Power Systems -- MCQ's with Answer's

Power Systems -- MCQ's with Answer's
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1.     An industrial consumer hall a daily load pattern of 2000 KW, 0.8 lag for 12 Hra and 1000 kW UPF for 1J Hr. The load factor i= _____.
(a) 0.5    
(b) 0.75
(c) 0.6    
(d) 2.0
Ans: c
2.     What is the maximum value of a load which consume 500 KWh per day at a load factor of 0.40, if the consumer increases the load factor of 0.50 without increasing the maximum demand?    
(a) 52.08 kW    
(b) 50.8 kW
(c) 4.5 kW    
(d) 60 kW
Ans: a
3.     A consumer consume. 600 kWh per day at a load factor of 0.40. If the coneumer increases the load factor of 0.70 without increasing the maximum demand, what is the consumption of energy in kWh
(a) 950 kWh    
(b) 1000 kWh
(c) 1050 kWh    
(d) 1100 kWh
Ans: c
4. The yearly load duration curve of a power plant is a straight line. The maximum load is 750 MW and the minimum load is 600 Mw. The capacity of the plant is 900 MW. What is the capacity factor and utilization factor?
(a) 0.56,0.80    
(b) 0.83,0.75
(c) 0.78, 0.9    
(d) 0.75, 0.83
Ans: d
5. What is the utilization factor of a power station which supplies the following loads?
Load A:  Motor load of200 kW between 10 AM to7PM
Load B : Lighting load of 100 kW between 7 PM to 11 PM
Load C : Pumping load of 110 kW between 3 PM to 10 AM
(a) 1.60
(c) 1.00
(b) 1.32
(d) 2.56
Ans: b
6. A power station supplies the peak load of 60 Mw, 40 MW and 70 MW to three localities. The annual load factor is 0.50 p.u. and the diversity factor of the load at the station is 1.55. The maximum demand on the station and average load respectively will be
(a) 120 MW, 60.8    
(b) 90 MW, 50.6
(c) 103.2 MW, 51.61
(d) 100 MW, 0.51
Ans: c
7. The load duration curve for a system, is shown in the figure below. The load factor will be
 

(a) 0.83 
(b) 0.96
(c) 0.67
(d) 0.50
Ans: a

8. A generating station has a maximum demand of 50 Mw, a load factor of 60%, a plant capacity factor of 45% and if the plant while running as per schedule, were fully loaded. The daily energy produced will be
(a) 400 MW    
(b) 720 MW
(c) 500 MW    
(d) 600 MW
Ans: b

9. A generating st ation has a maximum, demand of 20 mW, load factor of 60%, a plant capacity factor of 50% and a plant
Use factor of 72%. What is the reserve capacity of the plant, if the plant, while running as per schedule, were fully loaded?
(a) 10 MW    
(b) 15 MW
(c) 2 MW    
(d) 5 MW
Ans: d

10. In the above question, the maximum energy that could be produced daily is
(a) 500 MWhlday    
(b) 360 MWhIday
(c) 600 MWhlday    
(d) 720 MWhlday
Ans: a

11. In a DC transmission line
(a) it is necessary for the sending end and receiving end to be operated in synchronism.
(b) the effects of inductive and capacitive reactances are greater than in an AC transmission line of the same rating.
(c) there are no effects due to inductive and capacitive reactances.
(d) power transfer capability is limited by stability considerations.
Ans: c

12. The impedance of a circuit is given by z=3+j4. Its conductance will be
(a) 1/3    
(b) 3/5
(c) 3/25
(d) 4/5
Ans: c

13.    A 100 km transmiesion line ia deaigned for a nominal voltage of 132 kV and conaiala of one conductor per phase. The line reactance is 0.726 ohm/km. The static transmission capacity of the line, in Megawatts, would be
(a) 132    
(b) 240
(c) 416    
(d) 720
Ans: c

14.    The per unit impedance ofa circuit element is 0.15. If the base kV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be
(a) 0.075    
(b) 0.15
(c) 0.30    
(d) 0.600
Ans: c

15.    The conductor of a 10 km long, single phase, two wire line are separated by a distance of 1.5 m. The diameter of each conductor is 1 cm, If the conductors are of copper, the inductance of the circuit is
(a) 50.0 mH    
(b) 45.3 mH
(c) 23.8 mH    
(d) 19.6 mH
Ans: c
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16.    For a single phase overhead line having solid copper conductors of diameter 1 cm, spaced 60 cm between centers, the inductance in mH/km is
(a) 0.05 + 0.2 ln 60
(b) 0.2 ln 60
(c) 0.05 + 0.2 ln (6010.5)
(d) 0.2 ln (60/0.5)
Ans: c

17.    A 100 km long transmission line is loaded at 110 kV.if the loss of line is 5 MW and the load is 150 MVA, the resistance of the line is
(a) 8.06 ohms per phase
(b) 0.806 ohms per phase
(c) 0.0806 ohms per phase
(d) 80.6 ohms per phase
Ans: a

18.    A 3-phase, 11 kv, 50 Hz, 200 kW load has a power factor of 0.8 lag. A delta connected 3-phase capacitor is used to improve the power factor to unity. The capacitance perphase of the capacitor in micro-farads is
(a) 3.948    
(b) 1.316
(c) 0.439    
(d) 11.844
Ans: b

19.    For equilateral spacing of conductors of an untrasposed 3-phase line, we have
(a) balanced receiving end voltage and no communication interference
(b) unbalanced receiving end voltage and no communication interference
(c) balanced receiving end voltage and communication interference
(d) unbalanced receiving end voltage and communication interference.
Ans: c

20. For a 500 Hz frequency excitation, a 50 #em long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data insufficient for decision
Ans: c

21. Which one of the following statement. is not correct for the use of bundled conductors in transmission lines?
(a) Control of voltage gradient
(b) Reduction in corona 1088
(c) Reduction in radio interference
(d) Increase in interference with communication lines
Ans: d

22. The main consideration for higher and higher operating voltage of transmission is to
(a) increase the efficiency of transmission
(b) reduce power losses
(c) increase power transmission capability
(d) both (a) and (b) above
Ans: c

23. A single phaae transmisson line of impedance j 0.8 ohm supplies a resistive load of 500 A at 300 V. The sending end
power factor is
(a) unity
(b) 0.8 lagging
(c) 0.8 leading
(d) 0.6 lagging
Ans: d

24. A medium line with parameters A, B, C, D is extended by connecting a short line of impedance Z in series The overall ABCD parameteres of the series combinatton will be
(a) A, AZ, C + D/Z, D
(b) A, AZ + B, C, CZ + D
(c) A + BZ, B, C + DZ, D
(d) AZ, B, C/Z, D
Ans: b

25. When bundle conductors are used in place of single conductors, the effective inductance and capacitance will respectively
(a) increase and decrease
(b) decrease and increase
(c) decrease and remain unaffected
(d) remain unaffected and increase
Ans: c

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
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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

51.    Series capacitive compensation in EHV transmission lines is used to
(a) reduce the line loading
(b) improve the stability of the system
(c) reduce the voltage profile
(d) improve the protection of the line
Ans: b

52.    A lossless radial tranemission line with surge impedance loading
(a) takes negative VAr at sending end and zero VAr at receiving end
(b) takes positive VAr at sending end and zero VAr at receiving end
(c) has flat voltage profile and unity power factor at all points along it
(d) has sending end voltage higher than receiving end voltage and unity power factor at sending end
Ans: a
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53.    The X:R ratio of 220 kV line as compared to 400 kV line is
(a) greater
(b) smaller
(c) equal
(d) it could be anything
Ans: b

54.    If a line is 100 % series compensated it may result into series resonance at power frequency of
(a) 50 Hz
(c) 150 Hz
(b) 100 Hz
(d) none of the above
Ans: a

55.    A 60 Hz, 320 km loesless line has Bending end voltage 1.0 p.u, The receiving end voltage on no load is
(a) 1.1 p.u.    
(b) 1.088 p.u.
(c) 1.116 p.u.    
(d) none of the above
Ans: b

56.    With 100 % series compensation of line.
(a) the circuit is series resonant at power frequency
(b) low transient voltage
(c) high transient current
(d) both (a) and (c)
Ans: d

57.    For certain geometry and operating voltage of the uncompensated transmission line, the ratio of power transfer capability to the surge inpedance loading with increase in length
(a) increases    
(b) remains unchanged
(c) decreases    
(d) uncertain
Ans: c

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