Top Most Power systems Objective Questions Part – 5
1.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?
52.08 kW
50.8 kW
4.5 kW
60 kW
ANSWER : : 52.08 kW
2.For equilateral spacing of conductors of an untrasposed 3-phase line, we have
balanced receiving end voltage and no communication interference
unbalanced receiving end voltage and no communication interference
balanced receiving end voltage and communication interference
unbalanced receiving end voltage and communication interference.
ANSWER : : balanced receiving end voltage and communication interference
3.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
132
240
416
720
ANSWER : : 416
4.In a DC transmission line
it is necessary for the sending end and receiving end to be operated in synchronism.
the effects of inductive and capacitive reactances are greater than in an AC transmission line of the same rating.
there are no effects due to inductive and capacitive reactances.
power transfer capability is limited by stability considerations.
ANSWER : : there are no effects due to inductive and capacitive reactances.
5.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
8.06 ohms per phase
0.806 ohms per phase
0.0806 ohms per phase
80.6 ohms per phase
ANSWER : : 8.06 ohms per phase
6.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?
10 MW
15 MW
2 MW
5 MW
ANSWER : : 5 MW
7.Which one of the following statement. is not correct for the use of bundled conductors in transmission lines?
Control of voltage gradient
Reduction in corona 1088
Reduction in radio interference
Increase in interference with communication lines
ANSWER : : Increase in interference with communication lines
8.For a 500 Hz frequency excitation, a 50 #em long power line will be modelled as
short line
medium line
long line
data insufficient for decision
ANSWER : : long line
9.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
400 MW
720 MW
500 MW
600 MW
ANSWER : : 720 MW
10.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
unity
0.8 lagging
0.8 leading
0.6 lagging
ANSWER : : 0.6 lagging
11.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
120 MW, 60.8
90 MW, 50.6
103.2 MW, 51.61
100 MW, 0.51
ANSWER : : 103.2 MW, 51.61
12.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
1.60
1.00
1.32
2.56
ANSWER : : 1.32
13.When bundle conductors are used in place of single conductors, the effective inductance and capacitance will respectively
increase and decrease
decrease and increase
decrease and remain unaffected
remain unaffected and increase
ANSWER : : decrease and remain unaffected
14.In the above question, the maximum energy that could be produced daily is
500 MWhlday
360 MWhIday
600 MWhlday
720 MWhlday
ANSWER : : 500 MWhlday
15.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
0.075
0.15
0.30
0.600
ANSWER : : 0.30
16.The impedance of a circuit is given by z=3+j4. Its conductance will be
1/3
3/5
3/25
4/5
ANSWER : : 3/25
17.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
950 kWh
1000 kWh
1050 kWh
1100 kWh
ANSWER : : 1050 kWh
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
3.948
1.316
0.439
11.844
ANSWER : : 1.316
19.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
0.05 + 0.2 ln 60
0.2 ln 60
0.05 + 0.2 ln (6010.5)
0.2 ln (60/0.5)
ANSWER : : 0.05 + 0.2 ln (6010.5)
20.The main consideration for higher and higher operating voltage of transmission is to
increase the efficiency of transmission
reduce power losses
increase power transmission capability
both (a) and (b) above
ANSWER : : increase power transmission capability
21.The load duration curve for a system, is shown in the figure below. The load factor will be
0.83
0.96
0.67
0.50
ANSWER : : 0.83
22.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, AZ, C + D/Z, D
A, AZ + B, C, CZ + D
A + BZ, B, C + DZ, D
AZ, B, C/Z, D
ANSWER : : A, AZ + B, C, CZ + D
23.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?
0.56,0.80
0.83,0.75
0.78, 0.9
0.75, 0.83
ANSWER : : 0.75, 0.83
24.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
50.0 mH
45.3 mH
23.8 mH
19.6 mH
ANSWER : : 23.8 mH
25.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
forms capacitances with link-pins to carry the charging current from link pins
forms capacitances which help to cancel the charging current from link pins
increases the capacitances of lower insulator units of cause equal voltage drop
decreases the capacitances of upper insulators units to cause equal voltage drop
ANSWER : : forms capacitances which help to cancel the charging current from link pins
26.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?
4.5 m
6.4 m
7.0 m
5 m
ANSWER : : 6.4 m
27.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.
1.52 m
1.6 m
0.75 m
1.25 m
ANSWER : : 1.52 m
28.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?
1.42 x 10-9 s/km
3.25 x 10-8 s/km
4.8 x 10-9 s/krn
3.06 x 10-9 s/km
ANSWER : : 3.06 x 10-9 s/km
29.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
8.2 mHlkm
7.281 mHlkm
5.0 mHlkm
2 mHlkm
ANSWER : : 7.281 mHlkm
30.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?
79.50 m
54.94 m
60 m
51.4 m
ANSWER : : 54.94 m
31.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
5.36
4.1 m
3.9 m
3.01 m
ANSWER : : 5.36
32.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?
1.08 m
5.0 m
5.22 m
4.62 m
ANSWER : : 5.22 m
33.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
51.07 kVAr
51.70 kVAr
40.0 kVAr
60.5 kVAr
ANSWER : : 51.70 kVAr
34.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
9.74 x 10-9 F/km
4.87 x 10-9 F/km
3.05 x 10-9 F/km
None of these
ANSWER : : 4.87 x 10-9 F/km
35.For a 500 Hz frequency excitation, a 50 km, long power line will be modelled as
short line
medium line
long line
data insufficiency for decision
ANSWER : : long line
36.The charging current per kill of the line is
0.497 Amp
0.61 Amp
0.68 Amp
0.21 Amp
ANSWER : : 0.497 Amp
37.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.
10.Osec
1.92sec
4.5 sec
2.4 sec
ANSWER : : 1.92sec
38.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
average capacitance and inductance will increase
average capacitance will decrease and inductance will increase
average capacitance will increase and inductance will decrease
surge impedance loading of the line Increases
ANSWER : : average capacitance and inductance will increase
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?
1.19 kH/km
1.24 mH/km
2.38 mH/km
0.59 mH/km
ANSWER : : 1.19 kH/km
40.If in a short transmission line, resistance and inductance are found to be equal and regulation appear. to be zero, then the load will
have unity power factor
have zero power factor
be 0.707 lagging
be 0.707 lagging
ANSWER : : be 0.707 lagging
41.For a 500 Hz frequency excitation, a 50 km long power line will be modelled as
short line
medium line
long line
data isufficient decision
ANSWER : : long line
42.Bundled conductors are employed to
reduce the short circuit current
improve system stability
decreases system stability
increase the short circuit current
ANSWER : : decreases system stability
43.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
9.7 pF/m
10.2 pF/m
8.7 uF/km
2.4 uF/m
ANSWER : : 9.7 pF/m
44.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
0.43 ClIkm
0.65 0Jkm
0.70 O/km
0.79 nIkm
ANSWER : : 0.79 nIkm
45.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
< 80%
80%
90%
100%
ANSWER : : 80%
46.”Expanded ACSR” are conductors composed of
larger diameter individual strands for a given cross-section of the aluminium strangs
larger diameter of a central steel strands for a given overall diameter of the conductor
larger diamter of the aluminium strands only for a given overall diameter of the conductor
a fillter between the inner steel and the outer aluminium strands to increase the overall diameter of the conductor
ANSWER : : a fillter between the inner steel and the outer aluminium strands to increase the overall diameter of the conductor
47.A conductor is composed of seven identical copper .Iranu, each having a radius r. The self GMD of the conductors will be
2.177 r
2.645 r
2.141 r
1.21 r
ANSWER : : 2.177 r
48.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.
1.016 m
2.40 m
3.6 m
4.2 m
ANSWER : : 3.6 m
49.An RLC series. circuit remains predominantly inductive
at resonance frequency
below resonance frequency
above resonance frequency
at the lower half power frequency
ANSWER : : above resonance frequency
50.A voltage of 1000 kV is applied to an overhead line with its receiving end open. If the surge impedance of the line is 500 ohm, then the total surge power in the line ill
2000 MW
500 MW
2 MW
0.5 MW
ANSWER : : 2000 MW
51.A lossless radial tranemission line with surge impedance loading
takes negative VAr at sending end and zero VAr at receiving end
takes positive VAr at sending end and zero VAr at receiving end
has flat voltage profile and unity power factor at all points along it
has sending end voltage higher than receiving end voltage and unity power factor at sending end
ANSWER : : takes negative VAr at sending end and zero VAr at receiving end
52.The corona loss on a particular system at 50 Hz is 1 kw/phase per km. The corona loss on the same system with supply frequency 25 Hz will be
1 kW/phase/km
0.5 kW/phase/km
0.667 kW/phase/km
none of the above
ANSWER : : 0.667 kW/phase/km
53.A 60 Hz, 320 km loesless line has Bending end voltage 1.0 p.u, The receiving end voltage on no load is
1.1 p.u.
1.088 p.u.
1.116 p.u.
none of the above
ANSWER : : 1.088 p.u.
54.The order of the sub-harmonic during SSR for 50 Hz nornal frequency is
25 Hz
16 2/3 Hz
10 HZ
none of the above
ANSWER : : none of the above
55.Corona losses are minimized when
conductors size is reduced
smooth conductor is reduced
sharp points are provided in the line hardware
current density in conductors is reduced
ANSWER : : smooth conductor is reduced
56.The non-uniform distribution of voltage across the units in a string of suspention type insulators is due to
unequal self-capacitance of the units
non-uniform distance of separation of the units from the tower body
the existence of stray capacitance between the metallic junctions of the units and the tower body
non-uniform distance between the cross-arm and the units
ANSWER : : the existence of stray capacitance between the metallic junctions of the units and the tower body
57.For a long uncompensatedline the limit to the line loading ill governed by
thermal limit
voltage drop
stability limit
corona loss
ANSWER : : stability limit
58.The time taken for a surge to travel a 600 km long overhead transmission line is
6s
1s
0.02s
0.002s
ANSWER : : 0.002s
59.With 100 % series compensation of line.
the circuit is series resonant at power frequency
low transient voltage
high transient current
both (a) and (c)
ANSWER : : both (a) and (c)
60.The X:R ratio of 220 kV line as compared to 400 kV line is
greater
smaller
equal
it could be anything
ANSWER : : smaller
61.Whenever the conductors are dead-ended of there is a change in the direction of transmission line, the insulator. used are of the
pin type
suspension type
strain type
shackle type
ANSWER : : strain type
62.The main criterion for selection of the size of a distribution for a radial distribution system is
voltage drop
corona loss
temperature rise
capital cost
ANSWER : : voltage drop
63.The effect of series capacitance compensation is
to decrease the virtual surge impedance
to decrease the effective length of the line
to increase virtual surge impedance loading
all of the above
ANSWER : : all of the above
64.The low voltage winding of a 400/230 V, 1-phase, 50 Hz transformer is to be connected to a 25 Hz, the supply voltage should be
230 V
460 V
115 V
65 V
ANSWER : : 115 V
65.If an induction machine is run at above synchromous speed, it acts as
a synchronous motor
an indcution generator
an inductor motor
none of the above
ANSWER : : an indcution generator
65.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
increases
remains unchanged
decreases
uncertain
ANSWER : : decreases
66.For any fixed degree of inductive shunt compensation, additional series capacitive compensation
increase the effective length of line
increase virtual surge impedance line
decrease virtual surge impedance loading of the line
none of the above
ANSWER : : none of the above
67.For reducing tower footing resistance it is better to Use
chemical and ground rods only
chemical and counterpoise only
ground rod and counterpoise only
chemical, ground rods and counterpoise
ANSWER : : ground rod and counterpoise only
68.The function of the earth wire in an extra high voltage line is to
prevent earth fault
provide a safety measure for any high-flying object
provide a shield to the phase con-ductors from direct lightning stroke
provide mechanical strength to the towers
ANSWER : : provide a shield to the phase con-ductors from direct lightning stroke
69.A loss less line terminated with its surge impedance has
flat voltage profile
transmission line angle is greater than actual length of line
transmission line agnle is less than the actual length
both (a) and (b) above
ANSWER : : flat voltage profile
70.With 100 % inductive shunt compensation, the voltage profile is flat for
100 % loading of line
50 % loading of line
zero loading of line
none of the above
ANSWER : : zero loading of line
71.If a line is 100 % series compensated it may result into series resonance at power frequency of
50 Hz
150 Hz
100 Hz
none of the above
ANSWER : : 50 Hz
71.An alternator has a phase sequence of RYB for itB phase voltage. In case offield current is reversed, the phase sequence will become
RBY
RYB
YRB
none of these
ANSWER : : RYB
72.Pure inductive circuit takes power (reactive) from the a.c. line when
both applied voltage and current rise
both applied voltage anti current decrease
applied voltage decreases but current Increases
none of these
ANSWER : : both applied voltage anti current decrease
73.The insulation of modern EHV lines is designed based on
the lightning voltage
corona
radio interface
switching voltage
ANSWER : : switching voltage
74.With the help of a reactive compensator it is possible to have (u) constant voltage opei ation only
unity p.f. operation only
both constant voltage and unity p.f.
either constant voltage or unity p.f.
either constant voltage or unity p.f.
ANSWER : For a long uncompensated line the limit to the line loading is governed by
75.At a particular unbalanced node, the real powers specified are Leaving the node : 20 Mw, 25 Mw, Entering the node: 60 Mw, 30 MW. The balance power will be
30 MW leaving the node
45 MW leaving the node
45 MW entering the node
22.5MW entering the node and 22.5 MW leaving the node
ANSWER : : 45 MW leaving the node
76.A synchronous motor connected to an infinite bUB takes power at a lag p.f. If its excitation is increased
the terminal voltage increases
the load angle increases
the p.f. of motor increases
all of the above
ANSWER : : the p.f. of motor increases
77.An alternator has a phase sequence of RYB for its phase voltage. In case the direetior of rotation of alternator is reversed, the phase sequence will become
RBY
RYB
YRB
none of these
ANSWER : s: a
78.When a d.c source is switched is purely inductive, the current response is
an exponentially rising curve
an exponentially decaying curve
a straight line passing through the origin
a straight line off-set from the origin
ANSWER : : a straight line passing through the origin
79.In case ora 3 phase short circuit in a system the power fed into the system is
mostly reactive
mostly active
active and reactive both equal
reactive only
ANSWER : : mostly reactive
80.In a 3-core extra-high voltage cable, a metallic screen around each core�i,..ulation i. provided to
facilitate heat dissipation
give mechanical strength
obtain radial electric stress
obtain longtiudinal electric stress
ANSWER : : obtain radial electric stress
81.Corona loss can be reduced by the use of hollow conductors because
the current density is reduced
the eddy current in the conductor is eliminated
for a given cross-section, the radius of the conductor is increased
of better ventilation in the conductor
ANSWER : : of better ventilation in the conductor
82.Series capacitive compensation on EHV transmission lines is used to
reduce the line loading
improve the stability of the system
reduce the voltage profile
improve the protection of the line
ANSWER : : improve the protection of the line
83.The transmission line feeding power on either side of the main transmission line i. called
Secondary distribution
Secondary transmission
Primary transmission
Primary distribution
ANSWER : : Secondary transmission
84.A square matrix is called singular if its
determina is unity
determinant is zero
determinant is infinity
rank is unity
ANSWER : : determinant is zero
85.Shunt conapenBation in an EHV line is “Bed
improve stability
reduce fault level
improve the voltage profile
subsitute for synchronous phase modifier
ANSWER : : subsitute for synchronous phase modifier
86.Gauss-Seidel iterative method can be used for solving a set of
linear differential equations only
linear algebraic equation only
both linear and nonlinear algebraic equations
both linear and nonlinear differential equations
ANSWER : : linear algebraic equation only
87.A star-conneted 440 V, 50 Hz alternator has per phase synchronous reactance of 10 n. It supplies a bal anced capacitive load current of 20 A, as shown in per phase equivalent circuit of the given figure. It is desirable to have zero voltage regulation. The load power factor should be
0.82
0.47
0.39
0.92
ANSWER : s: a
88.The voltage of CI generator and an infinite bus are given as O.92LIO 0 and 1.0L’O 0 respectively. The active power will flow from
generator to infinite bus
infinite bus to generator
the data is insufficient to judge
none of the above
ANSWER : s: a
89.If transformer frequency is changed from 60 Hz, to 60 Hz the ratio of eddy current loss 60 Hz to 50 Hz, at constant voltage will be
5/6
25/36
6/5
1.0
ANSWER : : 1.0
90.The aingle pbase line of 280 V and 3 pha.e line of 400 V which feed different domestic circuit. and induetrial loade represent
primary distribution
secondary distribution
secondary transmission
none of the above
ANSWER : : secondary distribution
91.In load flow analysis, the load connected at a bUs is represented as
constant current drawn from the bus
constant impedance connected at the bus
voltage and frequency dependent source at the bus
constant real and reactive drawn from the bus
ANSWER : : constant real and reactive drawn from the bus
92.A 10k VA, 400 V/200 V single phase transformer with 10 % impedance draws a steady short circuit line current of
50 A
150 A
250 A
350 A
ANSWER : : 150 A
93.For a transmission line with negligible losses, the lagging reactive power (VAR) delivered at Ihe receiving end, for a given receiving end voltage, is directly proportional to the
square of the line voltage drop
line voltage drop
line inductive reactance
line capacitive reactance
ANSWER : : line voltage drop
94.The percentage resistance and percentage reactance of a 10 kVA, 400 V/200 V, 3-phase transformer are 2% and 10% respectively. If the constant losses in the machine are 1 %, the maximum possible percentage efficiency of the transformer is
98.32
97.25
96.85
96.12
ANSWER : : 96.85
95.A synchronous generator connected to an infinite bUB delivers power at a lag p.r. If its excitation is increased
the terminal voltage increases
voltage angle 8 increases
current delivered increases
all of the above
ANSWER : : current delivered increases
96.A 100 kVA transformer has 4% impedance and 50 k VA transformer has 3% impedance when they are operated in parallel, which 6 transformer will reacb full load first
3%
4%
data is insufficient
none of the above
ANSWER : : 3%