Some standards like the IEEE 519 requests the calculation of a Total Demand Distortion (TDD). Other standard like the IEEE Std 2800 requests the calculation of a Total Rated Current Distortion (TRD).

In contrast to the general definition of the Total Harmonic Distortion (THD) according to IEC 61000-4-7, the TDD does not refer to the fundamental current, but to an individual maximum demand current. According to the paper "Interpreting IEEE Std 519 and Meeting its Harmonic Limits in VFD Applications" by Tony Hoevenaars, Kurt LeDoux and Matt Colosino the TDD can be seen equal to the TRD, which is based on the rated current.

In PowerFactory, there is no special TDD or TRD variable, but it is possible to change the basis of the THD from the fundamental to the rated value.

The important settings can be found in the Harmonic Load Flow command under Advanced Options.

To calculate the TDD according to the IEEE 519, use the following settings:

-          Calculate HD and THD “Based on rated voltage/current”

-          Set the max. harmonic order of calculation of THD and THF to 50

-          Make sure, that the rated current of the components is set to the maximum demand current or accept the definition from the paper.

After a harmonic load flow with these settings, the THD result can be seen as TRD or TDD.

The “Example_TDD-THD.pfd” shows some application cases and the “Example_TDD-THD_Calc.xlsx” shows the corresponding calculation.