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    Electrical / Power quality

    Harmonic Analysis

    Total harmonic distortion, the K-factor a transformer has to be rated for, and the derating that follows. Non-linear loads put current back into the supply at multiples of the fundamental.

    THD38.5%True RMS1.071 puK-factor4.8
    THD
    38.5%
    Above the usual limit
    True RMS
    1.071 pu
    Including harmonics
    K-factor
    4.8
    Transformer rating
    Derating
    0.93 pu
    Capacity multiplier
    Harmonic spectrum
    THD is the RMS of the harmonics over the fundamental; K-factor weights them by order squared.
    Harmonic spectrum
    OrderMagnitudeContribution
    320%0.36
    530%2.25
    712%0.71
    116%0.44
    Inspect the model
    Choose a quick result view, a scaled comparison, or the complete diagnostic set.
    THD against the 5th harmonic
    The 5th usually dominates a six-pulse drive.
    THD against the 5th harmonic0.00010.4620.9231.3841.8352.290%0%10%10%20%20%30%30%40%40%Harmonic Analysis
    Canonical equations
    The exact relationships implemented by this engine.

    √(Σ I_h²) / I_1 · Total harmonic distortion.

    Σ (I_h/I_1)²·h² · Transformer heating.

    engineering methodology

    A clear path from inputs to results.

    Total harmonic distortion, the K-factor a transformer has to be rated for, and the derating that follows. Non-linear loads put current back into the supply at multiples of the fundamental.

    Step-by-step methodWorked exampleAssumptions explained

    How to use

    1. Set 3rd harmonic (%).
    2. Set 5th harmonic (%).
    3. Set 7th harmonic (%).
    4. Set 11th harmonic (%).
    5. Read the headline metrics, then check the table for the detail.

    The formula

    √(ΣIh2)/I1√(Σ I_h²) / I_1

    Reference: THD and the K-factor transformer rating.

    Worked example

    At the default inputs

    Inputs
    • 3rd harmonic (%): 20; 5th harmonic (%): 30; 7th harmonic (%): 12; 11th harmonic (%): 6
    Calculation path
    1. 1

      THD: 38.5% · True RMS: 1.071 pu · K-factor: 4.8 · Derating: 0.93 pu

    Result

    THD: 38.5% · True RMS: 1.071 pu · K-factor: 4.8

    Interpreting the result

    This spectrum is 38.5% THD with a K-factor of 4.8.

    Assumptions & limitations

    • Steady-state spectrum.
    • No resonance or filter effects.

    Frequently asked questions

    What causes harmonics?

    Non-linear loads such as drives, rectifiers and LED supplies.

    What is K-factor?

    A transformer rating that weights harmonic heating by order squared.

    Methodology last reviewed 2026-10-22. Results are informational and not financial or engineering advice — see our disclaimer.