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The efficiency of a properly designed synchronous motor will usually fall in range 85 to 95%.

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Description : Which motor have more efficiency, synchronous motor or induction motor?

Answer : Synchronous motor has more efficiency.

Answer : Generators for peak load plants are usually designed for maximum efficiency at 50 to 75 percent full load.

Answer : The braking retardation is usually in the range 10 to 15 km phps.

Answer : D.C. generators are normally designed for maximum efficiency around full-load.

Answer : If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then the stator current will be zero.

Answer : The range of efficiency for shaded pole motors is 5% to 35%.

Answer : The duration of sudden short-circuit test on a synchronous motor is usually about one second.

Answer : In case one phase of a three-phase synchronous motor is short-circuited the motor will not start.

Description : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as?

Answer : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as pull-in torque.

Answer : If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will stop.

Description : The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as?

Description : If we change the excitation of synchronous machine will it affect on motor speed?

Answer : No, If we change the excitation of synchronous machine it will not affect on motor speed.

Description : If the load of the normally excited synchronous motor is increased the power factor will?

Answer : If the load of the normally excited synchronous motor is increased the power factor will become lagging.

Description : If the field of synchronous motor is under excited, power factor will be?

Answer : If the field of synchronous motor is under excited, power factor will be lagging.

Description : The synchronous motor will develop maximum power when the load angle is?

Answer : The synchronous motor will develop maximum power when the load angle is 900.

Description : what will happen when excitation of an unloaded salient pole synchronous motor suddenly gets disconnected?

Answer : When excitation of an unloaded salient pole synchronous motor suddenly gets disconnected the motor will stop.

Description : Three phase synchronous motor will have how many sliprings?

Answer : Three phase synchronous motor will have two sliprings.

Answer : The wattage rating for a ceiling fan motor will be in the range 50 to 150 W .

Answer : In a A.C. series motor armature coils are usually connected to commutator through resistance.

Answer : In a shaded pole motor, the shading coil usually consist of a single turn of heavy copper wire which is short-circuited and carries only induced current.

Answer : The power factor of a single-phase induction motor is usually lagging.

Answer : Slip-rings in a synchronous motor carry direct current.

Answer : A synchronous motor running with normal excitation adjusts to load increases essentially by increase in armature current.

Answer : In a synchronous motor, the armature current has large values for high and low excitation.

Answer :  The size of a synchronous motor decreases with the increase in flux density.

Description : What is the maximum value of torque angle in synchronous motor?

Answer : The maximum value of torque angle in synchronous motor is 90 degrees electrical.

Description : Hunting in synchronous motor cannot be due to?

Answer : Hunting in synchronous motor cannot be due to windage friction.

Description : The damping winding in synchronous motor is generally used to?

Answer : The damping winding in synchronous motor is generally used to provide starting torque and prevent hunting.

Description : In a synchronous motor which losses varies with load?

Answer : In a synchronous motor, copper losses varies with load.

Description : A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?

Answer : A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because stator supply is not required to produce magnetic field.

Answer : The operating speed of a synchronous motor can be changed to new fixed value by changing frequency.

Answer : A synchronous motor can develop synchronous torque at synchronous speed.

Answer : The construction of a synchronous motor resembles an alternator.

Answer : The coupling angle or load angle of synchronous motor is defined as the angle between the rotor and the stator poles of opposite polarity.

Answer : The armature current of the synchronous motor has large values for low and high excitation.

Description : How can we reverse the direction of rotation of synchronous motor?

Answer : By reversing supply phase sequence we can reverse the direction of rotation of synchronous motor.

Description : The synchronous motor which works on leading power factor and does not drive any mechanical load is called?

Answer : The synchronous motor which works on leading power factor and does not drive any mechanical load is called synchronous condenser.

Description : An unexcited single phase synchronous motor is ?

Answer : An unexcited single-phase synchronous motor is reluctance motor.

Description : A synchronous motor can be made self starting by providing?

Answer : A synchronous motor can be made self-starting by providing damper bar.

Description : The back emf of synchronous motor depends on?

Answer : The back emf of synchronous motor depends on load angle.

Description : Synchronous motor always runs at which speed?

Answer : Synchronous motor always runs at synchronous speed.

Description : Can we use the synchronous motor as the synchronous capacitor?

Answer : Yes, we can use the synchronous motor as the synchronous capacitor when the synchrnous motor is overexcited.

Answer : In case of a reluctance motor, when the load is increased so that it cannot maintain synchronous speed the motor will run as induction motor.

Description : The synchronous speed of an 8 pole induction motor supplied power from a 50 Hz source will be ?

Answer : Ns         equals        f/pair pole 50/4      - 12.5

Description : List different torques in synchronous motor. 

Answer : Different Torques in Synchronous Motor: 1) Starting torque 2) Running torque 3) Pull-in torque 4) Pull-out torque

Description : Damper winding in a synchronous motor

Answer : Damper winding in a synchronous motor Serves to start the motor.

Description : In a self-controlled synchronous motor fed from a variable frequency inverter  (1) the rotor poles invariably have damper windings  (2) there are stability problems  (3) the speed of the rotor decides stator frequency  (4) the frequency of the stator decides the rotor speed

Answer : In a self-controlled synchronous motor fed from a variable frequency inverter the frequency of the stator decides the rotor speed

Answer : If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in damage to the starting winding.

Description : In synchronous motor, does the winding losses vary with load?

Answer : No, in the synchronous motor the winding losses do not vary with load.

Description : List different starting methods of three phase synchronous motor. Explain any one of them.

Answer : Different Starting Methods of Three Phase Synchronous Motor: As synchronous motor is not self starting, different methods of starting are as follows: 1) By using an Induction (Pony) motor 2) ... . The rotor gets pulled into synchronism and starts running at constant speed as a synchronous motor. 

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