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 4

1, 2, and 3

1 and 3

2, 3 and 4

1, 2 and 4

1, 2, and 3

1 and 3

2, 3 and 4

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Electrical Machines
Diverters are used only in

series motors

None of these

either of these

shunt motors

series motors

None of these

either of these

shunt motors

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Electrical Machines
Mechanical energy is supplied to DC generator at the rate of 4200 J / s. The generator delivers 32.2 Amp at 120 V. What is the percentage efficiency of the generator?

210 V.

212 V.

201.02 V.

205 V.

210 V.

212 V.

201.02 V.

205 V.

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Electrical Machines
For the purpose of starting an induction motor, star/delta switch is an equivalent to auto transformer of ratio

50%

57.7%

33.3%

66.3%

50%

57.7%

33.3%

66.3%

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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

33.33 MW and 66.67 MW respectively

any of the above

50 MW and 50 MW respectively

66.67 MW and 33.33 MW respectively

33.33 MW and 66.67 MW respectively

any of the above

50 MW and 50 MW respectively

66.67 MW and 33.33 MW respectively

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Electrical Machines
A 240 V dc series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 Ω. The value of resistance which must be added to obtain rated torque at 1000 rpm is

2.2 Ω

6 Ω

1.9 Ω

5.7 Ω

2.2 Ω

6 Ω

1.9 Ω

5.7 Ω

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Electrical Machines

Electrical Machines Diverters are used only in

Electrical Machines Mechanical energy is supplied to DC generator at the rate of 4200 J / s. The generator delivers 32.2 Amp at 120 V. What is the percentage efficiency of the generator?

Electrical Machines For the purpose of starting an induction motor, star/delta switch is an equivalent to auto transformer of ratio

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

Electrical Machines A 240 V dc series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 Ω. The value of resistance which must be added to obtain rated torque at 1000 rpm is

Electrical Machines
Diverters are used only in

Electrical Machines
Mechanical energy is supplied to DC generator at the rate of 4200 J / s. The generator delivers 32.2 Amp at 120 V. What is the percentage efficiency of the generator?

Electrical Machines
For the purpose of starting an induction motor, star/delta switch is an equivalent to auto transformer of ratio

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

Electrical Machines
A 240 V dc series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 Ω. The value of resistance which must be added to obtain rated torque at 1000 rpm is