Aux 1 Unit 15 Q8

Correct Answer: B) The number of poles would decrease

Explanation: If the rotational speed of the generator increased while maintaining a 50Hz supply, the required number of poles would decrease. This is because higher speed means more revolutions per minute, which requires fewer poles to generate the same frequency.

Correct Answer: A)​

Explanation: The correct formula to determine the number of poles required is where $P$ is the number of poles, $f$ is the frequency (in Hz), and $N$ is the rotational speed (in rpm).

Correct Answer: C) 8 poles

Explanation: Using the formula P = (120×f)/N​, we get P=(120×50)/750 = 8 poles.  Therefore, an 8-pole generator is required to achieve a 50Hz supply at a rotational speed of 750rpm.

Correct Answer: B) Because it allows the generator to produce the same frequency with fewer rotations, as more poles mean more magnetic field interactions per revolution

Explanation: Increasing the number of poles allows the generator to produce the same frequency with fewer rotations. Each additional pole pair contributes to the frequency, meaning the generator can operate at a lower rotational speed while still generating the required frequency.

Correct Answer: B) The pole windings (or field windings)

Explanation: In a salient pole rotor, the pole windings (or field windings) are wound with copper wire. These windings generate the magnetic field when current is passed through them, which is necessary for the generator's operation.

Correct Answer: B) Laminated steel

Explanation: The pole cores in a salient pole rotor are typically made of laminated steel. Laminations help reduce eddy current losses, improving the efficiency and performance of the generator.

Correct Answer: B) To stabilize the rotor during transient conditions and reduce oscillations

Explanation: Damper windings are used in a salient pole rotor to stabilize the rotor during transient conditions, such as sudden load changes, and to reduce oscillations. This helps maintain smooth and stable operation of the generator.

Correct Answer: B) The poles are bolted or riveted to the rotor core

Explanation: The poles in a salient pole rotor are typically bolted or riveted to the rotor core. This method of attachment ensures that the poles are securely fixed to the rotor while allowing for the necessary protrusion to generate the magnetic field.

Correct Answer: B) The poles are large and protrude outwards from the rotor core

Explanation: In a salient pole rotor, the poles are large and protrude outwards from the rotor core. This construction allows for the rotor to generate strong magnetic fields, which are essential for the operation of low-speed a.c. generators.

Correct Answer: B) Because they can produce strong magnetic fields with large, protruding poles, which are effective at lower rotational speeds

Explanation: Salient pole rotors are used in low-speed a.c. generators because their large, protruding poles can produce strong magnetic fields, which are necessary for generating electricity at lower rotational speeds.