Definition
Harmonics are voltage or current components at integer multiples of the fundamental line frequency, for example 180 Hz (3rd) and 300 Hz (5th) on a 60 Hz system. They appear whenever a nonlinear load draws current in pulses rather than smoothly. The switch-mode power supplies inside ASIC miners are textbook nonlinear loads, so a room full of miners can inject significant harmonic current onto the shared wiring.
How harmonics are quantified
Total harmonic distortion (THD) is the standard metric: the RMS of all harmonic components expressed as a percentage of the fundamental. IEEE 519 sets recommended limits for both voltage and current distortion, measured at the point of common coupling where a facility connects to the utility. Keeping current THD within those limits is part of being a good neighbor on a shared transformer.
Why harmonics matter in a mining facility
Harmonic currents cause extra heating in conductors, transformers, and especially neutral wires. They can overload equipment that looks fine on a simple ammeter, because the heating depends on the true RMS current including all harmonics, not just the fundamental. Transformers feeding heavy nonlinear load are often derated or specified as K-rated to survive the added losses.
Mitigation ranges from oversizing neutrals to installing harmonic filters. Closely related issues include triplen harmonics, which add up in the neutral, and the crest factor of the pulsed load current. See power quality for context.
In Simple Terms
Harmonics are voltage or current components at integer multiples of the fundamental line frequency, for example 180 Hz (3rd) and 300 Hz (5th) on a…