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Answer :

The armature may burn if the back e.m.f. of a D.C. motor vanishes suddenly.

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Description : What is the back EMF of a dc motor?

Last Answer : The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is 0.5.

Last Answer : 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.

Last Answer : If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens this will make armature to take heavy current, possibly burning it.

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

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Description : What is the back EMF of the motor?

Description : The counter e.m.f. of a d.c. motor?

Last Answer : The counter e.m.f. of a d.c. motor helps in energy conversion.

Last Answer : When the armature of a D.C. motor rotates, e.m.f. induced is back e.m.f.

Description : What is back emf? 

Last Answer : Back EMF: When a current carrying conductor is placed in a magnetic field it experiences a force; when it moves due to the force it (conductor) cuts the magnetic field due to which an emf is ... (hence the applied armature voltage) is opposed by the induced emf which is therefore called as Back emf.

Description : Do AC induction motors have back EMF?

Description : What is back EMF in inductor?

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Description : What is the back EMF?

Last Answer : When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The ... that energy conversion in a d.c. motor is only possible due to the production of back emf.

Last Answer : 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.

Description : As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit?

Last Answer : As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit a resistance is connected in series with armature.

Description : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is  (1) 1000V (2) 100V (3) 600V (4) 10,000V

Last Answer : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is 1000V

Last Answer : In a differentially compounded D.C. motor, if shunt field suddenly opens the motor will first stop and then run in opposite direction as series motor.

Last Answer : If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses.

Description : 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 :

Last 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

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

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

Last 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

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

Last 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

Description : A 200 V dc shunt motor is running at 1000 rpm and drawing a current of 10 A. Its armature winding resistance is 2 Ohm. It. is braked by plugging. The resistance to be connected in series with armature to restrict armature current to 10 A, is

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Description : The function of a brush and commutator arrangement in a dc motor is to  (1) produce unidirectional torque (2) produce unidirectional current in the armature (3) help in changing the direction of rotation of the armature (4) reduce sparking

Last Answer : The function of a brush and commutator arrangement in a dc motor is to produce unidirectional torque

Last Answer : If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor.

Last Answer : For a D.C. shunt motor if the excitation is changed torque will change but power will remain constant.

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

Last 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

Last Answer : At the instant of starting when a D.C. motor is put on supply, it behaves like a low resistance circuit.

Last Answer : The speed of a D.C. shunt motor can be increased by increasing the resistance in field circuit.

Last Answer : The armature voltage control of D.C. motor provides constant torque drive.

Last Answer : The armature torque of the D.C. shunt motor is proportional to armature current.

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

Last Answer : Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be cumulatively compounded.

Last Answer : Sparking, is discouraged in a D.C. motor because commutator gets damaged.

Last Answer : D.C. Series motor is generally preferred for cranes and hoists.

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Last Answer : Sparking at the commutator of a D.C. motor may result in damage to commutator segments, damage to commutator insulation, increased power consumption.

Last Answer : Cumulatively compounded D.C. motor will be suitable along with flywheel for intermittent light and heavy loads.

Last Answer : Differentially compounded D.C. motor has got maximum self loading property.