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

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Answer :

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

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Description :

The ratio of full -load volt-amperes to short-circuit volt-amperes is equal to :

Answer :

The ratio of full -load volt-amperes to short-circuit volt-amperes is equal to : Z (p.u)

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Description :

In an AC. circuit, a low value of kVAR compared with kW indicates?

Answer :

In an AC. circuit, a low value of kVAR compared with kW indicates high power factor.

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471 views 1 answer
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

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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 current decreases and the power factor also decreases  (C) The armature current decreases and the power factor increases 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

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Description :

Answer :

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

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Description :

Answer :

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

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Description :

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

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.

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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.

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Description :

V - curve of synchronous machine shows the relation between?

Answer :

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

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Description :

Why synchronous machine is called doubly excited machine?

Answer :

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.

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Description :

Which machine is the exciter of synchronous machine?

Answer :

DC shunt machine is the exciter of synchronous machine.

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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

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 

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368 views 1 answer
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 and shunt capacitances.  (2) assumes accelerating power acting on the rotor as constant.  (3) ignores the effect of voltage ... inherent damping present in the machine.  (4) takes into consideration the possibility of machine losing synchronism after it has survived during the first swing.

Answer :

1

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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)

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

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172 views 1 answer
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

Answer :

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

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Description :

Answer :

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

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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.

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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.

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94 views 1 answer
Description :

Answer :

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

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Description :

write short notes on Low-pass filter.

Answer :

low-pass filter (1) filter exhibiting frequency selective characteristic that allows low-frequency components of an input signal to pass from filter input to output unattenuated all high-frequency components are ... the bandwidth of the filter. A filter whose impulse response is a low-pass signal.

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Description :

Given a unity feedback system with G(s)=k/s (s+4), the value of k for damping ratio of 0.5 is

Answer :

Given a unity feedback system with G(s)=k/s (s+4), the value of k for damping ratio of 0.5 is 16

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Description :

Answer :

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

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Description :

Answer :

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

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Description :

In a synchronous motor which losses varies with load?

Answer :

In a synchronous motor, copper losses varies with load.

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Description :

Answer :

To limit the operating temperature an electrical machine should have proper current rating.

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Description :

At very low frequencies a series R-C circuit behaves as almost purely?

Answer :

At very low frequencies a series R-C circuit behaves as almost purely capacitive.

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Description :

A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively

Answer :

A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively 19,17

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Description :

Answer :

Slip-rings in a synchronous motor carry direct current.

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Description :

Answer :

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

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Description :

Answer :

A synchronous motor can develop synchronous torque at synchronous speed.

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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.

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Description :

Answer :

The construction of a synchronous motor resembles an alternator.

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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?

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Description :

A synchronous motor can be made self starting by providing?

Answer :

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

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Description :

Answer :

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

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Description :

Answer :

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

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Description :

Answer :

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

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Description :

Answer :

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

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Description :

Answer :

Exciters of synchronous machines are d.c. shunt machines.

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Description :

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.

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Description :

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.

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Description :

Answer :

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

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Description :

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

Answer :

Synchronous motor has more efficiency.

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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.

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226 views 1 answer
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.

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Description :

Hunting in synchronous motor cannot be due to?

Answer :

Hunting in synchronous motor cannot be due to windage friction.

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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.

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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.

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135 views 1 answer
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