Voltage Flicker

Voltage flicker is the visible fluttering of lighting caused by repeated, rapid variations in supply voltage. It is not a single event like a sag or swell but an ongoing fluctuation, typically from loads that switch or vary their current draw cyclically. The human eye is sensitive to these fluctuations in a specific frequency band, which is why flicker is defined in terms of perception rather than raw voltage change.

How flicker is measured

The IEC 61000-4-15 flickermeter model, also adopted in IEEE 1453, produces two severity indices. Pst, the short-term flicker severity, is evaluated over a 10-minute window, with a value of 1.0 representing the threshold of perceptible annoyance. Plt, the long-term severity, is derived as a cubic mean of consecutive Pst values over a two-hour period. Keeping Pst at or below 1.0 is the usual planning target.

Relevance to mining loads

Miners running at steady state produce little flicker, but equipment that cycles on and off, such as fans, pumps, immersion-cooling gear, or staggered ASIC start sequences, can create fluctuations large enough to be noticed on the same circuit. On weak supplies, repeated switching of large blocks of hashrate can push flicker into the perceptible range and signal that the feeder is undersized for the load profile.

Flicker sits alongside the other voltage-fluctuation phenomena tracked under power quality, and like harmonics it is most pronounced on shared, high-impedance circuits.