chapter  5
50 Pages

Application and Ratings of Circuit Breakers and Fuses according to ANSI Standards

WithJ.C. Das

This chapter reviews the ratings of circuit breakers and fuses according to American National Standards Institute, mainly from the short circuit and switching point of view, and examines their applications. With respect to the application of circuit breakers for capacitance switching consider type of application that is overhead line, cable or capacitor bank, or shunt capacitor filter switching, power frequency and system grounding, and presence of one-or-two-phase-to-ground faults. The difference in total and symmetrical ratings depends on how the asymmetry in short-circuit current is addressed. The symmetrical rating takes asymmetry into account in the rating structure of the breaker itself. Prior to 1964, high-voltage circuit breakers were rated on a total current basis. For circuit breakers rated on a total current rating basis, short-circuit interrupting capabilities are expressed in total rms current. Available frame sizes range from 15 to 6000 A, interrupting ratings from 10 to 100 kA symmetrical without current-limiting fuses and to 200 kA symmetrical with current-limiting fuses.