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Answer :

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

Related questions

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

Description : Draw and explain bulk correction method for power factor & control.

Last Answer : Bulk correction method for power factor & control: i) Here individual starter controls the capacitors located at distribution panel. ii) Centralized compensation is employed in large industrial plants where many ... capacitor units in steps to maintain P.F. more than preset limit (0.95). 

Description : The benefit of power factor correction in a power system is (A) lower power consumption (B) increased demand charge (C) reduced load carrying capabilities in existing lines (D) reduced voltage profile

Last Answer : The benefit of power factor correction in a power system is lower power consumption

Description : Capacitors for power factor correction are rated in?

Last Answer : Capacitors for power factor correction are rated in kVAR.

Description : What is the use of power factor correction?

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.

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

Description : In a synchronous generator delivering lagging power factor load  (1) the excitation emf leads terminal voltage by the power angle (2) the excitation emf lags terminal voltage by the power angle (3) ... by the power factor angle (4) excitation emf lags the terminal voltage by the power factor angle

Last Answer : In a synchronous generator delivering lagging power factor load the excitation emf leads terminal voltage by the power angle

Description : The power factor angle and torque angle of a salient pole synchronous generator drawing a current of 1.0 pu from a lagging load are 45o and 15o, respectively. The direct axis and quadrature axis currents, respectively, are (A) 0.5 pu ... pu, 0.5 pu (C) 0.707 pu, 0.707 pu (D) 0.5 pu, 0.5 pu

Last Answer : The power factor angle and torque angle of a salient pole synchronous generator drawing a current of 1.0 pu from a lagging load are 45o and 15o, respectively. The direct axis and quadrature axis currents, respectively, are 0.866 pu, 0.5 pu

Last Answer : In a distribution system, in order to improve power factor, the synchronous capacitors are installed at the receiving end.

Description : Can a synchronous condenser improve power factor?

Last Answer : Yes, synchronous condenser can improve power factor.

Description : How can we improve power factor using synchronous motor?

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

Description : SYNCHRONOUS MOTORS MCQ

Last Answer : 101. In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then (a) the motor is said to be fully loaded (b) the torque ... square of the applied voltage (c) inversely proportional to applied voltage (d) none of the above Ans: a

Description : Damper winding is provided in 3 phase synchronous motors to :

Last Answer : Damper winding is provided in 3 phase synchronous motors to : provide starting torque and prevent hunting

Description : What is the difference between synchronous and asynchronous motors?

Last Answer : The motor which rotates at constant speed is called synchronous motor. And that constant speed is called as synchronous speed.  And the motor which does not rotates at constant speed are called asynchronous motor. Asynchronous motor is also called as Induction motor.

Last Answer : Air blast circuit breakers for 400 kV power system are designed to operate in 50 millisecond.

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

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

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

Description : The efficiencies of transformers compared with that of electric motors of the same power are?

Last Answer : Transformers have high efficiency than the same ratted motors

Description : A 50 Hz, 3-phase induction motor delivers a full load speed of 1440 r.p.m. The number of poles of the motor will be

Description : The maximum reluctance power of a salient-pole synchronous motor having direct-axis reactance, 1.0 pu and quadrature-axis reactance, 0.5 pu, and input voltage, 1.0 pu is (A) 0.25 pu (B) 0.5 pu (C) 1.0 pu (D) 1.5 pu

Last Answer : The maximum reluctance power of a salient-pole synchronous motor having direct-axis reactance, 1.0 pu and quadrature-axis reactance, 0.5 pu, and input voltage, 1.0 pu is 0.5 pu

Last Answer : The relay with inverse time characteristic will operate within 5 to 10 sec.

Last Answer : Circuit breakers usually operate under transient state of short-circuit current.

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%.

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

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

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