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Electrical Machines
φA 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 speed when running as a motor taking 40 A at 250 V. Armature reaction weakens the field by 4%.
940 RPM
920 RPM
960 RPM
970 RPM
940 RPM
920 RPM
960 RPM
970 RPM
Answer
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What is the speed of stator rotating magnetic field with respect to rotor rotating magnetic field?
None of these
Zero
Synchronous speed
Slip speed
None of these
Zero
Synchronous speed
Slip speed
Answer
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Electrical Machines
The demagnetising component of armature reaction in a DC generator
results in sparking trouble.
increases armature speed.
reduces generator emf.
reduces inter poles flux density.
results in sparking trouble.
increases armature speed.
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reduces inter poles flux density.
Answer
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Electrical Machines
Which of the following methods of speed control is not affected through stator side?
Change of supply voltage.
Change of number of pole.
Change of supply frequency.
Change of rotor resistance.
Change of supply voltage.
Change of number of pole.
Change of supply frequency.
Change of rotor resistance.
Answer
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Electrical Machines
When maximum flux density is constant, the eddy current losses are proportional to
f2
V
f
V2
f2
V
f
V2
Answer
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Electrical Machines
The slight curvature at the lower end of the OCC of a self excited DC generator is due to
high speed.
high field resistance.
residual flux.
magnetic inertia.
high speed.
high field resistance.
residual flux.
magnetic inertia.
Answer
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