Power Systems

Power Systems

Power Systems
| Power Systems |
Q.1
A 3-phase transformer rated for 33 kV/11 kV is connected in delta/star as shown in figure. The current transformers (CTs) on low and high voltage sides have a ratio of 500/5. Find the currents i1 and i2, if the fault current is 300A as shown in figure.
 
A.
B.
C.
D.
Answer : Option A
Explaination / Solution:




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Q.2
A nuclear power station of 500 MW capacity is located at 300 km away from a load center. Select the most suitable power evacuation transmission configuration among the following options
A.
B.
C.
D.
Answer : Option A
Explaination / Solution:
No Explaination.


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Q.3
A negative sequence relay is commonly used to protect
A. an alternator
B. an transformer
C. a transmission line
D. a bus bar
Answer : Option A
Explaination / Solution:
No Explaination.


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Q.4
For enhancing the power transmission in along EHV transmission line, the most preferred method is to connect a
A. Series inductive compensator in the line
B. Shunt inductive compensator at the receiving end
C. Series capacitive compensator in the line
D. Shunt capacitive compensator at the sending end
Answer : Option C
Explaination / Solution:



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Q.5
A load center of 120MW derives power from two power stations connected by 220kV transmission lines of 25km and 75km as shown in the figure below. The three generators G1,G2 and G3 are of 100MW capacity each and have identical fuel cost characteristics. The minimum loss generation schedule for supplying the 120 MW load is

A.
B.
C.
D.
Answer : Option A
Explaination / Solution:

Loss α p; Loss α length 
For checking all options only option A gives less losses. 

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Q.6
In a 100 bus power system, there are 10 generators. In a particular iteration of Newton Raphson load flow technique (in polar coordinates), two of the PV buses are converted to PQ type. In this iteration,
A. the number of unknown voltage angles increases by two and the number of unknown voltage magnitudes increases by two.
B. the number of unknown voltage angles remains unchanged and the number of unknown voltage magnitudes increases by two.
C. the number of unknown voltage angles increases by two and the number of unknown voltage magnitudes decreases by two.
D. the number of unknown voltage angles remains unchanged and the number of unknown voltage magnitudes decreases by two.
Answer : Option A
Explaination / Solution:



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Q.7
If the star side of the star-delta transformer shown in the figure is excited by a negative sequence voltage, then

A.  VAB leads Vab by 60º
B. VAB lags Vab by 60º 
C. VAB leads Vab by 30º
D. VAB lags Vab by 30º
Answer : Option D
Explaination / Solution:



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Q.8
Two generator units G1 and G2 are connected by 15 kV line with a bus at the mid-point as shown below.

G1 = 250 MVA, 15kV, positive sequence reactance X = 25% on its own base
G2 = 100 MVA, 15kV, positive sequence reactance X = 10 % on its own base
L1 and L2 = 10km, positive sequence reactance X = 0.225 Ω / km
For the above system, the positive sequence diagram with the p.u values on the MVA common base is
A.
B.
C.
D.
Answer : Option A
Explaination / Solution:



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Q.9
Two generator units G1 and G2 are connected by 15 kV line with a bus at the mid-point as shown below.

G1 = 250 MVA, 15kV, positive sequence reactance X = 25% on its own base
G2 = 100 MVA, 15kV, positive sequence reactance X = 10 % on its own base
L1 and L2 = 10km, positive sequence reactance X = 0.225 Ω / km
In the above system, the three-phase fault MVA at the bus 3 is
A. 82.55MVA
B. 85.11MVA
C. 170.91MVA
D. 181.82MVA
Answer : Option A
Explaination / Solution:



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Q.10
A solar energy installation utilize a three – phase bridge converter to feed energy into power system through a transformer of 400V/400 V, as shown below.

The energy is collected in a bank of 400 V battery and is connected to converter through a large filter choke of resistance 10Ω.
The maximum current through the battery will be
A. 14 A
B. 40 A
C. 80 A
D. 94 A
Answer : Option A
Explaination / Solution:



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