Ieee std 1159-1995, ieee recommended Practice for Monitoring Electric Power Quality

3.1.73 voltage variation, short duration: A variation of the rms value of the voltage from nominal voltage
for a time greater than 0.5 cycles of the power frequency but less than or equal to 1 minute. Usually further
described using a modifier indicating the magnitude of a voltage variation (e.g. sag, swell, or interruption) and
possibly a modifier indicating the duration of the variation (e.g., instantaneous, momentary, or temporary).
3.1.74 waveform distortion: A steady-state deviation from an ideal sine wave of power frequency princi-
pally characterized by the spectral content of the deviation [B13].
3.2 Avoided terms
The following terms have a varied history of usage, and some may have speciÞc deÞnitions for other appli-
cations. It is an objective of this recommended practice that the following ambiguous words not be used in
relation to the measurement of power quality phenomena:
blackout
frequency shift
blink
glitch
brownout (see 4.4.3.2)
interruption (when not further qualiÞed)
bump
outage (see 4.4.3.3)
clean ground
power surge
clean power 
raw power
computer grade ground
raw utility power
counterpoise ground
shared ground
dedicated ground
spike
dirty ground
subcycle outages
dirty power
surge (see 4.4.1)
wink

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IEEE
Std 1159-1995
IEEE RECOMMENDED PRACTICE FOR
8
3.3 Abbreviations and acronyms
The following abbreviations and acronyms are used throughout this recommended practice:
3.3.1 A: amperes
3.3.2 ac: alternating current
3.3.3 ASD: adjustable speed drive
3.3.4 CRT: cathode-ray tube
3.3.5 CT: current transformer
3.3.6 CVT: constant voltage transformer