Electrical Machines (Test 2)

Gate Exam : Ee Electrical Engineering

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Electrical Machines

Electrical Machines
| Electrical Machines |
Q.1
A two-phase load draws the following phase currents:   These currents are balanced if ϕ1 is equal to
A.
B.
C.
D.
Answer : Option D
Explaination / Solution:



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Q.2
The slip of an induction motor normally does not depend on
A. rotor speed
B. synchronous speed
C. shaft torque
D. core-loss component
Answer : Option D
Explaination / Solution:



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Q.3
The direction of rotation of a single-phase capacitor run induction motor is reversed by
A. interchanging the terminals of the AC supply.
B. interchanging the terminals of the capacitor.
C. interchanging the terminals of the auxiliary winding.
D. interchanging the terminals of both the windings.
Answer : Option C
Explaination / Solution:
No Explaination.


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Q.4
Three single-phase transformers are connected to form a delta-star three-phase transformer of 110 kV/ 11 kV. The transformer supplies at 11 kV a load of 8 MW at 0.8 p.f. lagging to a nearby plant. Neglect the transformer losses. The ratio of phase currents in delta side to star side is
A. 1 : 10√3
B. 10√3 : 1
C. 1 : 10
D. √3 :10
Answer : Option A
Explaination / Solution:



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Q.5
A 220 V, 15 kW, 1000 rpm shunt motor with armature resistance of 0.25 Ω has a rated line current of 68 A and a rated field current of 2.2 A. The change in field flux required to obtain a speed of 1600 rpm while drawing a line current of 52.8 A and a field current of 1.8 A is
A. 18.18 % increase
B. 18.18 % decrease
C. 36.36 % increase
D. 36.36 % decrease
Answer : Option D
Explaination / Solution:



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Q.6
The locked rotor current in a 3-phase, star connected 15 kW, 4-pole, 230 V, 50 Hz induction motor at rated conditions is 50 A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor is connected to a 236 V, 57 Hz supply is
A. 58.5 A
B. 45.0 A
C. 45.7 A
D. 55.6 A
Answer : Option B
Explaination / Solution:



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Q.7
A 4 pole induction machine is working as an induction generator. The generator supply frequency is 60 Hz. The rotor current frequency is 5 Hz. The mechanical speed of the rotor in RPM is
A. 1350
B. 1650
C. 1950
D. 2250
Answer : Option C
Explaination / Solution:



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Q.8
Leakage flux in an induction motor is
A. flux that leaks through the machine
B. flux that links both stator and rotor windings
C. flux that links none of the windings
D. flux that links the stator winding or the rotor winding but not both
Answer : Option D
Explaination / Solution:
No Explaination.


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Q.9
The angle δ in the swing equation of a synchronous generator is the
A. angle between stator voltage and current
B. angular displacement of the rotor with respect to the stator
C. angular displacement of the stator mmf with respect to a synchronously rotating axis.
D. angular displacement of an axis fixed to the rotor with respect to a synchronously rotating axis.
Answer : Option D
Explaination / Solution:
No Explaination.


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Q.10
A single-phase transformer has no-load loss of 64 W, as obtained from an open circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both LV and HV windings, he measured loss is 81 W. The transformer has maximum efficiency when operated at
A. 50.0% of the rated current.
B. 64.0% of the rated current.
C. 80.0% of the rated current.
D. 88.8% of the rated current.
Answer : Option C
Explaination / Solution:
No Explaination.


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EE Electrical Engineering