Power quality
Harmonics, IEEE 519 limits, voltage sags, IEEE 1159, ITIC, mitigation strategies.
Lessons
Harmonics & IEEE 519 — THD, TDD, triplens, mitigation
Fourier decomposition: i(t) = Σ I_h·sin(h·ω·t+φ_h). THD vs TDD. Six-pulse rectifier h = 6k±1 (5,7,11,13) at THD ≈ 25-30%. Triplen harmonics (3,9,15) = zero-sequence → add in neutral; Δ winding traps. IEEE 519 limits: V-THD ≤ 5% (<69kV), current TDD per ISC/IL class at PCC. Mitigation: line reactor → 12/18-pulse → passive/active filter → active front-end. Resonance f_r = 1/(2π·sqrt(LC)).
Voltage sags & power-quality events — IEEE 1159, ITIC, SARFI
Sag = 0.1-0.9 pu for 0.5 cyc to 1 min (IEEE 1159) — 80-90% of PQ complaints. ITIC/CBEMA ride-through envelope: 0% @ 0.5 cyc → 70% @ 30 cyc → 90% steady. SARFI-X (IEEE 1564) counts events below threshold. Causes: remote faults (60-80%), motor start (5-7× FLC), transformer inrush (8-10×). Mitigation: equipment-RT → CVT → UPS → DVR → SSTS → active-front-end VFD. Flicker (IEEE 1453) Pst/Plt.