The application of circuit breakers and fuses must be considered to determine
which offers the most appropriate protection. Consideration should be given
to anti-single-phase devices when three-pole interrupter swit ches with fuses
are used, because fuses are single-pole interrupter switches. An arcing fault
may not be stopped by a single-pole interruption. It can be backfed from the
other energized phases. Because of this condition, severe equipment burndowns
may occur. Ferroresonance is the result of interaction between the reactance
of a saturable magnetic device, such as a transformer, and system
capacitance. Ferroresonance can also occur due to a single phasing condition.
This phenomenon occurs mostly in high- and medium-voltage systems and
results in a very high voltage on the order of three to fi ve normal system voltage
which is imposed on the circuit involved, causing equipment failure.
Always keep in mind that fuses should be applied in systems where the
system voltage is compatible with the fuse voltage rating. The reason for this
is that the arc voltage generated by a fuse when interrupting is several times
its voltage rating and, if misapplied, could subject the system to overvoltage
conditions, causing equipment failure.