Abstract

Harmonic Distortion has long been recognized as a primary concern in power quality, traditionally monitored only through the 51st harmonic. This boundary was sufficient for decades, when most nonlinear loads were dominated by line-frequency distortions from older VFDs, fluorescent lighting, and low-frequency switching equipment. Today, however, there is a new type of frequency-based waveform distortion. Fast switching from inverters and VFDs causes waveform distortion beyond the 51st harmonic. This distortion is not quantified or limited by IEEE 519 or other standards. In this paper we show how to identify “supraharmonics”, components that extend past 3 kHz.

High-order harmonics (above the 51st) introduce new challenges: although they don’t increase transformer heating or generate large current in the way low-order harmonics traditionally interfere with equipment, they still produce problems. Protective devices such as GFCI breakers are often more sensitive in the kHz range than at 60 Hz. Other electronic loads such as LED bulbs may be fooled into dimming when subjected to high frequency noise. Many low-cost electric loads rectify the incoming 60 Hz voltage to a DC bus with little high frequency filtering, assuming there is no signal in that band. Their specific misoperation modes are highly dependent on the circuit design, making compatibility difficult to predict.

System resonances can amplify high frequency noise as well, especially on transformer secondaries inside customer facilities, where higher frequency resonances are more common. This paper explains the concepts behind high-order harmonics, why their importance today is critical, and the limitations of older PQ monitoring practices. It also outlines how modern analysis tools such as PQ Canvass allow PQ engineers to visualize, quantify, and diagnose high-frequency distortion with resolution and clarity not previously available.