Issue

The ION meters calculate Total Harmonic Distortion (THD) by default and the user would like to calculate Total demand distortion (TDD) instead.

Product line

ION 7550/7650, PM8000, ION 8650/8600, ION7330/ION7350, ION9000

Environment
ION Setup 3.0

Resolution
Total demand distortion as defined in the IEEE 519 standard is he total root-sum-square harmonic current distortion, in percent of the maximum demand load current and can be calculated using the following formula:

The IL above is peak or maximum demand load current at the fundamental frequency component measured at the point of common coupling (PCC) derived from the 15 minute or 30 minute billing KVA. With the load already in the system, you can calculate I_L as the average of the maximum demand current for the preceding 12 months. for a new installation, you can estimate I_L by using predicted load profiles.

One can either setup the ION meter to record the maximum demand current or we can input a calculated value as following:

1. Navigate the ION meter in advanced mode (ctrl + left click)
2. Select the 'Maximum Modules' folder and then right click the white space to insert a new module
3. The source of this new module should be the sliding demand current input as shown below.
   
4. Change the output register’s name to make it easier to link later on.
5. Now create maximum modules for I b/ I c current demand accordingly following the same process.
6. Navigate to Harmonic Measurements Modules and link the Max Demand input each to the output of the maximum module created in step 2.
7. Do this for each: Ia = I1, Ib = I2, and Ic = I3.
   
8. In the setup tab, change the display mode to “MAGNITUDE OUTPUTS DISPLAYED AS PERCENTAGES“ and the THD display mode to Percentages.

Alternatively, if the IL is to be calculated, one can input a constant using an arithmetic module as following:

1. Navigate to arithmetic modules and insert a new module
2. Link Source1 to I a mean from the sliding demand window modules.
3. In the setup tab, change formula one to the constant calculated in Amps
   
4. Change the Output register’s name to make it easier to link.
5. Navigate to harmonic measurements module and then link the Max Demand input to the output of the arithmetic module created created in step 2
6. In the setup tab, change the display mode to “MAGNITUDE OUTPUTS DISPLAYED AS PERCENTAGES “ and the THD display mode to Percentages

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