Low-frequency transients are oscillatory
voltages (from power frequency to
a few kHz), weakly damped and of relatively
long duration (i.e., seconds, or even
minutes).
• Slow front transients refer to the class of
excitation caused by switching operations,
fault initiation, or remote lightning
strokes. They can be oscillatory (within a
frequency range between power frequency
and 20 kHz) or unidirectional (with a front
time between 0.02 y 5 ms), highly damped,
and of short-duration (i.e., in the order of
milliseconds).
• Fast front transients are normally aperiodic
waves, generally associated to lightning
surges with a front time between 0.1 and
20 μs, although the current chopping of a
vacuum breaker can produce transient periodic
excitation whose frequency range
may be included within this category.