【PM8240】Regarding "maximum values" of current and voltage THD

[Miyai]

Hello,

What is the maximum value for Modbus communication regarding THD(V, I)?

I understand that the Modbus definition is in FLOAT32 format and the maximum value is 3.402823466 x10^(38).

However, I don't think PM8000 outputs such a large value, so if there is an upper limit, please let me know.

Best regards,

Miyai

[Charles_Murison]

Hello @Miyai ,

The THD can be greater than 100%, so the limit of floating point kind of is the maximum theoretical limit the number can get to. To get a number this big would require a system with almost no fundamental signal and a huge harmonic signal, to not really practical to see a number that large. Can't really give a practical limit.

Regards,

Charles

[DanL · Accepted solution]

The default shipping configuration for the Harmonic Measurement Modules is to show THD as a Percentage ratio of the measured rms harmonic distortion and the fundamental.

The "Percentages" option behaves the same as "Percent Fundamental" when the "Max Demand" input is left unlinked (as done by default on all modules). To prevent a divide-by-zero, this calculation is skipped and a 0 value returned when the fundamental (denominator) is below the "force level" (0.01% of FS on current and by default 0.02% of FS on voltage). Based on this, I suspect the theoretical upper bound is on the order of 1,000,000% when full scale harmonics and a very small non-zero fundamental are present.

The "Percent RMS" option effectively normalizes results to 100% (100% is the maximum possible value because the denominator includes all the harmonic signal)

https://www.productinfo.schneider-electric.com/ion9000/viewer?docidentity=HarmonicsMeasurementModule...

[Miyai]

Hello @DanL , @Charles_Murison ,

Thank you for advice.

I will reply to the customer with the maximum value of the float.

If the customer wants to narrow the upper limit again, I will answer with 1,000,000%.

Best regards,

Miyai