SEMINAR PRESENTATIon ON C IRCUIT B REAKER DEPT. OF ELECTRICAL ENGG. JALPAIGURI GOVT. ENGG. COLLEGE PRESENTED BY Madhusudan Mahato Malay Ghosh Manas Dera Subrata Mandal

Circuit Breaker:  A Circuit Breaker is an equipment that breaks the circuit either manually or automatically under all conditions full load, no load or short circuit condition; by making use of its fixed & moving contacts. This contact can be open manually or by remote control whenever required.

Working principle  Two contacts called electrode remains closed under normal operating condition.When fault occurs on any part of the system, trip coil of the C.B. get energized and contacts are separated.

Arc Phenomena An arc is struck when the contacts are separated.The current is thus able to continue. Thus the main duty of C.B is to distinguish the arc within the shortest possible time. The arc provides low resistance path to the current and the current in the circuit remains uninterrupted. During arcing period, the current flowing between the contacts depends on the arc resistance. The greater the resistance, the smaller the current that flows between the contacts.

Arc resistance depends upon the following factors : Degree of Ionization Length of arc Cross section of the arc

Methods of Arc extinction 1.High Resistance Method. 2.Low resistance or zero current method.  High Resistance Method : This method is used to increase the arc resistance with time so that the current is reduced to a value which is insufficient to maintain arc. Following are process by which the arc resistance can be increased.

Type of High Resistance Method High Resistance Method Lengthening the arc Cooling the arc Splitting the arc Reduce X- Section of ARC

Low resistance or zero current method All modern high power A.C. circuit breaker employ this method for arc extinction because there is natural zero current present in A.C. system. In a case of a 50 Hz supply there are 100 zeros per second. This method is explain by two theories:-  Recovery Rate Theory (Slepain’s Theory)  Energy Balance Theory SLEPAIN’S THEORY This theory states that Arc is interrupted if ions are removed from the gap at a rate faster than the rate of ionization.

Energy Balance Theory This theory states that if the rate of heat dissipation is (i.e rate of removal of heat) between electrode is greater than the rate at which heat is generated, the Arc will be extinguished otherwise it will re-strike

COMPONENTS OF CB BUSHING C.B CONTACTS CT & PT BUS BAR & CONDUCTORS

Location of CB

INSTRUMENT TRANSFORMER CURRENT TRANSFORMER POTENTIAL TRANSFORMER

CURRENT TRANSFORMER A current transformer is essentially a step up transformer which step down the current to know the ratio 100/5 amp That's mean line current is 100 amp and secondary is 5 amp

POTENTIAL TRANSFORMER It is essentially a step down transformer to step down the voltage to know the ratio 66kv/110 volt That’s mean primary is 66kv we get by pt 110 volt

RELAY A relay is a device which protects the CB or other equipments & it senses the fault

SPECIFICATION OF CB VOLTAGE RATING – 240/415 VOLT A.C CURRENT RATING – 0.5 TO 63 AMPS RATED FREQUENCY- 50HZ TO 60HZ

CLASSIFICATION TYPE OF C.B OIL CIRCUIT BREAKER AIR BLAST CIRCUIT BREAKER SF6 CIRCUIT BREAKER VACUUM CIRCUIT BREAKER

BREAKER USED IN 132kV SUB STATION  OIL CIRCUIT BREAKER  SF6 CIRCUIT BREAKER  VACUUM CIRCUIT BREAKER

OIL CIRCUIT BREAKER MOCBBOCB OIL CIRCUIT BREAKER

In such breakers oil is used as an arc quenching medium. Breaking capacity 75 MVA to 250MVA It is employed on 11kV to 66kV

MOCB

Advantages It acts as an insulator and permits smaller clearance between live and earthed. It has excellent cooling property. Disadvantages It is inflammable and there is a risk of fire. It requires more maintenance. Oil leakage problem. Absorbs moisture,so dielectric strength reduces.

AIR BLAST CB  In this CB a compressed air pressure of 18 to 20kg/Cm 2 is employed for arc extinction.  Its breaking capacity is 6000MVA and above.  It is applicable at 132kV and above

Types of Air Blast CB ABCB Axial- blast type Cross- blast type Radial- blast type

Advantages  Risk of fire is eliminated,  The arcing time is very small due to rapid build up of the dielectric strength,  Due to lesser arc energy, so it is very suitable where frequent operation is required. Disadvantages  IT is very sensitive to the RRRV  It requires more maintenence.  It has low arc quenching properties.

Sulpher Hexafluoride (Sf 6 )2.8kg/ cm 2 is used as an arc quenching medium, Its Breaking capacity is 60kA and voltage range of 50-80kV.  It is applicable at kV and power rating of 10-20MVA.

Advantages Due to superior arc quenching property of SF6 gas such breakers have very short arcing time. Due to more dielectric strength such breakers can interrupt much larger current. This breaker gives noiseless operation. There is no risk of fire in such breakers because SF6 gas is non inflammable. Disadvantage It is very costly due to the high cost of sf6. Additional equipments are required to reconditioned after operation.

Vacuum circuit breaker  Vacuum ( To10 -5 torr )is used as arc quenching medium.  Its Breaking capacity is 100MVA.  It is applicable at 22kV to 66kV

Advantage  They are compact, reliable and have longer life.  There no fire hazards.  They have low arc energy.  Do not form gas during and after operation.  Less maintenance.  Withstand lightening surges.