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Objective questions and answers or MCQ of Electrical Machines page-12


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191. The synchronous reactance is defined as the

a) Reactance due to armature reaction of the machine
b) Reactance of synchronous machine
c) Reactance due to leakage flux
d) Combined reactance due to leakage of flux and armature reaction

Ans: (d)

192. In case of leading load power factor, the terminal voltage of alternator as the fall on removing the full load.

a) True
b) False

Ans: (a)

193. The rise of the voltage of alternator when the load is thrown off is same as the fall in the voltage when full load is applied.

a) True
b) False

Ans: (b)

194. Give the three methods of determining the voltage regulation of the alternator.

i) Synchronous Impedance Method
ii) M.M.F. Method
iii) Potier Triangle Method

Ans: ()

195. The synchronous impedance method will not give accurate voltage regulation because

a) The value of synchronous impedance found is always less than actual value
b) The value of synchronous impedance found is always less than the actual value
c) The value of the synchronous impedance is independent of saturation
d) The reactance due to armature reaction is considered separately

Ans: (b)

196. The value of the voltage regulation found by the M.M.F. method is always less than the actual value.

a) True
b) False

Ans: (a)

197. Which of the following methods is better to find the voltage regulation?

a) M.M.F. Method
b) Potier Triangle Method
c) Synchronous Impedance Method
d) None of the above

Ans: (b)

198. The operation of connecting an alternator in parallel with another alternator or with common bus bar is known as

a) Proper machine
b) Mechanizing
c) Synchronizing
d) Asynchronizing

Ans: (c)

199. Give the three conditions for the proper synchronization of alternator

i) The terminal voltage for the incoming alternator must be same as bus bar voltage.
ii) The speed of the incoming machine must be such that its frequency (=pn/120) equals bus bar frequency.
iii) The phase of the alternator voltage must be identical with the phase of the bus bar
voltage. It means that switch must be closed at (or very near) the instant of the two voltage have correct relationship.

Ans: ()

200. In three phase alternators, it is necessary to synchronize one phase only, the other phases will be synchronized automatically.

a) True
b) False

Ans: (a)

201. When the alternators are running in proper synchronism the synchronizing power will be zero

a) True
b) False

Ans: (a)

202. If the two alternators are running in proper synchronism and the voltage of one machine is suddenly increased

a) The machine will burn
b) Both of the machines will stop
c) The synchronization torque will be produced to restore further synchronism
d) Synchronization cannot be attained automatically

Ans: (c)

203. If the input prime-move of an alternator is kept constant but the excitation is changed then

a) The reactive component of the output is changed
b) The active component of the output is changed
c) The power factor of the load remains constant
d) (a) and (b) takes place simultaneously

Ans: (a)

204. The load taken up by the alternator directly depends upon the driving torque or in other words upon the angular advance of its rotor.

a) True
b) False

Ans: (a)

205. A synchronous motor is inherently self-starting motor.

a) True
b) False

Ans: (b)


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