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%

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Electrical Machines
Consider the following statements regarding dc machines : 1. possible resistance of shunt-field winding is 1 Ω 2. possible resistance of series-field winding is 1 Ω 3. electrographite brushes are used for 230 V, 10 A machines 4. Copper-graphite brushes are used for 230 V, 10 A machines 5. Possible armature-circuit resistance is 1 Ω From these, the correct statements are

 2, 4 ,5
 1, 4
 2, 3 , 5
 1, 3, 5

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Electrical Machines
Ward-Leonard system for controlling the speed of a DC motor is used where

 The accuracy in speed control is required.
 All of above.
 The speed in both the direction is required.
 Very fine speed control over the whole range from zero to normal speed is required.

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Electrical Machines
Two generators operating in parallel with rating 50MW and 100MW respectively. Both their respective governor settings are identical as 4%, consider same no load frequency. How will the machine share a common load of 100 MW

 any of the above
 33.33 MW and 66.67 MW respectively
 50 MW and 50 MW respectively
 66.67 MW and 33.33 MW respectively

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