IEEE
Std 1159-1995
IEEE RECOMMENDED PRACTICE FOR
18
4.4.2.3 Swells
A
swell is deÞned as an increase in rms voltage or current at the power frequency for durations from
0.5 cycles to 1 min. Typical magnitudes are between 1.1 and 1.8 pu. Swell
magnitude is also is also
described by its remaining voltage, in this case, always greater than 1.0.
As with sags, swells are usually associated
with system fault conditions, but they are much less common
than voltage sags. A swell can occur due to a single line-to-ground fault on the system resulting in a tempo-
rary voltage rise on the unfaulted phases. Swells can also be caused by switching
off a large load or switch-
ing on a large capacitor bank. Figure 8 illustrates a voltage swell caused by a SLG fault.
Swells are characterized by their magnitude (rms value) and duration. The severity of a voltage swell during
a fault condition is a function of the fault location,
system impedance, and grounding. On an ungrounded
system, the line-to-ground voltages on the ungrounded phases will be 1.73 pu during a line-to-ground fault
condition. Close to the substation
on a grounded system, there will be no voltage rise on the unfaulted phases
because the substation transformer is usually connected delta-wye, providing
a low impedance zero-
sequence path for the fault current.
In some publications, the term
momentary overvoltage is used as a synonym for the term
swell. A formal
deÞnition of swell in IEEE Std C62.41-1991 is ÒA momentary increase in the power-frequency voltage
delivered
by the mains, outside of the normal tolerances, with a duration of more than one cycle and less
than a few seconds [B14].Ó This deÞnition is not preferred by the power quality community.
Do'stlaringiz bilan baham: 
