Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech III POWER SYSTEMS II Previous Question Paper (March 2021 - R13)
Answer any five questions. All questions carry equal marks.
Main
Derive the expression for inductance of a 3-phase overhead transmission line when the conductors are symmetrically spaced.
Answer
For a 3-phase overhead transmission line with conductors A, B, and C symmetrically spaced, the distance between any two conductors is equal, denoted as D. The inductance of one conductor in a 3-phase system is derived by considering the flux linkages of a single conductor.
The flux linkage of conductor A due to currents IA, IB, and IC is given by:
Since the system is balanced, IA + IB + IC = 0, which implies IB + IC = -IA. Substituting this into the equation:
The inductance per phase L is defined as λA / IA:
Where r' is the geometric mean radius (GMR) of the conductor, given by r' = r × e-1/4 = 0.7788r, and r is the actual radius of the conductor.
A three-phase overhead transmission line has its conductors arranged at the corners of an equilateral triangle of 2m side. Calculate the inductance of each line conductor per km. If the diameter of the conductor is 1.25 cm.
Answer
Given: D = 2 m, Diameter = 1.25 cm, so radius r = 0.625 cm = 0.00625 m.
First, calculate the GMR (r'):
The inductance per phase per meter is:
Converting to H/km:
Derive an expression for the capacitance per km of a single phase line taking into account the effect of ground.
Answer
Sign in to view the complete answer paper.
A conductor in a single phase transmission line are 6m above ground, each conductor has a diameter of 1.5 cm and the two conductors are spaced 3 m apart. Calculate the capacitance/km of the line (i) excluding ground effect (ii) including ground effect.
Answer
Sign in to view the complete answer paper.
Derive the expression for A, B, C, D parameters of nominal-T medium length transmission line.
Answer
Sign in to view the complete answer paper.
A 3-Φ, 50Hz, 25km long overhead line supplies 1.2MW at 11kV at 0.8 pf lagging. The line resistance and inductance are 0.04Ω and 0.8mH per phase per km. Determine regulation and Transmission efficiency of the line.
Answer
Sign in to view the complete answer paper.
A 3-Φ, 50Hz transmission line has the following parameters per km: R=0.2Ω, L=1.3mH and C=0.01μF. Determine regulation and the efficiency of the line if the line is 160km long and delivers 40MW at 132kV and 0.8 p.f lagging.
Answer
Sign in to view the complete answer paper.
What is the travelling wave? Explain the development of such a wave on an overhead line.
Answer
Sign in to view the complete answer paper.
A surge of 100kV traveling in a line of natural impedance 600ohms arrives at a junction with two lines of impedances 800ohms and 200ohms respectively. Find the surge voltages and currents transmitted into each branch line. Also find the reflected surge voltage and current.
Answer
Sign in to view the complete answer paper.
State and explain the factors that affect the corona loss.
Answer
Sign in to view the complete answer paper.
Determine the critical disruptive voltage and corona loss for a 3-phase line operating at 110kV which has conductor of 1.25 cm dia arranged in a 3.05 meter delta. Assume air density factor of 1.07 and the dielectric strength of air to be 21kV/cm.
Answer
Sign in to view the complete answer paper.
Discuss the methods for improving string efficiency of over head line insulators.
Answer
Sign in to view the complete answer paper.
In a three phase overhead system, each line is suspended by a string of three insulators. The voltage across top unit and middle unit are 10kV and 11kV respectively. Calculate the ratio of shunt capacitance to self capacitance, Line voltage and String efficiency.
Answer
Sign in to view the complete answer paper.
Derive the expression for insulation resistance of a single core cable.
Answer
Sign in to view the complete answer paper.
What is the necessity of grading of cables? Explain briefly the various grading methods of cables.
Answer
Sign in to view the complete answer paper.