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In case of conductively compensated D.C. series motors, the compensating winding is provided in series with armature winding.

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When two D.C. series motors are connected in parallel, the resultant speed is normal speed.

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During rheostat braking of D.C. series motors motor is run as a generator.

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In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to improve power factor.

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In case of D.C. shunt motors the speed is dependent on back e.m.f. only because flux is practically constant in D:C. shunt motors.

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Damper winding is provided in 3 phase synchronous motors to :

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

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In D.C. shunt motors as load is reduced the speed will remain almost constant.

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Starters are used with D.C. motors because to restrict armature current as there is no back e.m.f. while starting.

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Differentially compound D.C. motors can find applications requiring low starting torque.

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In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to 25% of the previous value.

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

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A D.C. series motor is that which has its field winding consisting of thick wire and less turns.

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The direction of rotation of a D.C. series motor can be changed by interchanging field terminals.

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A.C. series motor as compared to D.C. series motor has smaller brush width, less number of field turns, more number of armature turns, less air gap.

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Answer :

If a D.C. series motor is operated on A.C. supply, it will spark excessively, have poor efficiency, have poor power factor.

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In A.C. series motor compensating winding is employed to reduce sparking at the brushes.

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D.C. shunt motors are used for driving machine tools.

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The D.C. motors preferred for traction applications beacuse the speed is inversely proportional to the torque and the torque is proportional to square of armature current.

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In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is :

Answer :

In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is : 0.075

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Describe the reason of using dc series motor for electric trains.

Answer :

Electric trains require an inverse torque speed characteristics for proper operation. That is a higher torque is required at start (when speed is nil or low) and as the train picks up ... torque - speed characteristics of DC series motors match, these motors are suitable for electric trains

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Why are DC motors used in trains and not AC motors ?

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The reason is torque. torque is inversely proportional to speed..i.e when th knowe train comes to rest position to motion.. initial speed is zero..so it requires high starting torque for ... current will flow through field and armature coils then maximum torque is available at the intial condition.

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In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be 8.

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Which of the following motors can run on both AC and DC? A) Universal motor B) Dual wattage motor C) Flexible motor D) All the above

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Which of the following motors can run on both AC and DC? A) Universal motor B) Dual wattage motor C) Flexible motor D) All the above

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If  equalising bar is connected to the 2 DC generators  the current will be equal in 2 generators irrespective of parallel connection so that we connect equaliser bar

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When a D.C. series motor is connected to A.C. supply, the power factor will be low because of high inductance of field and armature circuits.

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State the modification to be done in dc series motor to work satisfactorily as ac series motor. State applications of ac series motor.

Answer :

Modifications are necessary in a dc series motor so that it operates satisfactorily on ac supply. The modifications are as follows:  1) AC series motor is built with a few field turns as ... and grinders 5) High speed vacuum cleaners 6) Sewing machines 7) Food processors 8) Drilling machine 

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We connected a 35V dc supply to a resistance of 600 Ohm in series with an unknown resistance R.A. voltmeter having a resistance of 1.2 kOhm is connected across 600 Ohm resistance and read 5v. The value of resistance R will be

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We connected a 35V dc supply to a resistance of 600 Ohm in series with an unknown resistance R.A. voltmeter having a resistance of 1.2 kOhm is connected across 600 Ohm resistance and read 5v. The value of resistance R will be 2.4 kOhm

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Brake test on DC series motor

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A DC voltage source is connected across a series RLC circuit. Under steady-state conditions, the applied DC voltage drops entirely across the

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A DC voltage source is connected across a series RLC circuit. Under steady-state conditions, the applied DC voltage drops entirely across the C only

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What are the advantages of DC series motor?

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Why dc series motor should not be started at no load?

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Why a dc series motor has a high starting torque?

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Stepper motors are used in  (1) printers (2) lifts (3) amplifiers (4) oscillators

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Stepper motors are used in printers 

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Slot harmonics are reduced in induction motors by using (A) fractional-pitch windings (B) fractional-slot windings (C) integral-slot windings (D) distributed windings

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Slot harmonics are reduced in induction motors by using fractional-slot windings

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Generally, Crawling in squirrel cage induction motors is tendency to run stably at speeds as low as (A) One-third of their synchronous speed (B) One-fifth of their synchronous speed (C) One-seventh of their synchronous speed (D) One-ninth of their synchronous speed

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Generally, Crawling in squirrel cage induction motors is tendency to run stably at speeds as low as One-seventh of their synchronous speed

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Which of the following motors is being extensively used in servo applications ? A. AC motor B. Field controlled dc motor C. Armature controlled dc motor D. None of these

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The capacitors used in single-phase capacitor motors have no polarity marking.

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What are the five types of single phase motors used in the industry?

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Which of the following test is usually conducted to determine the efficiency of traction motors ? (A) Field’s test (B) Swinburne’s test (C) Hopkinson’s test (D) Retardation test.

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Which of the following test is usually conducted to determine the efficiency of traction motors ? (A) Field’s test (B) Swinburne’s test (C) Hopkinson’s test (D) Retardation test.

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A direct online starter is used for starting motors up to 5 H.P.

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Most of the fractional horsepower motors have either plain or sleeve bearings.

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As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for sound equipment.

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What is the difference between synchronous and asynchronous motors?

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.

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The large d.c. motors used in steel rolling mills are always provided with compensating . windings for (a) opposing the armature mmf (b) maintaining the voltage (c) maintaining the speed (d) none of these

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In a D.C. generator in case the resistance of the field winding is increased, then output voltage will decrease.

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In case of D.C. machine winding, number of commutator segments is equal to number of armature coils.

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In a A.C. series motor armature coils are usually connected to commutator through resistance.

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In D.C. machines fractional pitch winding is used to reduce the sparking.

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In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will remain unchanged.

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In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be less than 50%.

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