Electrical Machines( Synchronous Machines/Alternator ) Part-10

Electrical Machines( Synchronous Machines/Alternator ) :

Q- 246. The direct axis reactance (X_d) and quadrature axis reactance (X_q) obtained from slip test are

a. X_d = minimum voltage/minimum current , X_q = maximum voltage/maximum current
b. X_d = minimum voltage/maximum current , X_q = maximum voltage/maximum current
c. X_d = maximum voltage/minimum current , X_q = minimum voltage/maximum current
d. X_d = maximum voltage/maximum current , X_q = minimum voltage/minimum current

Q- 247. In a salient pole synchronous generator if E_a is the internal induced emf with I_d and I_q be the direct axis and quadrature axis component of armature current, then

a. I_q is in phase with E_a
b. I_d is in phase with E_a
c. I_d is at 90 degree to E_a
d. Both (a) & (c)
e. None of these

Q- 248. The method used to determine X_d and X_q, the direct and quadrature axis reactance is called

a. Reactance test
b. Blondel’s two reaction theory
c. Slip test
d. All of the above

Q- 249. Depending upon the reluctances offered along the direct axis and quadrature axis, the armature reaction flux will

a. Lead the armature current
b. Lags behind the armature current
c. In phase with the armature current
d. None of these

Q- 250. In Blondel’s two reaction theory, if I_a is armature current per phase, R_a is armature resistance, X_d is direct axis synchronous reactance, X_q is quadrature axis synchronous reactance and V is the terminal voltage, then the voltage in phase with direct axis will be

a. V + I_aR_a + I_a X_d
b. V + I_aR_a + I_aX_q
c. V + I_aX_d + I_aX_q
d. V + I_aR_a + I_aX_d + I_aX_q

Q- 251. The reluctance offered to the mmf wave is lowest when

a. It is aligned with the field pole axis
b. It is oriented at 90 degree to the field pole axis
c. Both (a) and (b)
d. None of these

Q- 252. According to Blondel’s two reaction theory, the armature mmf component acting along direct axis can be

a. Demagnetizing
b. Magnetizing
c. Cross magnetizing
d. Either (a) or (b)

Q- 253. According to Blondel’s two reaction theory the armature mmf is divided into components, direct axis component and quadrature axis component. The component acting along quadrature axis is

a. Magnetizing
b. Demagnetizing
c. Cross magnetizing
d. None of these

Q- 254. Blondel’s two reaction theory which gives the method of analysis of disturbing effects caused by

a. Salient pole construction
b. Non salient pole construction
c. Both (a) and (b)
d. None of these

Q- 255. The synchronous generator supplies leading power factor and lagging power factor respectively when it is

a. Over excited, under excited
b. Over excited, over excited
c. Under excited, under excited
d. Under excited, over excited

Q- 256. The electrical power output of an alternator will be maximum, if the power angle is equal to

a. 0 degree
b. 45 degree
c. 90 degree
d. 180 degree

Q-257. The electrical power output in case of synchronous machine is

a. Directly proportional to the power angle
b. Inversely proportional to the power angle
c. Directly proportional to the square of power angle
d. None of these

Q- 258. What does the pointer of synchroscope indicate when it is rotating in anticlockwise direction and when it is rotating in clockwise direction?

a. Incoming machine is running slow, incoming machine is running faster
b. Incoming machine is running faster, incoming machine is running slow
c. Pointer rotates only in clockwise direction
d. all of the above

Q- 259. For synchronization of alternators, the most suitable method is

a. Lamps method
b. Voltmeter
c. Synchroscope
d. None of the above

Q- 260. While synchronization of three phase alternators by lamps bright and dark method, if the lamps pair become dark and bright simultaneously, it indicates

a. Incorrect phase sequence
b. That the frequencies of alternators are different
c. That voltage of the alternators are not in phase opposition
d. All of these

Q- 261. For synchronization of single phase alternators which method gives the more accurate result?

a. Lamps dark method
b. Lamps bright method
c. Both (a) and (b)
d. None of these

Q- 262. If the frequencies of the two alternators in lamp dark method for synchronization of alternators are unequal, then the two lamps will

a. Glow together
b. Become alternately bright and dark
c. Not glow at all
d. None of the above

Q- 263. In lamps dark method for synchronization of single phase alternator, if the frequency of two alternators is exactly same as well as their voltages are in exact phase opposition then the resultant voltage will be

a. Sum of the voltages of two alternators
b. Equal to the voltage of alternators
c. Zero
d. None of these

Q- 264. To have effective synchronization without any interruption, the necessary conditions which must be satisfied are

a. The terminal voltage and frequency of the incoming machine must be same as that of bus bar voltage and frequency
b. With respect to the external load, the phase of alternator voltage must be identical with that of the bus bar voltage
c. Both (a) and (b)
d. None of these

Q- 265. What happens if a stationary alternator is connected to live bus bar?

a. It can result in short circuit
b. A large emf will be induced by alternator
c. Both (a) and (b)
d. None of these

Q- 266. The direct method for finding the voltage regulation of an alternator is/are

a. E.M.F method
b. M.M.F. method
c. Z.P.F method
d. None of these

Q- 267. The synchronous generator is loaded for obtaining zero power characteristics by using

a. D.C. motor
b. Lamp load
c. Synchronous motor
d. All of these

Q- 268. In Potier’s triangle method, to determine armature leakage reactance and armature reaction mmf separately, the tests performed are

a. Open circuit test and short circuit test
b. Open circuit test and zero power factor test
c. Short circuit test and zero power factor test
d. Open circuit test, short circuit test and zero power factor test

Q- 269. If the value of SCR in an alternator is low then the air gap and voltage drop across synchronous reactance will be

a. Low, high
b. High, low
c. Low, low
d. High, high

Q- 270. ow value of SCR in an alternator indicates

a. High stability limit
b. Low stability limit
c. None of these

Q- 271. Short circuit ratio of an alternator is given by

a. I_{f for rated short circuit current} / I _{f for rated short circuit voltage}
b. I_{f
for rated short circuit Voltage} / I_{f for rated short circuit
current}
c. I_{f
for rated open circuit Voltage} / I_{f for rated short circuit
current}
d. I_{f
for rated short circuit current} / I_{f for rated open circuit
voltage}