Alternator MCQ | Synchronous Generator MCQ

161. The main advantage of distributing the winding in slots is to

  1. reduce the size of the machine
  2. add mechanical strength to the winding
  3. reduce the amount of copper required
  4. reduce the harmonics in the generated emf
Answer
Answer. d

162. The synchronous reactance of a 500 V, 50 kVA alternator having an effective resistance of 0.2 Ω, if an excitation current of 10 A produces 200 A armature current on short circuit and an emf of 450 volts on open circuit, is

  1. 2.6 Ω
  2. 5.2 Ω
  3. 2.24 Ω
  4. 4.5 Ω
Answer
Answer. c

163. Damper bars in case of salient pole rotors of hydro-alternators are usually inserted in pole faces to

  1. strengthen the excitation current of the poles
  2. damp out the rotor oscillations during transient state owing to sudden change in load conditions.
  3. help improve the power factor of load.
  4. reduce the no-load current when load is thrown-off.
Answer
Answer. b

164. A synchronous generator connected to an infinite bus is supplying electrical power at unity power factor to the bus. If the field current is increased

  1. both the active and reactive power output of the machine will remain unchanged.
  2. the active power of the machine will remain unchanged but the machine will also supply lagging reactive power.
  3. the active power output of the machine will increase and the machine will draw leading reactive power from the bus.
  4. the active power output of the machine will remain unchanged but the machine will also supply leading reactive power
Answer
Answer. b

165. A large synchronous generator is feeding power into an infinite bus at slightly lagging power factor. If a total loss of field occurs and the system can supply sufficient reactive power without a large terminal voltage drop, the unit will

  1. continue to run as a synchronous generator and no tripping is necessary.
  2. get short-circuited and it should be tripped instantaneously.
  3. run as an induction generator and it should be tripped after a time delay.
  4. run as a synchronous motor and it should be tripped after a time delay.
Answer
Answer. c

166. A Synchronous generator has its effective internal impedance Zs = 10 Ω and resistance ra = 1.0 Ω. Its generated voltage Ef and terminal voltage Vt are both 500 V. The maximum power output is

  1. 50000 W
  2. 45500 W
  3. 30000 W
  4. 22500 W
Answer
Answer. c

167. A 500 MW, 13.8 kV star connected synchronous generator at 0.8 p.f. will deliver a full load current of

  1. 12.1 kA
  2. 21.0 kA
  3. 26.15 kA
  4. 46.5 kA
Answer
Answer. c

168. Consider the following:

  1. EMF
  2. Reversal
  3. MMF
  4. Direct

Which methods among these are for the determination of voltage regulation of an alternator?

  1. i and ii only
  2. i, ii,iii and iv
  3. i and iii only
  4. ii and iii only
Answer
Answer. c

169. A 3-phase, 11 kV, 5 MVA alternator has synchronous reactance of 10 Ω per phase. Its excitation is such that the generated e.m.f. is 14 kV. If the alternator is connected to infinite bus bar, the maximum output at the given excitation is

  1. 8,000 kW
  2. 15,400 KW
  3. 5,135 kW
  4. 6,200 kW
Answer
Answer. b

170. Power factor of an alternator driven by constant prime mover input can be changed by changing its

  1. Load
  2. Speed
  3. Field excitation
  4. Phase sequence
Answer
Answer. c
Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18