Harmonics in Industrial Motor Systems

Harmonic distortion is often ignored as a mere “power quality” nuance, yet it acts as a primary degradation mechanism for critical rotating equipment. This document outlines the mathematical physics of harmonic damage (skin-effect heating, negative sequence torque) and demonstrates how Artesis Edge-Processing provides the visibility needed to prevent failures.

1-Introduction: The Physics of Distorted Power

In an ideal alternating current system, voltage and current waveforms are pure sinusoids. However, non-linear loads (VFDs, UPS systems) introduce periodic distortions. Mathematically, any distorted waveform is defined by the Fourier Series. While the fundamental component produces torque, higher-order components produce almost exclusively heat and vibration.

 

2-The Mathematics of Asset Damage

Harmonics are not benign; they impose specific, calculable physical stresses on induction motors.

2.1 Thermal Stress & The Skin Effect

Harmonics increase the RMS current, causing standard I2R heating. However, the damage is accelerated by the Skin Effect, where high-frequency currents crowd the conductor surface, increasing resistance.

The AC resistance Rac at a harmonic order h can be approximated as:

This implies that a 7th harmonic current generates significantly more heat per amp than the fundamental current, rapidly degrading insulation life.

2.2 Torque Ripple & Mechanical Fatigue

Harmonic currents interact with the fundamental magnetic flux to create parasitic torques. The direction of rotation depends on the sequence:

• Positive Sequence (h = 1, 4, 7…): Rotates with the motor.

• Negative Sequence (h = 2, 5, 8…): Rotates against the motor (Magnetic Braking).

The net torque (Tnet) becomes a summation of opposing forces:

 

3-Visualizing the Invisible: Symmetrical Components

To understand why a motor vibrates despite being mechanically aligned, we must look at the Symmetrical Components. Artesis utilizes the Fortescue Transformation to decompose the 3-phase system (Va, Vb, Vc) into Positive (V1), Negative (V2), and Zero (V0) sequences:

 

The Artesis Solution: Model-Based ESA

Traditional vibration sensors cannot detect these root causes until the bearing is already damaged. Artesis devices utilize a specialized System-on-Chip (SoC) to perform high-speed DSP at the edge, calculating Total Harmonic Distortion (THD) and Symmetrical Components in real-time. This data is visualized in the OmniSight platform, converting complex electrical data into actionable insights.

 

Comparison: Why Artesis?

Conclusion

Harmonics are a physical force that generates heat, opposes rotation, and fatigues mechanical components. Monitoring RMS current alone hides these dangers. By integrating Electrical Signature Analysis (ESA) with Model-Based Fault Detection, Artesis technology makes the invisible visible. It allows maintenance teams to detect thermal stress caused by harmonics before it melts insulation or destroys bearings.