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

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, 3 , 5

1, 4

1, 3, 5

2, 4 ,5

2, 3 , 5

1, 4

1, 3, 5

2, 4 ,5

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Electrical Machines
If an additional resistance is connected in series with a DC motor operating at rated speed, the speed of the motor will

Remain unaltered.

Increase.

Reduce.

Oscillate around the normal speed.

Remain unaltered.

Increase.

Reduce.

Oscillate around the normal speed.

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Electrical Machines
A bipolar dc machine with interpoles has a main-pole flux of ф per pole and an interpole flux of Фᵢ per pole. The yoke of the machine is devide into four quadrants by the main-pole axis and The commutation axis. The flux-distribution in the quadrants will be

½ ( ф + фᵢ ) in two diametrically opposite quadrants and ½ ( ф - фᵢ ) in the remaining two Quadrants

½ ( ф - фᵢ ) in all the four quadrants

½ ( ф + фᵢ ) in all the four quadrants

½ ( ф + фᵢ ) in two adjacent quadrants and ½ ( ф - фᵢ ) in the remaining two quadrants

½ ( ф + фᵢ ) in two diametrically opposite quadrants and ½ ( ф - фᵢ ) in the remaining two Quadrants

½ ( ф - фᵢ ) in all the four quadrants

½ ( ф + фᵢ ) in all the four quadrants

½ ( ф + фᵢ ) in two adjacent quadrants and ½ ( ф - фᵢ ) in the remaining two quadrants

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Electrical Machines
An inverted V-curve of synchronous motor shows the variation of

power factor and dc excitation at constant load

All of these

power factor and supply voltage during hunting

supply voltage and field current at constant excitation

power factor and dc excitation at constant load

All of these

power factor and supply voltage during hunting

supply voltage and field current at constant excitation

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Electrical Machines
Use of fractional pitch winding

results in reduced axial length of the machine.

make it stiffer.

All of these

results in reduced leakage reactance.

results in reduced axial length of the machine.

make it stiffer.

All of these

results in reduced leakage reactance.

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Electrical Machines
A 200 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 Ω. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, the ratio of motor speed to generator speed is

0.95

0.87

1.06

0.96

0.95

0.87

1.06

0.96

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Electrical Machines

Electrical Machines If an additional resistance is connected in series with a DC motor operating at rated speed, the speed of the motor will

Electrical Machines A bipolar dc machine with interpoles has a main-pole flux of ф per pole and an interpole flux of Фᵢ per pole. The yoke of the machine is devide into four quadrants by the main-pole axis and The commutation axis. The flux-distribution in the quadrants will be

Electrical Machines An inverted V-curve of synchronous motor shows the variation of

Electrical Machines Use of fractional pitch winding

Electrical Machines A 200 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 Ω. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, the ratio of motor speed to generator speed is

Electrical Machines
If an additional resistance is connected in series with a DC motor operating at rated speed, the speed of the motor will

Electrical Machines
A bipolar dc machine with interpoles has a main-pole flux of ф per pole and an interpole flux of Фᵢ per pole. The yoke of the machine is devide into four quadrants by the main-pole axis and The commutation axis. The flux-distribution in the quadrants will be

Electrical Machines
An inverted V-curve of synchronous motor shows the variation of

Electrical Machines
Use of fractional pitch winding

Electrical Machines
A 200 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 Ω. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, the ratio of motor speed to generator speed is