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Electrical Machines
A DC shunt machine generates 250 V on open circuit at 1000 RPM. Armature resistance is 0.5 Ω, field resistance 250 Ω. When running as a motor takes 4 A at 250 V. Calculate the efficiency when running as a motor taking 40 A at 250 V. Armature reaction weakens the field by 4%.
72.5%
67.5%
78.5%
82.5%
72.5%
67.5%
78.5%
82.5%
Answer
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Related Question
Electrical Machines
In a 3-phase induction motor, torque and supply voltage are related as
T ∝ 1/V
T ∝ 1/V²
T∝ V²
T ∝ V
T ∝ 1/V
T ∝ 1/V²
T∝ V²
T ∝ V
Answer
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Electrical Machines
Slip test is performed to determine
All of these
slip
direct axis reactance and quadrature axis reactance
positive sequence reactance and negative sequence reactance
All of these
slip
direct axis reactance and quadrature axis reactance
positive sequence reactance and negative sequence reactance
Answer
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Electrical Machines
Which of the following alternators contain large number of poles?
Aame in both alternators.
Turbo alternators.
Hydro alternators.
None of these
Aame in both alternators.
Turbo alternators.
Hydro alternators.
None of these
Answer
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Electrical Machines
A 400 V, 50 Hz, 30 Hp, three phase IM is drawing 50 A current at 0.8 p.f lagging. The stator and rotor copper losses are 1.5 KW and 900 W respectively. The friction and windage losses are 1050 W and core losses are 1200 W. The air gap power of the motor will be
26.21 kW.
24.11 kW.
25 kW.
23.06 kW.
26.21 kW.
24.11 kW.
25 kW.
23.06 kW.
Answer
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Electrical Machines
DC motors are stopped by opening line switches and not by forcing the handle of the motor starter back to OFF position. This is due to occurance of
None of these.
Both of above.
Heavy sparking at the first stud of starting resistance steps.
Heavy sparking at brushes.
None of these.
Both of above.
Heavy sparking at the first stud of starting resistance steps.
Heavy sparking at brushes.
Answer
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