In alternator operation, load angle δ increases with

 

301. In a synchronous generator, the generated EMF per phase is proportional to

A) Frequency and flux per pole
B) Frequency only
C) Flux only
D) Armature current
Answer: A
Explanation:
$E = 4.44 f Φ N$; hence EMF ∝ frequency × flux per pole.

---

302. The armature current of a synchronous generator depends on

A) Load power factor
B) Load magnitude
C) Excitation
D) All of these
Answer: D
Explanation:
Armature current depends on the load and excitation as it determines the terminal voltage and reactive power.

---

303. If the load power factor of an alternator is leading, the armature reaction is

A) Magnetizing
B) Demagnetizing
C) Cross-magnetizing
D) None
Answer: A
Explanation:
Leading PF → current leads voltage → magnetizing effect → voltage rises.

---

304. A lagging power factor load causes the alternator terminal voltage to

A) Rise
B) Fall
C) Remain constant
D) Oscillate
Answer: B
Explanation:
Lagging PF current produces demagnetizing armature reaction → voltage drop.

---

305. The type of prime mover used for alternators in thermal power stations is

A) Steam turbine
B) Water turbine
C) Gas turbine
D) Diesel engine
Answer: A
Explanation:
High-speed steam turbines are used, hence cylindrical rotor alternators are suitable.

---

306. In hydroelectric stations, alternators are generally

A) Low-speed, salient pole type
B) High-speed, cylindrical rotor type
C) Induction type
D) None
Answer: A
Explanation:
Hydro turbines operate at low speed, hence salient pole rotors are used.

---

307. The field system of an alternator is excited by

A) AC supply
B) DC supply
C) Both AC and DC
D) None
Answer: B
Explanation:
DC excitation is used to produce a steady magnetic field on the rotor.

---

308. The voltage induced in a coil rotating in a magnetic field is maximum when

A) Coil sides are parallel to the field
B) Coil sides are perpendicular to the field
C) Coil is stationary
D) Field is zero
Answer: A
Explanation:
Maximum rate of flux cutting occurs when coil sides are parallel to magnetic flux lines.

---

309. The generated EMF in a 3-phase alternator is

A) 120° displaced in time
B) 180° displaced in time
C) In phase
D) Randomly displaced
Answer: A
Explanation:
Three-phase windings are placed 120° apart electrically → EMFs displaced by 120°.

---

310. The waveform of generated voltage in an alternator is improved by

A) Short-pitch winding
B) Distributed winding
C) Both A and B
D) Increasing speed
Answer: C
Explanation:
Both distributed and short-pitch windings help in reducing harmonics and improving waveform.

---

311. The main reason for using short-pitched coils is to

A) Reduce copper loss
B) Reduce harmonics
C) Increase EMF
D) Increase torque
Answer: B
Explanation:
Short-pitching reduces certain harmonic EMFs, giving a more sinusoidal output.

---

312. When two alternators are operating in parallel, their load sharing depends on

A) Speed and excitation
B) Power factor only
C) Frequency only
D) Phase sequence
Answer: A
Explanation:
Active power sharing depends on governor setting (speed), while reactive power sharing depends on excitation.

---

313. An alternator is said to be under-excited when

A) Field current is less than normal
B) Field current is more than normal
C) Load is zero
D) Speed is high
Answer: A
Explanation:
Under-excited alternator takes lagging vars from the system (acts like an inductive load).

---

314. The voltage regulation of an alternator supplying leading power factor load is

A) Positive
B) Negative
C) Zero
D) Infinite
Answer: B
Explanation:
At leading PF, internal EMF < terminal voltage, hence negative regulation.

---

315. If the alternator is over-excited, it behaves as

A) Inductive generator
B) Capacitive generator
C) Purely resistive
D) None
Answer: B
Explanation:
Over-excited alternator supplies reactive power (capacitive behavior).

---

316. In a synchronous generator, the load angle δ is the angle between

A) Rotor magnetic field and stator magnetic field
B) Terminal voltage and internal EMF
C) Armature current and terminal voltage
D) None
Answer: B
Explanation:
Load angle δ = angle between internal generated voltage (E) and terminal voltage (V).

---

317. The synchronizing power per mechanical degree is maximum when

A) δ = 0°
B) δ = 90°
C) δ = 45°
D) δ = 60°
Answer: A
Explanation:
Synchronizing power $P_s = \frac{EV}{X_s}\cos δ$; it’s maximum at δ = 0°.

---

318. The EMF method of voltage regulation is also called

A) Synchronous impedance method
B) Zero power factor method
C) MMF method
D) Direct load test
Answer: A
Explanation:
The EMF method calculates regulation using synchronous impedance obtained from OC and SC tests.

---

319. The efficiency of an alternator is maximum at

A) Unity power factor
B) Lagging power factor
C) Leading power factor
D) Zero power factor
Answer: A
Explanation:
At unity PF, reactive current component is zero → minimum losses → maximum efficiency.

---

320. If a 4-pole alternator runs at 1500 rpm, its frequency is

A) 25 Hz
B) 50 Hz
C) 60 Hz
D) 100 Hz
Answer: B
Explanation:
$f = (P×N)/120 = (4×1500)/120 = 50\,Hz.$

---

321. The EMF generated in each phase of an alternator is

A) Induced by mutual induction
B) Induced by rotation of magnetic field
C) Induced by relative motion of conductor and field
D) None
Answer: C
Explanation:
According to Faraday’s law, EMF is induced due to relative motion between conductor and magnetic field.

---

322. The armature reaction at unity power factor is

A) Purely demagnetizing
B) Purely cross-magnetizing
C) Purely magnetizing
D) None
Answer: B
Explanation:
At unity PF, current and voltage are in phase, so armature reaction is cross-magnetizing.

---

323. The alternator efficiency is given by

A) $\eta = \frac{\text{Output Power}}{\text{Input Power}} \times 100$
B) $\eta = \frac{\text{Input Power}}{\text{Output Power}} \times 100$
C) $\eta = \frac{\text{Losses}}{\text{Input Power}} \times 100$
D) None
Answer: A
Explanation:
Efficiency = Output / Input × 100%. Losses include Cu and iron losses.

---

324. The torque developed in a synchronous generator is proportional to

A) sin δ
B) cos δ
C) tan δ
D) δ
Answer: A
Explanation:
Electromagnetic torque $T \propto \sin δ$.

---

325. A synchronous generator can operate at

A) Unity PF
B) Lagging PF
C) Leading PF
D) All of these
Answer: D
Explanation:
By controlling excitation, alternator can operate at lagging, leading, or unity PF.

---

326. In alternators, field poles are laminated to

A) Reduce eddy current losses
B) Reduce hysteresis losses
C) Both A and B
D) None
Answer: A
Explanation:
Rotor field poles are laminated to minimize eddy current losses.

---

327. The leakage reactance of an alternator depends on

A) Slot design and winding layout
B) Core length only
C) Speed
D) Frequency
Answer: A
Explanation:
Leakage reactance is affected by coil pitch, slot shape, and air-gap flux distribution.

---

328. The voltage regulation of an alternator can be zero at

A) Unity power factor
B) Leading power factor
C) Lagging power factor
D) No-load condition
Answer: B
Explanation:
At some leading PF, the rise in voltage due to magnetizing current cancels the IR drop → zero regulation.

---

329. The core loss in an alternator depends mainly on

A) Frequency and flux density
B) Armature current
C) Load
D) Temperature
Answer: A
Explanation:
Iron loss = hysteresis + eddy current loss ∝ $f \times B^2$.

---

330. The efficiency of large alternators is usually

A) 60–70%
B) 80–85%
C) 90–98%
D) 50–60%
Answer: C
Explanation:
Large alternators are highly efficient, typically between 90% and 98%.

---

331. The reactive power supplied by an alternator depends on

A) Field excitation
B) Load
C) Speed
D) Armature resistance
Answer: A
Explanation:
Reactive power output is controlled by varying excitation current.

---

332. The main function of the stator frame is to

A) Support and protect the core and windings
B) Produce flux
C) Carry armature current
D) Act as a magnetic core
Answer: A
Explanation:
The stator frame provides mechanical support and protection for internal components.

---

333. The armature core is laminated to

A) Reduce eddy current losses
B) Reduce hysteresis losses
C) Increase magnetic strength
D) Reduce copper losses
Answer: A
Explanation:
Lamination breaks the eddy current path, reducing eddy losses.

---

334. When alternators operate in parallel, equal load sharing requires

A) Identical speed regulation and excitation
B) Identical size
C) Identical voltage rating
D) None
Answer: A
Explanation:
Proper load sharing occurs when alternators have same speed-load and voltage-excitation characteristics.

---

335. If one alternator in parallel becomes under-excited, it will

A) Draw lagging reactive power
B) Draw leading reactive power
C) Supply lagging vars
D) Supply real power only
Answer: B
Explanation:
Under-excited alternator absorbs reactive power from the system (behaves inductively).

---

336. The no-load losses of an alternator include

A) Core loss and mechanical loss
B) Copper loss
C) I²R loss
D) Load loss only
Answer: A
Explanation:
No-load losses = core (iron) + mechanical (friction & windage) losses.

---

337. The copper losses in an alternator depend on

A) Load current
B) Excitation
C) Frequency
D) Voltage
Answer: A
Explanation:
Copper loss $= I^2R$, hence directly proportional to the square of load current.

---

338. The synchronous reactance of an alternator increases with

A) Saturation
B) Load
C) Leakage flux
D) None
Answer: C
Explanation:
Leakage flux causes inductive reactance → increases total synchronous reactance.

---

339. In alternator operation, load angle δ increases with

A) Load power
B) Speed
C) Field excitation
D) Frequency
Answer: A
Explanation:
As load increases, δ increases to balance developed torque and load torque.

---

340. The voltage regulation of an alternator is independent of

A) Power factor
B) Load current
C) Frequency
D) Excitation
Answer: C
Explanation:
Voltage regulation depends on PF, current, and excitation, but not on frequency.

---

341. Synchronous generators used in power plants are generally

A) Three-phase
B) Single-phase
C) Two-phase
D) DC
Answer: A
Explanation:
Power systems operate on three-phase supply for efficiency and balance.

---

342. The load sharing between two alternators running in parallel is adjusted by

A) Governor and excitation control
B) Frequency alone
C) Voltage alone
D) Mechanical coupling
Answer: A
Explanation:
Governor adjusts real power; excitation adjusts reactive power.

---

343. If excitation of an alternator connected to bus-bar is increased, it will

A) Supply more reactive power
B) Supply less reactive power
C) Draw reactive power
D) Stop generating
Answer: A
Explanation:
Increased excitation → over-excited → supplies lagging reactive power.

---

344. The frequency of generated EMF depends on

A) Rotor speed
B) Number of poles
C) Both A and B
D) None
Answer: C
Explanation:
$f = PN/120$; both speed and poles determine frequency.

---

345. When the load is purely resistive, the armature reaction is

A) Cross-magnetizing
B) Demagnetizing
C) Magnetizing
D) None
Answer: A
Explanation:
At unity PF, armature reaction is cross-magnetizing.

---

346. The prime mover for a 2-pole, 3000 rpm alternator is usually

A) Steam turbine
B) Water turbine
C) Diesel engine
D) None
Answer: A
Explanation:
High-speed steam turbines suit 2-pole, 3000 rpm alternators.

---

347. The voltage of an alternator can be increased by

A) Increasing field current
B) Decreasing speed
C) Decreasing excitation
D) Reducing poles
Answer: A
Explanation:
Voltage ∝ field current (flux).

---

348. Alternators are rated in

A) kVA
B) kW
C) kVAR
D) HP
Answer: A
Explanation:
They are rated in kVA because losses depend on current and voltage, not PF.

---

349. The reactive component of current in alternator depends on

A) Excitation
B) Load PF
C) Terminal voltage
D) Both A and B
Answer: D
Explanation:
Reactive current changes with excitation and power factor of the load.

---

350. The constant-speed characteristic of a synchronous generator is maintained by

A) Governor control of prime mover
B) AVR
C) Excitation
D) Load
Answer: A
Explanation:
Governor adjusts input torque to maintain constant speed and frequency.

When alternator supplies leading PF load, terminal voltage

 

251. The main function of a voltage regulator in an alternator is to

A) Control load current
B) Maintain constant terminal voltage
C) Control mechanical speed
D) Maintain constant frequency
Answer: B
Explanation:
A voltage regulator adjusts the field excitation to keep the terminal voltage constant under varying load conditions.

---

252. The excitation current of a synchronous generator is adjusted to control

A) Frequency
B) Load angle
C) Power factor and terminal voltage
D) Speed
Answer: C
Explanation:
By varying field current, the alternator’s reactive power and terminal voltage are controlled, thus adjusting power factor.

---

253. Hunting in a synchronous machine occurs due to

A) Load fluctuations
B) Speed variations of prime mover
C) Mechanical vibrations
D) Field circuit faults
Answer: A
Explanation:
Hunting is oscillation of the rotor about its equilibrium due to sudden load changes.

---

254. The damping torque in a synchronous generator is provided by

A) Damper windings
B) Field windings
C) Armature resistance
D) Load reactance
Answer: A
Explanation:
Damper windings (copper bars embedded in the rotor pole faces) provide damping torque to suppress hunting.

---

255. Which test provides the magnetization characteristic of an alternator?

A) Short-circuit test
B) Open-circuit test
C) Load test
D) Heat run test
Answer: B
Explanation:
The Open-Circuit Test gives the relationship between field current and generated voltage — known as the magnetization characteristic.

---

256. The pitch factor in alternator windings is always

A) Equal to 1
B) Greater than 1
C) Less than 1
D) Zero
Answer: C
Explanation:
Pitch factor $K_p = \cos(\alpha/2)$. For fractional-pitch windings, $K_p < 1$.

---

257. The distribution factor depends on

A) Number of slots per pole per phase
B) Flux per pole
C) Speed of rotation
D) Frequency
Answer: A
Explanation:
Distribution factor $K_d = \frac{\sin(m\alpha/2)}{m\sin(\alpha/2)}$, depends on the slot angle and number of slots per pole per phase.

---

258. The voltage per phase of a distributed winding alternator is

A) Higher than concentrated winding
B) Lower than concentrated winding
C) Same as concentrated winding
D) Independent of winding type
Answer: B
Explanation:
Distributed winding reduces EMF due to phase spread, but it improves waveform and reduces harmonics.

---

259. The synchronous reactance of an alternator is the sum of

A) Leakage reactance and armature reaction reactance
B) Armature resistance and reactance
C) Armature current and voltage
D) Inductive and capacitive reactance
Answer: A
Explanation:
$X_s = X_l + X_{ar}$, where $X_l$ = leakage reactance and $X_{ar}$ = armature reaction reactance.

---

260. The main factor affecting voltage regulation of an alternator is

A) Load current
B) Power factor of load
C) Excitation
D) All of these
Answer: D
Explanation:
Voltage regulation depends on load current, load power factor, and excitation level.

---

261. In a salient pole alternator, reluctance power is due to

A) Unequal air gap
B) Armature reaction
C) Field resistance
D) Friction losses
Answer: A
Explanation:
Salient pole machines have variable air-gap reluctance causing an additional torque component called reluctance power.

---

262. The power developed per phase in a salient pole machine is

A) $\frac{EV}{X_d}\sin\delta$
B) $\frac{EV}{X_q}\sin\delta$
C) $\frac{EV}{X_d}\sin\delta + \frac{V^2}{2}( \frac{1}{X_q} - \frac{1}{X_d})\sin2\delta$
D) None
Answer: C
Explanation:
Power has two components — excitation power and reluctance power.

---

263. Which method gives the most accurate voltage regulation?

A) Synchronous impedance method
B) Ampere-turn method
C) Zero power factor method
D) EMF method
Answer: C
Explanation:
ZPF method is most accurate because it accounts for the saturation and leakage effects under load.

---

264. The armature winding of an alternator is always placed on

A) Rotor
B) Stator
C) Either
D) None
Answer: B
Explanation:
Stator houses armature winding to facilitate insulation and cooling, while rotor carries field winding.

---

265. Frequency of generated EMF is

A) $f = \frac{P \times N}{120}$
B) $f = \frac{N}{60}$
C) $f = \frac{2P}{N}$
D) $f = \frac{P \times N}{60}$
Answer: A
Explanation:
This is the fundamental relation linking speed and pole count to output frequency.

---

266. For a 4-pole, 1500 rpm alternator, frequency is

A) 25 Hz
B) 50 Hz
C) 60 Hz
D) 75 Hz
Answer: B
Explanation:
$f = (4×1500)/120 = 50\,Hz$.

---

267. The number of pole pairs in a 6-pole alternator is

A) 2
B) 3
C) 6
D) 12
Answer: B
Explanation:
Number of pole pairs = P/2 = 6/2 = 3.

---

268. The function of prime mover in alternator is to

A) Supply field current
B) Rotate rotor at synchronous speed
C) Maintain constant voltage
D) None
Answer: B
Explanation:
Prime mover provides mechanical energy to rotate rotor at the desired speed.

---

269. The terminal voltage of an alternator drops on load due to

A) Armature reaction
B) Armature impedance drop
C) Both A and B
D) None
Answer: C
Explanation:
Voltage drop occurs due to reactance and resistance of armature and armature reaction effect.

---

270. The excitation system in alternators is used to

A) Produce magnetic flux
B) Supply mechanical energy
C) Control frequency
D) Reduce armature reaction
Answer: A
Explanation:
Excitation provides DC field current producing the main magnetic flux.

---

271. Synchronous generators are preferred for power generation because

A) They operate at constant speed
B) They maintain constant frequency
C) They can operate at any power factor
D) All of these
Answer: D
Explanation:
Synchronous generators run at constant speed, maintain system frequency, and handle wide PF range.

---

272. Slip in a synchronous machine is always

A) Zero
B) One
C) Variable
D) Infinite
Answer: A
Explanation:
Rotor speed = synchronous speed ⇒ Slip = 0.

---

273. The direction of induced EMF in an alternator is given by

A) Fleming’s left-hand rule
B) Fleming’s right-hand rule
C) Lenz’s law
D) None
Answer: B
Explanation:
Right-hand rule gives the direction of induced EMF in conductors.

---

274. Armature reaction is strongest at

A) Lagging power factor
B) Leading power factor
C) Unity power factor
D) No-load
Answer: A
Explanation:
At lagging PF, current lags voltage, producing demagnetizing and cross-magnetizing effects.

---

275. Harmonics in the generated voltage are reduced by

A) Using distributed winding
B) Using short-pitch coils
C) Both A and B
D) Increasing flux
Answer: C
Explanation:
Distributed and short-pitch windings reduce harmonics and improve voltage waveform.

---

276. A turbo alternator is generally

A) High speed, cylindrical rotor
B) Low speed, salient pole rotor
C) DC machine
D) None
Answer: A
Explanation:
Steam turbines run at high speed, so alternators use cylindrical rotors for mechanical balance.

---

277. In alternators, salient pole type is preferred for

A) Low-speed hydro units
B) High-speed steam units
C) Both
D) None
Answer: A
Explanation:
Hydro turbines are slow-speed, so salient poles are used to produce required frequency.

---

278. A 2-pole alternator runs at 3000 rpm. Frequency generated is

A) 25 Hz
B) 50 Hz
C) 60 Hz
D) 100 Hz
Answer: B
Explanation:
$f = (2×3000)/120 = 50\,Hz$.

---

279. If an alternator runs at 1000 rpm and produces 50 Hz, the number of poles is

A) 4
B) 6
C) 10
D) 12
Answer: C
Explanation:
$P = 120f/N = 120×50/1000 = 6$ poles ⇒ 6 poles.

---

280. The field winding of an alternator is usually

A) Lap wound
B) Wave wound
C) Coil wound on rotor poles
D) None
Answer: C
Explanation:
Rotor carries field winding supplied by DC excitation system.

---

281. The main cause of voltage dip at load is

A) Armature reactance
B) Field weakening
C) Resistance of winding
D) Poor cooling
Answer: A
Explanation:
Armature reactance causes large voltage drop at lagging power factors.

---

282. The frequency of voltage generated is directly proportional to

A) Speed only
B) Poles only
C) Both speed and poles
D) None
Answer: C
Explanation:
$f = PN/120$. Both speed and poles affect frequency.

---

283. The maximum efficiency of alternator occurs when

A) Copper losses = Iron losses
B) Load current is maximum
C) Power factor is unity
D) Voltage is maximum
Answer: A
Explanation:
Efficiency is max when variable (Cu) losses = constant (iron) losses.

---

284. The function of automatic voltage regulator (AVR) is

A) Adjust excitation
B) Maintain power factor
C) Control mechanical torque
D) Synchronize alternators
Answer: A
Explanation:
AVR senses terminal voltage and adjusts excitation to maintain constant voltage.

---

285. The main advantage of rotating field type alternator is

A) Less weight of rotating part
B) High current capacity
C) Easy cooling
D) All of these
Answer: D
Explanation:
Rotor carries only DC, making it lighter, easier to insulate and cool.

---

286. Alternator output is connected to

A) DC load
B) AC grid
C) Battery bank
D) Rectifier
Answer: B
Explanation:
Alternators generate AC power, directly supplied to the grid.

---

287. Synchronization of alternators requires matching

A) Voltage, frequency, phase sequence
B) Power factor only
C) Speed only
D) Excitation only
Answer: A
Explanation:
Before connecting alternators in parallel, their voltage, frequency, and phase sequence must match.

---

288. The reactive power in alternator is controlled by

A) Excitation current
B) Speed
C) Mechanical torque
D) Load current
Answer: A
Explanation:
Excitation controls reactive power flow in alternator operation.

---

289. If excitation increases at constant load, alternator

A) Supplies lagging reactive power
B) Supplies leading reactive power
C) Remains unchanged
D) Becomes unstable
Answer: A
Explanation:
Over-excited alternator supplies lagging vars (inductive reactive power).

---

290. The unit of synchronous reactance is

A) Ohm
B) Henry
C) Volt
D) None
Answer: A
Explanation:
Reactance is measured in ohms.

---

291. The waveform of generated EMF in alternator is

A) Purely sinusoidal
B) Approximately sinusoidal
C) Square
D) Triangular
Answer: B
Explanation:
Due to slot harmonics, waveform is nearly but not perfectly sinusoidal.

---

292. The excitation voltage of alternator is supplied by

A) Exciter
B) Transformer
C) Rectifier
D) Inductor
Answer: A
Explanation:
Exciter is a small DC generator or rectifier supplying DC field current.

---

293. The generated EMF per phase is directly proportional to

A) Flux per pole and speed
B) Current
C) Resistance
D) Frequency only
Answer: A
Explanation:
$E = 4.44 f Φ N$; since $f \propto N$, $E \propto Φ \times N$.

---

294. If frequency increases while maintaining flux constant, EMF

A) Increases
B) Decreases
C) Remains same
D) None
Answer: A
Explanation:
EMF $E = 4.44 f Φ N$; directly proportional to frequency.

---

295. If field current increases, terminal voltage

A) Increases
B) Decreases
C) Remains same
D) Becomes zero
Answer: A
Explanation:
Higher field current → more flux → higher induced EMF → higher voltage.

---

296. For parallel operation, alternators must have same

A) Frequency
B) Phase sequence
C) Voltage
D) All of these
Answer: D
Explanation:
Synchronizing requires matching voltage, frequency, and phase sequence.

---

297. If alternator load changes, frequency

A) May vary slightly
B) Remains constant
C) Decreases greatly
D) Increases linearly
Answer: A
Explanation:
Governor adjusts prime mover torque, but slight transient frequency variations may occur.

---

298. Synchronous impedance method generally gives

A) Higher regulation
B) Lower regulation
C) Accurate result
D) Zero regulation
Answer: A
Explanation:
EMF method overestimates voltage regulation due to ignoring saturation effects.

---

299. The alternator efficiency under unity power factor is

A) Maximum
B) Minimum
C) Zero
D) Constant
Answer: A
Explanation:
At unity PF, reactive current component is zero, reducing losses → max efficiency.

---

300. When alternator supplies leading PF load, terminal voltage

A) Increases
B) Decreases
C) Remains same
D) None
Answer: A
Explanation:
Leading PF load causes a voltage rise due to reactive power behavior in circuit