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Posted Date: 14 Dec 2007 Posted By:: veeraprasad Member Level: Bronze Points: 5 (₹ 1)
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2007 Sri Venkateswara Institute of Medical Sciences B.Tech Electrical and Electronics Engineering power systems-1 University Question paper
FOUR YEAR B.TECH DEGREE EXAMINATION, NOVEMEBER 2007
Third year examination
first semester
electrical and electronics engineering
POWER SYSTEMS - 1
TIME : 3 HOURS Maximum:100 Marks
Answers any FIVE questions, choosing onequestion from each unit.
All questions carry equal marks.
Assue any missing data suitably
Unit - 1
1. (a) Define base load, peak load, load duration curve,types of loads. (8 marks)
(b) A generating station has a maximum demand of 75 MW and ayeariy load factor of 40%.Generating costs inclusive of station capital costs are Rs. 60 per annum per KW demand plus 4 paise per kWh transmitted. The annual capacity charges for transmission system are Rs. 20,00,000 and for distribution systems Rs. 15,00,000 the respective diversity factors being 1.2 and 1.25. The efficiency of transmission system is 90% and that of the distribution system inclusive of substation losses is 85%. find yearly cost 1 KW demand and per kWh supplied. (a) at substation .
(b) at consumer premises. (12 Marks)
or
2.(a) Write expression for cost of electrical energy and two methods for determining depreciation. ( 8 marks)
(b) A hydroelectric plant costs Rs. 3,000 per KW of installed capacity. The total annual charges consists of 5% as interest, depreciation at 2% operation and maintenance at 2% and insurance, rent, etc at 1.5%. Determine a sutiable 2- part traiff. If the losses in transmission and distribution are 12.5% and diversity of load is1.25. Assume that Maximum demand on the station is 80% of the capacity and annual load factor is 40%. What is the overall cost of generation per kWh. (12 marks)
Unit - 2
3. (a) Explain Kelvin's law . state its limitations. ( 8 marks)
(b) A 3 phase overhead transmission line supplies a constant load of 6 MW at 33 kv nad 0.8 p.f. lagging through out the year. The cost of line is Rs.( 80000 ? + 3500)/km where '?' is the cross section of each conductor in cm². The cost of energy is 25 P/kWh nad interest and depreciation total 10% /annum. assuming specific resistance of conductor material at 1.8 µ? cm, find the economical size of conductor. (12 marks)
or
4. (a) Discuss the design of primary distribution system with respect to sze of feeders. ( 7 marks)
(b) Explain types of secondary distribution systems with neat diagrams. (13 marks)
Unit - 3
5.(a) Discuss the main Ewuipment used in substations.(10 marks)
(b) Draw neatly the Key diagram of a typical primary subtation.
( 10 marks)
or
6. (a) What are the methods of eualizing the potential in overhead line Insulators. (8 marks)
(b) A 3 phase 66 Kv transmission line is carried b strings of 5 suspension insulators. The capacity of each unit insualtor to the capacity relative to earth is 4:1. Cla culate the potential across each unit and the string efficiency.( Assume that thre is no leakage). (10 marks)
unit - 4
7. (a) Derive an expression for the capcitance of a simple core cable. (8 marks)
(b) A single core cable has an inner diameter of 5 cms and a core diameter of 1.5 cm. its paper dielectric has a working maximum dielectric stress 60 KV/ cm. Calculate he maximum permissible line voltage when such cables are used on a 3 phase system.
(12 marks)
or
8.(a) What is the most general criterion for classification of cables? Draw the skstch and labe the various parts of a single core low tension cable. (10 marks)
(b) A length of 3- core , 3phase metal sheathed cable gave the following results on test for capacitance: (i) Capacitance between bunched condutors and sheath is µF.(ii) Capacitance between two conductors bunched with sheath and the thrid conductor is 0.6 µF. with the sheath isolated , find the capacitance ( a) between two conductors and (b) between any two bunched conductors and the third conductor. (10 marks)
Unit - 5
9. (a) Give brief description of corona phenomenon. ( 8 marks)
(b) Derive the expression petential gradient at the surface of a conductor 1- phase transmission line. (12 marks)
or
10. (a) Clearly explain what is meant by GMR and GMD of a transmisson line . (6 marks)
(b) What is equivalent spacing of a 3-phase line? What is its significance? (6 marks)
(c) Calculate the inductance of each conductor in a 3-phase, 3 wore system when the conductors are arranged horizontally with spacing such that = 4m ;= 3m ; = 2m.The conductors are trasposed and each has a diameterof 2.5 m. (8 marks)
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