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Transients
attenuation may result from intrawinding capacitances, but interwind-
ing capacitances may actually increase the voltage. Common-mode
voltages are transferred to the secondary through the interwinding
capacitances and can be effectively stopped by an electrostatic shield
between the windings. Absent the shield, however, they can appear on
the secondaries with a magnitude close to that on the primary. This
can be a severe problem on medium-voltage systems where there is
the possibility of 10 kV or more being developed on secondaries to
ground.
The best protection from line-induced transients of all types on sec-
ondaries is a set of MOVs. Line-to-line MOVs on the secondary are
best for differential-mode voltages, and line-to-ground ...