CIRCUIT BREAKER

                               CIRCUIT BREAKER

CIRCUIT BREAKER

A CIRCUIT BREAKER IS A TYPE OF EQUIPMENT THAT IS USED TO MAKE OR BREAK A CIRCUIT EITHER MANUALLY OR BY REMOTE CONTROL UNDER THE NORMAL CONDITION. IT IS ALSO USED TO BREAK A CIRCUIT AUTOMATICALLY UNDER FAULT CONDITIONS.

A CIRCUIT BREAKER INCORPORATES MANUAL ( OR REMOTE CONTROL) AS WELL AS AUTOMATIC CONTROL FOR SWITCHING FUNCTIONS. THE LATTER CONTROL EMPLOYS RELAYS AND OPERATES ONLY UNDER FAULT CONDITIONS.

PRINCIPLE OF CIRCUIT BREAKER

A CIRCUIT BREAKER IS CONSISTING OF FIXED AND MOVING CONTACTS, CALLED ELECTRODES. UNDER NORMAL OPERATING CONDITIONS, THESE CONTACTS REMAIN CLOSED AND WILL NOT OPEN AUTOMATICALLY UNTIL AND UNLESS THE SYSTEM BECOMES FAULTY.

WHEN A FAULT OCCURS ON ANY PART F THE SYSTEM, THE TRIP COILS OF THE CIRCUIT BREAKER GET  ENERGISED AND THE MOVING CONTACTS ARE PULLED APART BY SOME MECHANISM, THUS OPENING THE CIRCUIT.

WHEN THE CONTACT OF A CIRCUIT BREAKER IS SEPARATED UNDER FAULT CONDITIONS, AN ARC IS STRUCK BETWEEN THEM. THE CURRENT IS THUS ABLE TO CONTINUE UNTIL THE DISCHARGE CEASES. THE PRODUCTION OF ARC NOT ONLY DELAYS THE CURRENT INTERRUPTION PROCESS BUT IT IS ALSO GENERATES ENORMOUS HEAT WHICH MAY CAUSE DAMAGE TO THE SYSTEM OR TO THE CIRCUIT BREAKER ITSELF. 

CLASSIFICATION OF CIRCUIT BREAKER

WE CAN CLASSIFY CIRCUIT BREAKERS IN MANY OF THE WAYS. THE MOST GENERAL WAY TO CLASSIFY THE CIRCUIT BREAKER IS ON THE BASIS OF THE MEDIUM USED FOR ARC EXTINCTION. THE MEDIUM USED FOR ARC EXTINCTION IS USUALLY OIL, AIR, SULPHUR HEXAFLUORIDE SF6, OR VACUUM.

OIL CIRCUIT BREAKER

IN AN OIL CIRCUIT BREAKER, THERE IS SOME INSULATING OIL LIKE TRANSFORMER OIL IS USED AS AN ARC QUENCHING MEDIUM. THE CONTACTS ARE OPENED UNDER OIL AND AN ARC IS STRUCK BETWEEN THEM. THE HEAT OF THE ARC EVAPORATES THE SURROUNDING OIL AND DISSOCIATES IT INTO A SUBSTANTIAL VOLUME OF GASEOUS, HYDROGEN AT HIGH PRESSURE. THE HYDROGEN GAS OCCUPIES A VOLUME ABOUT ONE THOUSAND TIMES THAT OF THE OIL DECOMPOSED. THE OIL IS, THEREFORE, PUSHED AWAY FROM THE ARC AND AN EXPANDING HYDROGEN GAS BUBBLE SURROUNDS THE ARC REGION AND ADJACENT PORTIONS OF THE CONTACTS. THE ARC EXTINCTION IS FACILITATED MAINLY BY TWO PROCESSES.

TYPES OF OIL CIRCUIT BREAKER

1. BULK OIL CIRCUIT BREAKERS

a. PLAIN BREAK OIL CIRCUIT BREAKERS

b. ARC CONTROL OIL CIRCUIT BREAKERS

# BULK OIL CIRCUIT BREAKER

THIS TYPE OF BULK OIL CIRCUIT BREAKER IS USED AS A LARGE QUANTITY OF OIL. THE OIL HAS TO SERVE TWO PURPOSES. FIRST, IT EXTINGUISHES THE ARC DURING THE OPENING OF CONTACTS, AND THE SECOND, IT INSULATES THE CURRENT-CONDUCTING PARTS FROM ONE ANOTHER AND FROM THE EARTHED TANK.

# PLAIN BREAK OIL CIRCUIT BREAKER

IN PLAIN BREAK OIL CIRCUIT BREAKER IT CONSIST OF A SIMPLE PROCESS OF SEPARATING THE CONTACTS UNDER THE WHOLE OF THE OIL IN THE TANK. THERE IS NO SPECIAL SYSTEM FOR ARC CONTROL OTHER THAN THE INCREASE IN LENGTH CAUSED BY THE SEPARATION OF CONTACTS. THE ARC EXTINCTION OCCURS WHEN A CERTAIN GAP BETWEEN THE CONTACTS IS REACHED.

a plain-break oil circuit breaker is the earliest type from which all other circuit breakers have developed. It has a very simple construction. It consists of fixed and moving contacts enclosed in a strong weather-tight earthed tank containing oil up to a certain level and an air cushion above the oil level. The air cushion provides sufficient room to allow for the reception of the arc gases without the generation of unsafe pressure in the dome of the circuit breaker. It also absorbs the mechanical shock of the upward oil movement. a double break plain oil circuit breaker. It is called a double break because it provides two breaks in series.

Under normal operating conditions, the fixed and moving contacts remain closed and the breaker carries the normal circuit current. When a fault occurs, the moving contacts are pulled down by the protective system and an arc is struck which vapourises the oil mainly into hydrogen gas.

ARC CONTROL OIL CIRCUIT BREAKER

there is very little artificial control over the arc. Therefore, comparatively long arc length is essential in order that turbulence in the oil caused by the gas may assist in quenching it. However, it is necessary and desirable that final arc extinction should occur while the contact gap is still short. For this purpose, some arc control is incorporated and the breakers are then called arc control circuit breakers.