A synchronous motor is essentially a motor with

A synchronous motor is essentially a motor with 

 (a) Constant speed (b) Leading power factor (c) Unity power factor (d) Lagging power factor 
by

1 Answer

Answer :

a
by

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Description : In a 3-phase synchronous motor;  (A) the speed of the stator MMF is always more than that of the rotor MMF (B) the speed of the stator MMF is always less than that of the rotor MMF (C) the ... that of the rotor MMF is zero (D) the rotor and the stator MMF are stationary with respect to each other

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Description : A four pole, 60 Hz, three-phase synchronous motor comes up to 1760 RPM when started as an induction motor. What is the percent slip after the rotor field is energized? A. 0 B. 1.1 C. 2.2 D. 3.3

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Which of the listed motors will operate at the highest RPM, assuming that each operates at the same frequency? A. A four-pole synchronous motor under normal load. B. A four-pole induction motor under no load. C. A six-pole synchronous motor under normal load. D. A six-pole induction motor under full load.

Description : Which of the listed motors will operate at the highest RPM, assuming that each operates at the same frequency? A. A four-pole synchronous motor under normal load. B. A four-pole induction motor under ... A six-pole synchronous motor under normal load. D. A six-pole induction motor under full load.

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A four-pole 60-hertz induction motor has a synchronous speed of 1800 RPM and a slip of 4 percent at full load. What will be its full load speed? A. 1728.0 RPM B. 1730.7 RPM C. 1800.0 RPM D. 1872.0 RPM

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If the synchronous speed of a 12 pole, polyphase, induction motor operating at 60 Hz were 600 RPM, how many poles will be required in a similar motor operating at the same frequency but having a synchronous speed of 900 RPM? A. 4 B. 6 C. 8 D. 18

Description : If the synchronous speed of a 12 pole, polyphase, induction motor operating at 60 Hz were 600 RPM, how many poles will be required in a similar motor operating at the same frequency but having a synchronous speed of 900 RPM? A. 4 B. 6 C. 8 D. 18

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The effect of carrying field excitation excessively high on a synchronous motor will result in a _____________. A. tendency for the motor to fall out of step B. tendency for the motor to overspeed C. tendency for the motor to overheat D. loss of motor speed regulation

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If a synchronous motor begins to vibrate severely and pull out of synchronism, the cause may be ____________. A. an overload B. an open in the field coils C. no exciter voltage D. all of the above

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The speed of a synchronous motor is varied by _____________. A. interchanging any two of the three live leads B. changing the voltage of the system C. changing the input frequency D. increasing the field excitation

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Which of the instruments listed could be use to locate a grounded field coil in a synchronous motor? A. Ammeter B. Voltmeter C. Megohmmeter D. Frequency meter

Description : Which of the instruments listed could be use to locate a grounded field coil in a synchronous motor? A. Ammeter B. Voltmeter C. Megohmmeter D. Frequency meter

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The propeller shaft speed in a turbo-electric, synchronous, propulsion drive motor is changed by varying the __________. A. turbine speed B. number of motor poles C. field strength of the generator D. field strength of the motor

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If an induction motor were to be operated at 90% rated voltage, _____________. A. there would be an increase in starting torque B. starting current would increase slightly C. synchronous speed would decrease slightly D. the slip would increase

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The speed of a wound-rotor induction motor _____________. A. will be fixed by the number of field poles B. can be varied by a rheostat-type control C. can only be synchronous speed at full load D. can only attain synchronous speed at no load

Description : The speed of a wound-rotor induction motor _____________. A. will be fixed by the number of field poles B. can be varied by a rheostat-type control C. can only be synchronous speed at full load D. can only attain synchronous speed at no load

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The synchronous speed of an induction motor is the ________. A. speed at which the rotor turns B. speed of the rotating field C. frequency of the rotor current D. slip in per cent of rotor RPM

Description : The synchronous speed of an induction motor is the ________. A. speed at which the rotor turns B. speed of the rotating field C. frequency of the rotor current D. slip in per cent of rotor RPM

Last Answer : Answer: B

An increase in which of the listed conditions will increase the speed of a synchronous motor? A. Frequency B. Voltage C. Armature current D. Inductance

Description : An increase in which of the listed conditions will increase the speed of a synchronous motor? A. Frequency B. Voltage C. Armature current D. Inductance

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The rotor of a synchronous motor operates in synchronism with the rotating field because ______________. A. of the amortisseur windings B. the rotor is magnetically locked into step with the rotating magnetic field by the excitation current C. the field strength varies directly with rotor slip D. the stator flux rotates in the opposite direction

Description : The rotor of a synchronous motor operates in synchronism with the rotating field because ______________. A. of the amortisseur windings B. the rotor is magnetically locked into step with the ... field strength varies directly with rotor slip D. the stator flux rotates in the opposite direction

Last Answer : Answer: B

Which of the listed instruments can be best used to locate a grounded field coil in a synchronous motor? A. Frequency meter B. Megohmmeter C. Voltmeter D. Multimeter

Description : Which of the listed instruments can be best used to locate a grounded field coil in a synchronous motor? A. Frequency meter B. Megohmmeter C. Voltmeter D. Multimeter

Last Answer : Answer: B

A shaded-pole motor is a ____________. A. synchronous motor B. three-phase induction motor C. compound-wound motor D. single-phase induction motor

Description : A shaded-pole motor is a ____________. A. synchronous motor B. three-phase induction motor C. compound-wound motor D. single-phase induction motor

Last Answer : Answer: D

The purpose of squirrel-cage windings in a synchronous motor is to ______________. A. provide more precise balancing B. produce a higher power factor C. eliminate arcing between the stator and the frame D. provide a means for starting

Description : The purpose of squirrel-cage windings in a synchronous motor is to ______________. A. provide more precise balancing B. produce a higher power factor C. eliminate arcing between the stator and the frame D. provide a means for starting

Last Answer : Answer: D

The purpose of amortisseur windings in a synchronous motor is to ______________. A. reduce eddy current losses B. produce a higher power factor C. provide a means for starting D. eliminate arcing between the stator and the rotor

Description : The purpose of amortisseur windings in a synchronous motor is to ______________. A. reduce eddy current losses B. produce a higher power factor C. provide a means for starting D. eliminate arcing between the stator and the rotor

Last Answer : Answer: C

A damper winding is designed as part of a synchronous motor to ____________. A. increase efficiency B. provide starting torque C. provide excitation D. eliminate slippage

Description : A damper winding is designed as part of a synchronous motor to ____________. A. increase efficiency B. provide starting torque C. provide excitation D. eliminate slippage

Last Answer : Answer: B

The most common source of excitation for synchronous motors is a/an _____________. A. low voltage battery B. motor attenuator set C. DC exciter generator D. AC supply

Description : The most common source of excitation for synchronous motors is a/an _____________. A. low voltage battery B. motor attenuator set C. DC exciter generator D. AC supply

Last Answer : Answer: C

On an engine throttle control system, the auxiliary control circuits are provided with devices to prevent excessive overtravel of the pilot valve by the synchronous motor. These devices are called _________________. A. overlap sensors B. limit switches C. overtravel relays D. proximity switches

Description : On an engine throttle control system, the auxiliary control circuits are provided with devices to prevent excessive overtravel of the pilot valve by the synchronous motor. These devices are called _________________. A. overlap sensors B. limit switches C. overtravel relays D. proximity switches

Last Answer : Answer: B

The function of amortisseur, or damper windings in a synchronous motor is to _____________. A. eliminate slippage B. provide excitation C. provide starting torque D. increase efficiency

Description : The function of amortisseur, or damper windings in a synchronous motor is to _____________. A. eliminate slippage B. provide excitation C. provide starting torque D. increase efficiency

Last Answer : Answer: C

A synchronous motor maintains synchronism with the rotating field because _____________. A. field strength varies directly with rotor slip B. DC current applied to the rotor coils causes the rotor magnets to lock in with the rotating flux of the stator C. the stator poles are dragged around due to the flux created by the excitation current D. the stator flux rotates in the opposite direction

Description : A synchronous motor maintains synchronism with the rotating field because _____________. A. field strength varies directly with rotor slip B. DC current applied to the rotor coils causes the rotor ... the flux created by the excitation current D. the stator flux rotates in the opposite direction

Last Answer : Answer: B

The function of damper windings in a synchronous motor is to _____________. A. eliminate slippage B. provide excitation C. provide starting torque D. increase efficiency

Description : The function of damper windings in a synchronous motor is to _____________. A. eliminate slippage B. provide excitation C. provide starting torque D. increase efficiency

Last Answer : Answer: C

Amortisseur windings are installed in a synchronous motor to _____________. A. reduce eddy current losses B. produce a higher power factor C. provide a means for starting D. eliminate arcing between the stator and the rotor

Description : Amortisseur windings are installed in a synchronous motor to _____________. A. reduce eddy current losses B. produce a higher power factor C. provide a means for starting D. eliminate arcing between the stator and the rotor

Last Answer : Answer: C

The purpose of a cage rotor winding placed on the rotor of a synchronous motor is to _____________. A. provide excitation to the DC field B. start the machine as an induction motor C. contribute extra torque at synchronous speed D. prevent the machine from falling out of step

Description : The purpose of a cage rotor winding placed on the rotor of a synchronous motor is to _____________. A. provide excitation to the DC field B. start the machine as an induction motor C. contribute extra torque at synchronous speed D. prevent the machine from falling out of step

Last Answer : Answer: B

A motor using a rheostat in the motor circuit to vary the speed is called a ____________. A. squirrel-cage induction motor B. regenerative braking motor C. wound-rotor induction motor D. synchronous motor

Description : A motor using a rheostat in the motor circuit to vary the speed is called a ____________. A. squirrel-cage induction motor B. regenerative braking motor C. wound-rotor induction motor D. synchronous motor

Last Answer : Answer: C

In an AC synchronous motor electric propulsion plant, propeller speed is controlled by varying the _____________. A. prime mover speed B. electric coupling field strength C. number of energized main motor poles D. propulsion generator field strength

Description : In an AC synchronous motor electric propulsion plant, propeller speed is controlled by varying the _____________. A. prime mover speed B. electric coupling field strength C. number of energized main motor poles D. propulsion generator field strength

Last Answer : Answer: A

While starting a main propulsion synchronous motor, the ammeter pegs out at maximum and then returns to the proper value after synchronization. This indicates the _____________. A. motor has started properly B. field windings are grounded C. slip rings are dirty D. power transmission cables are grounded

Description : While starting a main propulsion synchronous motor, the ammeter pegs out at maximum and then returns to the proper value after synchronization. This indicates the _____________. A. motor has started ... field windings are grounded C. slip rings are dirty D. power transmission cables are grounded

Last Answer : Answer: A

Which of the following statements is true concerning a polyphase synchronous propulsion motor? A. The motor is started as an induction motor. B. Resistance is gradually added to the rotor circuit. C. The starting current is held below the rated current. D. The field winding is energized for starting purposes only.

Description : Which of the following statements is true concerning a polyphase synchronous propulsion motor? A. The motor is started as an induction motor. B. Resistance is gradually added to the rotor circuit. C. ... is held below the rated current. D. The field winding is energized for starting purposes only.

Last Answer : Answer: A

Hunting of a synchronous motor:

Description : Hunting of a synchronous motor:

Last Answer : When the mechanical load is constant, the rotor settles down to an absolutely constant speed with the torque angle fixed by the particular delivered power. When there is a change in load the rotor speed ... are short circuited; copper bars are embedded in the faces of the field poles of the motor.