THD · Total harmonic distortion
The share of waveform distortion injected by non-linear loads; it is capped at the point of common coupling, which drives active-front-end, filter, and transformer decisions.
Current numbers
5% THD-VIEEE 519-2022 PCC voltage limit above 1 kV to 69 kV (3% per harmonic); 8% THD up to 1 kV