Damage from a short circuit is a constant threat to any electric power system. Insulation damaged by aging an accident or lightning strike can unloose immense fault currents practically the only limit on their size being the impedance of the system between their location and power sources. At their worst, faults can exceed the largest current expected under normal load ? the nominal current by a factor of 100 producing mechanical and thermal stresses in proportion to the square of the current?s value.
All power system components must be designed to withstand short circuit stresses for certain period determined by time needed for circuit breakers to activate (20-300 ms). The higher the fault currents anticipated the higher will be the equipment and also the maintenance cost. So there obviously is a big demand for devices that under normal operating conditions have negligible influence on power system but in case of fault will limit the prospective fault current. A device of this kind is called fault current limiter.
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