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 and 3

1, 2 and 4

2, 3 and 4

1, 2, and 3

1 and 3

1, 2 and 4

2, 3 and 4

1, 2, and 3

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Electrical Machines
The rotor of a three phase induction motor has an impedance of 0.4 + j4 ohm per phase at standstill the maximum torque occurs at a slip of _____________.

15 %.

10 %.

25 %.

50 %.

15 %.

10 %.

25 %.

50 %.

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Electrical Machines
In field flux method speed control of DC Motor is

constant torque drive below the base speed.

constant hp drive below the base speed.

constant torque drive above the base speed.

constant power drive above base speed.

constant torque drive below the base speed.

constant hp drive below the base speed.

constant torque drive above the base speed.

constant power drive above base speed.

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Electrical Machines
Two dc machines A and B, using the same conductor material, have armature circuit resistances of 0.4 Ω and 1.2 Ω respectively. Of the two machines,

A is bigger than B for the same current rating

both are of the same size for the same current rating

B is bigger than A for the same current rating

A is bigger than B for the same voltage rating

A is bigger than B for the same current rating

both are of the same size for the same current rating

B is bigger than A for the same current rating

A is bigger than B for the same voltage rating

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Electrical Machines
A DC Shunt Motor having shunt field resistance of 250 Ω and armature resistance of 0.5 Ω is connected to 250 V supply and load current of 21 A. What is the back emf generated ?

150 V.

240 V.

230 V.

210 V

150 V.

240 V.

230 V.

210 V

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Electrical Machines
The rotor of a 3 - ÃŽÂ¦ wound induction motor is provided with

heavy copper or aluminium bars placed in rotor slots.

three phase winding.

heavy short-circuited end rings.

single phase winding.

heavy copper or aluminium bars placed in rotor slots.

three phase winding.

heavy short-circuited end rings.

single phase winding.

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Electrical Machines

Electrical Machines The rotor of a three phase induction motor has an impedance of 0.4 + j4 ohm per phase at standstill the maximum torque occurs at a slip of _____________.

Electrical Machines In field flux method speed control of DC Motor is

Electrical Machines Two dc machines A and B, using the same conductor material, have armature circuit resistances of 0.4 Ω and 1.2 Ω respectively. Of the two machines,

Electrical Machines A DC Shunt Motor having shunt field resistance of 250 Ω and armature resistance of 0.5 Ω is connected to 250 V supply and load current of 21 A. What is the back emf generated ?

Electrical Machines The rotor of a 3 - ÃŽÂ¦ wound induction motor is provided with

Electrical Machines
The rotor of a three phase induction motor has an impedance of 0.4 + j4 ohm per phase at standstill the maximum torque occurs at a slip of _____________.

Electrical Machines
In field flux method speed control of DC Motor is

Electrical Machines
Two dc machines A and B, using the same conductor material, have armature circuit resistances of 0.4 Ω and 1.2 Ω respectively. Of the two machines,

Electrical Machines
A DC Shunt Motor having shunt field resistance of 250 Ω and armature resistance of 0.5 Ω is connected to 250 V supply and load current of 21 A. What is the back emf generated ?

Electrical Machines
The rotor of a 3 - ÃŽÂ¦ wound induction motor is provided with