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

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Description : In a synchronous generator if the excitation increased from a low value to normal value, with a fixed load  (A) The armature current increases and the power factor decreases  (B) The armature ... but is lagging  (D) The armature current decreases and the power factor increases and is leading

Answer : In a synchronous generator if the excitation increased from a low value to normal value, with a fixed load The armature current decreases and the power factor increases and is leading

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 : Synchronous motor always runs at which speed?

Answer : Synchronous motor always runs at synchronous speed.

Description : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ (A) directly proportional to α and Φ (B) ... proportional to α and inversely proportional to Φ (D) directly proportional to Φ and inversely proportional to α

Answer : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ directly proportional to α and inversely proportional to Φ

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

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.

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.

Answer : Centrifugal switch disconnects the auxiliary winding of the motor at about 70 to 80 percent of synchronous speed.

Description : Why the speed of synchronous motor is constant?

Answer : A synchronous machine with low value of short-circuit ratio has lower stability limit.

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 : 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.

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

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 : 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 : The relay operating speed depends upon the spring tension, the rate of flux built up, armature core air gap.

Description : Hunting in synchronous motor cannot be due to?

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

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

Description : Two synchronous generators operating in parallel supply a common load of 2.5 MW. The frequency-power characteristics have a common slope of 1 MW/Hz and the no-load frequencies of the generators are 51.5 Hz and 51.0 Hz, ... system frequency is (A) 50 Hz (B) 51 Hz (C) 51.25 Hz (D) 51.5 Hz

Answer : Two synchronous generators operating in parallel supply a common load of 2.5 MW. The frequency-power characteristics have a common slope of 1 MW/Hz and the no-load frequencies of the generators are 51.5 Hz and 51.0 Hz, respectively. Then the system frequency is 50 Hz

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 : 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 : 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.

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 : An electric motor in which both stator field and rotor rotates with same speed is called?

Answer : An electric motor in which both stator field and rotor rotates with same speed is called synchronous motor.

Description : The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

Answer : The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

Answer : The speed of a D.C. shunt motor can be increased by increasing the resistance in field circuit.

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

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

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

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.

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

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 : The construction of a synchronous motor resembles an alternator.

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?

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

Answer : Synchronous motor has more efficiency.

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

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

Description : The back emf of synchronous motor depends on?

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

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.

Description : In a single-phase induction motor, the operating direction is determined by the ________ A) Rotor B) Stator C) Starting circuit D) None of these

Answer : In a single-phase induction motor, the operating direction is determined by the Starting circuit

Answer : Yes, we can make the power factor of synchronous motor leading by adjusting its excitation.

Answer : The value of starting capacitor of a fractional horse power motor will be 300 uF .

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