Most Latest Synchronous Machine Stability MCQs ( Electrical Machines ) MCQs – Electrical Machines MCQs

Most Latest Synchronous Machine Stability MCQs ( Electrical Machines ) MCQs – Electrical Machines MCQs

Latest Electrical Machines MCQs

By practicing these MCQs of Synchronous Machine Stability MCQs ( Electrical Machines ) MCQs – Latest Competitive MCQs , an individual for exams performs better than before. This post comprising of objective questions and answers related to Synchronous Machine Stability MCQs ( Electrical Machines ) Mcqs “. As wise people believe “Perfect Practice make a Man Perfect”. It is therefore practice these mcqs of Electrical Machines to approach the success. Tab this page to check “Synchronous Machine Stability MCQs ( Electrical Machines )” for the preparation of competitive mcqs, FPSC mcqs, PPSC mcqs, SPSC mcqs, KPPSC mcqs, AJKPSC mcqs, BPSC mcqs, NTS mcqs, PTS mcqs, OTS mcqs, Atomic Energy mcqs, Pak Army mcqs, Pak Navy mcqs, CTS mcqs, ETEA mcqs and others.

Electrical Machines MCQs – Synchronous Machine Stability MCQs ( Electrical Machines ) MCQs

The most occurred mcqs of Synchronous Machine Stability MCQs ( Electrical Machines ) in past papers. Past papers of Synchronous Machine Stability MCQs ( Electrical Machines ) Mcqs. Past papers of Synchronous Machine Stability MCQs ( Electrical Machines ) Mcqs . Mcqs are the necessary part of any competitive / job related exams. The Mcqs having specific numbers in any written test. It is therefore everyone have to learn / remember the related Synchronous Machine Stability MCQs ( Electrical Machines ) Mcqs. The Important series of Synchronous Machine Stability MCQs ( Electrical Machines ) Mcqs are given below:

Synchronizing Power and Synchronizing Torque

1. The coupling angle or load angle of a synchronous motor is defined as the space angle between __________
a) rotor and stator poles of opposite polarity
b) rotor and stator poles of same polarity
c) rotor and stator teeth
d) rotor and resultant magnetic field
Answer: a
Explanation: It is measured between stator and rotor poles of opposite polarity.


2. What is Synchronizing power?
(i) Stiffness coefficient of electromagnetic coupling between stator and rotor
(ii) Stability measure of synchronous machine
(iii) Power consumption factor
a) i,ii
b) ii, iii
c) iii, i
d) i, ii, iii
Answer: a
Explanation: Synchronizing power is stiffness coefficient representation as well the a measure of stability.


3. Large stiffness coefficient represents ____________
a) motor speed remains practically constant
b) large fluctuations due to mechanical load
c) motor speed is variable to changes
d) no such significance with speed
Answer: a
Explanation: Large stiffness represents the tight coupling in the machine and more stability.


4. An over excited synchronous machine is more stable than under excited.
a) True
b) False
Answer: a
Explanation: Synchronizing power is directly proportional to the excitation.


5. Consider the below remarks for an alternator.
(i) An over excited machine is more stiff
(ii) Machine with longer air-gap is less stable than one with smaller air-gap
a) (i) is True, (ii) is False
b) (i) is False, (ii) is True
c) (i) is True, (ii) is True
d) (i) is False, (ii) is False
Answer: a
Explanation: Larger the air gap smaller than the reactance.


6. As load angle is increased, degree of stability __________
a) reduces
b) increases
c) remains same
d) no change in stability
Answer: a
Explanation: Synchronizing power = EV*cosδ/X.


7. Synchronizing power is __________
a) transient in nature
b) steady state in nature
c) pulsating at small frequencies
d) constant for a machine
Answer: a
Explanation: It is transient in nature and determines stability while disturbances.


8. Which of the following makes synchronizing power to come to play in the machine?
a) Disturbance in power mover
b) Disturbance in field current
c) Disturbance in load
d) All of the mentioned
Answer: a
Explanation: Any disturbance will lead to transients to arise and so the synchronizing power.


9. Which of the following is/are used in synchronous machines to maintain mechanical stability?
a) Damper winding
b) Interpole winding
c) Compensating winding
d) Equalizer rings
Answer: a
Explanation: Damper windings are the dummy windings which help to stablize the machine during transient instability.


10. For a 4-pole 3 phase, 400V alternator has synchronizing power of 300 units. Then the synchronizing power per mechanical degree is?
a) 300
b) 1200
c) 900
d) 600
Answer: a
Explanation: P(sy, mech) = Poles* P(sy,ele)/2
P(sy,ele) = 300 units.


11. Electromagnetic torque is present in rotating machines when ____________
a) both stator and rotor windings carry current
b) rotor windings carry current
c) stator windings carry current
d) any of the mentioned
Answer: a
Explanation: Synchronous machine is a doubly excited machine.


12. The operation of a synchronous motor operating on constant excitation across infinite bus will not be stable if power angle δ?
a) exceeds internal angle θ
b) is less than θ
c) is more than θ/2
d) is less than θ/2
Answer: a
Explanation: Power angle should not exceed θ, to operate under normal conditions.


13. In a synchronous motor the back emf peak set up in the stator depends on ___________
a) rotor excitation
b) supply voltage
c) rotor speed
d) load on the motor
Answer: a
Explanation: It will depend on the excitation.


14. Variation in the dc excitation of a synchronous motor causes variation in ___________
a) armature current and power factor
b) power factor
c) armature current
d) speed
Answer: a
Explanation: Armature current and power factor both will vary by varying the dc excitation.


15. Which motor can conveniently operate at lagging as well as leading power factor?
a) Synchronous motor
b) Slip ring induction motor
c) Squirrel cage induction motor
d) Stepper motor
Answer: a
Explanation: Its the synchronous motor which can favourably operate both at leading and lagging power factor.

Synchronous Machine Stability

1. Steady state stability limit is defined as maximum power flow possible through a particular point without loss of stability when the ___________
a) power is increased gradually
b) power is increased suddenly
c) power is reduced gradually
d) power is reduces suddenly
Answer: a
Explanation: Steady state analysis involves study of stability at gradual changes in the machine.


2. If the load angle is increased till 135°, the consequence will be ___________
a) loss of synchronism
b) no alternation of synchronism
c) increase in stability limit
d) reduction in stability limit
Answer: a
Explanation: Because load angle is more than 90°.


3. The steady state limit can be improved by ___________
i. Increasing excitation
ii. reducing reactance
iii. using series capacitors
a) i, ii, iii
b) i, ii
c) iii only
d) ii, iii
Answer: a
Explanation: Steady state limit = EV/X.


4. Series capacitors will improve the ___________
a) SSSL
b) Transient stability
c) Hunting
d) Stiffness
Answer: a
Explanation: Steady state limit = EV/X.


5. Transient stability limit is less important than SSSL.
a) True
b) False
Answer: b
Explanation: Transient stability is more of concern due to the reason that the machine may loose synchronism due to sudden disturbances.


6. (i) Transient stability is lower than SSSL.
(ii) Transient disturbances are more common.
a) i and ii both are true
b) i false, ii true
c) i true, ii false
d) Both are false
Answer: a
Explanation: Both are correct statements.

 

Efficiency And Regulation MCQs




7. The supply voltage to an induction motor is decreased by 10%. By what percentage, approximately, will the maximum torque decrease?
a) 5%
b) 10%
c) 20%
d) 40%
Answer: c
Explanation: Torque is proportional to V2.
Torque will change by twice percentage of the change in voltage i.e. 20%.


8. In a salient pole synchronous machine the air gap is least under the middle of the pole shoe and increases outwards.
a) True
b) False
Answer: a
Explanation: Air gap for a salient pole structure is minimum at mid of a given pole.


9. If it is planned to bring an incoming alternator to the operating alternator in parallel, then which of the criteria can be ignored?
a) Prime mover speed
b) Voltage magnitude
c) Frequency
d) Phase sequence of the alternator
Answer: a
Explanation: To operate under synchronising conditions, there must be same voltage, frequency and phase sequence for the machines in the parallel.


10. Which one of the following is the base reason to place field on rotor in the alternator?
a) Small power in field circuit
b) Insulation of high voltage is made easy on stator than on rotor
c) Huge power in stator
d) Large current in the stator
Answer: b
Explanation: Providing insulation becomes easier as the stator will be stationary.

Hunting and Damper Windings

1. The relative speed between rotor and stator field is zero. This means ___________
a) mechanical speed of rotor is equal to stator field speed
b) mechanical speed is zero
c) stator field is stationary
d) none of the mentioned
Answer: a
Explanation: The relative speed is between the rotor and the stator field.


2. The satisfactory operation of the synchronous machine means ___________
a) mechanical speed of rotor is equal to stator field speed
b) mechanical speed is zero
c) stator field is stationary
d) none of the mentioned
Answer: a
Explanation: The relative speed should be zero between the rotor and the stator field.


3. Variation of load angle delta, after sudden loading of an unloaded synchronous motor with no damping is?
a) electrical-machines-interview-questions-answers-freshers-q3a
b)electrical-machines-interview-questions-answers-freshers-q3b
c)electrical-machines-interview-questions-answers-freshers-q3c
d)electrical-machines-interview-questions-answers-freshers-q3d
Answer: a
Explanation: With no damping there will be oscillations in the rotor angle.


4. Variation of load angle delta, with loading of an unloaded synchronous motor with damping is?
a) electrical-machines-interview-questions-answers-freshers-q4a
b) electrical-machines-interview-questions-answers-freshers-q3a
c) electrical-machines-interview-questions-answers-freshers-q3c
d) electrical-machines-interview-questions-answers-freshers-q3d
Answer: a
Explanation: With damping the load angle damps out to nominal value.


5. Effects of hunting are/is ___________
a) mechanical stress
b) surge in current
c) rise in temperature
d) all of the mentioned
Answer: d
Explanation: Hunting causes all the mentioned effects on the synchronous machine.


6. What are the probable causes of hunting?
a) sudden change in load
b) fault in supply
c) sudden change in field current
d) all of the mentioned
Answer: d
Explanation: Changing the load suddenly, excitation or the faults will cause transients in the machine.


7. Using a _____ can be used to limit hunting.
a) Flywheel
b) DC Exciter
c) Large load
d) Any of the mentioned
Answer: d
Explanation: Any method mentioned will diminish the transients in the machine.


8. Employment of damper winding will reduce hunting.
a) True
b) False
Answer: a
Explanation: Damper winding are mechanical windings which also reduce the hunting.


9. Damper windings are made of ___________
a) copper
b) iron
c) silicon
d) cast iron
Answer: a
Explanation: They are made of copper as the current also flows through them.


10. The damper winding are placed in ___________
a) pole shoes
b) series with armature
c) series with field
d) rotor slots
Answer: a
Explanation: The damper winding are placed in pole shoes.


11. Turbo generators do not use damper winding due to ___________
a) solid steel rotor core
b) laminated armature
c) soft iron core
d) small current flow in pole shoes
Answer: a
Explanation: Because eddy current in the q-axis produce the same effect as the damper in salient pole machine.


12. Damper winding should have ___________
a) high resistance
b) low starting torque
c) low resistance
d) low reactance
Answer: c
Explanation: For desired hunting, the damper winding should have low resistance.


13. At synchronous speed, relative speed between rotating air-gap flux and damper is?
a) zero
b) Ns
c) lesser than Ns
d) more than zero
Answer: a
Explanation: It is zero.


14. When the rotor speed becomes greater than synchronous speed, which type of torque is produced in damper winding?
a) Induction generator
b) Synchronous generator
c) Reluctance motor
d) Induction motor
Answer: a
Explanation: The slip will become negative and it will operate in generating mode.


15. When an alternator is loaded suddenly the torque produced in damper is?
a) Induction motor
b) Induction generator
c) Synchronous motor
d) Synchronous generator
Answer: a
Explanation: Sudden loading will reduce the speed of the machine and so there will be small slip induced in the machine, making it operate as induction motor.

Most Latest Synchronous Machine Stability MCQs ( Electrical Machines ) MCQs – Electrical Machines MCQs

 

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