What is DC Motor ,Working of DC Motor,Types of Dc Motor,Speed Regulation of Dc Motor, Characteristics & Applications of Shunt Motor,Characteristics & Application of Series Motor,Advantages & Disadvantages of DC Motor,Losses fo DC Motor,Factors Controlling Speed of DC Motor.

Working Principle of DC Motor
           An electrical motor is a machine which converts electrical energy into mechanical energy( There is no basic difference between DC generator and a DC motor.The DC motor can be used as a DC generator).
            The working principle of DC motor is based on ,when a current carrying conductor is placed in a magnetic field it experiences a mechanical force whose direction is given by the Fleming's left hand rule and its magnitude is F=BIl newton.
Working of DC Motor
      Fig. Is shown a portion of the muiltipolar DC motor.
fig.

When the field magnets are exited and we supplied current from the main supply to the armature conductors.\the the armature experience a force which tries to rotate it.Armature conductors under N-pole are assumed to carry current downwards ant the conductors under S-pole carries current upwards.By using Fleming's left hand rule we can find the direction of the force on each conductor.This force is shown in the fig. with the help of small arrows on each conductor .It will be seen that each conductor experience a force F which tends to rotate the armature in anticlockwise direction.These forces collectively produce a driving torque which sets the armature rotating.
Main Types of DC Motors
          There are four main types of DC motors.
  1. Permanent Magnet Dc Motors:-                                                                               In this type of Dc motors we use a permanent magnet to create field flux.This type of DC motor provides great starting torque and has good speed regulation its torque is limited that's why this type of motors are typically found on low horse power applications.
  2. Dc Shunt Motors:-                                                                            In this type of motors the field is connected in parallel or shunt with the armature in parallel or shunt with the armature windings.Because the shunt field can be excited separately from the armature windings so these motors offer great speed regulations.
  3. Compound DC Motors:-                                                                   These types of Dc motors also have separate excited shunt field.These types of motors have good starting torque but have control problem in variable speed drive application.
  4. Series Dc Motors:-                                                                               In this type of DC motors the field is wound with a few turns of a large wire carrying the full current.This type of motors create a large amount of starting torque,but can not regulate speed and can be damaged by running with out load.That's why these type of DC motors are not good option for variable speed drive applications.
Speed Regulation of DC Motor
               The speed regulation is defined as the change in speed when the load on the motor is reduced from rated value to zero,expressed as per cent of the rated load speed .

          % Speed Regulation=(N.L. speed - F.L. speed/F.L. speed )*100
Characteristics of Shunt Motor
  • Speed of a shunt motor is sufficiently constant.
  • For the same current input its starting torque is not as high as that of series motor.
Applications of Shunt Motor 
  • Lathes.
  • Centri fugal pumps.
  • Machine tools.
  • Blowers and fans.
  • Reciprocating Pumps.
Characteristics of Series Motors 
  •  These motors have a relatively huge starting torque.
  • These motors have good accelerating torque.
  • These motors have low speed at high loads and dangerously high speed at low loads.
Applications of Series motors
  • Electric Locomotives.
  • Rapid Transit Systems.
  • Trolley Cars.
  • Cranes and hoists.
  • Conveyors.
Losses in DC Motors 
  1. Copper Losses.
  2. Magnetic Losses.
  3. Mechanical Losses.
Factors Controlling DC Motor Speed 
            We can control the speed of DC motor by the following factors.
  1. Flux/Poles.
  2. Resistance Ra of armature circuit.
  3. Applied voltage V.. 
Advantages of Dc Motor
             Following are the advantages of the DC motor.
  • Dc motors have higher starting torque.
  • Dc motors have quick starting and stopping.
  • We can varies the speed of DC motor with input voltage and its much easier than AC motors.
Disadvantages of DC Motor
  • High initial cost Dc motors have.
  • Due to the presence of commutator and brush gears the operation and maintenance of Dc motors are high.
  • We do not operate DC motors in hazard conditions due to sparking occur at brush. 

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