Total Harmonic Distortion (THD)

Total Harmonic Distortion (THD) measures how much a voltage or current waveform departs from an ideal sine wave. Formally, it is the ratio of the combined energy of all harmonic components (multiples of the fundamental 50/60 Hz frequency) to the energy of the fundamental, expressed as a percentage. A perfectly clean sine wave has 0% THD; the higher the number, the more distorted and "dirty" the waveform.

Why switch-mode loads create harmonics

Switch-mode power supplies the kind inside every ASIC miner rapidly chop the input between fully on and fully off, which is inherently non-linear. Without correction, they draw current in sharp pulses near the voltage peaks rather than smoothly following the sine wave, injecting harmonic currents back into the wiring. Banks of miners on a shared feeder can therefore raise current THD significantly.

Consequences in a Hashcenter

High THD overheats neutral conductors and transformers, degrades power factor, increases peak currents, and can cause nuisance tripping or premature failure of upstream equipment. Generators are especially sensitive: feeding non-linear mining loads from a generator with poor voltage regulation can push voltage THD high enough to disrupt sensitive electronics. Good ASIC PSUs include active power-factor correction, which both improves power factor and pulls current THD down toward single digits. For large deployments, harmonic filters or line reactors on the main feeders keep distortion within standards such as IEEE 519.

THD is a core power-quality figure to monitor alongside apparent power and inrush current when planning a clean, reliable mining feed.