# If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in?

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.

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

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 : 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 : Why the speed of synchronous motor is constant?

Description : Synchronous motor always runs at which speed?

Answer : Synchronous motor always runs at synchronous speed.

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

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 : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be

Answer : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be 474 V

Answer : If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then Electrolytic capacitor will, in all probability, suffer break down.

Description : In synchronous motor, does the winding losses vary with load?

Answer : No, in the synchronous motor the winding losses do not vary with load.

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

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

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.

Answer : Speed torque characteristic of a repulsion induction motor is similar to that of a D.C. compound motor.

Answer : In variable speed motor a weaker commutating field is needed at low speed than at high speed.

Answer : In a D.C. shunt motor, speed is independent of armature current.

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 : The speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min (A) 100 rpm (B) 200 rpm (C) 400 rpm (D) 800 rpm

Answer : The speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min 200 rpm

Answer : Series motor has the poorest speed control.

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 : As the load is increased the speed of D.C. shunt motor will reduce slightly.

Answer : For the same H.P. rating and full load speed, following motor has poor starting torque differentially compounded.

Answer : The speed of a D.C. series motor is inversely proportional to the armature current.

Answer : The speed of a universal motor is usually reduced by using gearing.

Answer : Speed control of a universal motor is achieved by varying field flux with tapped field windings, connecting rheostat in series, applying variable voltage by means of silicon controlled rectifier, applying variable voltage by means of variable auto-transformer.

Answer : The speed/load characteristics of a universal motor is same as that of D.C. series motor.

Answer : The speed control of universal motor used for sewing machines is by varying the resistance.

Description : What are the speed control methods of dc motor?

Answer : Field control of DC motor Armature control of DC motor

Description : speed control methods of three phase induction motor?

Answer : Speed control of three phase induction motor

Description : Damper winding in a synchronous motor

Answer : Damper winding in a synchronous motor Serves to start the motor.

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

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

Description : The effect of increasing load on a synchronous motor running with normal excitation is (A) Increase both its Ia and power factor. (B) Decrease Ia, but increase power factor. (C) Increase Ia, but decrease power factor (D) Decrease both Ia and power factor.

Answer : The effect of increasing load on a synchronous motor running with normal excitation is Increase Ia, but decrease power factor

Description : Why synchronous motor Cannot start itself?

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

Description : What is the principle of synchronous motor?

Description : What is the use of synchronous motor?

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

Description : what is the difference between synchronous and asynchronous motor?

Answer : Asynchronous motors and syncrouns motor are called as dc machines.  and also syncrouns motor called as induction motor. Asynonymous motor as are rotates with constant speed we not able to operate . ... It is able to operate. These are a small difference between syncrouns and asynchronous motors.

Description : Why does the speed of a DC shunt motor decrease as the load increases?

Answer : Because if the load is increasing then the torque must also be increase. If not then the speed of motor will decrease.

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 : If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will increase.

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

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 : 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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