440(S) June 2019) TRANSMISSION & DISTRIBUTION OF POWER Time Allowed: 3 Hours Full Marks: 70 Answer (o Question No.1 is compulsory and to be answered first. This answer is to be made in separate loose seript(s) provided for the purpose. ‘Maximum time allowed is 45 minutes, after which the loose answer scripts will be collected and fresh answer scripts for answering the remaining part of the question will be provided. ‘On early submission of answer scripts of Question No.1, a student will get the remaining seript earlier. Answer any five questions from Group-A & B, taking at least two from each group. 1. Choose the correct answer from the given alternatives (any twenty): 1x20 i) iv) vy vi) vii) viii) ix) x) xi) xii) xiii) ‘Transmission line connects (@) generating station to a switching station/step-down transformer station, (b) step-down transformer station to service transformer banks, (c) distribution transformer to consumer premises, (d) service points to consumer premises. Which law determines the economic size of conductor? ~ (a) Lenz's law, (b) Kelvin's law, (€) Norton's law, (4) None ofthese. ‘The primary transmission system is done by ~ (a) 3-phase 3-wire, (b) 3-phase 4-wire, (c) 3-phase - S-wire, (d) 3-phase 2-wire, Between two supports, due to sag the conductor takes the form of — (a) catenary, (b) triangle, (6) ellipse, (4) semi-circle. Suspension type insulators are used for voltages beyond — (a) 33 KV, (b) 400 KV, (c) 11 kV, (4) 66 KV, ‘The electrical breakdown strength of insulating materials depends on — (a) nature of applied voltage, (b) imperfection in dielectric material, (c) pressure, (d) all of the above. If the length of the line is increased, its capacitance will ~ (a) increase, (b) decrease, (¢) remain same, (d) none of these. ‘The fact that a conductor carries more current on the surface as compared to core, is known as — (@) skin effect, (b) corona, (c) permeability, (2) unsymmetrical faut Main drawbacks of underground system over overhead system is ~ (a) exposure to lightning, (b) heavy initial cost, (¢) exposure to atmospheric hazards, (d) inductive interference between power and communication circuits ‘The capacitance of a transmission line is a element. ~ (a) Series, (b) Parallel, (c) Both, (4) None of these. In a short transmission lin, effects of are neglected. ~ (a) Resistance, (b) Capacitance, (©) Inductance, (d) None ofthese. ‘The volume of the copper required for an ac transmission line is inversely proportional to — (a) current, (b) voltage, (c) pf, (A) both b and c Extra high voltage transmission means — (a) voltage less than 400Ky, (b) voltage in the range of 400-750Ky, (¢) voltage greater than 750Kvy, (d) none of above. 1xiv) xy) xvi) xvii) xviii) xix) xx) xxi) xxii) xxiii) ») b) b) For the transmission of high vollage better system is ~ (a) HVDC, (b) BIT AG, (¢) both, (d) none of the above. “The major part ofinvestinent on secondary distribution is made on ~ (a) Distribution transformers, (b) conductors, (2) pole fittings, (0) stay wire ‘A 3.wire ae. distribution makes available voltages. (a) one, (b) two, (c) three, (A) four Current flowing through the neutral of a 3-phase, 4-wire system is equal to ~ (a) the current in phase wire, (b) vector sum of the current in the phase wires, (c) vector difference of current in the phase wires, (4) none of these. Which of the equipment is not part of sub-station? — (a) switchgear, (b) booster transformer, (6) battery charger, (A) capacitor bank. Outdoor sub-station should be located ~ (a) load centre, (b) away from load centre, (c) rural area, (@ none of the above. 5 Low type outdoor sub-station is more suitable than indoor sub-station because ~ (a) maintenance is easy, (b) components are accessible, (c) connections are accessible, (d) all of the above. ‘The number of dises in a string of insulator for 400 ky ac overhead transmission line lies in the range of - (a) 32-33, (b) 22-23, (c) 15-19, (4) 9-10. 'A 3 phase 4 wire system is commonly used for - (a) primary distribution, (b) secondary distribution, (¢) primary transmission, (4) secondary transmission. ‘Transmission and distribution of electric system by underground’ system is superior to overhead system in respect of ~ (a) appearance and public safety, (b) maintenance cost, (c) frequency of faults, power failure and accidents, (4) all of the above. Group-A, What are the disadvantages of high voltagé transmission? ‘What are the limitations of Kelvin's law? S45 Describe the formation of corona ‘A transmission line has a span of 275 m between level supports. The conductor has an effective diameter of 1-96 cm and weighs 0-865 ka/m. Its ultimate strength is 8060 kg, Ifthe conductor has ice coating of radial thickness 1-27 em and is subjected to a wind pressure of 39 gm cm’ of, projected area calculate sag fora safety factor of 2, Weight of I c.. of ice is 0-91 gm. 46 Write down the expression of inductance and capacitance pet meter of a 3phase line has circular radius ‘ris replaced at the comer ofthe equilateral triangle of length *D” em, ‘What are the advantages of transposition of conductors? How and why itis cartied out? S+5. ‘Name and discuss various method of laying of underground cable. Draw the neat sketch of the cross-section of 3 core PILC cable andl mention various parts init, oH up-B {A 3.phase, 5 KW induction motor has « p.t. of 0°75 lagging. A bank of capacitors is connected in delta across the supply terminals and p.f, raised to 0-9 lagging. Determine the KVAR rating of the capacitors connected in each phase. Define the terms; Critical disruptive voltage Visual critical voltage Power loss due to corona, 5+5 ‘What are the advantages of HVDC transmis Discuss on few HVDC system in Indian scenario, 55 210. a) b) ») 2) With a neat diagram, explain the complete a.c. system for distribution of electrical energy. What isthe difference between feeder and distributor? 585 A single phase distributor one km long has resistance and reactance per conductor of 0-1 2 and 0-15 0 respectively. At the far end, the voltage Vj, = 200 V and the current is 100 A at apf. of 08 lagging. At the mid-point M of the distributor, a current of 100 A is tapped at a pf. of 06 lagging with reference to the voltage Vy atthe mid-point. Calculate ~ (i) voltage at mid-point, (i) sending end voltage Va, (ii) phase angle between Va and Vs. ‘What are the effects of high primary voltage on the distribution system? 64 ‘Write down the advantages and disadvantages of outdoor substation? ‘Draw the single line diagram of a sub-station with double bus-bar arrangement. 64