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

 
3.1.24 immunity (to a disturbance):
The ability of a device, equipment, or system to perform without deg-
radation in the presence of an electromagnetic disturbance.
b
 
3.1.25 impulse:
A 
 
pulse
that, for a given application, approximates a unit pulse.
b
When used in relation to
the monitoring of power quality, it is preferred to use the term 
 
impulsive transient
in place of 
 
impulse
.
 
3.1.26 impulsive transient:
A sudden nonpower frequency change in the steady-state condition of voltage
or current that is unidirectional in polarity (primarily either positive or negative).
 
3.1.27 instantaneous:
A time range from 0.5Ð30 cycles of the power frequency when used to quantify the
duration of a short duration variation as a modifier.
 
3.1.28 interharmonic (component): 
A frequency component of a periodic quantity that is not an integer
multiple of the frequency at which the supply system is designed to operate operating (e.g., 50 Hz or 60 Hz).
 
3.1.29 interruption, momentary (power quality monitoring):
A type of
 
 short duration variation
. The
complete loss of voltage (< 0.1 pu) on one or more phase conductors for a time period between 0.5 cycles
and 3 s.
 
3.1.30 interruption, sustained (electric power systems):
Any interruption not classified as a momentary
interruption.
 
3.1.31 interruption, temporary (power quality monitoring):
 
 
A type of
 
 short duration variation
. The com-
plete loss of voltage (< 0.1 pu) on one or more phase conductors for a time period between 3 s and 1 min.