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

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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. 

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

Answer : Three phase synchronous motor will have two sliprings.

Description : An unexcited single phase synchronous motor is ?

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

Answer : If the capacitor of a single-phase motor is short-circuited the motor will not start.

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

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

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

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.

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.

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 speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque  (1) Decreases (2) Increases (3) Remains constant (4) None of the above

Answer : The speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque Increases 

Description : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be

Answer : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be 25 N -m

Description : A 400 V, 50 Hz three-phase induction motor rotates at 1440 rpm on full -load. The motor is wound for

Answer : A 400 V, 50 Hz three-phase induction motor rotates at 1440 rpm on full -load. The motor is wound for 4 poles

Description : The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole)  (A) has q -axis current only (B) has d -axis current only (C) has both d and q axis currents (D) cannot be divided between q and d axis currents

Answer : The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole) has d -axis current only

Description : A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. lf its shaft load is reduced by half and field current is held constant then its new power factor will be

Answer : Leading

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

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

Answer : Synchronous motor has more efficiency.

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 : 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.

Description : List different types of stepper motor. State one application of stepper motor.

Answer : Types of stepper motor : (i)Variable - reluctance motor (ii) Permanent- magnet motors (iii) Hybrid motors. Applications of stepper motor : In robotics, In CNC machines, In computers, printers, ... In Watches, In biomedical applications such as X-ray machines, CT scan, In Process control systems. 

Description : The secondary of a current transformer is always short-circuited under operating conditions because it?

Answer : The secondary of a current transformer is always short-circuited under operating conditions because it avoids core saturation and high voltage induction.

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 : Why is a capacitor used in a single phase motor and not in three phase motor ?

Answer : In 1-phase induction motor capacitor work is generate the auxiliary winding current than excite the main winding to rotor starts rotate. After rotor start rotating about 75% of their speed than auxiliary ... emf to start the motor.so,in 3-phase induction motor is self start induction motor.

Description : What is mean by plugging in three phase induction motor?

Answer : Plugging in three-phase induction motor means interchanging of any two phases of a stator for quick stopping.

Description : Explain with neat circuit diagrams the procedures to perform no load and blocked rotor tests on three phase induction motor.

Description : Explain the need and steps to conduct the reduced voltage running up test on the three phase induction motor.

Description : State any four advantages of three phase induction motor. 

Answer : Advantages of three phase induction motor https://youtu.be/27OIOCKN05U

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