Potential questions eee

1. 1
Potential Questions for EEE – 441
Ch. 7
1. What is electric power supply system? Draw a single line diagram of a typical ac power supply
scheme.
2. What are the advantages and disadvantages of dc transmission over ac transmission?
3. Draw and state the flow chart for dc power supply system.
4. Briefly discuss the electric power supply system (generation, transmission and distribution) of
Bangladesh.
Ch. 8
1. List the important components of an overhead transmission line with their function.
2. Discuss the various conductor materials used for overhead lines. What are their relative
advantages and disadvantages?
3. Discuss the function and desirable properties of line conductor.
4. Discuss the function and desirable properties of insulators.
Ch. 9
1. What do you understand by the constants of an overhead transmission line? Draw the equivalent
circuit of a transmission line.
2. What is skin effect? Explain its mechanism with figure.
3. What factors affect the skin effect of a line conductor?
4. Why is skin effect absent in the dc system?
5. How does current density vary with skin depth?
Ch. 10
1. What do you know by performance of a transmission line?
2. How transmission line are classified?
3. Discuss the terms voltage regulation and transmission efficiency as applied to transmission
line.
4. Deduce an expression for voltage regulation and efficiency of a short transmission line, giving
the vector diagram.
5. What is the effect of load power factor on regulation and efficiency of a transmission line?
6. What do you understand bymedium transmission lines? How capacitance effects are taken into
account in such lines?
7. Show how regulation and transmission efficiency are determined for medium transmission
lines using:
(a) End condenser method (b) Nominal T method (c) Nominal Pi method
Illustrate your answer with suitable vector diagrams.
8. What do you understand by long transmission lines? How capacitance effects are taken into

2. 2
account in such lines?
9. Using rigorous method, derive expressions for sending end voltage and current for a long
transmission 1ine.
10. What do you understand by generalized circuit constants of a transmission line? What is their
importance?
11. Evaluate the generalized circuit constants for (i) Short transmission line and (ii) Medium
transmission line with — (a) nominal T method (b) nominal Pi method
12. What is the justification in neglecting line capacitance in short transmission lines?
13. What are the drawbacks of localized capacitance methods?
14. A long transmission line is open circuited at the receiving end. Will there be any current in the
line at the sending end? Explain your answer.
15. Why is leakage conductance negligible in overhead lines? What about underground system?
16. Why do we analyze a 3-phase transmission line on single phase basis?
Self-Test [Ch. 7]
1. Fill in the blanks by inserting appropriate words/figures.
(i) In Bangladesh ............... system is adopted for transmission of electric power.
(ii) ............... voltage is used for power transmission as a matter of economy.
(iii) The distribution system comprises of three elements viz. ............,and ......and .........
(iv) D.C. transmission is ............... to a.c. transmission.
(v) The higher the transmission voltage, the ............... is the conductor material required.
(vi) The choice of proper transmission voltage is essentially a question of ..................
(vii) In overhead system, the comparison of various systems is made on the basis of maximum
voltage between ...............
(viii) The economic size of conductor is determined by .................
(ix) In a transmission system, the cost of conductor is proportional to ............... of conductor.
(x) The economic transmission voltage is one for which the transmission cost is .................
2. Pick up the correct words/figures from brackets and fill in the blanks.
(i) Primary transmission is done by 3-phase ...............wire a.c. system. (3, 4)
(ii) The ......... distribution is done by 3-phase, 4-wire a.c. system. (primary, secondary).
(iii)The greater the power to be transmitted, the ........is the economic transmission voltage.
(smaller, larger)
(iv) The annual charge of a transmission line can be expressed as P1 + P2 = .......... (a, 1/a)
(v) The economic transmission voltage ........ the distance of transmission. (depends upon)
1. (i) 3-phase, 3-wire (ii) High (iii) feeders, distributors, service mains (iv) superior (v) lesser
(vi) economics (vii) conductor and earth (viii) Kelvin’s law (ix) area (x) minimum.
2. (i) 3 (ii) secondary (iii) larger (iv) a (v) depends upon.

3. 3
Self-Test [Ch. 8]
1. Fill in the blanks by inserting appropriate words/figures.
(i) Cross-arms are used on poles or towers to provide ............. to the insulators.
(ii) The most commonly used material for insulators of overhead lines is ...........
(iii) The potential across the various discs of suspension string is different because of ............
capacitance.
(iv) In a string of suspension insulators, the maximum voltage appears across the unit ........ to
the conductor.
(v) If the string efficiency is 100%, it means that ............. .
(vi) If shunt capacitance is reduced, then string efficiency is .............. .
(vii) If the spacing between the conductors is increased, then corona effect is ................
(viii) If sag in an overhead line increases, tension in the line ...............
(ix) By using a guard ring, string efficiency is ................
(x) Shunt capacitance in suspension insulators can be decreased by increasing the distance
of ........... from .................
2. Pick up the correct words/figures from the brackets and fill in the blanks.
(i) The insulator is so designed that it should fail only by ............(flash-over, puncture)
(ii) Suspension type insulators are used for voltages beyond ..............(33 kV,400 V, 11 kV)
(iii) In a string of suspension insulators, if the unit nearest to the conductor breaks down, then
other units will ............... (also breakdown, remain intact)
(iv) A shorter string has ......... string efficiency than a larger one. (less, more)
(v) Corona effect is .....pronounced in stormy weather as compared to fair weather. (more, less)
(vi) If the conductor size is increased, the corona effect is .......(increased, decreased)
(vii) The longer the cross arm, the ......... the string efficiency. (greater, lesser)
(viii) The discs of the strain insulators are used in ............ plane. (vertical, horizontal)
(ix) Sag is provided in line so that ……....(Safe tension is not exceeded, repair can be done)
(x) When an insulator breaks down by puncture, it is ............. damaged. (permanently, only
partially)
ANSWERS TO SELF TEST
1. (i) support (ii) porcelain (iii) shunt (iv) nearest (v) potential across each disc is the same (vi)
increased (vii) reduced (viii) decreases (ix) increased (x) conductor, tower.
2. (i) flash-over (ii) 33 kV (iii) also breakdown (iv) more (v) more (vi) decreased (vii) greater (viii)
vertical (ix) safe tension is not exceeded (x) permanently.

4. 4
Self-Test [Ch. 9]
1. Fill in the blanks by inserting appropriate words/figures.
(i) The power loss in an overhead transmission line is mainly due to ....................... .
(ii) If the length of a transmission line increases, its inductance is ....................... .
(iii) The d.c. resistance of a line conductor is ................... than its a.c. resistance.
(iv) If capacitance between two conductors of a 3-phase line is 4 micro-F, then capacitance of
each conductor to neutral is ................... .
(v) If the length of the line is decreased, its capacitance is .....................
(vi) Transposition of a 3-phase transmission line helps in ................ .
(vii) A neutral plane is one where ................. is zero.
(viii) In a single phase overhead line, the neutral plane lies at ..................... .
2. Pick up the correct words/figures from brackets and fill in the blanks
(i) If the supply frequency increases, then skin effect is .................... [increases, decreased]
(ii) An overhead transmission line has appreciable inductance because the loop it forms has
.............. X-sectional area. [large, small]
(iii) If the spacing between the conductors is increased, the inductance of the
line...........[increases, decreases]
(iv) The skin effect is ............. for stranded conductor than the solid conductor. [less, more]
(v) If the conductor diameter decreases, inductance of the line is .........(increased, decreased]
ANSWERS TO SELF-TEST
1. (i) Line conductor resistance (ii) increased (iii) less (iv) 8 micro-F (v) decreased (vi)
equalizing inductance and capacitance of the three phases (vii) electric intensity (viii) the
center of the distance between the conductors
2. (i) increased (ii) large (iii) increases (iv) less (v) increased

5. 5
Self-Test [Ch. 10]
1. Fill in the blanks by inserting appropriate words/figures.
(i) In short transmission lines, the effects of .................. are neglected.
(ii) ................. of transmission lines, is the most important cause of power loss in the line.
(iii) In the analysis of 3-phase transmission line, only ........................ is considered.
(iv) For a given VR and I, the regulation of the line .......... with the decrease in p.f. for
lagging loads.
(v) If the p.f. of the load decreases, the line losses .......................
(vi) In medium transmission lines, effects of ...................... are taken into account.
(vii) The rigorous solution of transmission lines takes into account the .................. nature of
line constants.
(viii) In any transmission line, AD - BC = ...........................
(ix) In a transmission line, generalized constants ................ and .................. are equal.
(x) The dimensions of constants B and C are respectively ............ and ................... .
2. Pick up the correct words/figures from the brackets and fill in the blanks.
(i) The line constants of a transmission line are ........[uniformly distributed, lumped]
(ii) The length of a short transmission line is up to about ….....[50 km, 120 km, 200km]
(iii) The capacitance of a transmission line is a ................. element. [series, shunt]
(iv) It is desirable that voltage regulation of a transmission line should be ................
[low, high]
(v) When the regulation is positive, then receiving end voltage (VR) is .......... than sending
end voltage (VS). [more, less]
(vi) The shunt admittance of a transmission line is 3 micro-Siemens. Its complex notation
will be ........ Siemen. [3 x 10 - 6 90º, 3 10-6 0º]
(vii) The exact solution of any transmission line must consider the fact that line constants
are .................... [uniformly distributed, lumped]
(viii) The generalized constants A and D of the transmission line have ........ [no dimensions,
dimensions of ohm]
ANSWERS TO SELF-TEST
1. (i) capacitance (ii) resistance (iii) one phase (iv) increases (v) increase (vi) capacitance
(vii) distributed (viii) 1 (ix) A and D (x) ohm, siemen
2. (i) uniformly distributed (ii) 50 km (iii) shunt (iv) low (v) less (vi) 3 x 10-6 vii)
uniformly distributed (viii) no dimensions