MCQOPTIONS
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MCQOPTIONS
This section includes 517 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 251. |
A synchronous generator connected to an infinite bus is overexcited. Considering only reactive power, from the point of the system, the machine acts as |
| A. | a capacitor |
| B. | an inductor |
| C. | a resistor |
| D. | none of these |
| Answer» B. an inductor | |
| 252. |
Consider the following advantages of a distributed winding in a rotating machine:1. Better utilization of core as a number of evenly placed small slots are used2. Improved waveform as harmonic emf’s are reduced3. Diminished armature reaction and efficient coolingWhich of the above advantages are correct? |
| A. | 1 and 2 only |
| B. | 1 and 3 only |
| C. | 2 and 3 only |
| D. | 1, 2 and 3 |
| Answer» E. | |
| 253. |
In a synchronous machine, in case the axis of field flux is in line with the armature flux then __________ |
| A. | the machine is working as synchronous motor |
| B. | the machine is working as synchronous generator |
| C. | the machine is said to be floating |
| D. | the machine will vibrate violently |
| Answer» D. the machine will vibrate violently | |
| 254. |
In alternators, damper winding are used to: |
| A. | Prevent hunting |
| B. | Reduce eddy current loss |
| C. | Reduce armature reaction |
| D. | Make the rotor dynamically balanced |
| Answer» B. Reduce eddy current loss | |
| 255. |
If the field current of a three-phase alternator is reversed, what happens to its phase sequence? |
| A. | Remains same |
| B. | Reverses |
| C. | Two phases are exchanged |
| D. | It becomes ac motor |
| Answer» B. Reverses | |
| 256. |
In a synchronous motor hunting occurs due to______. |
| A. | Over-excitation |
| B. | Over-loading for long periods |
| C. | Periodic variation of load |
| D. | Small and constant load |
| Answer» D. Small and constant load | |
| 257. |
Match List – 1 (Voltage regulation method of Alternator) with List-II (Relevant phasor) correctly.List – IA. Synchronous impedance methodB. MMF methodC. Zero power factor (ZPF) methodD. American Standard association methodList – II1. emf pahsor2. Predominatly mmf phasor3. both emf and mmf phasors4. emf and mmf phasors including saturation |
| A. | A-1, B-2, C-3, D-4 |
| B. | A-1, B-2, C-4, D-3 |
| C. | A-2, B-1, C-3, D-4 |
| D. | A-2, B-1, C-4, D-3 |
| Answer» B. A-1, B-2, C-4, D-3 | |
| 258. |
A uniformly distributed winding on the stator has three full-pitched coils, each coil having N turns and each turn carrying a current I. The mmf produced by this winding is |
| A. | sinusoidal in waveform with an amplitude 3 NI |
| B. | Sinusoidal in waveform with an amplitude \(3\frac{{NI}}{2}\) |
| C. | trapezoidal in waveform with an amplitude 3 NI |
| D. | trapezoidal in waveform with an amplitude \(3\frac{{NI}}{2}\) |
| Answer» E. | |
| 259. |
In which of the following conditions will a 3-phase synchronous motor work as a capacitor? |
| A. | None of these |
| B. | Critically Excited |
| C. | Under Excited |
| D. | Over Excited |
| Answer» E. | |
| 260. |
In an alternator, the armature reaction is assumed to be equal to an imaginary _____. |
| A. | Capacitance |
| B. | Current |
| C. | Inductance |
| D. | Reactance |
| Answer» E. | |
| 261. |
Field system of an alternator is usually excited from: |
| A. | Single phase ac voltage |
| B. | Square wave voltage |
| C. | Three phase ac voltage |
| D. | DC voltage |
| Answer» E. | |
| 262. |
In alternators, the distribution factor for the given number of phases is dependent only on the: |
| A. | Number of turns per coil |
| B. | Supply voltage |
| C. | Number of distributed slots under a given pole |
| D. | Type of the windings |
| Answer» D. Type of the windings | |
| 263. |
High-speed alternators are driven by |
| A. | diesel engines |
| B. | hydraulic turbines |
| C. | steam turbines |
| D. | None of the above |
| Answer» D. None of the above | |
| 264. |
Keeping its excitation constant, if steam supply of an alternator running in parallel with another identical alternator is increased, then: |
| A. | Its power factor would be decreased |
| B. | It will supply greater portion of the load |
| C. | It would over-run the other alternator |
| D. | Its rotor will fall back in phase with respect to the other machine |
| Answer» C. It would over-run the other alternator | |
| 265. |
If in a 3 phase 3.5 MVA, 4160 V star connected alternator, a field current of 200 A produces full load current on short circuit and 4750 V on open circuit, its synchronous impedance is: |
| A. | 9.77 Ω |
| B. | 23.75 Ω |
| C. | 5.64 Ω |
| D. | 13.7 Ω |
| Answer» D. 13.7 Ω | |
| 266. |
If an alternator is operating with unity power factor load, then the effect of armature reaction on the main-field flux of an alternator will be |
| A. | nominal |
| B. | distortional |
| C. | demagnetising |
| D. | magnetising |
| Answer» C. demagnetising | |
| 267. |
Consider a coil rotating at a speed of N rpm in the field of P poles. As the coil moves past successive north the south poles, one complete cycle is generated. What is the frequency of the generated voltage? |
| A. | \(\frac{{PN}}{{60}}\) |
| B. | \(\frac{{PN}}{{120}}\) |
| C. | \(\frac{{120\;P}}{N}\) |
| D. | \(\frac{{120\;f}}{P}\) |
| Answer» C. \(\frac{{120\;P}}{N}\) | |
| 268. |
Damper winding in synchronous motors is used to |
| A. | Suppress hunting |
| B. | Improve power factor |
| C. | Develop reluctance torque |
| D. | Improve the efficiency |
| Answer» B. Improve power factor | |
| 269. |
For a synchronous motor, the nature of speed-torque characteristic if torque is on Y axis and speed is on X axis is a: |
| A. | straight line parallel to Y axis |
| B. | straight line at 45 degree angle from X axis |
| C. | a parabolic line between two axis |
| D. | straight line parallel to X axis |
| Answer» B. straight line at 45 degree angle from X axis | |
| 270. |
In an alternator, the armature winding is kept stationary while the field winding is kept rotating for the following reasons:1. Armature handles very large current and high voltage2. Armature fabrication, involving deep slots to accommodate large coils, is easy if armature is kept stationary3. It is easier to cool the stator than the rotorWhich of the above reasons are correct? |
| A. | 1 and 2 only |
| B. | 1 and 3 only |
| C. | 2 and 3 only |
| D. | 1, 2 and 3 |
| Answer» E. | |
| 271. |
A synchronous motor is found more economical over a load of |
| A. | 2 kW |
| B. | 20 kW |
| C. | 50 kW |
| D. | 100 kW |
| Answer» E. | |
| 272. |
For a synchronous machine: |
| A. | Rotor speed > stator field speed |
| B. | Rotor speed = stator speed |
| C. | Rotor speed < stator field speed |
| D. | Rotor speed = stator field speed |
| Answer» E. | |
| 273. |
In a synchronous generator, a divided winding rotor is preferable to a conventional winding rotor because of |
| A. | Higher efficiency |
| B. | Increased steady – state stability limit |
| C. | Higher short – circuit ratio |
| D. | Better damping |
| Answer» E. | |
| 274. |
On which of the following does the back emf set up in the stator of a synchronous motor depend?I. Rotor speedII. Rotor excitationIII. Coupling angleChoose the correct answer from the options given below. |
| A. | Only II |
| B. | Only II and III |
| C. | I, II and III |
| D. | Only I and III |
| Answer» B. Only II and III | |
| 275. |
Damper windings are used in synchronous machines to provide: |
| A. | unity p.f in generators and motors |
| B. | unity p.f. in generators and maximum torque in motors |
| C. | starting torque in generators and motor action |
| D. | starting torque in synchronous motor and to prevent the hunting in generators |
| Answer» E. | |
| 276. |
In a synchronous motor, the breakdown torque is |
| A. | directly proportional to applied voltage |
| B. | directly proportional to the square of the applied voltage |
| C. | inversely proportional to applied voltage |
| D. | none of the above |
| Answer» B. directly proportional to the square of the applied voltage | |
| 277. |
In which of the following motors the stator and rotor magnetic field rotate at the same speed ? |
| A. | Universal motor |
| B. | Synchronous motor |
| C. | Induction motor |
| D. | Reluctance motor |
| Answer» C. Induction motor | |
| 278. |
The speed of a synchronous motor |
| A. | increases as the load increases |
| B. | decreases as the load decreases |
| C. | always remains constant |
| D. | none of the above |
| Answer» D. none of the above | |
| 279. |
In a synchronous motor, the damping winding is generally used to |
| A. | prevent hunting and provide the starting torque |
| B. | reduce the eddy currents |
| C. | provide starting torque only |
| D. | reduce noise level |
| Answer» B. reduce the eddy currents | |
| 280. |
In a synchronous motor, damper windings are provided on |
| A. | stator frame |
| B. | rotor shaft |
| C. | pole faces |
| D. | none of the above |
| Answer» D. none of the above | |
| 281. |
When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way |
| A. | augments it directly |
| B. | directly opposes it |
| C. | cross-magnetises it |
| D. | none of the above |
| Answer» C. cross-magnetises it | |
| 282. |
Which of the following motors will be used in electric clocks ? |
| A. | D.C. shunt motor |
| B. | D.C. series motor |
| C. | A.C. induction motor |
| D. | A.C. synchronous motor |
| Answer» E. | |
| 283. |
A synchronous motor running with normal excitation adjusts to load increases essentially by increase in |
| A. | back e.m.f. |
| B. | armature current |
| C. | power factor |
| D. | torque angle |
| Answer» C. power factor | |
| 284. |
Exciters of synchronous machines are |
| A. | d.c. shunt machines |
| B. | d.c. series machines |
| C. | d.c. compound machines |
| D. | any of the above |
| Answer» B. d.c. series machines | |
| 285. |
The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as |
| A. | slip torque |
| B. | pull-out torque |
| C. | breaking torque |
| D. | synchronising torque |
| Answer» E. | |
| 286. |
If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will |
| A. | stop |
| B. | run as induction motor |
| C. | function as static condenser |
| D. | burn with dense smoke |
| Answer» B. run as induction motor | |
| 287. |
A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because |
| A. | Speed of the motor is reduced |
| B. | Power factor is decreased |
| C. | Eb (back e.m.f.) becomes less than V (applied voltage) |
| D. | Er (net resultant voltage) in armature is increased |
| Answer» E. | |
| 288. |
The torque angle, in a synchronous motor, is the angle between |
| A. | the supply voltage and the back e.m.f. |
| B. | magnetising current and back e.m.f. |
| C. | the rotating stator flux and rotor poles |
| D. | none of the above |
| Answer» D. none of the above | |
| 289. |
Under which of the following conditions hunting of synchronous motor is likely to occur ? |
| A. | Periodic variation of load |
| B. | Over-excitation |
| C. | Over-loading for long periods |
| D. | Small and constant load |
| Answer» B. Over-excitation | |
| 290. |
Synchronsizingpower of a synchronous machine is |
| A. | direcly proportional to the synchronous reactance |
| B. | inversely proportional to the synchronous reactance |
| C. | equal to the synchronous reactance |
| D. | none of the above |
| Answer» C. equal to the synchronous reactance | |
| 291. |
Armature of a synchronous machine is |
| A. | Of reducing number of slip rings on the rotor |
| B. | Armature is associated with large power as compared to the field circuits |
| C. | Of difficulty of providing high voltage insulation on rotor |
| D. | All of the above reasons |
| Answer» E. | |
| 292. |
The maximum power developed in a synchronous motor will depend on |
| A. | the rotor excitation only |
| B. | the supply voltage only |
| C. | the rotor excitation and supply volt-age both |
| D. | the rotor excitation, supply voltage and maximum value of coupling angle (90°) |
| Answer» E. | |
| 293. |
The construction of a synchronous motor resembles |
| A. | a series motor |
| B. | an induction motor |
| C. | an alternator |
| D. | a rotary converter |
| Answer» D. a rotary converter | |
| 294. |
The speed regulation of a synchronous motor is always |
| A. | 1% |
| B. | 0.5% |
| C. | positive |
| D. | zero |
| Answer» E. | |
| 295. |
If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then |
| A. | the stator current will be zero |
| B. | the stator current will be very small |
| C. | the stator current will be very high |
| D. | the back e.m.f. will be more than the supply voltage |
| Answer» B. the stator current will be very small | |
| 296. |
The standard full-load power factor ratings for synchronous motors are |
| A. | zero or 0.8 leading |
| B. | unity or 0.8 lagging |
| C. | unity or 0.8 leading |
| D. | unity or zero |
| Answer» D. unity or zero | |
| 297. |
Synchronous motors are |
| A. | Not-self starting |
| B. | Self-starting |
| C. | Essentially self-starting |
| D. | None of the above |
| Answer» B. Self-starting | |
| 298. |
A synchronous motor can operate at |
| A. | lagging power factor only |
| B. | leading power factor only |
| C. | unity power factor only |
| D. | lagging, leading and unity power factors |
| Answer» E. | |
| 299. |
Synchronous motor always runs at |
| A. | the synchronous speed |
| B. | less than synchronous speed |
| C. | more than synchronous speed |
| D. | none of the above |
| Answer» B. less than synchronous speed | |
| 300. |
The effect of increasing the load on a synchronous motor running with normal excitation is to |
| A. | decrease both armature current and power factor |
| B. | decrease armature current but increase power factor |
| C. | increase armature current but decrease power factor |
| D. | increase both its armature current and power factor |
| Answer» D. increase both its armature current and power factor | |