1. On which of the following routine tests are conducted ?
2. SF6 gas
3. The arcing contacts in a circuit breaker are made of
4. With which of the following, a circuit breaker must be equipped for remote operation ?
5. Fault diverters are basically
6. A thermal protection switch can protect against
7. Arc in a circuit behaves as
8. D.C. shunt relays are made of
9.. Thermal circuit breaker has
10. Magnetic circuit breaker has ______ trip action.
11. The relay operating speed depends upon
12. In order that current should flow without causing excessive heating or voltage drop, the relay contacts should
13. Circuit breakers usually operate under
14. Circuit breakers are essentially
15. The current zero interruption, in oil and air blast circuit breakers, is achieved by
16. Air blast circuit breaker is used for
17. Burden of a protective relay is the power
18. An efficient and a well designed protective relaying should have
19. Directional relays are based on flow of
20. A differential relay measures the vector difference between
21.A transmission line is protected by
22.Large internal faults are protected by
23. When a transmission line is energized, the wave that propagates on it is
24.Protective relays are devices that detect abnormal conditions in electrical circuits by measuring
25.The voltage appearing across the contacts after opening of the circuit breakeris called______voltage.
26.Ionization in circuit breaker is facilitated by
27. In a circuit breaker the basic problem is to
28.Overheating of relay contacts or contact born out is due to
29.. The arc voltage produced in A.C. circuit breaker is always
30.. Insulation resistance of high voltage circuit breakers is more than
31.Interruption of large currents by relay requires
32.H.R.C. fuses provide best protection against
33.The delay fuses are used for the protection of ________ .
34. . Which of the following is the least expensive protection for overcurrent islowvoltage system ?
35.. The contacts of high voltage switches used in power systemare submerged in oil. The main purpose of the oil is to
36.In Railway applications ______ circuit breaker is used.
37. Resistance grounding is used for voltage between
38.Wave trap is used to trap waves of
39.The reflection co-efficient at the open circuited end of a transmissionline.
40.To protect most of the electrical equipment handling low power, the types of relays used are
41.Ungrounded neutral transmission system is not recommended because of system
42. For the protection of power station buildings against direct strokes therequirements are
43. Which of the following statements is incorrect?
44.Discrimination between main and back up protection is provided by theuseofrelays which are
45.The interaction between a transmission line and communication line is minimized by
46.. Induction cup relay is operated due to changes in
47 A.C. network analyser is used to solve problems of
48.Which of the following statements is incorrect ?
49.Short-circuit currents are due to
50.Which of the following circuit breakers has high reliability and minimum maintenance?
Explain:- SF6 circuit breaker is used for high voltage. It has high arc quenching property, and it is highly reliable and minimum maintenance.
51.Which of the following statements is INCORRECT while using plain-break circuit breakers at high voltages?
Explain:- The plain-break circuits breakers are employed for breaking of low current at comparatively lower voltages. They are used on low voltage dc circuits and on low voltage ac distribution circuits.
Their size becomes unduly larger for high voltages. Also, they require large amount of transformer oil. they are not suitable for auto reclosing. Their speed is slow. They can be used up to 11 kV with an interrupting capacity up to 250 MVA.
52.The time of closing the cycle, in modern circuit breakers is
Explain:- The time of closing the cycle of modern circuit breakers is 0.003 second.
53.SF6 gas:
Explain:- : The SF6 circuit breaker has fallowing characteristics.
(i) SF6 gas is colorless, odorless, nontoxic, and non-inflammable.
(ii) It has superior arc quenching property so It has very short arc time.
(iii) It does not need an auxiliary breaking chamber.
(iv) Short break time of 2 to 2.5 cycles
54.The Minimum Oil Circuit Breaker (MOCB) is named because of:
Explain:- The minimum oil circuit breaker places the interrupting Unit in insulating chamber at live potential. The insulating Oil is available only in interrupting chamber. The features of designing MOCB are to reduce requirement of oil and hence these breaker are called minimum oil circuit breaker.
55.A circuit breaker is designed to protect an electrical circuit from damage caused by:
Explain:- A circuit breaker is designed to protect an electrical circuit from damage caused by overload, Short circuit, and over current.
56.Which of the following circuit breakers is commonly used in India for rural outdoor applications ranging from 22kV to 66KV.
Explain:- (1) Air Break Circuit Breaker (ACB) – In A.C. upto 6.6 kV (r.m.s.) and in D.C. upto 12 kV
(2) Air Blast Circuit Breaker (ABCB) – Voltage more than 400 kV
(3) Vaccum Circuit Breaker – used from 6.6 kV to 220 kV.
(4) Oil Circuit Breaker (MOCB) – upto 66 kV.
Hence in rural electrification vacuum circuit breaker generally used.
57.The arc temperature in Oil Circuit Breaker may reach up to __________.
Explain:- The arc temperature in oil circuit breaker may reach up to 5000 K. Due to this high temperature the gas is liberated surround the arc very rapidly and forms an excessively fast growing gas bubble around the arc.
58.The basic function of any circuit breaker in the power system is to:
Explain:- : A circuit breaker is an automatically operated electrical switched designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. The basic function of circuit breaker is make or break the circuit
59.In circuit breakers, the current chopping tendency is minimised by using SF6 gas at relatively:
Explain:- In circuit breaker, the current chopping tendency is minimised by using SF6 gas at relatively low pressure and low velocity.
60.The power frequency rms voltage, that appears across the breaker contacts after the transient oscillations die out and final extinction of arc that results in all the poles is called
Explain:- Recovery voltage– RMS voltage which appear a across circuit breaker contact after arc is extinguished and transient oscillation are completely die out is known as recovery voltage.
61.In resistance switching, the function of shunt resistor
Explain:- : Resistance switching- It is used to reduce the restriking voltage, RRRV (rate of rise of restriking voltage) and transient oscillation. A resistance is connected across the circuit breaker contact this is known as Resistance switching.
Use in– Air blast circuit also use for remove current chopping phenomena.
62.The number of poles per phase of breaker is a function of
Explain:- : The number of poles per phase of breaker is a function of operating voltage. Based on the number of poles the breakers are classified as–
1. SP -Single pole
2. SPN - Single pole and Neutral
3. DP -Double pole
4. TP - Triple Pole
5. TPN - Triple pole and Neutral
6. 4 P - Four pole
Note– In SP MCCB, switching and protection is affected in only one phase.
63.The capacitor switching is easily done with
Explain:- Vacuum circuit breaker- In this circuit breaker vacuum is used as arc quenching medium-
1. Degree of vacuum in the range of 10–7 to 10–5 unit torr vacuum have very high dielectric strength and superior arc quenching property in comparison to other insulating medium.
2. Used up to 33 kV
3. Use is distribution line.
4. SF6 circuit breaker– Used 132 kV and above
64.Shunt resistor is connected across the contacts of a circuit breaker in order to :
Explain:- : The dielectric strength between contacts of circuit breaker increases as gap between fixed contact and moving contact increases. If dielectric strength between C.B. contacts increases factor than TRV (transient restrike voltage), arc will not restrike.
To provide damping a resistance R is connected across C.B. contacts
65.The highest current that a circuit breaker is capable of breaking at recovery and re striking voltage is
Explain:- The highest current that a circuit breaker is capable of breaking and restriking voltage is breaking capacity.
66.The air blast circuit breaker have best application in system of operating voltage
Explain:- Air Blast circuit breaker is operated at 132 kV to 400 kV
67.The use of reactors permits the installation of circuit breakers of
Explain:-The use of reactor permits the installation of CB of lower ratings because reactor can reduced the short circuit MVA and current hence this can allow the lower of the interrupting duty cycle of CB.
68.Which is the most serious problem in vacuum circuit breaker
Explain:- Current chopping in circuit breaker is defined as a phenomenon in which current is forcibly interrupted before the natural current zero. Current chopping is mainly observed in the vacuum circuit breaker and air blast circuit breaker. There is no such phenomenon in oil circuit breaker.
69.In a circuit breaker, the total time duration from the instant of occurrence of the fault to the instant of arc extinction is called
Explain:- : In a circuit breaker, the total time duration from the instant of occurrence of the fault to the instant of arc extinction is called total fault clearing time
70.To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of
Explain:- In vacuum CB, the current chopping depends upon the vapour pressure and the electrons emission property of the contact material- Therefore, to reduce the current level for chopping to occur, a high vapour pressure and low conductivity metal is desirable. Since gas pressure is low in a vacuum switch. A low conductive material will maintain contact surface temperature and vaporization for a longer time to maintain the arc stability which is necessary for current chopping.
71.CB used for over current protection of thyristor operates when the fault current is
Explain:- : CB used for over current protection of thyristor operates when the fault current is of long period. As tripping time of CB is generally large for this type of protection.
72.A 3 phase circuit breaker is rated at 1200A, 2000 MVA, 100 kV, 4 sec. The rated symmetrical breaking current is
Explain:-
73.A three phase 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. The symmetrical breaking current is-
Explain:-
74.Making capacity of the circuit breaker depends on-
Explain:-
75.The transient voltage that appears across the contacts at or near current zero during arcing period is known as:
Explain:-
