On the other hand, it is well known that the vacuum
switch has the drawback of its switching overvoltage. In
the 1960s, the application of vacuum switches raised the
problem of switching overvoltage due to current
chopping. Current chopping is the phenomenon by
which, when interrupting inductive current, the current
may cease to flow abruptly before the natural current
zero. This phenomenon may result in switching
overvoltages. These arise due to the magnetic energy
still stored in the inductances, and may be especially
troublesome when interrupting inductive loads such as
motors [ 1]. In the 1980s, however, the overvoltages due
to current chopping were minimized by careful selection