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Thermal circuit breaker has delayed trip action.

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Answer : Magnetic circuit breaker has instantaneous trip action.

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

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 : 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.

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

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

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

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 : 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.

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

Answer : Thermal overload relays are used to protect the motor against overcurrent due to heavy loads.

Answer : A thermal protection switch can protect against overload.

Description : Explain the thermal triggering method of SCR. Enlist different triggering methods of SCR.

Answer : Types of Triggering: 1) Forward voltage triggering 2) Thermal triggering (Temperature triggering) 3) Radiation triggering (Light triggering) 4) dv/dt triggering 5) Gate triggering ... generated leakage current increases. This current gets multiplied internally and thyristor is turned on. 

Description : Define thermal runaway.

Answer : Thermal runaway  The problem with increasing temperature causing increasing collector current is that more current increase the power dissipated by the transistor which, in turn, increases its temperature ... self-reinforcing cycle is known as thermal runaway, which may destroy the transistor. 

Description : Classify condensers used in thermal power station. Explain each type in brief. 

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Description : "Efficiency of thermal power station is low". — Justify. 

Answer : Justification: Efficiency of thermal power station is low":- Overall efficiency of T.P.P depends upon efficiency of boiler, turbine and alternator. The heat produced due to combustion of coal ... losses in thermal power plant is 71%, So efficiency of thermal power plant is less about 29% 

Description : State advantages of Pulverized coal w.r.t. thermal power plant. 

Answer : Advantages of Pulverized coal w.r.t. thermal power plant.  1. Due to pulvarization amount of fuel required to produce same amount of heat reduces. 2. Time required for combution reduces ... of air and thorough mixing of air and fuel, very high-combustion temperatures can be attained.

Description : State the function of super heater of a thermal power plant. 

Answer : Function of Super heater: -  Its function is to increase the temperature of steam by absorbing heat from exhausted hot flue gases.

Description : Describe thermal runaway of transistor and explain how it can be avoided.

Answer : Concept of thermal runaway:  1.We know that  IC = β IB + (1+ β) ICO  Where ICO is the leakage current and ICO is strongly dependent on temperature. 2. Leakage current approximately doubles for ...   Thermal runaway can be avoided by : 1) Using stabilization circuitry 2) Heat sink 

Description : State the function of cooling tower and condenser in thermal power station.

Answer : 1. Condenser:   Function of condenser is to convert exhaust steam again into water by reducing its temperature with the help of cold water. Also it reduces back pressure of steam turbine 2 ... tower : The function of cooling tower is to reduce the temperature of water coming from condenser.

Description : Write any four advantages and four disadvantages of thermal power plant.

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Description : Explain ash disposal and dust collection in a thermal power plant.

Answer : Ash disposal:-  Various methods of disposal of ash are:  Mechanical handling system.  Pneumatic system. Hydraulic system  Steam jet system  Commonly used ash handling ... be done either manually or automatically.  This removed fly ash is collected in separate container

Description : State any four factors governing Selection of site for thermal power station. 

Answer : Following Factors are to be considered:- 1. It should locate near coal mine. 2. Sufficient quantity of water should be available. 3. Sufficient large space should be available. 4. It should be located ... laws of the land and the town planning. 14. The interests of national defense must be served.

Description : The overall efficiency of Thermal Power Plant is equal to _______________ .  (A) Regenerative Cycle Efficiency (B) Renkine Cycle Efficiency (C) Carnot cycle efficiency (D) None of the above

Answer : The overall efficiency of Thermal Power Plant is equal to Regenerative Cycle Efficiency. 

Description : In a thermal power plant, ash is collected in

Answer : In a thermal power plant, ash is collected in hoppers or bunkers

Description : The unit heat rate characteristic of a thermal power unit shows :  (A) Heat input per kWh of output versus the megawatt output of unit  (B) Heat input per kW of output versus the megawatt output ... hour output of unit  (D) Heat input per kW of output versus the megawatt hour output of unit

Answer : The unit heat rate characteristic of a thermal power unit shows : Heat input per kWh of output versus the megawatt output of unit 

Description : What is thermal runaway of a transistor?

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 

Answer : 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 

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 : 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

Answer : 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

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

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

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.

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

Answer : Circuit breakers usually operate under transient state of short-circuit current.

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.

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