TABLE OF CONTENTS S.M. Ghufran Ali
This chapter describes the design, development and operation of switch-gear [1 7]. It also describes how the development of generation and transmission has influenced switchgear evolution (Appendix). Factors which have contributed to the simplicity of design and increased the reliability of SF 6 switchgear are addressed and the important features of various manufacturers designs in first, second and third generation interrupters and improvements in circuit-breaker performance are highlighted. It also addresses issues associated with installation and on-site operations and monitoring.
A circuit-breaker is a device which breaks or interrupts the flow of current in a circuit. It is used for controlling and protecting the distribution and transmission of electrical power. It is connected in series with the circuit it is expected to protect. It has to be capable of successfully:
interrupting (i) any level of current passing through its contacts from a few amperes to its full short-circuit currents, both symmetrical and asymmetrical, at voltages specified in IEC 62271-100 and (ii) up to 25% of full short-circuit currents at twice the phase voltage
closing up to full short-circuit making current (i.e. 2.5 I sym) at phase voltage and 25% of full making currents at twice the phase voltage
switching (making or breaking) inductive, capacitive (line, cable or capacitor bank) and reactor currents without producing excessive overvoltages to avoid overstressing the dielectric withstand capabilities of a system
performing opening and closing operations whenever required
carrying the normal current assigned...
