200 Important Synchronous Motor MCQ Question and Answer | PDF Free Download
1.In a 3-phase synchronous motor, the magnitude of back emf setup in the stator depends on
- ARotor excitation
- BSupply voltage
- CRotor speed
- DLoad on motor
2.The magnitude of counter or back emf in a s synchronous motor
- AIs always less than supply voltage
- BIs always more than supply voltage
- CIs always equal to supply voltage
- DMay be either equal to or less than or more than supply voltage
3.In a synchronous motor the excitation voltage on no load is approximately equal to the applied voltage. This will happen
- AWhen developed torque is maximum
- BWith zero excitation
- CWith 100% excitation
- DNone of the above
4.Which motor can conveniently operate at lagging as well as leading power factor?
- ASquirrel cage induction motor
- BWound rotor induction motor
- CSynchronous motor
- DDC shunt motor
5.At constant load, the magnitude of armature current drawn by a synchronous motor is large for
- ALow excitation
- BHigh excitation
- CBoth low and high values of field excitation
- D100% excitation
6.Variation in dc excitation of a synchronous motor causes variation in
- ASpeed motor
- BPower factor
- CArmature current
- DBoth armature current and power factor.
7.If the field of a synchronous motor is under excited, the power factor will be
- ALagging
- BLeading
- CUnity
- DMore than unity
8.A synchronous motor is operating on no load at unity power factor. If the filed current is increased, the power factor will become
- ALeading and the current will decrease
- BLagging and the current will increase
- CLagging and the current will decrease
- DLeading and the current will increase
9.A three-phase, salient pole synchronous motor is connected to an infinite bus. It is operated at no load at normal excitation. The field excitation of the motor is first reduced to zero and then increased in the reverse direction gradually. Then the armature current
- AIncreases continuously
- BFirst increases and then decreases steeply
- CFirst decrease and then increases steeply
- DRemains constant
10.A 3-phase synchronous motor is operating at a given load. If an increase in excitation reduces the armature current, it can be concluded that the motor is
- AOperating at lagging power factor and absorbing reactive power from the mains
- BOperating at leading power factor and delivering reactive power to the mains
- CEither (a) and (b)
- DNone of the above
11.A synchronous motor installed at end of a transmission line is operating at lagging power factor. With the fall in supply voltage, the power factor of the synchronous motor will
- AGo down
- BImprove
- CRemain unchanged
- DNone of the these
12.Armature reaction in a synchronous motor at rated voltage and zero power factor (lead) is
- AMagnetizing
- BCross magnetizing
- CBoth magnetizing and cross magnetizing
- DDemagnetizing
13.The torque angle of a synchronous machine operating from a constant voltage bus, is usually defined as the space angle between
- ARotor mmf wave and stator mmf wave
- BRotor mmf wave and resultant flux density wave
- CStator mmf wave and resultant flux density wave
- DStator mmf wave and resultant mmf wave
14.The V-Curve of synchronous motor shows the relation between
- AArmature current and field current
- BPower factor and field current
- CArmature current and torque
- DTorque and field current
15.An inverted V-curve of synchronous motor shows the variation of
- APower factor and dc excitation at constant load
- BSupply voltage and field current at constant excitation
- CPower factor and su9pply voltage during hunting
- DSupply voltage and excitation current at constant load
16.Keeping the excitation voltage same, the load on the motor is increased such that the motor current increases by 20%. The operating power factor will become
- A0.995 lagging
- B0.995 leading
- C0.791 lagging
- D0.848 leading
17.Synchronous capacitor is
- AAn ordinary static capacitor bank
- BAn overexcited synchronous motor driving mechanical load
- CAn overexcited synchronous motor without mechanical load
- DNone of the above
18.An induction motor and synchronous motor are connected to a common feeder line. To operate the feeder line at a unity pf, the synchronous motor should be
- AUnder excited
- BOverexcited
- CNormally excited
- DDisconnected from the common terminals
19.Synchronous condensers, when operated at power factor ranging from lagging through unity to leading for voltage control, are called the
- AVoltage boosters
- BSynchronous reactors
- CMechanical synchronous
- DNone of the above
20.The power factor of a synchronous motor
- AImproves with increase in excitation and may even become leading at higher excitation.
- BDecreases with increase in excitation
- CIs independent of excitation
- DIncreases with loading for a given excitation