Almost every modern civilization field, there isthe need of electrical energy which has resulted in a considerable high ofelectrical power utilization. To reach the large electrical energy demand, thesize of the power generating stations has become large. Now days, in manycases, the generating stations are connected among themselves by interconnectednetworks (power grids) and makes the utility systems extremely large. Modernelectrical power grids also have put forward to go for increased use ofdistributed generation (DG) which is placing smaller local generation sourcescloser to the loads. Usually the consumption area of electrical power isvery wide, the chances of any kind of accident, fault or abnormal condition isvery common. In a power utility network, an short circuit is created by suddenaccidents. The sudden reduction of the impedance of the power utility networkduring short circuit causes an increase in current, termed a fault current.
Itis a large fault current surging through the various parts of power grids andresponsible for causing a voltage reduction too. The increase of electric power consumption hasnecessitated an increase in the system fault current levels which has led tolarger mechanical and thermal stresses and endangers the mechanical integrityof power system hardware viz. circuit breakers, transformers and otherequipments. The increase in load, generation, interconnection and penetration ofDG into power network rapidly increase the short circuit fault current level toor exceeds the capacity of protective switchgear such as circuit breaker. Theshort circuit fault current level in some places becomes so high that thebreaking capacity of the circuit breaker reached to its maximum possible ratingwhich is limited by the physics of the applied dielectric medium. Hence, thecircuit breaker must either be upgraded or replaced in the near future. Neitherup gradation nor replacement is economical and feasible from utilitiesperspective as the levels of fault currents would continue to grow with theincrease in power demand.
Because of these reasons the importance of limitingthe fault current has been increased considerably. With the limited faultcurrent, a breaker with a low rating or existing rating can be used and is costeffective compared to the breaker replacement.