THD-V = √(Σ Vh²) / V₁ × 100 [IEEE 519-2014 Table 1]
TDD-I = √(Σ Ih²) / IL × 100 [IEEE 519-2014 §10.2]
Isc/IL ratio selects the current distortion limit row from Table 2 (≤69 kV), Table 3 (69–161 kV), or Table 4 (>161 kV).
Even harmonics are limited to 25% of odd harmonic limits in the same group (§5.1).
Harmonic groups: h<11 · 11≤h<17 · 17≤h<23 · 23≤h<35 · h≥35
Voltage distortion limits (Table 1): LV ≤1 kV → THD 8%, indiv 5%; MV ≤69 kV → THD 5%, indiv 3%; HV 69–161 kV → THD 2.5%, indiv 1.5%; EHV >161 kV → THD 1.5%, indiv 1%.