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Harmonic Distortion (THD) & IEEE 519 Calculator electrical
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Harmonic Distortion (THD) & IEEE 519 Calculator

Calculate Voltage THD (THDv), Current THD (THDi), and Total Demand Distortion (TDD) to verify compliance with IEEE 519 harmonic distortion standards.

Fundamental & Demand Currents

Harmonic Components (Current Amps)

Distortion & Compliance Results

Current Total Harmonic Distortion (THDi)
-- %
Total Demand Distortion (TDD): --%
IEEE 519 Limit
5.0 %
Max Allowable TDD
Compliance Status
--
Point of Common Coupling
Total Harmonic RMS Current: -- A
True Total RMS Current: -- A
Estimated Bus Voltage THDv: -- % (IEEE limit: 8.0%)
IEEE 519 benchmarks harmonic distortion at the Point of Common Coupling (PCC) to prevent overheating utility transformers.

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Frequently Asked Questions

What is the difference between THD and TDD in IEEE 519?

Total Harmonic Distortion (THD) divides harmonic current by the present fundamental current (I1), which artificially inflates to huge percentages at light loads. Total Demand Distortion (TDD) divides harmonic current by the maximum 15-to-30 minute peak demand current (IL), providing a realistic measure of distortion impact on the utility grid.

Why do non-linear loads like VFDs produce 5th and 7th harmonics?

Standard 6-pulse VFD rectifiers conduct current in six distinct pulses per AC cycle. Fourier series analysis shows this generates characteristic harmonics at frequencies h = 6k ± 1 (5th, 7th, 11th, 13th, etc.). The 5th harmonic rotates backwards against motor rotation, causing severe heating.

What methods eliminate harmonic distortion in industrial plants?

Methods include AC line reactors (3% to 5% impedance, cuts THD from 80% to 35%), 12-pulse or 18-pulse phase-shifting transformers (cancels 5th, 7th, 11th, 13th), passive tuned LC harmonic traps, and Active Harmonic Filters (AHF) that inject counter-phase currents to cancel harmonics down to < 5% TDD.