Power Systems Objective Questions: Part1

POWER SYSTEM OBJECTIVE QUESTIONS FROM COMPETITIVE QUESTIONS(GATE, IES)

(1)- Power is transfered from system A to system B by an HVDC link as shown in the figureA.If the voltages V_AB and V_CD are as indicated in the figureA, and I>0,then

fig.A

   A.. VAB<0,VCD<0,VAB>VCD

   B. VAB>0,VCD>0,VAB>VCD

   C. VAB>0,VCD>0,VAB<VCD

   D. VAB>0,VCD<0

Ans:C

(2)- Consider a step voltage wave of magnitude 1pu travelling along a lossless transmission line that terminates in a reactor.The voltage magnitude across the reactor at the instant the travelling wave reaches the reactor is

fig.B

   A. -1pu

   B.  1pu

   C.  2pu

   D.  3pu

Ans: A

(3)- Consider two buses connected by an impedance of (0+j5)Ω. The bus 1 voltage is 100∠30° V, and bus 2 voltage is 100∠0° V. The real and reactive power supplied by bus 1, respectively are

   A. 1000W,268Var

   B. -1000W,-134Var

   C. 276.9W,-56.7Var

   D. -276.9W,56.7Var

Ans:A

(4)- A three-phase, 33kV oil circuit breaker is rated 1200A, 2000MVA, 3s. The symmetrical breaking current is

   A. 1200A

   B. 3600A

   C. 35kA

   D. 104.8kA

Ans:C

(5)- Consider a stator winding of an alternator with an internal high-resistance ground fault.The currents under the fault condition are as shown in the figure.The winding is protected using a differential current scheme with current transformers of ratio 400/5A as shown. The current through the operating coil is

 A. 0.17875A

 B. 0.2A

 C. 0.375A

 D. 60kA

Ans: C