A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The external resistance to be added in the armature circuit to limit the armature current to 125% of its rated value is

Electrical Machines
A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The external resistance to be added in the armature circuit to limit the armature current to 125% of its rated value is

15.9 Ω

15.1 Ω

31.1 Ω

31.9 Ω

15.9 Ω

15.1 Ω

31.1 Ω

31.9 Ω

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Electrical Machines
Minimum allowable resistivity of power transformer insulating oil is generally taken as

4 X 1012 Ω - cm at 27°C and 0.4 X 1012

3 X 1012 Ω - cm at 27°C and 0.3 X 1012

2 X 1012 Ω - cm at 27°C and 0.2 X 1012

1 X 1012 Ω - cm at 27°C and 0.1 X 1012

4 X 1012 Ω - cm at 27°C and 0.4 X 1012

3 X 1012 Ω - cm at 27°C and 0.3 X 1012

2 X 1012 Ω - cm at 27°C and 0.2 X 1012

1 X 1012 Ω - cm at 27°C and 0.1 X 1012

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Electrical Machines
Why are capacitors used with large AC induction motor?

Improve voltage level.

Improve power factor.

Improve current level.

Improve power level.

Improve voltage level.

Improve power factor.

Improve current level.

Improve power level.

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Electrical Machines
In a DC generator, the ripples in the direct emf generated are reduced by employing

equalizer rings.

graphite brushes.

commutator with large number of segments.

carbon brushes.

equalizer rings.

graphite brushes.

commutator with large number of segments.

carbon brushes.

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Electrical Machines
Consider the following statements: To control the speed of a dc shunt motor above the base speed over a reasonably wide range, the motor must 1. have compensating winding 2. have interpole winding 3. be started using a 3-point starter 4. be started using a 4-point starter Of these statements

1 and 3 are correct

1, 2 and 4 are correct

1, 2 and 3 are correct

2 and 4 are correct

1 and 3 are correct

1, 2 and 4 are correct

1, 2 and 3 are correct

2 and 4 are correct

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Electrical Machines
Crawling in an induction motor is due to

space harmonics produced by winding currents.

insufficient starting torque.

time harmonics in supply.

slip ring rotor.

space harmonics produced by winding currents.

insufficient starting torque.

time harmonics in supply.

slip ring rotor.

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Electrical Machines

Electrical Machines Minimum allowable resistivity of power transformer insulating oil is generally taken as

Electrical Machines Why are capacitors used with large AC induction motor?

Electrical Machines In a DC generator, the ripples in the direct emf generated are reduced by employing

Electrical Machines Crawling in an induction motor is due to

Electrical Machines
Minimum allowable resistivity of power transformer insulating oil is generally taken as

Electrical Machines
Why are capacitors used with large AC induction motor?

Electrical Machines
In a DC generator, the ripples in the direct emf generated are reduced by employing

Electrical Machines
Crawling in an induction motor is due to