Switchgear and Protection Part-2

 

Switchgear and Protection

1. The primary function of a fuse is to___________.

a. Prevent excessive currents from flow through the  circuit

b. Protect the line

c. Protect the appliance

d. Open the circuit

2. The material used in liquid fuses is____________.

a.Transformer oil

b. Carbon tetra chloride

c. Distilled water

d. SF₆

3. In comparison to rewirable fuses HRC fuses have the advantage(s) of_______.

a. High speed operation

b. High rupturing capacity

c. No ageing effect

d. All of the above

4. In HRC fuse the time between cut-off and final current zero is called the______.

a. Pre-arcing time

b. Arcing time

c. Total operating time

d. None of these

5. If a combination of HRC fuse and circuit breaker is employed, the circuit breaker operates for________.

a. The combination is newer employed in practice

b. Under all abnormal currents

c. Low overload currents

d. Short-circuit current

6. The least expensive protection for overcurrent in low-voltage system is______.

a. Air-break switch

b. Circuit breaker

c. Isolator

d. Rewirable fuse

7. A circuit breaker normally operats________.

a. Whenever fault occurs in the line

b. When the switch is to be put on

c. When the line is to be tested

d. When the power is to be supplied

8. When a fault occurs in a high voltage transmission line, first the________.

a. Isolator operates, then successively the relay and the circuit breaker

b. Relay operates, then successively the isolator and the circuit breaker

c. Relay operates then the circuit breaker

d. Circuit breaker operates then the relay

9. The initiation of electric arc at the instant of contact separation is caused by______.

a. Field emission of electrons

b. Thermionic emission of electrons

c. (a) and (b) both

d. None of the above

10. Arcing voltage will be the least in case of_______.

a. Tungsten

b. Silver

c. Copper

d. Carbon

11. The heat produced at the contact point owing to flow of electric current is least affected by__________.

a. Duration of flow of current

b. Magnitude of electric current flowing

c. Contact resistance

d. Temperature of the surrounding medium

12. Which of the following should have low value for the contacts and their material?

a. Thermal conductivity

b. Contact resistance

c. Thermal capacity

d. None of these

13. In a CB contact wipe is necessary_______.

a. To decrease the speed of operating of the CB

b. To increase the speed of opening and reduce the arcing of contacts

c. To increase the dielectric strength across the CB contacts

d. None of the above

14. Interrupting medium in a contactor may be______.

a. Compressed air

b. SF₆

c. Oil

d. Any of these

15. The fluids used in circuit breakers should be of_______.

a. Arc extinguishing ability

b. Noninflammability

c. High dielectric strength and thermal stability

d. All of the above

16. Sparking between contacts can be reduced by inserting

a. A capacitor in parallel with the contacts

b. A reactor in the line

c. A capacitor in series with the contacts

d. A resistor in the line

17. For magnetic blow out of arc the magnetic field is produced________.

a. In the loud circuit

b. At right angles to the axis of the arc

c. In line with the axis of the arc

d. Any of the above

18. In a circuit breaker, ionization is facilitated by __________.

a. Increase in field strength

b. Increase of mean free length

c. High temperature of surrounding medium

d. All of the above

19. In circuit breaker the contact space is ionized by______.

a. Thermal ionization of gas

b. Thermal emission from the contact surface

c. Field emission from the contacts surface

d. Any of the above

20. The stability of arc in vacuum depends on________.

a. The contacts material only

b. The contact material and its vapour pressure

c. The circuit parameters only

d. The combination of (b) and (c)

21. The interrupting time of a circuit breaker is the period between the instant of_______.

a. Initiation of short circuit and the arc extinction on an opening operation

b. Energizing of the trip circuit and the arc extinction on an opening operation

c. Initiation of short circuit and the parting of primary arc contacts

d. Energizing of the trip circuit and the parting of primary arc contacts

22. The resistance of an electric arc can be increased by_______.

a. Increasing the arc X-section

b. Splitting the arc

c. Reducing the arc length

d. Increasing the concentration of ionized particles

23. In circuit breaker, the active recovery voltage depends upon_____.

a. Armature reaction

b. Power factor

c. Circuit breaker

d. All of these

24. In a circuit breaker the current that exist at the instant of contact separation is called the _____current.

a. Recovery

b. Arc

c. Breaking

d. Restriking

25. The RRRV depends upon the____.

a. Inductance and capacitance of the system

b. Inductance of the system only

c. Capacitance of the system only

d. Type of the circuit breaker