# Why synchronous machine is called doubly excited machine?

Why synchronous machine is called doubly excited machine?

The synchronous machine is called doubly excited machine because in synchronous machine both stator and rotor are excited.

Armature windings of synchronous machines either deliver 3 phase AC or absorb 3 phase AC source,  whereas field windings are energized from DC source. Thus due to presence of AC on armature and DC on field windings, synchronous machines are often referred as doubly excited machines.

## Related questions

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

Last 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?

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

Last Answer : An over excited synchronous motor on noload is known as synchronous condenser.

Last Answer : Synchronsizing power of a synchronous machine is inversely proportional to the synchronous reactance.

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

Description : If we change the excitation of synchronous machine will it affect on power factor?

Last Answer : Yes, If we change the excitation of synchronous machine it will affect on power factor. If the synchronous motor is overexcited then it will have leading power factor and if the motor is underexcited then it will have lagging power factor.

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

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

Description : V - curve of synchronous machine shows the relation between?

Last Answer : V - curve of synchronous machine shows the relation between AC armature current and DC field current.

Description : Which machine is the exciter of synchronous machine?

Last Answer : DC shunt machine is the exciter of synchronous machine.

Description : In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as  (1) synchronous motor (2) synchronous generator (3) asynchronous motor (4) asynchronous generator

Last Answer : In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as synchronous generator

Description : The 'Equal area criterion' for the determination of transient stability of a synchronous machine connected to an infinite bus  (1) ignores line as well as synchronous machine resistance ... consideration the possibility of machine losing synchronism after it has survived during the first swing.

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

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

Description : During a disturbance on a synchronous machine, the rotor swings form A to B before finally setting down to steady state at point C on the power angle curve. The speed of the machine during oscillation is synchronous at point(s)

Last Answer : During a disturbance on a synchronous machine, the rotor swings form A to B before finally setting down to steady state at point C on the power angle curve. The speed of the machine during oscillation is synchronous at point(s) only at C

Description : Torque angle for the synchronous machine is the angle between (A) stator magnetic field and rotor magnetic field (B) stator magnetic field and net magnetic field in the air gap (C) rotor magnetic field and net magnetic field in the air gap (D) excitation voltage and impedance voltage drop

Last Answer : Torque angle for the synchronous machine is the angle between rotor magnetic field and net magnetic field in the air gap

Description : With a neat diagram explain doubly fed induction generator (DFIG).

Last Answer : Diagram of Doubly fed induction generator (DFIG):  Explanation :-  DFIG can feed power through the stator as well as rotor to the grid. The stator is directly connected to the fixed frequency ... voltage is 690 V AC. So it must be step up to 33 KV to connect to power grid.

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

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

Description : A separately excited dc motor operating in first quadrant is fed from 3-phase semi -converter free -wheeling diode is open circuited, then the motor :  (A) can be operated in first quadrant (B) ... in first & second quadrants (C) can be operated in first & fourth quadrants (D) cannot be operated

Last Answer : A separately excited dc motor operating in first quadrant is fed from 3-phase semi -converter free -wheeling diode is open circuited, then the motor : can be operated in first & fourth quadrants

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

Last 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

Last Answer : In a separately excited generator supplying rated load the armature reaction is always present.

Description : Separately Excited DC motor

Last Answer : Separately Excited DC motor

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

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

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

Last 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.

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

Last Answer : The standard full-load power factor ratings for synchronous motors are unity or 0.8 leading.

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

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

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

Last Answer : Synchronous motors are generally not self-starting because the direction of instantaneous torque reverses after half cycle.

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

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

Last 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?

Last 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.

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

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

Last Answer : For power factor correction, synchronous motors operate at no-load and greatly over-excited fields.

Last Answer : Exciters of synchronous machines are d.c. shunt machines.

Last 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.

Last 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.

Last 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?

Last Answer : Synchronous motor has more efficiency.

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

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

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

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

Description : Hunting in synchronous motor cannot be due to?

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

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

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

Description : An unexcited single phase synchronous motor is ?

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

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

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

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

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

Description : The back emf of synchronous motor depends on?

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

Description : Synchronous motor always runs at which speed?

Last Answer : Synchronous motor always runs at synchronous speed.