Interview Questions.

Question 1. What Is A Circuit Breaker?

Answer :Circuit Breaker is a mechanical device designed to shut or open contact individuals, as a consequence final or starting an electrical circuit under the ordinary or strange conditions.

Question 2. How Does A Circuit Breaker Different From Switch?

Answer :Switch is just a device when may be able to open and close the circuit during ordinary operation. Whereas on the other hand circuit breaker has the potential to open and near the contacts during ordinary or fault conditions. Thus circuit breaker has the potential to break and make heavy short circuit currents. Auto-reclosures in the circuit beaker has the capacity to re-near after sure designed period to verify whether or not the fast circuit changed into cleared.

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Question three. What Is Meant By Making Capacity Of The Circuit Breaker?

Answer :The making capacity of the circuit breaker when closed on a quick circuit is the height value of the most present day wave (along with dc issue) in the first cycle of the cutting-edge after the circuit is closed by means of the circuit breaker.

Question 4. Why Current Chopping Is Not Common In Oil Circuit Breakers?

Answer :Current chopping isn't always commonplace in oil circuit breakers due to the fact in most of the oil circuit breakers the arc extinguishing energy is proportional to the significance of contemporary to be interrupted.

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Question five. Name The Materials Used For The Contacts Of Vacuum Circuit Breakers?

Answer :Copper-Bismuth, Copper-lead, Copper-tellurium, Silver-bismuth, Silver-lead and Silver-tellurium are a number of the alloys employed as touch materials in the vacuum circuit breakers.

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Question 6. Why Current Chopping Considered As Serious Drawback In A Circuit Breaker?

Answer :The contemporary cutting is considered as severe disadvantage as it sets up excessive voltage brief across the breaker contacts.

Question 7. For Ehv Applications Which Type Of Circuit Breaker Is Mostly Preferred?

Answer :For Exta High Voltage (EHV) packages SF6 fuel insulated switchgear is preferred.

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Question 8. What Are The Duties Of Circuit Breakers?

Answer :

Some of the obligations of the circuit breakers are indexed under:

Interruption of small inductive currents
Switching of unloaded transmission lines and unloaded cables
Switching of capacitor banks and reactors
Interruption of terminal faults
Interruption of brief line faults
Asynchronous switching
Question nine. What Is The Meaning Of Rupturing Capacity Of A Circuit Breaker?

Answer :

Rupturing capability of a circuit breaker means the most energy a circuit breaker can interrupt beneath a fault. It is typically expressed in Mega volt Ampere (MVA) and it's far then the fabricated from the rated breaking current in kilo amperes and rated voltage expressed in kilo volts.

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Question 10. What Do You Mean By The Term “making Current” And “breaking Current” Of A Circuit Breaker?

Answer :

The ‘Making Current’ of a circuit breaker is the overall maximum modern peak which takes place during the first cycle at once after the circuit is closed on a quick circuit.
The ‘Breaking Current’ of a circuit breaker is the total most contemporary peak that may be accurately damaged by using the circuit breaker at the time of separation of the contacts at its rated voltage.
Question eleven. What Do You Understand By The Term “quick Circuit Mva”? How S The Breaking Capacity Specified?

Answer :

“Short Circuit MVA” is the rupturing capability or breaking ability of a circuit breaker in case of a three phase symmetrical fault which determines the scale of the circuit breaker. The breaking capacity of a circuit breaker is designated either in terms of symmetrical breaking current/MVA or asymmetrical breaking modern/MVA.

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Question 12. Why Is It Necessary To Know The Fault Level At The Incoming Point Of Supply? Who Furnishes This Information ?

Answer :

To choose the MVA rating of the circuit breaker of a excessive voltage installation the fault stage at the incoming factor of deliver ought to be known. Power supply authority furnishes the fault degree.

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Question thirteen. In What Value The Making Current Of A three-phase 3000 Mva, 33 Kv Breaker?

Answer :

the making modern-day is usually laid out in top price.

Breaking modern-day = 3000/(√three×33) KA = 52.48 KA

Making modern = 2.55 × 52.48 = 133.82 KA.

Question 14. What Do You Mean By “asymmetrical Breaking Current” And “symmetrical Breaking Current”?

Answer :

The asymmetrical breaking present day is the r.M.S. The value of the total cutting-edge at the initial instant of touch separation and is identical to the rectangular root of the sum of the squares of the symmetrical breaking current and of the direct factor of the modern-day at the same instant. The symmetrical breaking modern is the r.M.S. The value of the symmetrical modern (a.C. Factor of contemporary) on the initial instant of touch separation. Actually, the score of the breaker is laid out in terms of symmetrical breaking current & voltage.

Question 15. Why Is The Rating Of A Circuit Breaker Decided On The Basis Of Symmetrical Short Circuit Currents?

Answer :

As the symmetrical fault is most excessive in a three segment line and imposes the heavy responsibility at the control tools, consequently, the circuit breaker is rated on the idea of symmetrical brief circuit currents.

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Question sixteen. Why Is Symmetrical Fault More Severe Than The Unsymmetrical Fault In A three-phase System?

Answer :

In a symmetrical fault seeing that all of the 3 conductors are quick circuit collectively causing identical fault currents to flow through the line then the symmetrical fault due to the fact more excessive.

Question 17. What Is The Importance Of Base Kva In Short Circuit Calculations?

Answer :

As the diverse device used in the strength gadget have one of a kind KVA score with one-of-a-kind percentage reactances so for smooth calculation it's far vital to locate the percentage reactances of all system on a commonplace KVA score. This not unusual KVA score is referred to as base KVA.

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Question 18. Does The Value Of Short Circuit Current Vary For Different Values Of Base Kvas?

Answer :

No. Whatever can be the value of base KVA the value of quick circuit present day stays unchanged.

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Question 19. What Do You Mean By The ‘recuperation Voltage’ Of A Circuit Breaker?

Answer :

The recovery voltage is described to be the r.M.S. The cost of the road voltage of service frequency that reappears throughout the poles of the circuit breaker short after arc extinction in all the poles and after damping of the temporary phenomena.

Question 20. What Do You Mean By The Term ‘restriking Voltage’ Of A Circuit Breaker?

Answer :

The restriking voltage or the transient healing voltage is the voltage between the contacts of a pole of the circuit breaker after the extinction of the arcs even as the temporary nation persists.

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Question 21. Why The Circuit Breakers To Be Used On 6.6 Kv, 11 Kv, 33 Kv, 66 Kv, And 132 Kv Lines Should Be Of Rated Voltage 7.2 Kv, 12 Kv, 36 Kv, seventy two Kv, And 145 Kv Respectively?

Answer :

As the voltage score of circuit breaker corresponds to highest gadget voltage so the circuit breaker for use on 6.6 kV line should be of rated voltage 7.2 kV and so forth.

Question 22. On What Factors Does The Rate Of Rising Of Restriking Voltage Depend?

Answer :

The rate of rising of restriking voltage depends upon the inductance and capacitance of the system.

Question 23. Why Is Current Interruption Easier In An A.C. Circuit Than In A D.C. Circuit ?

Answer :

Due to natural modern-day zeros in alternating cutting-edge waves interruption of an a.C. Circuit turns into greater less difficult.

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Question 24. Is An A.C. Circuit Breaker Suitable For D.C. Supply Line?

Answer :

Generally a.C. The circuit breaker isn't always suitable for d.C. Supply line because of a.C. Circuit breaker quenches arc without problems at present day zero of an alternating wave which is not viable in d.C. Due to nonexistence of cutting-edge 0.

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Question 25. (a) Is A 50 Hz Circuit Breaker Suitable For 60 Hz Supply? (b) Can A 12 Kv Circuit Breaker Be Used For 6.6 Kv Application?

Answer :

(a) It is possible most effective whilst the breaker is kind examined at 60 Hz frequency, otherwise no longer.

(b) A 12 kV circuit breaker can use for any voltage up to its rated voltage beneath the condition that the breaking cutting-edge is inside its breaking capacity.

Question 26. What Is The Difference Between Low Voltage Circuit Breakers And High Voltage Circuit Breakers?

Answer :

Low voltage circuit breakers are used in indoor control gears for controlling strength ingesting devices of circuits beneath rated voltage a thousand volt a.C. Or 1200 volts d.C. Whereas excessive voltage circuit breakers are utilized in both indoor and outdoor controllers in high voltage deliver system.
Low voltage circuit breakers perform regularly than the excessive voltage circuit breaker.
Low voltage circuit breakers are greater compact than excessive voltage circuit breakers because of much less segment to phase and section to ground clearances.
Testing necessities of a high voltage circuit breaker are quite distinct from the ones of low voltage circuit breakers.
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Question 27. How Are The Rating Of A Circuit Breaker Given?

Answer :

The score of a circuit breaker are given via

the most voltage in kV,
the maximum non-stop current wearing capability in amperes,
the maximum interrupting ability in MVA and kilo amperes (kA),
the deliver frequency 
the making capacity in amperes.
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