Power System

POWER SYSTEMS:

Q1:Why computer humming sound occurred in HT transmission line? Q2:What is different between resistance grounding system and resistance earthing system? Q3:Why should be the frequency 50 Hz 60Hz only why not others like 45, 95 56 or anything , why should we maintain the frequency constant if so why it is only 50 Hz 60Hz? Q4:what are the points to be consider for MCB(miniature circuit breaker selection?Q5:In three pin plug 6 Amp. 220v AC rating. why earth pin diameter is higher than othter two pin? what its purpose ? Q6:What is reverse power relay?Q7:What is the difference between isolators and electrical circuit breakers? What is bus-bar?Q8:What are the advantage of free wheeling diode in a Full Wave rectifier?Q9:What is the different between digital phase converter and ordinary phase converter? Q10:What is the main use of rotary phase converter ? Q11:What are HRC fuses and where it is used?Q12:Which power plant has high load factor?Q13:What is use of lockout relay in ht voltage?Q14:Why temperature rise is conducted in bus bars and isolators? Q15:When voltage increases then current also increases then what is the need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only? Q16:Why ELCB can't work if N input of ELCB do not connect to ground?Q17:What is the difference between MCB & MCCB, Where it can be used?Q18:Where should the lighting arrestor be placed in distribution lines?Q19:Define IDMT relay?Q20:What is SF6 Circuit Breaker?Q21:what is ferrantic effect?Q22: what is meant by insulation voltage in cables? explain it?Q23:Explain the working principal of the circuit breaker?Q24:What is the function of anti-pumping in circuit breaker?Q25:Why use the VCB at High Transmission System ? Why can't use ACB?Q26:What is the difference between surge arrestor and lightning arrestor?

Q27:What will happen when power factor is leading in distribution of power?Q28:Why, when birds sit on transmission lines or current wires doesn't get shock?Q29:what is ACSR cable and where we use it?Q30:What is vaccum currcuit breaker.define with cause and where be use it Device?

MULTIPLE CHOICE QUESTIONS:

1. Which of the following is not the transmission voltage in America ?

(A) 66 kV

(B) l32kV

(C) 264 kV

(D) 400 kV

2. Which of the following is usually not the generating voltage ?

(A) 6.6 kV

(B) 9.9 kV

(C) 11kV

(D) 13.2 kV.

3. Boosters are basically

(A) inductors

(B) capacitors

(C) transformers

(D) synchronous motors.

4. Which of the following is not the distribution system normally used

(A) 3 phase-4 wire

(B) 3 phase-3 wire

(C) Single phase - 3 wire

(D) Single phase -4 wire.

5. Conductors for high voltage transmission lines are suspended from towers

(A) to reduce clearance from ground

(B) to increase clearance from ground

(C) to reduce wind and snow loads

(D) to take care of extension in length during summer.

6. Transmission efficiency increases as

(A) voltage and power factor both increase

(B) voltage and power factor both decrease

(C) voltage increases but power factor decreases

(D) voltage decreases but power factor increases.

7. With same maximum voltage to earth, which ac system (with p.f. 0.8) will require more copper as compared to dc 2 wire system

(A) single phase. 2 wire (mid point earthed)

(B) single phase. 3 wire (neutral=1/2 outer)

(C) three phase three wire

(D) three phase-four wire (neutral = outer).

8. When alternating current passes through a conductor

(A) it remains uniformly distributed throughout the section of conductor

(B) portion of conductor near the surface carries more current as compared to the core

(C) portion of conductor near the surface carries less current as compared to the core

(D) entire current passes through the core of the conductor.

9. The fact that a conductor carries more current on the surface as compared to core, is known as

(A) skin effect

(B) corona

(C) permeability

(D) unsymmetrical fault.

10. The effective resistance of a conductor will be the same as ohmic resistance when

(A) current is in true sine wave form

(B) voltage is low

(C) power factor is unity

(D) Current is uniformly distributed in the conductor cross-section.

11. Skin effect results in

(A) reduced effective resistance but increased effective internal reactance of the conductor

(B) increased effective resistance but reduced effective internal reactance of. the conductor

(C) reduced effective resistance as well as effective internal reactance

(D) increased effective resistance as well as effective internal reactance.

12. Skin effect depends on

(A) size of the conductor

(B) frequency of the current

(C) resistivity of the conductor material

(D) all of the above.

13. The skin effect of a conductor will reduce as the

(A) diameter increases

(B) frequency increases

(C) permeability of conductor material increases

(D) resistivity of conductor material increases.

14. Skin effect is proportional to

(A) diameter of conductor

(B) (diameter of conductor)1/2

(C) (diameter of conductor )2

(D) (diameter of conductor )2.

15. In overhead transmission lines the effect of capacitance can be neglected when the length of line is less than

(A) 200 km

(B) 160 km

(C) 100 km

(D) 80 km.

16. For constant voltage transmission the voltage drop is compensated by installing

(A) synchronous motors

(B) capacitors

(C) inductors


17. The disadvantage of constant voltage transmission is

(A) short circuit current of the system is increased

(B) load power factor in heavy loads

(C) large conductor area is required for same power transmission

(D) air of the above.

18. The surge impedance for over head line is taken as

(A) 10-20 ohms

(B) 50-60 ohms

(C) 100-200 ohms

(D) 1000-2000 ohms.

19. Pin insulators are normally used up to voltage of about

(A)100kV

(B) 66 kV

(C) 33 kV

(D) 25 kV.

20. Strain type insulator arc used where the conductors arc

(A) dead ended

(B) at intermediate anchor towers

(C) any of the above

(D) none of the above.

21. For 66 kV lines the number of insulator discs used are

(A) 3

(B) 5

(C) 8

(D) 12.

22. Ten discs usually suggest that the transmission line voltage is

(A) 11 kV

(B) 33 kV

(C) 66 kV

(D) 132 kV.

23. The effect of corona is

(A) increased energy loss

(B) increased reactance

(C) increased inductance


24. Corona usually occurs when the electrostatic stress in the air around the conductor succeeds

(A) 30 kV (maximum value)/cm

(B) 22 kV (maximum value)/cm

(C) 11 kV (rms value)/cm

(D) 6.6 kv (rms value)/cm.

25. Corona effect can be detected by

(A) hissing sound

(B) faint luminous flow of bluish color

(C) presence of ozone detected by odor


26. The current drawn by the line due to corona losses is

(A) sinusoidal

(B) square

(C) non-sinusoidal

27. Presence of ozone as a result of corona is harmful because

(A) it gives bad odor

(B) it corrodes the material

(C) it transfers energy to the ground

(D) reduces power factor.

28. Between two supports, due to sag the conductor takes the form of

(A) catenary

(B) triangle

(C) ellipse

(D) semi-circle.

29. The inductance of a single phase two wire line is given by (D is the distance between conductors and 2v is the diameter of conductor)

(A) 0.4 loge (D/r) mH/km

(B) 0.55 loge (D/r) mH/km

(C) 0.4 loge (r/D) mH/km

(D) 0.55 loge (r/D) mH/km.

30. The effect of ice deposition on conductor is

(A) increased skin effect

(B) reduced corona losses

(C) increased weight

(D) reduced sag.

31. A 70/6 ACSR conduction is an aluminium conductor steel reinforced, having

(A) cross sectional area of aluminium as 70 mm2 and the cross-sectional area of steel as 6 mm2

(B) cross-sectional area of steel as 70 mm2 and the cross-sections area of aluminium as 6 mm2

(C) 70 aluminium conductors and 6 steel conductors

(D) 80 steel conductors and 6 aluminium conductors.

32. In aluminium conductors steel reinforced, the insulation between aluminium and steel conductors is

(A) any insulator

(B) bitumen

(C) insulin

(D) no insulation is required.

33. Under no load conditions the current in a transmission line is due to

(A) corona effects

(B) capacitance of the line

(C) back flow from earth

(D) spinning reserve.

34. Which distribution system is more reliable ?

(A) Ring main system

(B) Tree system

(C) Radial system

(D) All are equally reliable.

35. Out of the following systems of distribution, which system offers the best economy ?

(A) Direct current system

(B) AC single phase system

(C) AC 3 phase 3 wire system

(D) AC 3 phase 4 wire system.

36. What are the advantages of dc transmission system over ac transmission system ?

(A) DC system is economical

(B) There is no skin effect in dc system

(C) Corona limits are highest for dc circuits as compared to ac circuits

(D) All of the above.

37. The main advantage of ac. transmission system over d.c. transmission system is

(A) Easy transformation

(B) Less losses in transmission over long distances

(C) ) Less insulation problems

(D) Less problem of instability.

38. Step-up substations are associated with

(A) distributors

(B) consumer location

(C) concentrated load

(D) generating stations.

39. A section of a single bus scheme is shown in the figure. In this figure B represents

(A) Isolator

(B) Circuit breaker

(C) Current transformer

(D) Inductance.

40. An isolator is represented by

(A) A

(B) B

(C) C

(D) A and D.

41. C represents

(A) circuit breaker

(B) Mho's relay

(C) Earth switch

(D) None of the above.

42. When an alternator is connected to the infinite but bar and its excitation is gradually increased

(A) the terminal voltage will rise

(B) the terminal voltage will drop

(C) the terminal voltage will remain unaltered

(D) the terminal voltage will vary rapidly.

43. Consumers having low power factor equipment are advised to install

(A) tap changing transformer

(B) capacitor bank

(C) synchronous condensers

(D) none of the above.

44. A bus bar is rated by

(A) current only

(B) current and voltage only

(C) current, voltage, frequency

(D) current, voltage, frequency and short time current.

45. For increasing the capacity of a transmission line to transmit power which of the following must be decreased ?

(A) Voltage

(B) Capacitance

(C) Line inductance


46. In terms of constants A, B, C and D for short transmission lines, which of the following relation is valid ?

(A) A = B = 1

(B) B = D = 0

(C) A = C = 1

(D) C=0.

47.Which of the following is reduced due to the use of bundled conductors ?

(A) Capacitance of the circuit

(B) lnductance of the circuit

(C) Power loss due to corona


48. The ratio of capacitance from line to line capacitance from line to neutral is nearly

(A)1/4

(B) 1/2

(C) 1

(D) 2.

49. Following effects are associated with transmission lines

I. Corona effect

II. Proximity effect

III. Skin effect.

The effect resistance of a conductor is increased by

(A) I only

(B) II and III only

(C) I and III only

(D) I. II and III.

50. The sag of a transmission line is least affected by

(A) self weight of conductors

(B) temperature of surrounding air

(C) current through conductor

(D) ice deposited on conductor.

51. The sag of the conductors of a transmission line is 1.5 m when the span is 100 m. Now if the height of supporting towers is increased by 20%, the sag will

(A) increase by 20%

(B) increase by 10%

(C) reduced by 20%

(D) remain unchanged.

52. ACSR conductor having 7 steel stands surrounded by 25 aluminum conductor will be specified as

(A) 7/25

(B) 7/32

(C) 25/7

(D) 25/32.

53. The networks associated with transmission lines are

I. T-network

II. π network

III. Tree net.

A two terminal pair of network of a transmission line can be represented by

(A) I only

(B) II only

(C) Either of I or II

(D) Either of I, II or III.

54. Which of the following relationships is not valid for short transmission lines ?

(A) B = Z = C

(B) A = D = 1

(C) Is = Ir

(D) None of the above.

55. In order to improve the steady state stability of an overhead transmission lines, which of the following methods can be adopted

(A) Reducing impedance between the stations

(B) Adopting quick response excitation systems

(C) Using series capacitors to make X = (3 R)1/2

(D) Any of the above.

56. Transient disturbances arc due to

(A) Switching operations

(B) Load variations

(C) Faults

(D) Any of the above.

57. Which of the following short circuit is the most dangerous ?

(A) Line to line short circuit

(B) Dead short circuit

(C) Line to ground short circuit

(D) Line to line and ground short circuit.

58. In case line to line fault occurs, the short circuit current of an alternator will .depend on its

(A) Synchronous reactance

(B) Transient reactance

(C) Short circuit resistance


59. Transient state stability is generally improved by ,

(A) using high speed governors on machines by

(B) using low inertia machines

(C) dispensing with neutral grounding

(D) any of the above.

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