Learning the Lingo: Standard IEEE Terminology

-- Consulting-Specifying Engineer, 1/1/2001

Engineers hear and use many terms associated with power-quality issues, but there is often confusion as to the precise meaning of the common words and phrases. Some of the more common ones-brownout, transient, spike, surge and dip-are inaccurate and do not adequately reflect the true duration and magnitude of power-quality disturbances. The definitions of the terms as used in IEEE 1159 are as follows:

• Transient. An increase in voltage of up to eight times the nominal voltage level of very short duration, on the order of microseconds.

• Instantaneous voltage sag or swell. A decrease (sag) or increase (swell) in voltage that lasts from 0.5 to 30 cycles with a magnitude of 0.1 to 0.9 times the nominal voltage levels.

• Momentary voltage sag or swell. A decrease or increase in voltage generally having the same magnitudes as the instantaneous events, but with a duration of from 30 cycles to 3 seconds.

• Temporary voltage interruption. A complete loss of voltage lasting from 3 seconds to one minute.

• Sustained undervoltage. A decrease in voltage of between 0.8 and 0.9 times the nominal voltage for a period greater than one minute.