Harmonic Filter Sizing (AHF / Passive)
Estimate the active-filter compensation current required for a target current distortion and screen whether a series passive filter is a credible option for the connected nonlinear loads.
Calculation method
For each load row the tool derives fundamental current from RMS current and THDi, then sums the estimated harmonic current conservatively. If a measured overall THDi is entered it overrides the load-mix estimate. Required AHF compensation current is I1 × max(THDi before − THDi target, 0), with the selected margin applied afterwards. The default margin is 10%.
THDi, TDD and Isc/IL
IEEE 519-2022 applies current-distortion limits at the point of common coupling to the complete installation. Its Isc/IL bands set TDD limits, not equipment THDi limits. The Isc/IL option therefore shows a PCC TDD reference only; it does not turn the selected THDi target into automatic IEEE 519 compliance.
AHF versus passive filtering
AHF is sized in compensation amperes and is suited to mixed or changing harmonic sources. A series passive filter can be efficient for stable 6-pulse drive branches, but final L/C selection requires the actual harmonic spectrum and system impedance.
Selection guide: Active vs Passive Harmonic Filters explains the topology choices, PCC boundary and screening assumptions used here.
Manufacturer reference points
The screen follows public guidance from REVCON, TDK/EPCOS and Sinexcel: active filters are rated by compensation current and can be paralleled; passive products are selected against the actual nonlinear branch current and application. TDK PQSine S publishes 25–150 A modules with larger systems available; Sinexcel publishes 5–300 A module ratings; REVCON publishes RHF-Active ratings and branch-sized RHF passive filters.
Engineering limits
The calculator does not solve individual harmonic orders, phase cancellation, frequency-dependent network impedance, resonance, capacitor/reactor stress, neutral-current spectrum or manufacturer thermal derating. For THDv above 10%, resonance concerns, significant 3rd harmonic content, generators/weak grids, multiple transformers, capacitor banks or a compliance study, perform a detailed harmonic study.