VISITORS: 15

Harmonics can significantly affect the measurement of inductance because practical inductors do not have the same impedance at all frequencies. When a voltage or current waveform contains harmonic components, each harmonic experiences a different inductive reactance, $X_L=2\pi fL$ , so the measured voltage, current, and phase angle may no longer represent the fundamental-frequency inductance accurately. Core losses, winding resistance, skin effect, proximity effect, and magnetic saturation can also vary with frequency, causing the apparent inductance to change. As a result, instruments measuring inductance from distorted waveforms may indicate an erroneous value, particularly when higher-order harmonics are significant. For accurate measurement, a clean sinusoidal test signal at a specified frequency should preferably be used, and harmonic distortion should be minimized or filtered.

Interactive Simulation – Effect of Harmonics on Inductance Measurement

Harmonics and Inductance Measurement

Interactive demonstration of how harmonic components can change the apparent impedance and measured inductance of a practical inductor.

1. Simulation Controls

Fundamental Frequency 50 Hz

Nominal Inductance 100 mH

Winding Resistance 2 Ω

3rd Harmonic 0 %

5th Harmonic 0 %

7th Harmonic 0 %

Frequency-Dependent Loss 0 %

Saturation Effect 0 %

2. Electrical Principle

X_L = 2πfL

Z = √(R² + X_L²)

L_apparent ≈ X_L / (2πf)

For a pure sinusoidal test signal, the instrument can determine inductance from the voltage, current and phase relationship at the specified frequency. When harmonics are present, however, each harmonic sees a different inductive reactance because X_L = 2πfL.

3. Waveform Display

Fundamental voltage Distorted voltage Inductor current

4. Harmonic Components

5. Measurement Results

Fundamental Reactance —

Fundamental Impedance —

3rd Harmonic Reactance —

5th Harmonic Reactance —

7th Harmonic Reactance —

RMS Voltage —

RMS Current —

Apparent Inductance —

Measurement Error —

6. What the Simulation Demonstrates

With a clean sinusoidal signal, the measured inductance is close to the nominal inductance. Add harmonics to observe how the waveform becomes distorted and how the apparent measurement can change.

7. Why Harmonics Affect Practical Inductors

Different reactance: The inductive reactance increases with frequency. Therefore, a 7th harmonic experiences approximately seven times the fundamental-frequency reactance for the same inductance.

Core losses: Higher-frequency components can increase magnetic core losses.

Skin effect: Higher-frequency current tends to concentrate toward the surface of the conductor, increasing effective winding resistance.

Proximity effect: Magnetic fields from nearby conductors can further increase AC resistance.

Saturation: Large waveform peaks can move the magnetic core toward saturation, making the effective inductance nonlinear.

Result: An inductance meter exposed to a significantly distorted waveform may obtain a value that does not represent the inductance measured with a clean, specified-frequency sinusoidal test signal.