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How does PM5500 series meter calculates TDD (Total Demand Distortion)

Published date: 21 May 2020

Product Line
PM5500 series


  • Total demand distortion (TDD) is the per-phase harmonic current distortion against the full load demand of the electrical system
  • TDD indicates the impact of harmonic distortion in the system
  • For example, if your system is showing high THD values but a low demand, the impact of harmonic distortion on your system might be insignificant 
  • However at full load, the THD value for the current harmonics is equal to TDD, so this could negatively impact your system
  • TDD (total demand distortion) evaluates the harmonic currents between an end user and a power source
  • The harmonic values are based on a point of common coupling (PCC), which is a common point where each user receives power from the power source
  • The meter uses the following equation to calculate TDD:
  • Where ILoad is equal to the maximum demand load on the power system and HC is Harmonics Count
  • Harmonic content (HC) is equal to the RMS value of all the non-fundamental harmonic components in one phase of the power system.
  • The meter uses the following equation to calculate HC:

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