Total Harmonic Distortion
Total Harmonic Distortion (THD) is the ratio of the root mean square (RMS) of all harmonic voltage or current components (integer multiples of the fundamental frequency, e.g., 120 Hz, 180 Hz for a 60 Hz system) to the RMS of the fundamental frequency, expressed as a percentage: THD = sqrt(V2^2 + V3^2 + ... + Vn^2) / V1.
In shop floor maintenance, THD is monitored via power quality analyzers integrated with CMMS to flag electrical asset degradation. High THD triggers maintenance alerts for motors, transformers, and capacitor banks. In predictive maintenance, rising THD trends indicate non-linear loads (e.g., PWM drives, VFDs) or insulation breakdown, prompting scheduled inspections before catastrophic failure. ServiceGrid assets tagged with THD thresholds (e.g., >5% voltage THD) auto-generate work orders for filter installation or load balancing.
- Transformer Overheating: High THD increases eddy current and hysteresis losses, causing premature core degradation and insulation failure.
- Motor Nuisance Tripping: Harmonic currents distort waveforms, triggering false protection relay trips and unplanned downtime in sensitive motor drives.
- Capacitor Bank Failure: Harmonics cause resonance, leading to overvoltage, dielectric breakdown, and explosive capacitor failures in power factor correction systems.
Why is THD+N preferred over THD in amplifier testing?
THD+N includes noise, providing a more accurate distortion factor for non-linear systems; THD alone may miss noise-induced errors.
What IEEE standard limits THD for <1 kV devices?
IEEE 519-2022 caps THD at 8% for devices under 1,000V to ensure grid stability.
How does THD affect true power factor?
Harmonic currents increase RMS voltage/current, reducing true power factor and increasing energy costs.