Objective Type Question or MCQ of B. Economics of Operation page-6

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51. Three insulating materials with breakdown strengths of 250 kV/cm, 200 kV/cm, 150 kV/cm and permittivities of 2.5, 3.0 and 3.5 are used in a single core cable. If the factor of safety for the materials is 5, the location of the materials with respect to the core of the cable will be

a) 2.5, 3.0, 3.5
b) 3.5, 3.0, 2.5
c) 3.0, 2.5, 3.5
d) 3.5, 2.5, 3.0

Ans: (a)

52. At a particular unbalanced node, the real powers specified are

Leaving the node 20 MW, 25 MW
Entering the node 60 MW, 30 MW
Balance power will be

a) 30 MW leaving the node.
b) 45 MW leaving the node.
c) 45 MW entering the node.
d) 22.5 entering the node and 22.5 MW leaving the node.

Ans: (b)

53. Three insulating materials with same maximum working stress and permittivities 2.5, 3.0, 4.0 are used in a single core cable. The location of the materials with respect to the core of the cable will be

a) 2.5, 3.0, 4.0
b) 4.0, 3.0, 2.5
c) 3.0, 2.5, 3.5
d) 4.0, 2.5, 3.0

Ans: (b)

54. Positive sequence component of voltage at the point of fault is zero when it is a

a) 3-phase fault
b) L-L fault
c) L-L-G fault
d) L-G fault

Ans: (a)

55. Select the correct statement

a) The negative and zero sequence voltages are minimum at the fault point and increase towards the neutral.
b) The negative and zero sequence voltages are maximum at the fault point and decrease towards the neutral.
c) The negative sequence is maximum and zero sequence minimum at the fault point and decreases and increase respectively towards the neutral.
d) None of the above.

Ans: (b)

56. If I_a1 is the positive sequence current of an alternator and Z₁, Z₂ and Z₀ are the sequence impedances of the alternator. The drop produced by the current Ia₁ will be

a) I_a1 Z₁
b) I_a1 (Z₁ + Z₂)
c) I_a1 (Z₁ + Z_{2 + Z₀)

d) I_a1 (Z₂ + Z₀)

Ans: (a)}

57. Tick out the correct one

a) The insulators and lightning arresters should have high impulse ratio.
b) The insulators and lightning arresters should have low impulse.
c) The insulators should have high impulse ratio and lightning arrester low.
d) The insulators arrester should have high impulse ratio but insulator low.

Ans: (c)

58. An overhead line with surge impedance 400 ohms is terminated through a resistance R. A surge travelling over the line does not suffer any reflection at the junction if the value of R is

a) 20 ohms
b) 200 ohms
c) 800 ohms
d) None of the above

Ans: (d)

59. In case of a large size alternator the voltage control becomes serious if

a) SCR is high.
b) SCR is low.
c) Voltage control is independent of SCR.
d) None of the above.

Ans: (b)

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Objective Type Question or MCQ of B. Economics of Operation page-6

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