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There are two types of fuses used for
capacitors; internal and external. When the reactive power of a
capacitor unit was only a few kvar, the most natural method to protect
the capacitor was with an external fuse, since in the case of a
breakdown the lost reactive power was small. However, now that one
capacitor element has a capacity about the same value as a unit had
previously it is reasonable to protect each separate element with an
internal fuse.
When using units protected by internal fuses
the number of internal series connections is determined by the bank
voltage and size. The breakdown of one element and the subsequent fuse
operation causes an overvoltage over the healthy units. In units where
all the elements are in parallel this overvoltage is very often under
0.5%.
When the unit voltage is low (approximately
500 volts), it is relatively easy to construct units where the fuse
operation is completely reliable and breaks the current from the
parallel elements and units. However, when the element voltage is
approximately 1500-2500 volts the breaking capacity of such a fuse is
not adequate to break the high current of a short circuit, even with
several kilovolts recovery voltage, unless the fuse is specially
constructed, as are ours. In the event of a fault it is operated quickly
and reliably by part of the unit energy before high energy from parallel
connected units has any adverse effect.
Internal fuses in capacitor units (.pdf) |
