Multiple Choice Questions on Power System - 3

Important multiple choice questions on power system

1.       A line trap in carrier current relaying tuned to carrier frequency presents

A)     High impedance to carrier frequency but low impedance to power frequency

B)      Low impedance to both carrier and power frequency

C)      High impedance to both carrier and power frequencies

D)     Low impedance to carrier frequency and high impedance to power frequency

2.       The use of fast acting relays and circuit breakers for clearing a sudden short circuit on a transmission link between generator and the receiving end bus improves the transient stability of the machine because

A)     Short circuit current becomes zero

B)      Post-fault transfer impedance attains a value higher than that during the fault

C)      Ordinate of the post-fault power-angle characteristic is higher than that of during fault characteristic

D)     Voltage behind the transient reactance increases to a higher value

3.       A thyrite type lightning arrestor

A)     Blocks the surge voltage appearing in a line

B)      Absorbs the surge voltage appearing in a line

C)      Offers a low resistance path to the surge appearing in the line

D)     Returns the surge back to the source

4.       The relay which is most sensitive to power swings (mal operation) is

A)     mho relay

B)      reactance relay

C)      impedance relay

D)     all are equally affected

5.       if the normal frequency is 50 Hz, the setting of the under-frequency relay for the most important load could be

A)     49 Hz

B)      48.5 Hz

C)      47.5 Hz

D)     There is no grading for under frequency relays

6.       In case of a 3 phase short circuit in a systems the power fed in to the system is

A)     Mostly reactive

B)      Mostly active

C)      Active and reactive both are equal

D)     Reactive only

7.       In the solution of load-flow equation, Newton-Raphson (NR) method is superior to the Gauss-seidel (GS) method, because

A)     Time taken to perform one iteration in the NR method is less than when compared to time taken in GS method

B)      Number of iterations required in the NR method is more when compared to that in the GS method

C)      Number of iterations required is not independent of the size of the system in NR method

D)     Convergence characteristics of the NR method are not affected by the selection of slack bus

8.       A square matrix is called singular if its

A)     Determinant is unity

B)      Determinant is zero

C)      Determinant is infinity

D)     Rank is unity

9.       The function of earth wire in extra high voltage line is to

A)     Prevent earth fault

B)      Provide a safety measure for any high-flying object

C)      Provide a shield to the phase conductors from direct lightning stroke

D)     Provide mechanical strength to the towers

10.   Corona losses are minimised when

A)     Conductors size is reduced

B)      Smooth conductor is used

C)      Sharp points are provided in the line hardware

D)     Current density is conductors is reduced