401 EEE/EE Jharkhand University of Technology, Ranchi 4th Semester B.Tech. Examination, 2022 Subject : Power System-I Subject Code : EE-401 Time Allowed : 3 Hours Full Marks : 70 thi Candidates are required to give their answers as far as practicable. Question No. 1 is mandatory and answer any four questions from the rest. The figures in the margin indicate full marks, ‘own words: 1. Choose the correct answer: 2xT=14 @_A transmission line has a p.u impedance of.0.3 on a base of 132 KV, 190 MVA. What will the p.u impedance of same line on a base of 220 KV, 50 MVA? (a) 0.420 (b) 0.216 (©) 0.054 (@) 1.666 (ii) The inductance of a 3-@ transmission line is 1.2 mH/phase/km. If the spacing of conductor ‘and the radius of the conductor are doubled, then the inductance of the li (@) 48 me/phaserem () 1.2 mH/phaseyem (©) (Un 4) x 0.2 mH/phase/km (@ (in 2) x 0.2 mH/phase/km_ (iii) A string insulator has 4 units. The voltage across the bottom-most unit is 33.33% of the total voltage. Calculate its string efficiency. 0 ue 3 (@) 25% (b) 33.33% (©) 66.7% (@) 75% (iv) The surge impedance of a 3-2, 400 kV transmission line is 400. The surge impedance loading (SIL) is (a) 400 MW (b) 100 MW (c) 1600 MW (d) 200 MW. (v) The capacitance of 3-core cable between any two conductors with sheath earthed is 2 uF. The capacitance per phase will be (@) 1 pF (b) 0.667 pF (c) 4yF (@) 1.414 pF Please Turn Over 571(350 Ha corona loss on the o corona loss on particular system at 50 Hz is ¥ KW/phase“im, The s iystem with supply frequency 25 Hz will be (b) 0.667 kW/phase/am (vi) The © same s (@) 1 kWephase/km (©) 0.5 kW/phase/km (vii) Ring main distribution system is (a) voltage drop in feeder is less and supply is. (@) None of these preferred to 2 radial system because more reliable, (b) voltage drop in the feeder is Tags and power factors high. (©) power factor is high and supply is more reliable. - (@) power factor is high and system is less expensive. (a) Derive inductance of a 3-phase overhead line with unsymmetrical spacing. What is 2 — transposition and how will it effect the inductance of a 3-phase line? ng at 132 KV. 381m, (b) Calculate the disruptive critical and visual corona voltage of grid line operatin ‘The data are given : Conductor diameter = 1.9 cm; Conductor spacing ‘Temperature=44°C; Biometric pressure =73.7em;Conductor surface factor:fine weather= 0.8 747: rough weather = 0.66. (a) Draw the equivatent circuit and phasor diagram of transmission line (end condenser method), Derive ABCD parameters for a long transmission line, (b) Determine the efficiency and regulation of a three phase, 100 km, 50 Hz transmi delivering 20 MW at a power factor of 0.8 (lagging) and 66 kV to a balanced load. The conductors are having resistance of 0.1 ohm/km, inductance of 11.67 x 10° H/mt and capacitance of 9.96x10" F/mt. (Assume Nominal T Configuration) 747214 4, (a) What do you mean by sag? Derive the expression for sag when the supports are at unequal levels. (b) Each conductor of a 3-phase high-voltage transmission line is suspended by a string of 4 suspension type disc insulators. If the potential difference across the second unit from top is 13.2 kV and across the third from top is 18 kV, determine the voltage between conductors. T+T=14 Calculate the string efficiency. 3. (a) What are the advantages and disadvantages of underground cables? What do you mean by grading of cables? Explain different methods of grading of cables. ch cable has a (b) A 33 kV 3-phase underground cable, 3 km long, uses a single core cable. conductor diameter of 1.5 cm and radial thickness of insulation is 0.5 cm. the relative permittivity of dielectric is 3.1. Calculate the capacitance and charging currentiphase. Also determine the dielectric loss/phase if power factor of unloaded cable is 0.03 TeT=14(3) (a) What is tariff? Explain different load curves with suitable examples and significance. Discuss about different types of tariffs, AC and DC transmission systems. Discuss their merits and 747214 6 (b) With neat diagram compa demerits, Tx2=14 1. Write short notes on any two: (a) Single tine diagram (b) Ferranti effect (©) Power factor improvement equipments (@ Skin effect