MODEL TEST PAPER

END TERM EXAMINATION

POWER SYSTEM – 1

Time: 3 hours Maximum marks: 75

Question one is compulsory. Attempt one question from each unit.

Question.1

(a)Why bundled conductor lines have lower inductance than single conductor lines? (4)

(b)What kind of insulators are used for high voltage transmission and why? (4)

(c)What is the relation in between sag and tension? Explain with the help of stringing chart? (5)

(d)Induced emf, due to electromagnetic induction line on a communication line ……………. With frequency. (1)

(e)A suitable value of conductor roughness factor is about ………….. . (1)

(f)Why Ferranti effect is not considered in short transmission line? (5)

(g)What is sag in overhead lines? Discuss the disadvantages of providing the too small or too large sag on a line. (5)

UNIT - 1

Question.2

(a)Why three phase supply system is preferred over single phase system?

OR

Explain the layout of single line diagram of power system? (5)

(b)A d.c three wire system is to be converted into a three phase, four wire system by adding afourth wire equal in X section to each outer of the d.c system. If the percentage power loss and voltage of consumer’s terminals are to the same in two cases, find the extra power at unitypower factor that can be supplied by the a.c system. Assume load to be balanced. (7.5)

Question.3

(a)Gives a comparisonin between ac and dc transmission?What are the limitations of high transmission voltage? (6.5)

(b)Write a short note on ‘overhead line conductors’ bringing out reasons for using ACSR conductors? (6)

UNIT – 2

Question.4

(a)Find the inductance per phase per km of double circuit three phase line shown in figure.1. The

Conductors are transposed and are of radius 0.75 cm each.

(8.5)

figure.1

(b)Explain the effect of surge impedance on loading line? (4)

Question.5

(a)A three phase 200 km long high voltage line has z=14.1+j 51.48 ohms and y= 0 + j 1.194* Siemens. Find the characteristics impedance, propagation constants and constant A, B,C,D for line? (8.5)

(b)Calculate the no load sending end voltage and the voltage rise from sending end to receiving end for a 50 HZ, 300 km long line if relieving end voltage is 220 kv? (4)

UNIT – 3

Question.6

(a)A three unit insulator string is fitted with a guard ring. The capacitance of the link pins metal work and guard ring can be assumed to be 15% and 5% of a capacitance of each unit. Determine the voltage distribution and string efficiency? (8.5)

(b)Discuss the method of equalizing the potential in insulators? (4)

Question.7

(a)A three phase 132 kv, 50 HZ, 150 km long transmission line consist of three stranded aluminum conductors spaced triangularly at 3.8 m between centres. Each conductor has a diameter of 19.53mm. The surrounding air is at temperature of 30and at barometric pressure of 750 mm of mercury. If breakdown strength of air is 21.1 kv (rms) per cm and surface factor is 0.85, determine the disruptive critical voltage? Also determine the visual critical voltages for local and general corona if surface factors are 0.72 and 0.82 for visual corona(local) and visual corona(general) respectively. (8.5)

(b)List all methods for reducing corona and radio interference and explain? (4)

UNIT – 4

Question.8

(a)Explain the vibration of power conductors and also the methods to dampout these vibrations?

(4)

(b)How is wind loading effect on the conductors? A transmission line has a span of 275 meters between level supports. The conductor has a diameter of 19.53 mm, weighs 0.844 kgf/m and has an ultimate breaking strength of 7950 kgf. Each conductor has a radial covering of ice 9.53 mm thick and is subjected to a horizontal wind pressure of 40 kgf/m2 of the ice covered projected area. If the factor, of safety is 2, calculate the deflected sag and the vertical component of the sag. One cubic metre of ice weighs 913.5 kgf. (8.5)

Question.9

(a)A single-core lead sheathed cable is graded by using three dielectrics of relative permittivity 5,4,3 respectively. The conductor diameter is 2 cm and overall diameter is 8 cm. If the three dielectrics are worked at the same maximum stress of 40 kv/cm. find the safe working voltage of cable. (8.5)

(b)Differentiate in between belted and screened cables on the basis of construction? (4)