Which of the following factors improve commutation in a dc machine ? 1. High contact resistance of brushes 2. High inductance of the coils undergoing commutation 3. Shifting of brushes in the direction of rotation for a generator and in the opposite direction For a motor 4. Narrow width for the commutation bars Select the correct answer using the codes given below : Codes :

Electrical Machines
Which of the following factors improve commutation in a dc machine ? 1. High contact resistance of brushes 2. High inductance of the coils undergoing commutation 3. Shifting of brushes in the direction of rotation for a generator and in the opposite direction For a motor 4. Narrow width for the commutation bars Select the correct answer using the codes given below : Codes :

1, 2, and 3

1, 2 and 4

1 and 3

2, 3 and 4

1, 2, and 3

1, 2 and 4

1 and 3

2, 3 and 4

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The low voltage winding of a 400/230 V single phase 50 Hz transformer is to be connected to keep the magnetization current at the same level in both the cases the voltage at 25 Hz should be

65 V

460 V

115 V

230 V

65 V

460 V

115 V

230 V

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At what power factor, the voltage regulation of a transformer can be zero ?

Zero power factor.

Lagging power factor.

Unity power factor.

Leading power factor.

Zero power factor.

Lagging power factor.

Unity power factor.

Leading power factor.

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The core flux in transformer depends mainly on

supply voltage and load

supply voltage and frequency

supply voltage

supply voltage, frequency and load

supply voltage and load

supply voltage and frequency

supply voltage

supply voltage, frequency and load

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Electrical Machines
For an ideal transformer the winding should have

minimum resistance on primary side and maximum resistance on secondary side

maximum resistance on primary side and least resistance on secondary side

equal resistance on primary and secondary side

no ohmic resistance on either side

minimum resistance on primary side and maximum resistance on secondary side

maximum resistance on primary side and least resistance on secondary side

equal resistance on primary and secondary side

no ohmic resistance on either side

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Electrical Machines
What is the function of inter pole in DC generator?

Both option B and C.

To get a superior commutation.

To neutralize the distortion of main field flux due to armature reaction.

To serve the economical aspects.

Both option B and C.

To get a superior commutation.

To neutralize the distortion of main field flux due to armature reaction.

To serve the economical aspects.

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Electrical Machines

Electrical Machines The low voltage winding of a 400/230 V single phase 50 Hz transformer is to be connected to keep the magnetization current at the same level in both the cases the voltage at 25 Hz should be

Electrical Machines At what power factor, the voltage regulation of a transformer can be zero ?

Electrical Machines The core flux in transformer depends mainly on

Electrical Machines For an ideal transformer the winding should have

Electrical Machines What is the function of inter pole in DC generator?

Electrical Machines
The low voltage winding of a 400/230 V single phase 50 Hz transformer is to be connected to keep the magnetization current at the same level in both the cases the voltage at 25 Hz should be

Electrical Machines
At what power factor, the voltage regulation of a transformer can be zero ?

Electrical Machines
The core flux in transformer depends mainly on

Electrical Machines
For an ideal transformer the winding should have

Electrical Machines
What is the function of inter pole in DC generator?