Arc Suppression Coil or Petersen Coil
Winding Resistance Test of Shunt Reactor
Measurement of Reactance of a Shunt Reactor
Tests of Shunt Reactor
Construction of a Shunt ReactorClosely Related Articles
DC Motor or Direct Current Motor
Speed Regulation of DC Motor
Speed Control of DC Motor
Working or Operating Principle of DC Motor
Torque Equation of DC Motor
Construction of DC Motor | Yoke Poles Armature Field Winding Commutator Brushes of DC Motor
Testing of DC Machine
Swinburne Test of DC Machine
Losses in DC Machine
Ward Leonard Method of Speed Control
Armature Reaction in DC Machine
Commutation in DC Machine or Commutation in DC Generator or Motor
Methods of Improving Commutation
Starting Methods to limit Starting Current and Torque of DC Motor
3 Point Starter | Working Principle and Construction of Three Point Starter
4 Point Starter | Working Principle and Construction of Four Point Starter
Electrical Motor | Types Classification and History of Motor
Working of Electric Motor
Types of DC Motor Separately Excited Shunt Series Compound DC Motor
Shunt Wound DC Motor | DC Shunt Motor
Series Wound DC Motor or DC Series Motor
Compound Wound DC Motor or DC Compound Motor
Permanent Magnet DC Motor or PMDC Motor | Working Principle Construction
Brushless DC Motors
DC Motor or Direct Current Motor
What is DC Motor ?Electrical motors are everywhere around us. Almost all the electro-mechanical movements we see around us are caused either by a AC or a DC motor. Here we will be exploring DC motors. This is a device that converts DC electrical energy to a mechanical energy.
Principle of DC MotorThis DC or direct current motor works on the principal, when a current carrying conductor is placed in a magnetic field, it experiences a torque and has a tendency to move. This is known as motoring action. If the direction of current in the wire is reversed, the direction of rotation also reverses. When magnetic field and electric field interact they produce a mechanical force, and based on that the working principle of DC motor is established. The direction of rotation of a this motor is given by Fleming’s left hand rule, which states that if the index finger, middle finger and thumb of your left hand are extended mutually perpendicular to each other and if the index finger represents the direction of magnetic field, middle finger indicates the direction of current, then the thumb represents the direction in which force is experienced by the shaft of the DC motor.
Structurally and construction wise a direct current motor is exactly similar to a DC generator, but electrically it is just the opposite. Here we unlike a generator we supply electrical energy to the input port and derive mechanical energy from the output port. We can represent it by the block diagram shown below. Here in a DC motor, the supply voltage E and current I is given to the electrical port or the input port and we derive the mechanical output i.e. torque T and speed ω from the mechanical port or output port.
The input and output port variables of the direct current motor are related by the parameter K. So from the picture above we can well understand that motor is just the opposite phenomena of a DC generator, and we can derive both motoring and generating operation from the same machine by simply reversing the ports.
Detailed Description of a DC MotorTo understand the DC motor in details lets consider the diagram below, The direct current motor is represented by the circle in the center, on which is mounted the brushes, where we connect the external terminals, from where supply voltage is given. On the mechanical terminal we have a shaft coming out of the Motor, and connected to the armature, and the armature-shaft is coupled to the mechanical load. On the supply terminals we represent the armature resistance Ra in series. Now, let the input voltage E, is applied across the brushes. Electric current which flows through the rotor armature via brushes, in presence of the magnetic field, produces a torque Tg. Due to this torque Tg the dc motor armature rotates. As the armature conductors are carrying currents and the armature rotates inside the stator magnetic field, it also produces an emf Eb in the manner very similar to that of a generator. The generated Emf Eb is directed opposite to the supplied voltage and is known as the back Emf, as it counters the forward voltage. The back emf like in case of a generator is represented by Where, P = no of poles φ = flux per pole Z= No. of conductors A = No. of parallel paths and N is the speed of the DC Motor. So, from the above equation we can see Eb is proportional to speed ‘N’. That is whenever a direct current motor rotates, it results in the generation of back Emf. Now lets represent the rotor speed by ω in rad/sec. So Eb is proportional to ω. So, when the speed of the motor is reduced by the application of load, Eb decreases. Thus the voltage difference between supply voltage and back emf increases that means E − Eb increases. Due to this increased voltage difference, armature current will increase and therefore torque and hence speed increases. Thus a DC Motor is capable of maintaining the same speed under variable load. Now armature current Ia is represented by Now at starting,speed ω = 0 so at starting Eb = 0. Now since the armature winding electrical resistance Ra is small, this motor has a very high starting current in the absence of back Emf. As a result we need to use a starter for starting a DC Motor. Now as the motor continues to rotate, the back Emf starts being generated and gradually the current decreases as the motor picks up speed.
Types of DC MotorsDirect motors are named according to the connection o the field winding with the armature. There are 3 types:
Working Principle of DC Motor-Video
Closely Related Articles Speed Regulation of DC MotorSpeed Control of DC MotorWorking or Operating Principle of DC MotorTorque Equation of DC MotorConstruction of DC Motor | Yoke Poles Armature Field Winding Commutator Brushes of DC MotorTesting of DC MachineSwinburne Test of DC MachineLosses in DC MachineWard Leonard Method of Speed ControlArmature Reaction in DC MachineCommutation in DC Machine or Commutation in DC Generator or MotorMethods of Improving CommutationStarting Methods to limit Starting Current and Torque of DC Motor3 Point Starter | Working Principle and Construction of Three Point Starter4 Point Starter | Working Principle and Construction of Four Point StarterMore Related Articles Electrical Motor | Types Classification and History of MotorWorking of Electric MotorTypes of DC Motor Separately Excited Shunt Series Compound DC MotorShunt Wound DC Motor | DC Shunt MotorSeries Wound DC Motor or DC Series MotorCompound Wound DC Motor or DC Compound MotorPermanent Magnet DC Motor or PMDC Motor | Working Principle ConstructionBrushless DC MotorsNew Articles Arc Suppression Coil or Petersen CoilWinding Resistance Test of Shunt ReactorMeasurement of Reactance of a Shunt ReactorTests of Shunt ReactorConstruction of a Shunt Reactor