The main purpose of damper windings in alternators is to

 

1. The frequency of the generated voltage in a synchronous generator depends on

A) The number of poles only
B) The speed of the rotor only
C) Both number of poles and rotor speed
D) The type of winding used
Answer: C
Explanation:
Frequency $f = \frac{P \times N}{120}$, where P = number of poles and N = speed in rpm.
Hence, frequency depends on both the number of poles and the speed of rotation.

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2. The generated EMF per phase in a synchronous generator is given by

A) $4.44 f \Phi N$
B) $2.22 f \Phi N$
C) $11 f \Phi N$
D) $1.11 f \Phi N$
Answer: A
Explanation:
The RMS value of generated EMF per phase is $E = 4.44 f \Phi N$, where f = frequency, Φ = flux per pole, and N = number of turns per phase.

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3. In a 3-phase synchronous generator, the rotor magnetic field rotates at

A) Synchronous speed
B) Rotor speed
C) Slip speed
D) Twice the synchronous speed
Answer: A
Explanation:
The magnetic field produced by the rotor poles rotates at synchronous speed relative to the stator, since the field is directly tied to rotor motion.

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4. The voltage regulation of an alternator can be

A) Always positive
B) Always negative
C) Either positive or negative
D) Zero only
Answer: C
Explanation:
Voltage regulation can be positive (lagging power factor), negative (leading power factor), or zero (unity PF).

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5. If load on an alternator increases, the armature reaction is

A) Purely demagnetizing
B) Purely magnetizing
C) Partly cross-magnetizing and partly demagnetizing
D) Purely cross-magnetizing
Answer: C
Explanation:
Depending on the power factor of the load, the armature reaction can have both demagnetizing and cross-magnetizing effects.

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6. The synchronous impedance of an alternator is obtained from

A) OC and SC tests
B) Direct load test
C) No-load test only
D) Load and efficiency test
Answer: A
Explanation:
Open Circuit (OC) and Short Circuit (SC) tests are used to determine synchronous impedance $Z_s = \frac{E_{oc}}{I_{sc}}$.

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7. The internal generated voltage of a synchronous generator is

A) Ahead of terminal voltage at lagging PF
B) Behind terminal voltage at lagging PF
C) Equal to terminal voltage always
D) In phase with terminal voltage
Answer: A
Explanation:
At lagging PF, the current lags voltage → internal EMF leads the terminal voltage due to voltage drops in resistance and reactance.

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8. The main purpose of damper windings in alternators is to

A) Improve voltage regulation
B) Prevent hunting
C) Improve efficiency
D) Reduce armature reaction
Answer: B
Explanation:
Damper (amortisseur) windings provide damping torque that prevents oscillations (hunting) during load changes.

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9. The power developed in a cylindrical rotor synchronous machine is proportional to

A) sin δ
B) cos δ
C) tan δ
D) δ
Answer: A
Explanation:
Power developed $P = \frac{EV}{X_s} \sin δ$, where δ is the load angle.

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10. The maximum power in a synchronous generator occurs when

A) δ = 45°
B) δ = 60°
C) δ = 90°
D) δ = 180°
Answer: C
Explanation:
Since $P \propto \sin δ$, maximum power occurs when $δ = 90°$.