Harmonic and THD equations
Orthogonal RMS harmonic components combine by root-sum-square.
THD = √(Σh>1 Xh²)/X1 × 100%Xrms = √(Σh≥1 Xh²)Xtriplen = √(X3² + X9² + ...)where:
- X1
- Fundamental RMS magnitude
- Xh
- RMS magnitude of harmonic order h
- THD
- Total harmonic distortion relative to the fundamental[%]
IEEE 519 compliance requires PCC and system-ratio data beyond THD.
How to use the Harmonic and THD Calculator
Calculate THD, total RMS, individual harmonic distortion, triplen content, crest-factor screen, and neutral-current warning from harmonic magnitudes. Start by choosing the operating mode, then enter values from nameplates, measurements, or project documents in the units shown. The result updates immediately and keeps intermediate quantities visible for review.
- Confirm the system and calculation mode.
- Enter measured or manufacturer-rated values.
- Review the primary result and intermediate metrics.
- Continue with the related protection or equipment-selection checks.
Calculation method and validation
The equations and symbol definitions above show the complete calculation basis. Inputs are checked before calculation so zero, negative, incompatible, or physically impossible combinations are flagged instead of silently producing a misleading result.
How to interpret the result
Use the main result as a starting value and read every supporting metric. Inputs are RMS magnitudes from one consistent measurement window Harmonic phase angles are unavailable Neutral warning assumes triplen harmonics may add in a three-phase four-wire system A passing or recommended result means the entered mathematical conditions are satisfied; it does not certify the complete installation or a particular product combination.
- Inputs are RMS magnitudes from one consistent measurement window
- Harmonic phase angles are unavailable
- Neutral warning assumes triplen harmonics may add in a three-phase four-wire system
Selection limits and next checks
Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions. THD alone does not establish IEEE 519 compliance; limits depend on PCC data, voltage, and Isc/IL. Exact neutral current requires phase-resolved magnitude and angle data. Compare the output with the current applicable standard, local rules, exact VIOX product datasheet, environmental conditions, protection coordination, and the engineer's project requirements before procurement or installation.
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Assumptions
- Inputs are RMS magnitudes from one consistent measurement window
- Harmonic phase angles are unavailable
- Neutral warning assumes triplen harmonics may add in a three-phase four-wire system
Important Warnings
- Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions.
- THD alone does not establish IEEE 519 compliance; limits depend on PCC data, voltage, and Isc/IL.
- Exact neutral current requires phase-resolved magnitude and angle data.