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Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE) PDF Download

Q19: For a fixed value of complex power flow in a transmission line having a sending end voltage V, the real loss will be proportional to      (2009)
(a) V
(b) V2
(c) 1/V2
(d) 1/V
Ans:
(b)
Sol: S = Complex power
S is defined as, S = VI
I = S/V
If R is the resistance of transmission line
Real power loss Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)
Since, S and R are fixed
Real power loss ∝ 1/V2

Q20: An extra high voltage transmission line of length 300 km can be approximate by a lossless line having propagation constant β = 0.00127 radians per km. Then the percentage ratio of line length to wavelength will be given by      (2008)
(a) 24.24 %
(b) 12.12 %
(c) 19.05%
(d) 6.06%
Ans:
(d)
Sol: Wave length = λ,
Propogation constant = β
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)
Q21: The total reactance and total suspectance of a lossless overhead EHV line, operating at 50 Hz, are given by 0.045 pu and 1.2 pu respectively. If the velocity of wave propagation is 3 × 10km/s, then the approximate length of the line is     (2007)
(a) 122km
(b) 172km
(c) 222km
(d) 272km
Ans:
(c)
Sol: For loss less line,
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)
Q22: Considered a bundled conductor of an overhead line consisting of three identical sub-conductors placed at the corners of an equilateral triangle as shown in the figure. If we neglect the charges on the other phase conductor and ground, and assume that spacing between sub-conductors is much larger than their radius, the maximum electric field intensity is experienced at
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)(a) Point X
(b) Point Y
(c) Point Z
(d) Point W
Ans: 
(b)
Sol: Electric field intensity at various points are shown as follow.
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)It is clear from the above diagrams that minimumcancellation of vector occurs at the point Y. Hence maximum electric field intensity.

Q23: A single phase transmission line and a telephone line are both symmetrically strung one below the other, in horizontal configurations, on a common tower, The shortest and longest distances between the phase and telephone conductors are 2.5 m and 3 m respectively. The voltage (volt/km) induced in the telephone circuit, due to 50 Hz current of 100 amps in the power circuit is      (2006)
(a) 4.81
(b) 3.56
(c) 2.29
(d) 1.27
Ans:
(c)
Sol: Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)where, P1 and P2 from power line and T1 and T2 from telephone line
Current in power circuit = I = 100 A
Mutual inductance between power line and telephone line
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)Voltage induced in the telephone line
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)
Q24: The A, B, C , D constants of a 220 kV line are :
 A = D = 0.94∠1°,  B = 130∠73°,  C = 0.001∠90°.
If the sending end voltage of the line for a given load delivered at nominal voltage is 240 kV, the % voltage regulation of the line is      (2006)
(a) 5
(b) 9
(c) 16
(d) 21
Ans: 
(c)
Sol: Sending end volatge Vs = 240kV
Full-load receiving end voltage
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)No-load receiving end voltage (per phase)
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)No-load receiving end voltage ( line to line)
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)
Q25: The concept of an electrically short, medium and long line is primarily based on the      (2006)
(a) nominal voltage of the line
(b) physical length of the line
(c) wavelength of the line
(d) power transmitted over the line
Ans:
(b)
Sol: L = length of line
If L ≤ 80 km
The line id short line.
If 80km < L ≤ 250km
The line is medium line.
If L > 250km
The line is long line.

Q26: The generalized circuit constants of a 3-phase, 220 kV rated voltage, medium length transmission line are
Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)If the load at the receiving end is 50 MW at 220 kV with a power factor of 0.9 lagging, then magnitude of line to line sending end voltage should be      (2004)
(a) 133.23 kV
(b) 220.00 kV
(c) 230.78 kV
(d) 246.30 kV
Ans:
(c)
Sol: Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)
Q27: The ABCD parameters of a 3-phase overhead transmission line are A = D = 0.9∠0°, B = 200 ∠90°Ω and  C = 0.95 × 10−3 ∠90°S. At no-load condition a shunt inductive, reactor is connected at the receiving end of the line to limit the receiving-end voltage to be equal to the sending-end voltage. The ohmic value of the reactor is      (2003)
(a) ∞ Ω
(b) 2000 Ω
(c) 105.26 Ω
(d) 1052.6  Ω
Ans: 
(b)
Sol: Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)
Q28: Bundled conductors are mainly used in high voltage overhead transmission lines to      (2003)
(a) reduces transmission line losses
(b) increase mechanical strength of the line
(c) reduce corona
(d) reduce sag
Ans:
(c)
Sol: By bonding of conductor, the self GMD of the conductors is increased.
Corona loss ∝ (V − V0)2
V0 is approximately directly proportional to the size of conductor, hence larger the size of the conductor lrger will be the critical disuptive voltage and smaller will be the factor (V − V0)2 and hence, smaller will be the corona loss.

Q29: A long wire composed of a smooth round conductor runs above and parallel to the ground (assumed to be a large conducting plane). A high voltage exists between the conductor and the ground. The maximum electric stress occurs at      (2002)
(a) the upper surface of the conductor
(b) the lower surface of the conductor
(c) the ground surface
(d) midway between the conductor and ground
Ans:
(b)

Q30: Consider a long, two-wire line composed of solid round conductors. The radius of both conductors is 0.25 cm and the distance between their centers is 1m. If this distance is doubled, then the inductance per unit length       (2002)
(a) doubles
(b) halves
(c) increases but does not double
(d) decreases but does not halve
Ans: 
(c)
Sol: Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)In(2d) > In d.

Q31: The conductors of a 10 km long, single phase, two wire line are separated by a distance of 1.5m. The diameter of each conductor is 1 cm. If the conductors are of copper, the inductance of the circuit is      (2001)
(a) 50 mH
(b) 45.3 mH
(c) 23.8 mH
(d) 19.6 mH
Ans:
(c)
Sol: Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 | Power Systems - Electrical Engineering (EE)

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FAQs on Previous Year Questions- Performance of Transmission Lines, Line Parameters and Corona - 2 - Power Systems - Electrical Engineering (EE)

1. What are the main parameters of transmission lines and how do they affect performance?
Ans. The main parameters of transmission lines include resistance (R), inductance (L), capacitance (C), and conductance (G). These parameters affect the performance of transmission lines by influencing voltage drop, power loss, and the line's ability to handle reactive power. Resistance leads to power losses as heat, inductance causes lagging power factor issues, capacitance can lead to voltage rise in long lines, and conductance represents leakage current, which can also contribute to losses.
2. What is corona discharge in transmission lines and how does it impact performance?
Ans. Corona discharge is the ionization of air surrounding a conductor due to high electric fields, typically occurring at voltages above 30 kV. It results in energy loss, radio interference, and can lead to the deterioration of conductor materials over time. Additionally, it can cause audible noise, which can be a concern for nearby communities. Managing corona effects is essential for maintaining efficient line performance.
3. How can transmission line parameters be determined or measured?
Ans. Transmission line parameters can be determined using various methods, such as the short-circuit test, open-circuit test, and series or parallel tests. Additionally, mathematical models and simulations can be employed to calculate parameters based on physical dimensions and material properties of the line. Field measurements using specialized equipment like impedance analyzers can also provide accurate results.
4. What are the different types of transmission lines based on their length and voltage levels?
Ans. Transmission lines can be classified into three categories based on length: short lines (less than 250 km), medium lines (250 km to 800 km), and long lines (greater than 800 km). They can also be categorized by voltage levels into low, medium, and high voltage lines. Each category has distinct characteristics and performance considerations, influencing the choice of design and technology used.
5. What measures can be taken to minimize losses in transmission lines?
Ans. To minimize losses in transmission lines, several measures can be implemented, including using conductors with lower resistance, optimizing line design (like increasing conductor size), employing high-voltage transmission to reduce current, and utilizing reactive power compensation devices such as capacitors or inductors. Regular maintenance and monitoring of line conditions can also help identify and mitigate factors contributing to losses.
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