ISOLATOR,CIRCUIT BREAKER, RELAY AND FUSE
SET - B
1. An isolator is designed to open a circuit under –
a) Full Load , b) normal condition , c) no load , d) Isolator can operate at any load .
2. For the same power , the least size is of –
a) Oil circuit breaker , b) Air- blast Circuit breaker , c) Vacuum circuit breaker , d) SF6 Circuit Breaker.
3. Switching surge is a –
a) High Voltage DC , b) High Voltage AC , c) Short duration transient voltage , d) Long duration transient
voltage.
4. The current rating is not necessary in case of –
a) Switch and Isolator , b) Isolator , c) Switch , d) Circuit Breaker .
5. A good fuse wire must have –
a) High melting point , b) High ohmic losses , c) High conductivity , d) High Dielectric strength.
6. A fuse is provided in an electric circuit for-
a) Safeguard the installation against heavy current , b) Reducing the current flowing in the circuit ,c)
Reduce the power consumption of the circuit , d) Protect the circuit against leakage current .
7. How should a fuse should be installed in a circuit-
a) Series with the load , b) Parallel with the load , c) At the earthing line , d) any of the above way.
8. Fusing factor of a fuse is defined as the ration of –
a) Maximum fusing current to the prospective current , b) Maximum fusing current to the cut off current ,
c) Rated carrying capacity to maximum fusing current, d) Maximum fusing current to the rated carrying
capacity .
9. A 3-phase circuit breaker is rated at 1200A, 2000 MVA , 100 KV , 4 sec . The symmetric breaking current is –
a) 1.67 KA , b ) 30 KA , c ) 20.25 KA , d ) 11.55 KA .
10. A 3-ph circuit breaker is rated at 1250A , 200 MVA , 33 KV . The making current will be –
11. The recovery voltage appears across the circuit breaker contacts will be maximum for power factor of -
a) Zero , b) 0.5 , c) 0.707 , d) unity .
12. The rate of rise of re-striking voltage in a circuit breaker depends upon the –
a) Type of circuit breaker , b) Inductance of line , c) Capacitance of the line , d) Both inductance and
capacitance of the line .
13. If the fault current in a line is 2000 A and the CT ratio is 400 : 5 with relay setting 50% , then the PSM will be-
14. A relay performs the function of –
a) Fault Isolation , b) Fault detection , c) Fault Prevention , d) Fault Absorption .
15. Buchholz relay is –
a) Gas actuated , b) Current actuated , c) Voltage actuated , d) Power actuated .
16. Mho relay is –
a) Current restrained current relay , b) voltage restrained directional relay , c) current restrained directional
relay , d) Voltage restrained current relay .
17. If the length of the arc in a circuit breaker increases ,its resistance –
a) Decreases , b) increases , c) remains same , d) none of the above .
18. During which part of fault current wave the fuse melts ?
a) Well before the first peak is reached , b) when the first peak is reached , c) after the first peak , d) none
of the above.
19. The time-current graph of a fuse -
a) Has linear characteristic , b) is a circle , c) has inverse characteristic , d) none of the above.
20. A Fuse should have –
A) Low melting point , B) High Resistance , C) High Melting Point , D) Low conductivity.
