MCQOPTIONS
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MCQOPTIONS
This section includes 244 Mcqs, each offering curated multiple-choice questions to sharpen your Power Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 201. |
Which of the following methods is used to control speed of 25 kV, 50 Hz singlephase traction ? |
| A. | Reduced current method |
| B. | Tap changing control of transformer |
| C. | Series parallel operation of motors |
| D. | All of the above |
| Answer» C. Series parallel operation of motors | |
| 202. |
In method of staging three phase induction motors the starting voltage is notreduced. |
| A. | auto-transformer |
| B. | star-delta |
| C. | slip ring |
| D. | any of the above |
| Answer» D. any of the above | |
| 203. |
A synchronous motor is found to be more economical when the load is above |
| A. | 1 kW |
| B. | 10 kW |
| C. | 20 kW |
| D. | 100kW. |
| Answer» E. | |
| 204. |
Motor used for elevators is generally |
| A. | synchronous motor |
| B. | induction motor |
| C. | capacitor start single phase motor |
| D. | any of the above. |
| Answer» C. capacitor start single phase motor | |
| 205. |
In case of ________ free running and coasting periods are generally long. |
| A. | main-line service |
| B. | urban service |
| C. | sub-urban service |
| D. | all of the above |
| Answer» B. urban service | |
| 206. |
Which of the following device should be used as a switch in a low power switched mode power supply (SMPS)? |
| A. | GTO |
| B. | BJT |
| C. | MOSFET |
| D. | TRIAC |
| Answer» D. TRIAC | |
| 207. |
As compared to squirrel cage induction motor, a wound rotor induction motor ispreferred when the major consideration is |
| A. | high starting torque |
| B. | low windage losses |
| C. | slow speed operation |
| D. | all of the above. |
| Answer» B. low windage losses | |
| 208. |
Which feature while selecting a motor for centrifugal pump will be of leastsignificance? |
| A. | Starting characteristics |
| B. | Operating speed |
| C. | Horse power |
| D. | Speed control |
| Answer» E. | |
| 209. |
Belted wound rotor induction motors are preferred for |
| A. | machine tools |
| B. | gyratory crushers |
| C. | belt conveyor |
| D. | water pumps. |
| Answer» C. belt conveyor | |
| 210. |
For blowers which of the following motor is preferred ? |
| A. | D.C. series motor |
| B. | D.C. shunt motor |
| C. | Squirrel cage induction motor |
| D. | Wound rotor induction motor |
| Answer» C. Squirrel cage induction motor | |
| 211. |
In case of contactors, the contacts are generally made of |
| A. | copper |
| B. | silver |
| C. | cadmium copper |
| D. | any of the above. |
| Answer» E. | |
| 212. |
In series motor which of the following methods can be used for changing the fluxper pole? |
| A. | Tapped field control |
| B. | Diverter field control |
| C. | Series-parallel control |
| D. | Any of the above |
| Answer» E. | |
| 213. |
Type-A chopper is used for obtaining which type of mode? |
| A. | Motoring mode |
| B. | Regenerative braking mode |
| C. | Reverse motoring mode |
| D. | Reverse regenerative braking mode |
| Answer» B. Regenerative braking mode | |
| 214. |
Which of the following motors always starts on load ? |
| A. | Conveyor motor |
| B. | Floor mill motor |
| C. | Fan motor |
| D. | All of the above |
| Answer» E. | |
| 215. |
........is not a part of ball bearing |
| A. | Inner race |
| B. | Outer race |
| C. | Cage |
| D. | Bush |
| Answer» E. | |
| 216. |
Which of the following is an advantage of electric traction over other methods oftraction ? |
| A. | Faster acceleration |
| B. | No pollution problems |
| C. | Better braking action |
| D. | All of the above |
| Answer» B. No pollution problems | |
| 217. |
In case of kiln drives |
| A. | starting torque is almost zero |
| B. | starting torque and running torque are nearly equal |
| C. | starting torque is more than double of the running torque. |
| D. | all |
| Answer» D. all | |
| 218. |
Which off the following motors is preferred when a smooth and resize speed control over a wide range is desired? |
| A. | DC motor |
| B. | Squirrel cage induction motor |
| C. | Wound rotor induction motor |
| D. | Synchronous motor |
| Answer» B. Squirrel cage induction motor | |
| 219. |
In which of the following applications variable speed operation is preferred ? |
| A. | Exhaust fan |
| B. | Ceiling fan |
| C. | Refrigerator |
| D. | Water pump |
| Answer» C. Refrigerator | |
| 220. |
Which of the following is essentially needed while selecting a motor ? |
| A. | Pulley |
| B. | Starter |
| C. | Foundation pedal |
| D. | Bearings |
| Answer» C. Foundation pedal | |
| 221. |
Calculate the time period of the waveform x(t)=24sin(24πt+π÷4). |
| A. | .064 sec |
| B. | .047 sec |
| C. | .083 sec |
| D. | .015 sec |
| Answer» D. .015 sec | |
| 222. |
Pole changing method of speed control is used in |
| A. | slip ring induction motor |
| B. | dc shunt motor |
| C. | dc series motor |
| D. | squirrel cage induction motor. |
| Answer» E. | |
| 223. |
Belt conveyors offer ..........starting torque |
| A. | High |
| B. | Low |
| C. | Medium |
| D. | Zero |
| Answer» B. Low | |
| 224. |
For derries and winches which of the following drives can be used ? |
| A. | Pole changing squirrel cage motors |
| B. | DC motors with word Leonard control |
| C. | AC slip rings motors with a variable resistance |
| D. | Any of the above |
| Answer» E. | |
| 225. |
The motor enclosure used in wood-working industry is |
| A. | Protected type |
| B. | Totally enclosed fan cooled type |
| C. | Flame proof type |
| D. | Splash proof type |
| Answer» C. Flame proof type | |
| 226. |
In case of contactors the ratio of the in service period to the entire period, expressed as a percentage is known as |
| A. | duty |
| B. | load factor |
| C. | class of contact |
| D. | none of the above. |
| Answer» C. class of contact | |
| 227. |
Which of the following happens in Kando system ? |
| A. | Three phase A.C. is converted into D.C. |
| B. | Single phase A |
| C. | is converted into |
| D. | C. |
| Answer» D. C. | |
| 228. |
A class I contactor should be mechanically sound to withstand |
| A. | 0.05 million times |
| B. | 0.25 million times |
| C. | 1.2 million times |
| D. | 5.0 million times. |
| Answer» C. 1.2 million times | |
| 229. |
have maximum unbalanced forces |
| A. | Diesel shunters |
| B. | Steam locomotives |
| C. | Electric locomotives |
| D. | Diesel locomotives |
| Answer» C. Electric locomotives | |
| 230. |
Choose the correct one. (* stands for multiplication, J represents the moment ofinertia, w represents angular spee(D). |
| A. | J*d(w)/dt = Load torque – Motor torque |
| B. | J*d(w)/dt = Load torque + Motor torque |
| C. | J*d(w)/dt = Motor torque – Load torque |
| D. | J*d(w)/dt = Load torque * Motor torque |
| Answer» D. J*d(w)/dt = Load torque * Motor torque | |
| 231. |
Ball-bearings are |
| A. | Used up to 75 kW motors |
| B. | Of long life and low friction loss |
| C. | Costlier and noisy particularly at high speed motor |
| D. | All of the above |
| Answer» E. | |
| 232. |
Major disadvantage of using three sets of SCRs for variable voltage speed control of a SCIM is the |
| A. | Considerable I2R loss |
| B. | Poor power factor |
| C. | Long delay of thyristor firing pulses |
| D. | Necessity of using a processor |
| Answer» B. Poor power factor | |
| 233. |
If a single motor drives a number of machines through belts from a common shaft, such a type of drive system is known as: |
| A. | Individual drive |
| B. | Complex motor drive |
| C. | Multi motor drive |
| D. | Group drive |
| Answer» E. | |
| 234. |
Consider following power electronic circuits related to two-quadrant operation of d.c. drive:1. Half controlled bridge converter2. Fully controlled bridge converter3. Dual converter4. ChopperOut of these statements: |
| A. | 1, and 2 are correct |
| B. | 2, 3 and 4 are correct |
| C. | 2, and 3 are correct |
| D. | 4, 1 and 2 are correct |
| Answer» C. 2, and 3 are correct | |
| 235. |
AC drives can be used to control:i. Induction motorii. Synchronous motor |
| A. | Only i |
| B. | Only ii |
| C. | Both i and ii |
| D. | Neither i nor ii |
| Answer» D. Neither i nor ii | |
| 236. |
If the induction motor drive is capable of bidirectional power flow where limited range of speed control is required for large power applications, then this arrangement is called |
| A. | Static conductance drive |
| B. | Static Scherbius drive |
| C. | Static compressive drive |
| D. | Static reluctance drive |
| Answer» C. Static compressive drive | |
| 237. |
Load curve for fan type of load is (ω is speed) |
| A. | T ∝ ω |
| B. | T ∝ ω2 |
| C. | T ∝ ω3 |
| D. | None of the above |
| Answer» C. T ∝ ω3 | |
| 238. |
Fork-lift truck is used for |
| A. | Lifting and lowering |
| B. | Vertical transportation |
| C. | Both ‘a’ and ‘b’ |
| D. | None of the above |
| Answer» D. None of the above | |
| 239. |
Net energy saved during regenerative braking of an electric train: |
| A. | increases with an increase in specific resistance |
| B. | is independent of the train weight |
| C. | is high with a high down gradient |
| D. | decreases with reduction in train speed due to braking |
| Answer» D. decreases with reduction in train speed due to braking | |
| 240. |
Harmonics in DC Drives as compared to AC drives is: |
| A. | Zero |
| B. | Moderate |
| C. | Low |
| D. | High |
| Answer» B. Moderate | |
| 241. |
__________ is the method of braking, in which motor armature remains connected to the supply and draws power from it producing torque opposite to the direction of motion. |
| A. | Rheostatic braking |
| B. | Regenerative braking |
| C. | Plugging |
| D. | Eddy current braking |
| Answer» D. Eddy current braking | |
| 242. |
In a closed-loop control of squirrel cage induction motor, the field-oriented control strategy implemented is |
| A. | Scalar control |
| B. | Vector control |
| C. | Adaptive control |
| D. | Frequency control |
| Answer» C. Adaptive control | |
| 243. |
In ac drives, stable operating point is when |
| A. | Load torque is equal to electromagnetic torque |
| B. | Load torque is greater than electromagnetic torque |
| C. | Load torque is less than electromagnetic torque |
| D. | None of the above |
| Answer» B. Load torque is greater than electromagnetic torque | |
| 244. |
A dc motor generates a back emf of 200 V. It is controlled by a pair of thyristors in a single-phase full-wave center-tapped circuit. The voltage between the center tap and each anode is 175 V ac, for firing angle 60° and Ra = 0.8 Ω, the armature current will be |
| A. | 7.88 A |
| B. | 12.52 A |
| C. | 14.14 A |
| D. | 15.45 A |
| Answer» E. | |