Harmonic Distortion Calculator

THD is a root-sum-square across all five entered harmonics — √(3rd² + 5th² + 7th² + 9th² + 11th²) ÷ fundamental × 100 — so it captures the combined effect of every harmonic together. Max Individual Distortion instead just takes whichever single harmonic current you entered is largest and expresses that one alone as a percentage of the fundamental, which matters because IEEE 519 caps individual odd harmonics (4% below the 11th) separately from the overall THD cap (5%), and a load can fail one check while passing the other.

Nonlinear loads with symmetric current waveforms — which describes most VFDs, rectifiers, and switch-mode supplies — produce almost entirely odd-order harmonics; even-order harmonics are typically negligible unless the waveform is asymmetric (like some single-ended converters). That's why this calculator's input set matches the harmonics that actually dominate in the equipment it's built around.

No — those are simplified defaults for general systems with a moderate short-circuit ratio. The real IEEE 519-2022 limits scale with the ratio of available fault current to load current (ISC/IL): systems fed from a 'stiffer' source with more available fault current are allowed more distortion, while weaker sources are held to tighter limits. Treat this calculator's fixed 5%/4% pair as a common-case check, and look up the actual ISC/IL-based table for a site-specific compliance determination.

For a six-pulse VFD or rectifier — the most common source of harmonic distortion — the 5th harmonic is typically the largest single contributor, often 18-25% of the fundamental, with the 7th close behind. Since Max Individual Distortion just reports whichever harmonic you entered is largest, a failing result is usually driven by the 5th harmonic current; standard mitigations are 12-pulse converter configurations, line reactors, or active harmonic filters.

IEEE 519-2022 (IEEE Std 519-2022, formally titled the IEEE Standard for Harmonic Control in Electric Power Systems) is a voluntary industry standard, not a building code — but utilities and facility engineers widely use it as the practical benchmark for acceptable harmonic distortion at the point of common coupling. This calculator's 5% THD and 4% individual-harmonic thresholds are the limits the standard assigns to general systems with a short-circuit ratio (ISC/IL) above 20; systems fed from weaker sources are held to tighter limits under the standard's full ISC/IL-based table.