Transmission Line Models MCQs

 Q51. For a lossless line, the characteristic impedance 

$Z_c$ is:
A) $\sqrt{\frac{L}{C}}$
B) $\sqrt{\frac{R}{G}}$
C) $\frac{L}{C}$
D) $\frac{R}{G}$
Ans: A

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Q52. The line efficiency decreases with:
A) Increase in resistance
B) Decrease in resistance
C) Decrease in reactance
D) None
Ans: A

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Q53. The Ferranti effect results in:
A) Receiving end voltage < sending end voltage
B) Receiving end voltage > sending end voltage
C) Both equal
D) Depends on load
Ans: B

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Q54. The propagation constant γ = α + jβ. Here α represents:
A) Phase constant
B) Attenuation constant
C) Propagation velocity
D) Reflection coefficient
Ans: B

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Q55. The natural load on a transmission line is also known as:
A) Surge impedance loading
B) Thermal loading
C) Maximum load
D) Steady load
Ans: A

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Q56. The voltage regulation of a line is negative when:
A) Line is unloaded
B) Load is leading
C) Load is lagging
D) Load is resistive
Ans: B

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Q57. The characteristic impedance of a cable is usually:
A) Low
B) High
C) Infinite
D) Zero
Ans: A

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Q58. The Ferranti effect is caused mainly due to:
A) Line capacitance
B) Line inductance
C) Line resistance
D) Both A and B
Ans: D

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Q59. The equivalent circuit of a long line is obtained by using:
A) Distributed parameters
B) Lumped parameters
C) Both
D) None
Ans: A

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Q60. The ABCD constants are also called:
A) Transmission parameters
B) Network parameters
C) Two-port parameters
D) All of the above
Ans: D

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Q61. The input impedance of a short-circuited line is:
A) $jZ_c \tan(\beta l)$
B) $-jZ_c \tan(\beta l)$
C) $Z_c \tan(\beta l)$
D) None
Ans: A

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Q62. For a lossless line, βl = 180°, then the line is:
A) Half wavelength long
B) Quarter wavelength long
C) Full wavelength long
D) None
Ans: A

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Q63. The surge impedance loading (SIL) for a 400 kV line (Zc = 400 Ω) is approximately:
A) 300 MW
B) 400 MW
C) 350 MW
D) 250 MW
Ans: B

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Q64. For an open-circuited line, the input impedance is:
A) $-jZ_c \cot(\beta l)$
B) $jZ_c \cot(\beta l)$
C) $Z_c \tan(\beta l)$
D) $-Z_c \tan(\beta l)$
Ans: B

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Q65. The hyperbolic form of ABCD parameters is used for:
A) Short line
B) Long line
C) Medium line
D) None
Ans: B

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Q66. The voltage and current on a transmission line are governed by:
A) Wave equations
B) Laplace equations
C) Differential equations
D) Fourier equations
Ans: A

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Q67. The condition for minimum distortion is:
A) $R/L = G/C$
B) $R/C = G/L$
C) $RL = GC$
D) $R = G$
Ans: A

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Q68. The reflection coefficient is given by:
A) $\frac{Z_L - Z_c}{Z_L + Z_c}$
B) $\frac{Z_c - Z_L}{Z_c + Z_L}$
C) $Z_L Z_c$
D) $Z_c / Z_L$
Ans: A

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Q69. The velocity of propagation in air is approximately:
A) $3 \times 10^8$ m/s
B) $3 \times 10^6$ m/s
C) $3 \times 10^5$ m/s
D) $3 \times 10^4$ m/s
Ans: A

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Q70. When the line is matched, the reflection coefficient is:
A) 1
B) 0
C) -1
D) ∞
Ans: B

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Q71. The nominal-π model is preferred when:
A) Capacitance is significant
B) Resistance is negligible
C) Inductance is negligible
D) None
Ans: A

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Q72. For a 132 kV, 200 km line, which model is appropriate?
A) Short line
B) Medium line
C) Long line
D) Nominal T
Ans: C

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Q73. A 33 kV, 40 km line is classified as:
A) Short
B) Medium
C) Long
D) None
Ans: A

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Q74. The constant power circles for a line are drawn using:
A) ABCD constants
B) Y parameters
C) Z parameters
D) None
Ans: A

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Q75. If $A = D = 1, B = 0, C = 0$, the line is:
A) Ideal
B) Short-circuited
C) Lossless
D) Open-circuited
Ans: A

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Q76. The sending-end power factor is:
A) Always lagging
B) Always leading
C) Depends on line parameters and load
D) Always unity
Ans: C

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Q77. For a long line, ABCD constants are expressed as:
A) Hyperbolic functions
B) Polynomial functions
C) Linear functions
D) None
Ans: A

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Q78. The surge impedance loading (SIL) is independent of:
A) Line length
B) Voltage
C) Frequency
D) Both A and C
Ans: D

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Q79. The effect of inductance in a transmission line is to:
A) Cause lagging current
B) Reduce voltage
C) Cause voltage drop
D) All of the above
Ans: D

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Q80. The receiving-end current leads sending-end voltage in:
A) Leading load
B) Lagging load
C) Unity power factor load
D) None
Ans: A

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Q81. The ABCD parameters are used to determine:
A) Voltage regulation
B) Efficiency
C) Power transfer
D) All of the above
Ans: D

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Q82. The surge impedance of a 132 kV overhead line is about:
A) 400 Ω
B) 50 Ω
C) 200 Ω
D) 300 Ω
Ans: D

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Q83. For a distortionless line, the velocity of propagation is:
A) Constant for all frequencies
B) Variable
C) Zero
D) Infinite
Ans: A

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Q84. The A constant for a short line is approximately:
A) 1
B) 0
C) j
D) Infinite
Ans: A

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Q85. In a transmission line, the shunt conductance G represents:
A) Leakage current
B) Dielectric loss
C) Both A and B
D) None
Ans: C

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Q86. The attenuation of a line is negligible when:
A) R and G are small
B) L and C are large
C) R = G
D) None
Ans: A

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Q87. The phase constant β determines:
A) Wavelength
B) Phase shift per unit length
C) Velocity of propagation
D) All of the above
Ans: D

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Q88. The wavelength of a signal on the line is given by:
A) $\lambda = \frac{2\pi}{\beta}$
B) $\lambda = \beta/2\pi$
C) $\lambda = 1/\beta$
D) $\lambda = \pi/\beta$
Ans: A

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Q89. The input impedance of a lossless line is real when:
A) Line length is nλ/2
B) Line length is λ/4
C) Line length is λ
D) None
Ans: A

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Q90. For a 100% compensated line:
A) The reactive drop is neutralized
B) The Ferranti effect is removed
C) Both
D) None
Ans: C

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Q91. The term “long line” in practice means when distributed constants are:
A) Significant
B) Negligible
C) Ignored
D) None
Ans: A

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Q92. The shunt capacitance in overhead lines mainly depends on:
A) Distance between conductors
B) Height of conductors
C) Permittivity of air
D) All of the above
Ans: D

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Q93. The effect of corona is to:
A) Reduce line efficiency
B) Cause power loss
C) Distort waveforms
D) All of the above
Ans: D

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Q94. The long line equations use:
A) Hyperbolic functions (cosh, sinh)
B) Trigonometric functions (sin, cos)
C) Exponential functions
D) Linear functions
Ans: A

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Q95. For a line length equal to half wavelength, the input impedance is:
A) Equal to load impedance
B) Inverse of load impedance
C) Zero
D) Infinite
Ans: A

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Q96. When the line is terminated with its characteristic impedance, input impedance is:
A) Equal to characteristic impedance
B) Infinite
C) Zero
D) Purely imaginary
Ans: A

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Q97. The magnitude of reflection coefficient cannot exceed:
A) 0.5
B) 1
C) 2
D) 10
Ans: B

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Q98. The sending-end power factor angle is denoted by:
A) Φs
B) Φr
C) β
D) γ
Ans: A

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Q99. The length of a line where Ferranti effect becomes noticeable is around:
A) 100 km
B) 150 km
C) 200 km
D) 250 km
Ans: C

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Q100. The ABCD parameters of a short line are:
A) A = D = 1, B = Z, C = 0
B) A = D = 0, B = 1, C = Z
C) A = D = Z, B = 0, C = 1
D) None
Ans: A