1. Introduction
In this chapter, The constructional aspects of circuit breakers have
been briefly discussed. The theoretical aspects regarding transient
variation of current and voltage, are extinction process and the various
types of circuit breakers have been described in detail in other
chapter.
The circuit breaker are automatics switches which can interrupt fault
currents. In some application like single phase traction system, single
pole circuit breakers are used. The part of the circuit breakers
connected in one phase is called the 'pole'. A circuit breaker suitable
for three phase system is called a 'triple-pole circuit breaker'.
Each pole of the circuit breaker comprise one or more 'interrupter' or
'arc-extinguishing chambers'. The interrupters are mounted on support
insulators. The interrupter encloses a set of 'fixed and moving
contacts'. The moving contacts can be drawn apart by means of the
operating links of the operating medium. The operating mechanism of the
circuit breaker gives the necessary energy for opening and closing of
contacts of the circuit breaker.
The arc produced by the separation of current carrying contacts is
interrupted by a suitable medium and by adopting suitable techniques for
arc extinction . The circuit breaker can be classified on the basis of
the arc extinction medium.
2. The Trip-Circuit
The basic connection of the circuit breaker control, for the opening operation, is illustrated in figure 1.
The
protected circuit is shown by dashed line. When a fault occurs in the
protected circuit. the relay connected to the CT and PT actuates and
closes its contacts. Current flows from the battery (source) in the trip
circuit. As the trip coil of the circuit breaker (C.B.) is energized,
the circuit breaker operating mechanism is actuated and it operates for
the opening operation. Auxiliary switch is an important item in the
circuit. such auxiliary switch has two position "open" and "close"
corresponding to the position of the circuit breaker. In each position,
some auxiliary circuits are opened and some are closed. The auxiliary
circuits serve several purposes such as:
( i ). Indication
breaker open or close by lamps, near C.B. and at a remote place.
( ii ). Electric Interlocks
The is electrically interlocked with isolators through the auxiliary switch.
( iii ). Connection
For auxiliary circuit of the operating mechanism.
