MCQ Questions on Transmission & Distribution

1. Which of the following is the disadvantage due to low power factor?

(a) Poor voltage regulation
(b) Increased transmission losses
(c) High cost of equipment for a given load
(d) All of the above

2. Which of the following is the disadvantage of static capacitor for power factor improvement?

(a) Easily damaged by high voltage
(b) Cannot be repaired
(c) Short service life
(d) All of the above

3. Galvanised steel wire is generally used as

(a) stay wire
(b) earth wire
(c) structural components
(d) all of the above

4. Multicore cables generally use

(a) square conductors
(b) circular conductors
(c) rectangular conductors
(d) sector-shaped conductors

5. The presence of ozone due to corona is harmful because it

(a) reduces power factor
(b) corrodes the material
(c) gives odour
(d) transfer energy to the ground

6. A feeder, in a transmission system, feeds power to

(a) distributors
(c) service mains
(b) generating stations
(d) all of the above

7. Which of the following is not a constituent for making porcelain insulators?

(a) Quartz
(c) Feldspar
(b) Kaolin
(d) Silica

8. Which of the following distribution systems is more reliable?

(a) Radial system
(b) Tree system
(c) Ring main system
(d) All are equally reliable

9. The voltage drop, for constant voltage transmission is compensated by installing

(a) inductors
(b) capacitors
(c) synchronous motors
(d) none of the above

10. The angular displacement between two interconnected stations is mainly due to

(a) armature reactance of both alternators
(b) reactance of the interconnector
(c) synchronous reactance of both the alternators
(d) all of the above

11. When a conductor carries more current on the surface as compared to core, it is due to

(a) permeability variation
(b) corona
(c) skin effect
(d) none of the above

12. Power loss due to corona is not directly proportional to

(a) spacing between conductors
(b) supply voltage frequency
(c) phase-neutral voltage
(d) all of the above

13. On which of the following does the size of feeder depend?

(a) Voltage drop
(b) Voltage
(c) Frequency
(d) Current carrying capacity

14. A guy wire

(a) protects conductors against short circuiting
(b) provides emergency earth route
(c) provides protection against surges
(d) supports the pole

15. Power system stability is least affected by

(a) reactance of generator
(b) input torque
(c) losses
(d) reactance of transmission line

16. The electrostatic stress in underground cables is

(a) zero at the conductor as well as on the sheath
(b) same at the conductor and sheath
(c) minimum at the conductor and minimum at the sheath
(d) maximum at the conductor and minimum at the sheath

17. By using bundle conductor, the critical voltage for the formation of corona will

(a) remain same
(c) increase
(b) decrease
(d) not occur

18. Which of the following insulation is used in cables?

(a) Varnished cambric
(b) Rubber
(c) Paper
(d) Any of the above

19. Empire tape is

(a) varnished cambric
(b) vulcanised rubber
(c) impregnated paper
(d) none of the above

20. The bedding on a cable consists of

(a) hessian cloth
(b) jute
(c) any of the above
(d) none of the above

21. The current carrying capacity of cables in D.C. is more than that in A.C. mainly due to

(a) absence of harmonics
(b) non-existence of any stability limit
(c) smaller dielectric loss
(d) absence of ripples

22. Dielectric strength of rubber is around

(a) 5 kV/mm
(b) 15 kV/mm
(c) 30 kV/mm
(d) 200 kV/mm

23. In the cables, the location of fault is usually found out by comparing

(a) the resistance of the conductor
(b) the inductance of conductors
(c) the capacitances of insulated conductors
(d) all above parameters

24. The intersheaths in the cables are used to

(a) minimize the stress
(b) avoid the requirement of good insulation
(c) provide proper stress distribution
(d) none of the above

25. The stability of arc in vacuum depends upon:

(a) The contact material only
(b) The contact material and its vapour pressure
(c) The circuit parameters
(d) The combination of (b) and (c)

26. An overhead line with surge impedance 400 ohms is terminated through a resistance R. A surge travelling over the line does not suffer any reflection at the junction if the value or R is

(a) 20 ohms
(c) 800 ohms
(b) 200 ohms
(d) None of the above

27. Tick out the correct one.

(a) The insulators and lightning arresters should have high impulse ratio.
(b) The insulators and lightning arresters should have low impulse ratio.
(c) The insulators should have high impulse ratio and lightning arrester low.
(d) The lightning arresters should have high impulse ratio but insulator low.

28. The voltage of a particular bus can be controlled by controlling the

(a) Phase angle
(b) Reactive power of the bus
(c) Active power of the bus
(d) Phase angle and reactive power

29. The inductance and capacitance of a line are respectively 1.0 H and 0.01  µ F if the instantaneous value of interrupted current is 10 A, the voltage across the breaker contacts will be

(a) 125 kV
(b) 75 kV
(c) 100 kV
(d) 66 kV

30. If δ is the loss angle of the cable, its power factor is

(a) sinδ
(b) cosδ
(c) Power factor is independent of δ
(d) Power factor depends upon δ but it is not as per (a) and (b)

31. The inertia constant H of a synchronous condenser is

(a) greater than that of hydro generator
(b) greater than that of turbo alternator
(c) equal to that of turbo alternator
(d) none of the above

32. If the effect of earth is taken into account, then the capacitance of line to ground

(a) decreases
(b) increases
(c) remains unaltered
(d) becomes infinite

33. Shunt compensation in an EHV line is used to

(a) improve stability
(b) reduce fault level
(c) improve the voltage profile
(d) substitute for synchronous phase modifier

34. The voltages across the various discs of a string of suspension insulators having identical discs is different due to

(a) surface leakage currents
(b) series capacitance
(c) shunt capacitances to ground
(d) series and shunt capacitances

35. Transmission lines are transposed to

(a) reduce copper loss
(b) reduce skin effect
(c) prevent interference with neighbouring telephone lines
(d) prevent short-circuit between any two lines

36. Hollow conductors are used in transmission lines to

(a) reduce weight of copper
(b) improve stability
(c) reduce corona
(d) increase power transmission capacity

37. Which of the following are the advantages of interconnected operation of power systems?

1. Less reserve capacity requirement
2. More reliability
3. High power factor
4. Reduction in short-circuit level

Select the correct answer using the codes given below
(a) 1 and 2
(b) 2 and 3
(d) 1 and 4
(c) 3 and 4

38. Steady-state stability of a power system is improved by

(a) reducing fault clearing time
(b) using double circuit line instead of single circuit line
(c) single pole switching
(d) decreasing generator inertia

39. For reducing tower footing resistance, it is better to employ

(a) Chemical and counterpoise
(b) Chemical and ground rods
(c) Ground rods and counterpoise
(d) Chemical, ground rods and counterpoise

40. Ring main distribution is preferred to a radial system because

(a) Voltage drop in the feeder is less and supply is more reliable.
(b) Voltage-drop in the feeder is less and power factor is high.
(c) Power factor is high and supply is more reliable.
(d) Power factor is high and system is less expensive.

41. A 3-phase transmission line conductors were arranged in horizontal spacing, with ‘d’ as the distance between adjacent conductors. If these conductors are rearranged to form an equilateral triangle with sides equal to ‘d’, then the

(a) Capacitance and the inductance will increase
(b) Capacitance will increase and the inductance will decrease
(c) Capacitance and the inductance will remain the same
(d) Capacitance will decrease and the inductance will increase

42. For an existing ac transmission line, the string efficiency is 80%. If dc voltage is supplied for the same set up, the string efficiency will be

(a) <80%
(c) 90%
(b) 80%
(d) 100%

43. In a string of suspension insulators, the voltage distribution across the different units of a string could be made uniform by the use of a grading ring, because it

(a) Forms capacitances with link-pins to carry the charging currents from link-pins to earthed structure.
(b) Forms capacitances which help to cancel the charging current from link-pins.
(c) Increase the capacitances of lower insulator units to cause equal voltage drop.
(d) Decrease the capacitances of upper insulator units to cause equal voltage drop.

44. A generator is connected to an infinite bus through a double circuit transmission. The fault occurring at the middle of one of the transmission lines is subsequently cleared by opening the circuit breakers at both the ends of the line simultaneously. The transient stability limit of the system is improved by

(a) Decreasing the excitation of generator.
(b) Decreasing the fault-clearing time.
(c) Increasing the fault-clearing time.
(d) Increase the transfer reactance between the generator and infinite bus.

45. A one kilometer long 11 kV 3-core three-phase metal sheathed cable gauge gives the following test results

(i) Capacitance between 2 conductors joined to sheath and the third conductor: 0.6μF
(ii) Capacitance between all the three bunched together and conductors sheet: 0.96 μF
The effective capacitance of each core to neutral is
(a) 0.12 μF
(b) 0.14 μF
(c) 0.74 μF
(d) 0.32 μF

46. A wave-trap is used at the termination of a HVAC overhead line to a station switchyard to

(a) Prevent the transformer magnetizing harmonics from reaching the overhead line
(b) Damp the incoming surge waves from the overhead lines
(c) Attenuate sub-harmonic oscillations
(d) Provide for carrier communication

47. The insulation resistance of a 20 km long underground cable is 8 MΩ. Other things being the same, the insulation resistance of a 10 km long cable will be

(a) 16 ΜΩ
(b) 32 ΜΩ
(c) 4 ΜΩ
(d) 2 ΜΩ

48. For an ac circuit if e(t)=160sin (ωt+10°) and i(t)=5sin (ωt-20°), then the reactive power absorbed by the circuit will be

(a) 400 VAR
(b) 346.4 VAR
(c) 200 VAR
(d) 136.8 VAR

49. A suspension type insulator has three units with self-capacitance C and ground capacitance of 0.2 C having a string efficiency of

(a) 78%
(c) 82%
(b) 80%
(d) 84%

50. A bundled conductor line compared to a single conductor line (with same conductor cross- sectional area and same mean distance between conductors) has

(a) Self GMD-Lower, Mutual GMD-Nearly same, Per phase inductance-Higher.
(b) Self GMD-Higher, Mutual GMD-Lower, Per Phase Inductance-Nearly same.
(c) Self GMD-Higher, Mutual GMD-Nearly same, Per Phase Inductance-Lower.
(d) Self GMD-Lower, Mutual GMD-Higher, Per Phase Inductance-Higher.