Electrical Machines - III Mid - I, September - 2014

1.The stator of an alternator is identical to that of a
  • DC generator
  • 3 - phase IM
  • 1 - phase IM
  • stepper motor
Answer: B
2.The salient pole construction is used for __________ alternator
  • 2 - pole
  • 4 – pole
  • 8 – pole
  • none
Answer: C
3.AC generators are rated in ___________
  • MVA or kVA
  • kVAR
  • MW
  • H.P
Answer: A
4.Fractional slot windings are used to eliminate
  • High frequency harmonics
  • 3rd harmonics
  • time harmonics
  • noise
Answer: A
5.In an alternator, the effect of armature reaction is minimum when the power factor is
  • 0.866 lagging
  • 0.866 leading
  • 0.5 lagging
  • unity
Answer: D
6.When the load increases, terminal voltage increases if the load power factor is
  • Unity
  • lagging
  • leading
  • zero
Answer: C
7.In order that two alternators be put in parallel, which of the following factors should be identical for both ?
  • Voltage
  • Frequency
  • Phase sequence
  • All of the above
Answer: D
8.When two alternators are running in exactly synchronism, the synchronizing power will be
  • zero
  • sum of the output of two
  • unity
  • 0.707
Answer: A
9.The zero power factor characteristics for a potier diagram can be obtained by loading the alternator using
  • Lamp load
  • synchronous motor
  • water load
  • DC motor
Answer: B
10.Which one of the following method will give higher than the actual value of regulation of an alternator
  • Zpf
  • ASA
  • EMF
  • MMF
Answer: C
11.Low speed alternators are driven by _____________ turbines
Answer: Hydraulic turbines
12.The frequency of emf generated in an 8 pole alternator running at 900 rpm is ________
Answer: 60 Hz
13.An alternator is said to be over excited when it is operating at _________ power factor
Answer: Lagging
14.Slip test is performed to determine _____________
Answer: Xd & Xq
15.In case of 4-pole machine, 1 mechanical degree corresponds to _______ electrical degrees
Answer: Two
16.A 30 MVA, 15 kV alternator will have a per phase nominal impedance of ______
Answer: 7.5 ohm
17.The stator winding of an alternator is normally connected in star to eliminate the ________ harmonic component of voltage waveforms
Answer: Third
18.In large alternators damper winding is used to improve _________
Answer: Stability
19.The rotor of an alternator has __________ slip rings for DC supply.
Answer: Two
20.Two-alternators are running in parallel. If the driving force of both the alternators is changed, this will result in change in __________
Answer: Frequency