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The type of D.C. motor used for shears and punches is cumulative compound D.C. motor.

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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.

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

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

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

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

Answer : For starting a D.C. motor a starter is required because it limits the starting current to a safe value.

Answer : Cumulative compound D.C. motor is preferred for elevators.

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

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

Description : State starters used for i) 3-Ph squirrel cage induction motor (3HP) ii) D.C. motor 

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

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Description : In a dc machine, interpoles are used to  (1) neutralize the effect of armature reaction in the interpolar region (2) generate more induced emf in the armature (3) avoid interference of the armature flux with the main -field flux (4) reduce the demagnetizing effect of armature reaction

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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

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

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

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?

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.

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

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

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

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.

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

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

Answer : The current drawn by the armature of D.C. motor is directly proportional to the torque required.

Answer : 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.

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

Answer : The starting resistance of a D.C. motor is generally low.

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Answer : In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be more than full-load current.

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

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

Answer : The speed of a D.C. shunt motor more than its full-load speed can be obtained by decreasing the field current.

Answer : If a D.C. motor is connected across the A.C. supply it will burn due to heat produced in the field winding by eddy currents.

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

Answer : If the field of a D.C. shunt motor gets opened while motor is running the motor will attain dangerously high speed.

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

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