Switchgear and Protection.pdf
Switchgear & Protection
Switch gear: It is a general term covering a wide range of equipment concerned with switching
and protection. All equipment’s associated with fault clearing process are covered by the term
switch gear. Switch gear includes switches, fuses, circuit breakers, isolators, relays, control
Control gear: It is used for switching and controlling power consuming device.
Circuit breakers (CB): It is one of the equipment in switch gear. This is a switching and current
It has two basic functions:
1) switching during normal operating condition for operation and maintenance.
2) Switching during abnormal condition for interrupting the fault current caused by short circuits.
Switch gear are necessary at every switching point in a power system. Between the generating
station and final load point, there are several voltage and fault levels. Hence in various
applications, the requirement of switchgear varies depending upon location, rating and local
Single pole circuit breaker: In this breaker fault current interrupting mechanism is involved
with one phase.
Triple pole circuit breaker: Fault interrupting is involved with three phases in this breaker.
Each pole consists of one or more interrupters or arc extinguishing chambers. The interruptions
are mounted on support insulators. The interrupters encloses a set of fixed and moving contacts
.The moving contact can be drawn apart by means of operating links of operating medium. The
operating mechanism provides the necessary energy for opening and closing the contacts of CB.
CB has two states only – close and open.
Under normal operating condition its operation can be manual or can be automatic remotely.
During fault condition its operation must be automatic. Operating mechanism is responsible for
the automatic operation.
Switchgear and protection