26. To increase the visual critical voltage of cporona for an overhead line, one solid phase-conductor is replaced by a “bundle” of four smaller conductors per phase, having an aggregate cross-sectional area equal to that of the solid conductor. If the radius of the solid conductor is 40 mm, then the radius of each of the bundle conductors would be
(a) 10 mm
(b) 20 mm
(c) 28.2 mm
(d) 30 mm
Ans: d
27. For an existing ac transmision line, the string efficiency is 80%, if dc voltage is supplied for the same set up, the string efficiency will be
(a) < 80%
(b) 80%
(c) 90%
(d) 100%
Ans: b
28. 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 current from link pins
(b) forms capacitances which help to cancel the charging current from link pins
(c) increases the capacitances of lower insulator units of cause equal voltage drop
(d) decreases the capacitances of upper insulators units to cause equal voltage drop
Ans: b
29. A three phase over head transmission line has its conductors horirzontally spaced with spacing between adjacent conductors equal to ‘d’. if now the conductors of the line are rearranged to form and equilateral triangle of sides equal to ‘d’ then
(a) average capacitance and inductance will increase
(b) average capacitance will decrease and inductance will increase
(c) average capacitance will increase and inductance will decrease
(d) surge impedance loading of the line Increases
Ans: a
30. For a 500 Hz frequency excitation, a 50 km, long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data insufficiency for decision
Ans: c
31. If in a short transmission line, resistance and inductance are found to be equal and regulation appear. to be zero, then the load will
(a) have unity power factor
(b) have zero power factor
(c) be 0.707 lagging
(d) be 0.707 lagging
Ans: c
32. “Expanded ACSR” are conductors composed of
(a) larger diameter individual strands for a given cross-section of the aluminium strangs
(b) larger diameter of a central steel strands for a given overall diameter of the conductor
(c) larger diamter of the aluminium strands only for a given overall diameter of the conductor
(d) a fillter between the inner steel and the outer aluminium strands to increase the overall diameter of the conductor
Ans: d
33. What is the sag for a span of 400m, if the ultimate tensile strength of conductor is 6000 kgf, and the weight of conductor is 550 kgf/km? Factor of safety is 2.
(a) 1.016 m
(b) 2.40 m
(c) 3.6 m
(d) 4.2 m
Ans: c
34. A transmission line haB a span of 275 m between level supporte. The conductor has a diameter of 19.58 mm, weight 0.844 kgpm and has an ultimate breaking strength of 7950 kgf. Each conductor has a radial covering of ice 9.58 mm thick and is subjected to a horizontal wind pressure of 40 k617m2 of ice covering projected area. If the factor of safety is 2, what is the deflected sag? Ice weight is 913.5 kg/m3
(a) 5.36
(b) 4.1 m
(c) 3.9 m
(d) 3.01 m
Ans: a
35. A transmission line conductor having a diameter of 19.5 mm, weight 850 kglkm. The span is 275 m. The wind pressure is 39 kg/m of projected area with ice coating of 13 mm. The ultimate strength of the conductor is’8000 kg. What is the maximum sag, if the factor of safety is 2 and ice weight 910 kg/m3?
(a) 4.5 m
(b) 6.4 m
(c) 7.0 m
(d) 5 m
Ans: b
36. A transmission line conductor at a river crossing is supported from two towers at height. of 30 m and 90m, above water level. The horizontal distance between the towers is 270m, if the tension in the conductor is 1800 kg and the conductor weight 1 kg/m. What is the clearance between the conductor and the water at a point midway between the towers?
(a) 79.50 m
(b) 54.94 m
(c) 60 m
(d) 51.4 m
Ans: b
37. An overhead transmission line has a span of 240m between level supports. What is the maximum sag if the conductor weight 727 kg/km and has a breaking strength of 6880 kg? Allow the factor of safety of 2. Neglecting wind and ice loading.
(a) 1.52 m
(b) 1.6 m
(c) 0.75 m
(d) 1.25 m
Ans: a
38. The line conductor of a transmission line has an overall diameter of 19.53 mm, weight 0.844 kg/m and an ultimate breaking strength of 7950 kg. If the factor of safety is to be 2, when conductor has an ice of 1 kg/m and a horizontal wind pressure of 1.5 kg/m. What is the vertical sag, corresponding to this loading for a 300 m span level supports?
(a) 1.08 m
(b) 5.0 m
(c) 5.22 m
(d) 4.62 m
Ans: c
39. A two conductor 1 – pi line operates at 50 Hz. The diameter of each conductor is 20 mm and the spacing between conductors is 3m. What is the inductance of each conductor per km?
(a) 1.19 kH/km
(b) 1.24 mH/km
(c) 2.38 mH/km
(d) 0.59 mH/km
Ans: a
40. A two conductor 1 – pi line operates at 50 Hz. The diameter of each conductor is 20mm and the spacing between conductor is 3m. When the conductor material is steel of relative permeability 50, the loop inductance per km of the line will be
(a) 8.2 mHlkm
(b) 7.281 mHlkm
(c) 5.0 mHlkm
(d) 2 mHlkm
Ans: b
41. A 1-pi line two conductors operate at 50Hz. The diameter of each conductor is 15 mm, and the spacing between the conductor is 3.5 m. The inductive reactance per km will be
(a) 0.43 ClIkm
(b) 0.65 0Jkm
(c) 0.70 O/km
(d) 0.79 nIkm
Ans: d
42. A conductor is composed of seven identical copper .Iranu, each having a radius r. The self GMD of the conductors will be
(a) 2.177 r
(b) 2.645 r
(c) 2.141 r
(d) 1.21 r
Ans: a
43. The charging current per kill of the line is
(a) 0.497 Amp
(b) 0.61 Amp
(c) 0.68 Amp
(d) 0.21 Amp
Ans: a
44. What is the time of operation of a relay of rating 5 amp 2.2 sec, IDMT and having a relay of setting of 125% Tms = 0.6 It is connected to a supply circuit through a CT, 400 ratio. The fault current is 400 amp.
(a) 10.Osec
(b) 1.92sec
(c) 4.5 sec
(d) 2.4 sec
Ans: b
45. A two conductor 1 – pi line operates at 50 Hz. The diameter of each conductor is 2 cm and are spaced 3m apart. What is the line to line capacitance
(a) 9.74 x 10-9 F/km
(b) 4.87 x 10-9 F/km
(c) 3.05 x 10-9 F/km
(d) None of these
Ans: b
46. A two conductor 1 – pi line operates at 50 Hz. The diameter of each conductor is 4 cm and are spaced 6 m apart. What is the capacitive susceptance to neutral per km?
(a) 1.42 x 10-9 s/km
(b) 3.25 x 10-8 s/km
(c) 4.8 x 10-9 s/krn
(d) 3.06 x 10-9 s/km
Ans: d
47. A three phase 50 Hz line consists of three conductors each of diameter 21 mm, The spacing between the conductors all follows:
A – B = 3m, B – C = 5m, C – A = 3.6m If the line operates at 132 k V, the reactive voltampere generatd by the line per km is
(a) 51.07 kVAr
(b) 51.70 kVAr
(c) 40.0 kVAr
(d) 60.5 kVAr
Ans: b
48. A two conductor 1 – pi line operates at 50 Hz. The diameter of each conductor is 20 mm and the spacing between the conductors is 3m, The height of conductor above the ground is 6 m. The capacitance of the line to neutral will be
(a) 9.7 pF/m
(b) 10.2 pF/m
(c) 8.7 uF/km
(d) 2.4 uF/m
Ans: a
49. For a 500 Hz frequency excitation, a 50 km long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data isufficient decision
Ans: c
50. Bundled conductors are employed to
(a) reduce the short circuit current
(b) improve system stability
(c) decreases system stability
(d) increase the short circuit current
Ans: c