Understanding the Relationship Between Total Harmonic Distortion and Total Demand Distortion in IEEE STD 519-2022: A Practical Discussion for Compliance Evaluations

When trying to apply the harmonic limits of IEEE Std 519-2022, there can often be confusion on the difference between Total Harmonic Distortion (THD) and Total Demand Distortion (TDD), and when each value is used. The intent of this paper is to provide clarity and direction on how to apply the Standard’s Current Distortion Limits as they were intended in a way that is practical for real world projects. This paper will outline how to apply the limits at an existing site and during the design stage of a new installation/project. This paper describes how to determine the maximum demand load current without the need to wait until after the system has been installed and operated for many months. Using this value, one can then calculate the appropriate demand distortion to compare against the IEEE Std 519 demand distortion requirements.