• A SHORT CIRCUITS computer program may be utilized in power system design to select, set, and coordinate protective equipment such as circuit breakers, fuses, relays, and instrument transformers.

• A circuit breaker is a mechanical switch capable of interrupting fault currents and of reclosing. When circuit-breaker contacts separate while carrying current, an arc forms. The breaker is designed to extinguish the arc by elongating and cooling it.

SHORT CIRCUIT CAPASITY (SSC)/ SHORT-CIRCUIT MVA

• where in amperes is the rms magnitude of the short-circuit current in a three-phase fault at the connect ion point.

• Base megavoltamperes are related to base kilovolts and base amperes

If base kilovolts equal nominal kilovolts, converts the former to per uni t , and we obtain

LW55-550-50 Type Tank Type SF6 Circuit Breaker

PEMILIHAN PEMUTUS RANGKAIAN (CIRCUIT BREAKER)HORT

• Kapasitas pemutus (atau rating) dari pemutus sirkuit dinyatakan sebagai :

The asymmetrical current wave decays gradually to a symmetrical current, the rate of decay of the dc component being determined by the L/R of the system supplying the current. The time constant for dc component decay can be found from

atau

• Dengan pemutus sirkuit yang bertindak cepat, arus yang sebenarnya akan diputus akan meningkat dengan komponen dc arus gangguan, dan nilai arus simetris awal rms meningkat dengan faktor yang spesifik yang tergantung pada kecepatan dari pemutus sirkuit.

The momentary duty (or rating) of a CB also includes this dc component of the fault current.

atau

The rms momentary current is the total rms current that includes both the ac and dc components and can be found from

and it is used for CBs of 115 kV and above

• The CB must be able to withstand this rms current during the first half cycle after the fault occurs. If the If,max is measured in peak amperes, then the peak momentary current is expressed as

FAKTOR K

TUGAS 5