Interharmonics — The Power Quality Disturbance That Doesn’t Show Up on Standard Harmonic Analysers
Interharmonics — frequency components that are not integer multiples of the fundamental (e.g. 75 Hz에서, 130 Hz on a 50 Hz system) — are produced by PV inverters, wind turbines, EV 충전기, cycloconverters, and HVDC links. Their most dangerous effect: an interharmonic at 58 Hz creates an 8 Hz beat frequency — squarely in the range of peak human visual sensitivity. Field case: simultaneous PV + EV charger + microwave on one LV circuit produces stochastic interharmonics causing light flicker. Standard IEC 61000-4-7 analysers cannot correctly characterise them.