The counter (or back) emf in a dc machine is 1. the same as generated emf in a dc motor 2. proportional to field flux and armature speed 3. not the same as generated emf in a dc motor 4.inversely proportional to field flux 5. proportional to number of armature conductors 6. constant from no load to full load From these, the correct answer is

Electrical Machines
The counter (or back) emf in a dc machine is 1. the same as generated emf in a dc motor 2. proportional to field flux and armature speed 3. not the same as generated emf in a dc motor 4.inversely proportional to field flux 5. proportional to number of armature conductors 6. constant from no load to full load From these, the correct answer is

1, 2, 5

2, 4, 5, 6

3, 4, 5

2, 3, 6

1, 2, 5

2, 4, 5, 6

3, 4, 5

2, 3, 6

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Electrical Machines
In a DC machine, for the same value of Ãâ€ , Z and N; which one of the following statements is correct?

Armature emf is less with wave winding than with lap winding.

Armature emf depends on weather the machine is running as a motor or generator.

Armature emf is same as long as the flux density in the air gap remains the same.

Armature emf is more with wave winding than with lap winding.

Armature emf is less with wave winding than with lap winding.

Armature emf depends on weather the machine is running as a motor or generator.

Armature emf is same as long as the flux density in the air gap remains the same.

Armature emf is more with wave winding than with lap winding.

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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%.

82.5%

67.5%

78.5%

72.5%

82.5%

67.5%

78.5%

72.5%

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Electrical Machines
Which DC motor will have least percentage increase of input current, for the same percentage increase in the torque

Compound Wound DC Motor

DC Series Motor

DC Shunt Motor

Separately Excited DC Motor

Compound Wound DC Motor

DC Series Motor

DC Shunt Motor

Separately Excited DC Motor

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Electrical Machines
Swinburne test is conducted under which of the following condition?

any of the above

no load

full load

half load

any of the above

no load

full load

half load

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Electrical Machines
Considering a galvanometer is connected to the rotor of a 3 - ÃŽÂ¦, 4 pole, 50 Hz IM and is making 130 oscillations in a minute, then calculate the rotor speed?

1435.

1500.

1450.

1440.

1435.

1500.

1450.

1440.

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Electrical Machines

Electrical Machines In a DC machine, for the same value of Ãâ€ , Z and N; which one of the following statements is correct?

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%.

Electrical Machines Which DC motor will have least percentage increase of input current, for the same percentage increase in the torque

Electrical Machines Swinburne test is conducted under which of the following condition?

Electrical Machines Considering a galvanometer is connected to the rotor of a 3 - ÃŽÂ¦, 4 pole, 50 Hz IM and is making 130 oscillations in a minute, then calculate the rotor speed?

Electrical Machines
In a DC machine, for the same value of Ãâ€ , Z and N; which one of the following statements is correct?

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%.

Electrical Machines
Which DC motor will have least percentage increase of input current, for the same percentage increase in the torque

Electrical Machines
Swinburne test is conducted under which of the following condition?

Electrical Machines
Considering a galvanometer is connected to the rotor of a 3 - ÃŽÂ¦, 4 pole, 50 Hz IM and is making 130 oscillations in a minute, then calculate the rotor speed?