Advanced Power System
Advanced Power System
Advanced Power System
52. A 50 MVA, 11kV three-phase alternator was subjected to different types of faults. The
faults current are as under: 3-phase fault- 2000A; line-to-line fault= 2600A; line-to-ground
fault= 4200A
The generator neutral is solidly grounded. Find the values of the three sequence reactance’s
of the alternator. Ignore resistances.
e) 3.175Ω, 4.121Ω,4.42Ω
f) 1.056Ω, 5.215Ω,1.235Ω
g) .305Ω,1.456Ω,3.445Ω
h) 3.175Ω, 1.056Ω,.305Ω
Problem 53-54
53. A 3-phase, 11kV, 25MVA generator with X₀=0.05p.u., X₁=0.2p.u.,and X₂=0.2 p.u. is
grounded through a reactance of 0.3Ω. Calculate the fault current for a single line to ground
fault.
a) 6188A
b) 5278A
c) 3613A
d) 7543A
60. The voltage control equipment is used at ……………………. in the power system.
e) one point
f) more than one point
g) no point
h) other point
Problem 61-62
61. The excitation control method is suitable only for …………………. lines.
a) long
b) very long
c) very short
d) Short
62. Induction regulators are used for voltage control in ……………… system.
e) main distribution
f) primary distribution
g) secondary distribution
h) lower distribution
Problem 63-64
63. The principal cause of voltage variation is the change of ……………… on the system.
a) current
b) voltage
c) load
d) Resistance
64. In a 3-phase, 4-wire, 400/230V system, a lamp of 100 watts is connected to one phase
and neutral and a lamp of 150 watts is connected to second phase and neutral. If the neutral
wire is disconnected accidentally, what will be the voltage across each lamp?
e) 240, 160 V
f) 350, 120 V
g) 312, 413 V
h) 245, 213 V
Problem 65-66
65. Calculate the voltage at a distance of 200 m of a 300m long distributor uniformly loaded
at the rate of 0.75 A per meter. The distributor is fed at one end at 250V. The resistance of the
distributor (go and return) per meter is 0.00018Ω. Aso find the power loss in the distributor.
a) 345.2V, 687.23W
b) 244.6V, 911.25W
c) 352.4V, 834.43W
d) 432.56V, 524.54W
66. A uniform 2-wire d.c. distributor 500 meters long is loaded with 0.4 ampere/meter and is
fed at one end. If the maximum permissible voltage drop is not exceed 10V, find the cross-
sectional area of the distributor conductor. Take p=1.7x10⁻¹⁰Ω cm.
e) 2.5cm²
f) 1.1cm²
g) 1.7cm²
h) 3.1cm²
Problem 67-68
67. Two tram cars (A&B) 2km and 6km away from sub-station return 40A and 20A repectively
to the rails. The sub-station voltage is 600V d.c. The resistance of trolley wire is 0.25Ω/km and
that of track is 0.03Ω/km. Calculate the voltage across each tram car.
a) 544.4, 300 V
b) 544, 275 V
c) 566.4, 234V
d) 544, 566.4 V
68. In a 500/250v d.c. 3-wire system, there is current of 1200A on the positive side and 1000A
on the negative side and a motor load of 200kW across the outers. The loss in each balancer
machine is 5kW. Calculate current of the main generator.
e) 1520A
f) 5424A
g) 3245A
h) 2144A
Problem 69-70
69. Refer to problem 68; calculate the load on each balancer machine.
a) 20,50 kW
b) 40,60 kW
c) 20,30 kW
d) 50,100 kW
70. The balancer machine connected to the heavily loaded side work as a ………….
e) generator
f) transformer
g) motor
h) corrector factor
Problem 71-72
71. In a 3-wire system, the area of X-section of neutral is generally …………… of
either outer.
a) half
b) triple
c) single
d) Small
74. In a balanced 3-wire d.c system, if voltages across the outers is 500V , then voltage
between any outer and neutral is …………….
e) 230V
f) 240V
g) 250V
h) 260V
Problem 75-76
75. The voltage drop in a doubly fed distributor is ………………. than the equivalent singly fed
distributor.
a) more
b) less
c) greater
d) Smaller
76. A load supplied on 3-wire d.c. system takes a current of 50A on the positive side and 40A
on the negative side. The resistance of each outer wire is 0.1Ω and the cross section of
middle wire is one-half of that of outer. If the system is supplied at 500/250V, find the voltage
at the load between each outer and middle wire.
e) 243, 248 V
f) 342, 452 V
g) 324, 523 V
h) 231, 142 V
Problem 77-78
77. A d.c. 3-wire system with 500V between outer has lighting loads of 150kW on the positive
side and 100kW on the negative side. The loss in each balancer machine is 3kW. Calculate the
total load on the main generator.
a) 245kW
b) 642kW
c) 122kW
d) 256kW
78. Refer to the problem 77; calculate the kW loading of each balancer machine.
e) 22, 28 kW
f) 45, 23kW
g) 52,89 kW
h) 14,65 kW
Problem 79-80
79. A 2-wire system has the voltage at the supply end maintained at 500V. The line is 3km
long. If the full load is 120A, what must be the booster voltage in order that the far end
voltage may also be 500V? Take the resistance of the cable at the working temperature as
0.5Ω/km.
a) 250V
b) 160V
c) 180V
d) 360V
80. Refer to problem 79; what must be the booster output in order that the far end voltage
may also be 500V?
e) 24.6kW
f) 21.6kW
g) 23.6kW
h) 27.1kW
Problem 81-82
81…………………….. cannot protect the equipment from the travelling waves reaching the
equipment.
a) lighting arrester
b) ground wires
c) circuit breaker
d) magnetic relay
82. The ………………… lightning strokes are very rare on the power system.
e) direct
f) fast
g) slow
h) indirect
Problem 83-84
83. Most of the lightning’s strokes are due to …………………. charged clouds.
a) negatively
b) positively
c) lightning
d) clouds
84. The section bus bars A and Bare linked by a bus bar reactor rated at 5000kVA with 10%
reactance. On bus bar A, there are two generators each of 10,000kVA with 10% reactance on
B two generators each of 8000kVA with 12% reactance. Find the steady MVA fed into a dead
short circuit between all phases on B with bus bar reactor in the circuit.
e) 162.43
f) 651.456
g) 232.12
h) 173.31
Problem 85-86
85. A 3-phase,20 MVA, 10kV alternator has internal reactance of 5% and negligible resistance.
Find the external reactance per phase to be connected in series with the alternator so that
steady current on short circuit does not exceed 8 times full load current.
a) .431Ω
b) .375Ω
c) .521Ω
d) .652Ω
86. A 20,000 kVA transformer with 10% reactance will have a reactance of …………….. at
10,000 kVA base.
e) 4%
f) 5%
g) 6%
h) 7%
Problem 87-88
87. The use of reactors permits installation of circuit breakers of ……………… ratings.
a) fair
b) higher
c) lower
d) Good
88. If the % age reactance of the system up to the fault point Is 20% and the base kVA is a
10,000, then short-circuited kVA is ……………..
e) 50,000
f) 30,000
g) 20,000
h) 10,000
Problem 89-90
89. Percentage reactance’s ………………. as they are referred through transformers.
a) remain unchanged
b) are changed
c) sometimes changed
d) not at all
94. The ................... short circuit faults give very heavy duty on the circuit breaker.
e) Single phase
f) Two phase
g) Three-phase
h) Polyphase
Problem 95-96
95. Cross jet explosion pot breaker can interrupt ................... short circuit currents
efficiently.
a) Heavy
b) Low
c) Moderate
d) Fair
96. In low oil circuit breakers, ....................... is used for insulation purposes.
e) Solid material
f) Liquid material
g) Oil material
h) Plasma
Problem 97-98
97. Current choppimg mainly occurs in ........................ circuit breakers.
a) Oil blast
b) Air blast
c) Open blast
d) Short blast