Electrical Engineering - Power System
Exam Duration: 45 Mins Total Questions : 30
A power station's plant load factor is defined as the rate of
- (a)
the energy generated to that of maximum energy that could have been generated
- (b)
average load to peak load
- (c)
maximum load to peak load
- (d)
minimum load to average load
In hydropower stations. what is an enlarged body of water just above the intake and used as a regulating reservoir?
- (a)
Spill ways
- (b)
Forebay
- (c)
Reservoir
- (d)
Penstock
The most appropriate operating speeds in rpm of generator used in thermal, nuclear and hydro power plants would be
- (a)
3000, 300 and 1500
- (b)
3000, 3000 and 300
- (c)
1500, 1500 and 3000
- (d)
1000, 900 and 750
A thermal power plant has installed capacity of 15000 MW. The annual load factor is 60% and capacity factor is 50%. The reverse capacity of the plant will be
- (a)
30.62%
- (b)
36.67%
- (c)
35.49%
- (d)
None of these
A single-phase 2 wire system supplies a load of 1000 kW. The voltage between the conductors is 11000 V. Return wire is earthed. Now, a third wire is added in the system and supply made is 3 phase. For same power factor the transmitted power will be
- (a)
1500 kW
- (b)
3000 kW
- (c)
2450 kW
- (d)
3100 kW
A load of (15 + j 10) MVA is supplied with power from the busbars of a power plant via a 3-phase, 110 kV line, 100 km long. The transmission line is represented by \(\pi \)model. It has the following parameters:
R = 26.4\(\Omega \), X = 33.9\(\Omega \), B = \(\omega \)C=219\(\times\)10-9 mho
The bus bar voltage is V1=116 kV
The power consumed from power plant is
- (a)
25.85 MW
- (b)
23.85 MW
- (c)
(15.66+j8.19) MVA
- (d)
None of these
Buses for load flow studies are classified as (I) the load bus, (II) the generator bus and (Ill) the slack bus. The correct combination of the pair of quantities specified having their usual meaning for different buses is
- (a)
Load bus Generator bus Slack bus P, |V| P, Q P, \(\delta \) - (b)
Load bus Generator bus Slack bus P, Q P, |V| |V|, \(\delta \) - (c)
Load bus Generator bus Slack bus |V|, Q P, \(\delta \) P, Q - (d)
Load bus Generator bus Slack bus P, \(\delta \) Q, |V| Q, \(\delta \)
In the network as shown in figure the marked parameters are per unit impedances. The bus admittance matrix of the network is
- (a)
\(\begin{bmatrix} 10 & -5 \\ -5 & 5 \end{bmatrix}\)
- (b)
\(\begin{bmatrix} 5 & -5 \\ -5 & 10 \end{bmatrix}\)
- (c)
\(\begin{bmatrix} -10 & 5 \\ 5 & -5 \end{bmatrix}\)
- (d)
\(\begin{bmatrix} -5 & 5 \\ 5 & -10 \end{bmatrix}\)
Zero sequence currents can flow from a line into a transformer ank, if the windungs are in
- (a)
grounded star/delta
- (b)
delta/star
- (c)
star/grounded star
- (d)
delta/delta
A round rotor generator with internal voltage E1 = 2.0 pu and X = 1.1 pu is connected to a round rotor synchronous motor with internal voltage E = 1.3 pu and X=1.2 pu. The reactance of the line connecting the generator to the motor is 0.5 pu. When the generator supplies 0.5 pu power, the rotor angle difference between the machines will be
- (a)
\({ 57.42 }^{ \circ }\)
- (b)
\({ 1 }^{ \circ }\)
- (c)
\({ 32.58 }^{ \circ }\)
- (d)
\({122.58 }^{ \circ }\)
At an industrial sub-station with a 4MW load, a capacitor of 2 MVAR is installed to maintain the load power factor at 0.97 lagging. If the capacitor goes out of service, the load power factor becomes
- (a)
0.85 lag
- (b)
1.00 lag
- (c)
0.80 lag
- (d)
0.90 lag
Consider a power system with three identical generators. The transmission losses are negligible. One generator (G1) has a speed governor which maintains its speed constant at the rated value, while the other generators (G2 and G3) have governors with a drop of 5%. If the load of the system is increased, then in steady state
- (a)
generation of G2 and G3 is increased equally while generation of G1 is unchanged
- (b)
generation of G1 alone is increased while generation of G2 and G3 is unchanged
- (c)
generation of G1, G2 and G3 is increased equally
- (d)
generation of G1, G2 and G3 is increased in the ratio 0.5: 0.25: 0.25
A single-phase overhead line consists of two conductors of radius 1 cm each. Also, spacing between conductor is 1.25 m and frequency is 50 Hz. Then, reactance per km will be
- (a)
\(0.64 \ \Omega /km\)
- (b)
\(0.64 \ k\Omega /m\)
- (c)
\(0.7 \ \Omega /m\)
- (d)
Data is insufficient
When a fixed amount of power is to be transmitted, the efficiency of transmission increases when
- (a)
voltage decreases, power factor remains constant
- (b)
voltage increases, power factor increases
- (c)
voltage decreases, power factor decreases
- (d)
voltage constant, power factor decreases
A 30 MVA, 11 kV, 3-phase alternator has \({ X }_{ d }^{ '' }\) = 0.25pu, Z2 =0.35 pu, Zo =0.1 pu. Its neutral is solidly grounded. A single line to ground fault occurs at the terminals of the alternator. The fault current will be
- (a)
-j 1575 A
- (b)
- j 3150 A
- (c)
-j 6755 A
- (d)
-j 4725 A
A round rotor generator with internal voltage E1 = 2.0pu and X = 1.1pu is connected to a round rotor synchronous motor with internal voltage E2 = 1.3pu and X = 1.2pu The reactance of the line connecting generator to the motor is 0.5 pu when the generator supplies 0.5 pu power, the rotor angle difference between the machines will be
- (a)
\({ 57.42 }^{ \circ }\)
- (b)
\({ 1 }^{ \circ }\)
- (c)
\({ 32.58 }^{ \circ }\)
- (d)
\({ 122.58 }^{ \circ }\)
An alternator having an induced emf of 2.4 pu is connected to an infinite bus of 1 pu. If the bus bar has reactance of 0.3 pu and alternate has reactance of 0.3 pu, the maximum power that can be transferred is given by
- (a)
6 pu
- (b)
7.67 pu
- (c)
2 pu
- (d)
4 pu
The distribution system shown in figure is to be protected by over current system of protection.
For proper fault discrimination directional over current relays will be required at location
- (a)
1 and 4
- (b)
2 and 3
- (c)
1, 4 and 3
- (d)
2, 3 and 5
A 50 MVA, 132/33 kV star/delta bulk supply transformer protected by merz price scheme has 1 A secondary CT rating. Then, the CT ratio of primary side will be
- (a)
1:378.78
- (b)
126.41:1
- (c)
378.78:1
- (d)
218.69:1
Choose two appropriate auxiliary components of a HVDC transmission system from the following:
P. DC line inductor
Q. AC line inductor
R. Reactive power sources
S. Distance relays on DC line
T. Series capacitance of AC line
- (a)
P and Q
- (b)
P and R
- (c)
Q and S
- (d)
S and T
The transmission line distance protection relay having the property of being inherently directional is
- (a)
impedance relay
- (b)
mho relay
- (c)
ohm relay
- (d)
reactance relay
A 220 kV, 20 km long, 3-phase transmission line has the following A, B, C, D constants:
\(A\ =\ D\ =\ 0.96\ \angle { 3 }^{ \circ }\)
\(B\ =\ 50\angle { 65 }^{ \circ }\Omega /phase\)
\(C\ =\ 0.5\ E\ -\ 04\ \angle { 80 }^{ \circ }S/phase\)
Its charging current per phase is
- (a)
\(\frac { 11 }{ \sqrt { 3 } } A\)
- (b)
11 A
- (c)
220 A
- (d)
\(\frac { 220 }{ \sqrt { 3 } } A\)
An industrial consumer has a daily load pattern of 2000 kW, 0.8 lag for 12 h and 1000 kW up f for 12 h. The load factor is
- (a)
0.5
- (b)
0.75
- (c)
0.6
- (d)
2.0
The incremental cost characteristics of two generators delivering 200 MW are as follows:
\(\frac { { dF }_{ 1 } }{ { d }P_{ 1 } } =2.0+0.01{ P }_{ 1 },\ \frac { { dF }_{ 2 } }{ { d }P_{ 2 } } =1.6+0.02\ P_{ 2 }\)
For economic operation, the generators P1 and P2 should be
- (a)
P1 = P2 = 100 MW
- (b)
P1 = 80 MW, P2 = 120 MW
- (c)
P1 = 200 MW, P2 = 0
- (d)
P1 = 120 MW, P2 = 80 MW
A surge of 20 kV magnitude travels along a lossless cable towards its junction with two identical lossless overhead transmission lines. The inductance and the capacitance of the cable are 0.4 mH and 0.5 j.1FIkm.The inductance and capacitance of the overhead transmission lines are 1.5 mH and 0.015 j.1F/km.The magnitude of the voltage at the junction due to surge is
- (a)
36.72 kV
- (b)
18.36 kV
- (c)
6.07 kV
- (d)
33.93 kV
A 50Hz, 4-pole, 500 MVA, 22 kV turbo-generator is delivering rated megavolt-amperes at 0.8 power factor. Suddenly a fault occurs reducing is electric power output input to the shaft. The accelerating torque in the generator in MN-m at the time of the fault will be
- (a)
1.528
- (b)
1.018
- (c)
0.848
- (d)
0.509
A generator feeds power to an infinite bus through a double circuit transmission line. A three-phase fault occurs at the middle point of one of the lines. The infinite bus voltage is 1 pu, the transient internal voltage of the generator is 1.1 pu and the equivalent transfer admittance during fault is 0.8 pu. The 100 MVA generator has an inertia constant of 5 MJ/MVA and it delivering 1.0 pu power prior of the fault with rotor power angle of \({ 30 }^{ \circ }\). The system frequency is 50 Hz. The initial accelerating power (in pu) will be
- (a)
1.0
- (b)
0.6
- (c)
0.56
- (d)
0.4
A generator feeds power to an infinite bus through a double circuit transmission line. A three-phase fault occurs at the middle point of one of the lines. The infinite bus voltage is 1 pu, the transient internal voltage of the generator is 1.1 pu and the equivalent transfer admittance during fault is 0.8 pu. The 100 MVA generator has an inertia constant of 5 MJ/MVA and it delivering 1.0 pu power prior of the fault with rotor power angle of \({ 30 }^{ \circ }\). The system frequency is 50 Hz. If the initial accelerating power is X pu, the initial acceleration in elec. deg/s2 and the inertia constant in MJ-s/elec. degree respectively will be
- (a)
31.4 X and 18
- (b)
18010 X and 0.056
- (c)
X/1800 and 0.056
- (d)
X/31.4 and 18
The network shown in figure has impedances in per unit as indicated. The diagonal element Y22 of the bus admittance matrix Ybus of the network is
- (a)
-j 19.8
- (b)
+j 20.0
- (c)
+j0.2
- (d)
-j 19.95
Consider a synchronous generator connected to an infinite bus by two identical parallel transmission lines. The transient reactance X of the generator is 0.1 pu and the mechanical power input to it is constant at 1.0 pu. Due to some previous disturbance, the rotor angle (\(\delta \)) is undergoing an undamped oscillation, with the maximum value of \(\delta \)(t) equal of 130°. One of the parallel line trips due to relay maloperation at an instant when \(\delta \)(t) =130° as shown in the figure. The maximum value of the per unit line reactance X, such that the system does not lose synchronism subsequent to this tripping is
- (a)
0.87
- (b)
0.74
- (c)
0.67
- (d)
0.54
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