configure of current input (channel A) and voltage.

There is a big error between these results  (reference meter =0.87  //  ADE7816(channel A)=0.98),

I have tried to do other exercises to solve that problem,

     -I tested other channel, with the same result.

     -I tested other load, same error

     -I checked CT, and I'm sure that doesn't introduce that error.

I am using ADE7816 Evaluation software, and I follow these steps to setup ADE7816....

• * write WTHR1=0x02

• *write VARTHR1=0x02

• * after several minutes read AVARHR & AWATTHR to calculate PF

with these initial values and start DSP, AD7816 start to accumulate active and reactive, but with a error so big.

What am I doing wrong? What do you think?

Thank you in advance.

Hi agarciaoteros

I will get back to you on the correctness of your Eval board jumper settings and measurement procedure soon. Just before that I wanted to make sure if you have done phase calibration. Without phase calibration, the results might not match. CTs provide a phase shift to the current channel and hence the angle measurements taken before phase calibration will not be accurate enough. Once you phase-calibrate your meter, let me know if you still have this issue.

Regards

hmani

Hi agarciaoteros

Have you changed the PCF_x_COEFF registers for all current channels as stated in the Quick Start section of the datasheet? Non-default values have to be written into those registers based on 50Hz or 60Hz frequency signal you are operating on. Also kindly check your phase calibration as stated in the 'Energy Phase Calibration' section of the datasheet as CTs can introduce considerable phase shift.

Regards

hmani