Jawaharlal Nehru Technological University Kakinada 2010-1st Sem B.E Electrical and Electronics Engineering Code No.V3110/R07 III B.TechRegular s emr, POWER SYSTEMS-II Set3 - Question Paper

Code No.V3110/R07
III B.Tech I Semester Regular exams November, 2010
POWER SYSTEMS-II
(Electrical and Electronics Engineering)
Time: three hours Max.Marks: 80
ans any 5 ques.
All ques. carry equal marks

1. a) discuss the bundled conductors with merits and demerits?
b) A 3-phase, 50 Hz, 66 kV overhead transmission line has its conductors organizes at the corners of an equilateral triangle of 2.5m sides and the diameter of every conductor is 1.3 cm. Determine the inductance and capacitance per phase, if the length of line is 120 km. And also compute the charging current (8+8)

2. a) discuss the effect of power factor on regulation and efficiency.
b)A three-phase, 50 Hz transmission line, 100 km long delivers 25 MW at 120kV and 0.8 p.f. lagging. The resistance and reactance of the lines per phase per km are 0.2 ohm and 0.5 ohm respectively while capacitance admittance is 2.2x10-6 mho/km/ph. compute the efficiency of transmission. Use nominal p method (8+8)

3. a) discuss the interpretation of the long line equations
b) A three-phase, 220 km long transmission line has the subsequent constants. Resistance/ ph/ km = 0.2 ohm, reactance/ ph/km = 0.3 ohm, shunt admittance/ph/km = 1.2×10-6 mho. compute by rigorous method, the sending-end voltage and current when the line is
delivering a load of 25MW at 0.8 p.f lagging. The receiving-end voltage is kept constant at 110 kV. (8+8)

4. a) discuss Bewley's Lattice diagram and provide its uses.
b) A 220 kV surge travels on a line of 300ohm surge impedance and reaches a junction where 2 branch lines of surge impedances 450ohm and 250ohm respectively are connected with the transmission line. obtain the surge voltage and current transmitted into every branch line. Also obtain the reflected voltage and current. (8+8)

5. a)What are the disadvantages of corona? discuss how the corona considerations affect the design of a line.
b) Determine the disruptive critical voltage and the visual critical voltages for local and general corona on a 3-phase overhead transmission line consisting of 3 stranded copper conductors spaced at 2.2 meters apart at the corners of an equilateral triangle. Air temperature and pressure are 210C and 73.5 cm of Hg respectively. Conductor diameter is 1.6 cm, irregularity factor (m0) 0.85, and surface factors (mv) 0.7 for local and general corona 0.7 and 0.8 respectively. Breakdown strength of air is 21.1 kV (r.m.s) / cm. (8+8)

6. a) discuss why the potential distribution is not, in general, uniform over the string in suspension kind of insulators
b) every conductor of a 3-phase high voltage transmission line is suspended from cross arm of steel tower by a string of four suspension kind disc insulators. If the voltage across the 2nd unit is 13.2 kV and that across the 3rd unit is 18 kV. compute the voltage ranging from the conductors. (8+8)

7. a) What is a sag template? discuss how this is useful for the location of towers and the stringing of power conductors.
b) Determine the sag of an overhead line for the subsequent data: span length 150 meters, conductor diameter 0.9 cm, weight per unit length of the conductor 0.65 kg/meter. Ultimate stress 4250 kg/cm2, wind pressure 40 kg/cm2 of projected area and factor of safety 4. (8+8)

8. a) explain the methods of grading cables. Why are they not used generally?
b) A single core two km long cable has a conductor radius of 1.3cm and an insulation thickness of 3.5 mm. If the resistivity of dielectric is 7×1012 ohm-m, determine the insulation resistance of the cable. (8+8)

Earning:   Approval pending.