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If a D.C. motor is to be selected for conveyors, Series motor would be preferred.

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

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

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.

Answer : 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.

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 : 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 : By looking at Commutator part of the motor, it can be easily confirmed that a particular motor is D.C. motor.

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.

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.

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

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

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

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.

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

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

Description : In an induction motor if the flux density is reduced to one-half, of its normal value then the torque will  (1) reduce to one-half (2) reduce to one-fourth (3) remain unchanged (4) increase four times

Answer : In an induction motor if the flux density is reduced.to one-half, of its normal value then the torque will reduce to one-fourth

Description : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be

Answer : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be 25 N -m

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.

Answer : If starting winding of a single-phase induction motor is left in the circuit, it will draw excessive current and overheat.

Answer : If a single phase induction motor runs slower than normal, the most likely defect is worn bearings.

Description : What will happen if you increase the current in the motor?

Answer : Increasing current means increasing frequency of the motor because current is directly proportional to rotations of the motor rotor

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 :

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

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.

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

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

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

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

Description : The number of poles of 8/6 stepper motor can be :

Answer : The number of poles of 8/6 stepper motor can be : 4

Answer : The direction of rotation of universal motor can be reversed the by reversing the flow of current through either armature winding or field winding.

Answer : if induction motor rotates exceed than its synchronous speed, it acts as a generator.

Description : What would happen if a DC motor was supplied with AC ?

Answer : With three phase induction motor, humming and not rotate, but if single phase universal motor like air blower, home mixture, motor run on constant speed..speed variation not possible...

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

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

Answer : 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.

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

Description : 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

Description : For using regenerative breaking, the most suitable motor is :  (A) DC series motor  (B) Slip ring induction motor  (C) Squirrel cage induction motor  (D) Synchronous motor

Answer : For using regenerative breaking, the most suitable motor is : Slip ring induction motor

Description : A 400 V, 50 Hz three-phase induction motor rotates at 1440 rpm on full -load. The motor is wound for

Answer : A 400 V, 50 Hz three-phase induction motor rotates at 1440 rpm on full -load. The motor is wound for 4 poles

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

Answer : The motor used for the compressors is capacitor-start capacitor-run motor.

Answer : The shaded pole motor is used for low starting torque.

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

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