Learning the Lingo: Standard IEEE Terminology

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.

By Consulting Specifying Engineer Staff January 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.

IEEE 1159-1995: Characteristics of Electromagnetic Phenomena

CategoryTypical DurationTypical Magnitude
Transients
Impulsive nsec. to msec. na
Oscillatory 3 msec. – 5 usec. 0-8 per unit (pu)
Short-Duration Variations
Instantaneous Sag 0.5-30 cycles 0.1-0.9 pu
Instantaneous Swell 0.5-30 cycles 1.1-1.8 pu
Momentary Interruption 0.5 cycles-3 sec. less than 0.1 pu
Momentary Sag 30 cycles-3 sec. 0.1-0.9 pu
Momentary Swell 30 cycles-3 sec. 1.1-1.4 pu
Temporary Interruption 3 sec.-1 min. less than 0.1 pu
Temporary Sag 3 sec.-1 min. 0.1-0.9 pu
Temporary Swell 3 sec.-1 min. 1.1-1.4 pu
Long-Duration Variations
Sustained Interruption & gt;1 min. 0.0 pu
Undervoltage & gt;1 min. 0.8-0.9 pu
Overvoltage & gt;1 min. 1.1-1.2 pu
Voltage Imbalance steady state 0.5-2%
Waveform Distortion
DC Offset steady state 0.0-0.1%
Harmonics steady state 0-20%
Inter-harmonics steady state 0-2%
Notching steady state na
Noise steady state 0-1%
Voltage Fluctuations intermittent 0.1-7%
Power Frequency Variations &10 sec. na