440(8) June 2018 ‘TRANSMISSION & DISTRIBUTION OF POWER Time Allowed: 3 Hours Full Marks: 70 ‘Maximum time allowed is 45, fresh answer seripts fo Answer to Question No.1 is compulsory and to be answered first. This answer is (0 be made in separate loose script(s) provided for the purpose. inutes, after which the loose answer scripts will be collected and mnswering 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 script earlier. ‘Answer any five questions from Group-A & B, taking at east two from each group. 1. Choose the correct answer from the given altematives (any twenty): 1x20 i) Transmission line connects — (a) generating station to a switching station/step-down transformer station (b) step-down transformer station to service transformer banks (¢) distribution transformer to consumer premises (d) service points to consumer premises. ii) Secondary power distribution is done by 3 phase __ wire system — (a) 11 (b) 2 (c) 3 (d) 4 iii) Which law determines the economic size of conductor? ~ (a) Lenz’s law (b) Kelvin's law (©) Norton's law (d) None of these. iv) With bundled conductors reduces — (a) power loss due to corona (b) surge impedance (c) radio interference (4) line inductance. ¥) Suspension type insulators are used for voltages beyond — (a) 33 KV (b) 400 kV (c) 11 KV (d) 66 KV. vi) The insulator is so designed that it should fail only by — (a) flash-over (b) puncture (¢) both of these (4) none of these. vii) If the length of the line is increased, its capacitance will - (a) Increase (b) Decrease (¢) remain same (4) none of these. viii) The dc. resistance of a line conductor is than it's acc. resistance ~ (a) Less (b) More (©) Medium (4) Cannot determine. ix) Voltage regulation ofa transmission line is desired to be — (a) High (b) Low (c) Negative (d) None of these. %) Ina short transmission line, effects of ___ are neglected — (a) Resistance (b) Capacitance (©) Inductance (d) None of these. xi) The smaller the lagging reactive power drawn by a circuit, the is its power factor ~ (@) smaller (b) greater (c) smallest (A) medium, xii) The maximum value of power factor can be ~(a) | (b) 0.5 (¢) 0.9 (d) 0. xiii) The line constants of a transmission line are ~ (a) Distributed (b) Lumped (c) Both (d) None of these,xiv) xv) xvi) xvii) xviii) xix) xxi) xxiii) a a) ») Extra high voage transmission means ~ (a) voltage less than 400K (b) voltage in the range of 400-750Kv (c) voltage greater than 750Ky (d) none of above, For the transmission of high vollage beter system is ~ (a) IIVDC (b) EHV AC (e) both () none of the above. the — (a) current carrying capacity (b) distance ‘The main consideration in the design of a feeder (©) voltage drop (a) cost. A 3ewire a.c. distribution makes available voltages — (a) one (b) two (c) three (d) four. “The major part of investment on secondary distribution is made on ~ (a) Distribution transformers (b) conductors (c) pole fittings (4) stay wire. elon For combined 30 power and lighting load, system is used 2 Wire (c) 3 Phase 3 Wire (d) 3 Phase 4 Wire. fa) 1 Phase 2 Wire (b) 2 Phase For purely domestic loads, __a.c. system is employed for distribution — (a) single phase 2-wire (©) 2-phase 2-wire (¢)3-phase 3-wire (d) 3-phase 4-wire. Low type outdoor sub-station is more suitable than indoor sub-station because — (a) maintenance is ceasy (b) components are acessible (c) connections are accessible (d) all of the above. ‘Outdoor sub-station should be located — (a) load centre (b) away from load centre (c) rural area (@) none of the above. Which of the equipments is not part of sub-station? - (a) switchgear (b) booster transformer (©) battery charger (d) capacitor bank. Group-A ‘What are the different operating voltages used for generation, primary and secondary transmission in AC power supply systems in India? ‘What are the limitations of Kelvin’s law? Discuss about the factors affecting choice of transmission voltage level. 34344 State the name of various conductor used in transmission line and explain any one, ‘The line support of an overhead line is 180 m apart and at the same level. The cross sectional area of conductor is 1.27em?. Calculate the maximum sag in stil air. Assuming the maximum stress in the line is not to increased 1/Sth of the ultimate strength 4220 kg /em’. The weight of the conductor per meter run is 1.13kg, 5+5 Explain skin effect. A S-phase transmission line is being supported by three disc insulators. The potentials across top unit (.e., near to the tower) and middle unit are 8 KV and 11 kV respectively. Calculate (i) the ratio of capacitance between pin and earth to the selfcapacitance of each unit (i) the line voltage and (ii) string efficiency. 46 ‘What are the necessary requirements of an underground cable? Describe the construction of gas filled (SF6) cables. 46 Group-B ‘What are voltage regulation and transmission efficiency” Deduce the expression for voltage regulation of short transmission line. A single phase transmission line has resistance 0.2 Q and inductive reactance of 0.4 ©. The line delivers power of ‘SOOkVA at 0.707 power factor lagging at voltage of 2 kV at the receiving end. Determine - i) Percentage voltage regulation ii) Sending end power factor jonefficiency. 44610. a) b) °) a) b) °) a) a) 1) List the advantages of EHVAC transmission system, Briefly discuss the regional grid system? Explain the difference between HDVC and HVAC, 34443 ‘What do you understand by distribution system? Discuss the relative merits and demerits of underground and overhead distribution systems. How does a. distribution differ from d.. distribution? Dass Discuss briefly the design considerations in distribution system. A single phase a.c. distributor AB 300 metres long is fed from end A and is loaded as under : ( 100 A at 0-707 pf. lagging 200 m from point A ({i) 200 A at 0-8 pf. lagging 300 m from point ‘A The load resistance and reactance of the distributor is 02 9 and 0-1 Q per kilometre. Calculate the total voltage drop in the distributor. The load power factors refer to the voltage at the farend. 46 Compare between indoor and outdoor type substation, ‘What are the factors which are to be considered for selection of site of an outdoor substation? 54+5