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The arcing contacts in a circuit breaker are made of copper tungsten alloy.

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Answer : The voltage appearing across the contacts after opening of the circuit breaker is called recovery voltage.

Description : The arc temperature in Oil Circuit Breaker may reach up to_______.  (A) 5,000° K (B) 8,000° K (C) 10,000° K (D) None of the above

Answer : The arc temperature in Oil Circuit Breaker may reach up to 5,000° K 

Description : The number of cycles in which a high speed circuit breaker can complete its operation is  (A) 3 to 8 (B) 10 to 18 (C) 20 to 30 (D) 40 to 50

Answer : The number of cycles in which a high speed circuit breaker can complete its operation is 3 to 8

Answer : Arc in a circuit breaker is interrupted at zero current.

Answer : The arc voltage produced in A.C. circuit breaker is always in phase with the arc current.

Answer : In a circuit breaker the basic problem is to transmit large power.

Answer : Ionization in circuit breaker is facilitated by high temperature, increase of mean free path, increasing field strength.

Description : A circuit breaker is designed to protect an electrical circuit from damage caused by :  (A) Over load (B) Short circuit (C) Over current (D) All of the above

Answer : A circuit breaker is designed to protect an electrical circuit from damage caused by :  (A) Over load (B) Short circuit (C) Over current (D) All of the above

Description : The Minimum Oil Circuit Breaker (MOCB) is named because of :  (A) Reduced requirement of oil (B) Reduced requirement of air (C) All of the above (D) None of the above

Answer : The Minimum Oil Circuit Breaker (MOCB) is named because of : Reduced requirement of oil 

Description : For selecting a circuit breaker, ______ should be determined.  (A) initial current that flows on occurrence of a short circuit only (B) transient current that flows at the time of circuit interruption only (C) resonant frequency only (D) (A) and (B) 

Answer : For selecting a circuit breaker, ______ should be determined. (A) initial current that flows on occurrence of a short circuit only (B) transient current that flows at the time of circuit interruption only (C) resonant frequency only (D) (A) and (B) 

Description : ln a minimum oil circuit breaker the oil is used

Answer : ln a minimum oil circuit breaker the oil is used to act as circuit breaking medium only

Answer : Air blast circuit breaker is used for repeated duty.

Answer : Magnetic circuit breaker has instantaneous trip action.

Answer : Thermal circuit breaker has delayed trip action.

Description : what is SF6 circuit breaker?

Answer : A circuit breaker in which SF6 under pressure gas is used toextinguish the arc is calledSF6 circuit breaker. SF6 (sulphur hexafluoride) gas has excellent dielectric , arc quenching, chemical and other physical properties and has proved its ...

Description : Breaking capacity of a circuit breaker is usually expressed in terms of  (1) Ampere (2) Volts (3) MW (4) MVA

Answer : Breaking capacity of a circuit breaker is usually expressed in terms of MVA

Description : The arc voltage in a circuit breaker is :

Answer : The arc voltage in a circuit breaker is : in phase with the arc current

Description : Which of the following is used in a circuit breaker as the medium in which the arc forms? A) Insulating gas B) Insulating oil C) Vacuum D) All the above

Answer : Which of the following is used in a circuit breaker as the medium in which the arc forms? A) Insulating gas B) Insulating oil C) Vacuum D) All the above

Description : Explain working of static AC circuit breaker. 

Answer : Static AC Circuit breaker: The circuit configuration of static AC circuit breaker using SCR is shown in the figure. When switch S' is closed, the SCRs T1 and T2 are fired in positive ... non-availability of gate current. Thus the maximum time delay for breaking the circuit is one half-cycle.

Description : Explain working of AC circuit breaker using SCR with circuit diagram.

Answer : AC Circuit Breaker:  The circuit configuration of static AC circuit breaker using SCR is shown in the figure. When switch S' is closed, the SCRs T1 and T2 are fired in positive ... to non-availability of gate current. Thus the maximum time delay for breaking the circuit is one half-cycle.

Description : State function of starter and ELCB. (Earth Leakage Circuit Breaker)

Answer : i) Function of Starter:- 1. To prevent the high starting current OR to minimize the starting current. 2. To give supply failure protection 3. To give over load and short circuit protection ... an installation and cut off the circuit from power supply and avoid electrical shock to the person.

Answer : The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to extinguish the arc.

Answer : In order that current should flow without causing excessive heating or voltage drop, the relay contacts should have low contact resistance, be clean and smooth, be of sufficient size and proper shape.

Answer : Overheating of relay contacts or contact born out is due to slow making and breaking of load circuit contacts, foreign matter on the contact surface, too low contact pressure.

Answer : Air blast circuit breakers for 400 kV power system are designed to operate in 50 millisecond.

Description : The following is/are the characteristics of SF6 circuit breakers:  (A) It does not need an auxiliary breaking chamber (B) Short break time of 2 to 2.5 cycles (C) All of the above (D) None of the above

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Answer : Circuit breakers are essentially current carrying contacts called electrodes.

Answer : A fuse in a motor circuit provides protection against short-circuit and overload.

Answer : The short circuit in any winding of the transformer is the result of impulse voltage.

Answer : The time of closing the cycle, in modern circuit breakers is 0.003 sec.

Description : The current zero interruption, in oil and air blast circuit breakers, is achieved by?

Answer : The current zero interruption, in oil and air blast circuit breakers, is achieved by lengthening of the gap, cooling and blast effect.

Description : Arc in a circuit behaves as?

Answer : Arc in a circuit behaves as a resistance decreasing with voltage rise across the arc.

Description : In which fault the maximum short circuit current occurs?

Answer : In three phase bolted fault the maximum short circuit occurs.

Description : If the % reactance upto the fault point is 20%, then the short circuit current will be

Answer : If the % reactance upto the fault point is 20%, then the short circuit current will be 5 times the full load current

Description : Which of the following circuit breakers has high reliability & minimum maintenance?  (A) Bulk oil type CB (B) Air blast CB (C) Vacuum CB (D) Sulphur hexafluoride CB 

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Answer : A switch tail ring counter is made by using a single D-FF. The resulting circuit is T-FF

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Answer : Which of the following medium is employed for extinction of arc in air circuit breaker ?(a) Water (b) Oil(c) Air (d) SF6

Description : Describe the construction of SF6 circuit breaker with neat diagram.

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Description : Define the following terms related to circuit breaker. 1) Breaking Capacity 2) Making Capacity 3) Short time rating and 4) Normal current rating

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Description : Explain construction and working of SF6 circuit breaker.

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Description : Which of the following are known as the short circuit parameters of a 2- port network? (A) Z- parameters. (B) H- parameters. (C) Y- parameters. (D) A,B,C,D, parameters.

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