A voltage swell is a short duration increase in voltage values. Voltage swells lasting longer than two minutes are classified as overvoltages. Voltage swells and overvoltages are commonly caused by large load changes and power line switching. If swells reach too high a peak, they can damage electrical equipment. The utility's voltage regulating equipment may not react quickly enough to prevent all swells or sags.
Flicker is caused by large, rapidly fluctuating loads such as arc furnaces and electric welders.
Flicker is rarely harmful to electronic equipment, but is more of a nuisance because it causes annoying, noticeable changes in lighting levels. This information is contained in SRP's Power Quality brochure .