SPEED CONTROL OF DC MOTORS

Speed control of DC Shunt motors are done by i) Flux Control method. ii) Armature Control method iii) Voltage Control method.
Speed control of DC Series motors are done by i)Flux Control method. ii) Variable Resistance in series with motor.

TORQUE SPEED CHARACTERISTICS OF DC MOTORS

DC Shunt motor is a constant speed motor.
DC Series motor has high starting torque .Therefore it is started with a minimum in order to avoid dangerous speeds.

TYPES OF DC MOTOR

DC motors are classified based on the type of winding arrangement.

1.DC Series Motor

                          In this type of motor, the field winding is connected in series with the armature winding.Thus the same current flows through both the field and armature winding.

2.DC Shunt Motor

                         In this type of motor, the field winding is connected in parallel with the armature winding.So the current is divided between these windings and the applied voltage is same across both the field and armature winding.

PARTS OF A DC MOTOR

Every motor consists of a stationary part called Stator and a rotating part called Rotor.In DC motor, field windings are placed in the stator and the armature windings are placed in the rotor.Therefore DC motor is said to have a rotating armature.

DC motor has the following parts

1. Magnetic Frame or Yoke

2. Pole Cores.

3. Field Coils.

4. Armature Core.

5. Armature Windings

6. Commutator.

7. Brushes.

TYPES OF MOTORS

Motors are the electromagnetic devices which converts electrical energy into mechanical energy.Its working is based up on the principle that when a current-carrying conductor is placed in a magnetic field,it experiences a mechanical force whose direction is given by Fleming's Left hand rule. 

Basically motors are classified based on the input electrical supply.They DC motors and AC motors.

DC motors are further classified as 

    i)  Separately excited DC motor.

    ii) DC shunt motor.

    iii) DC series motor.

    iv) DC compound motor.

           a)Cumulative-compound motors.

           b)Differential-compound motors. 

Classification of AC motors are given as

    i)Synchronous motors.

    ii)Asynchronous motors.

           a)Squirrel cage induction motor.

           b)Slip-ring or wound rotor induction motor. 
Other motors which come under special machines are
     i) Stepper motor.
    ii) Brushless DC motor.
    iii) Switched Reluctance motor.
    iv) Variable Reluctance motor.

BASIC ELECTROMAGNETIC LAWS

1.FARADAY'S LAW

It states that "If a conductor of length 'l' is moved with a velocity 'v' in a magnetic field of constant flux density 'B', then the EMF induced is equal to the rate of change of flux."

E=Blv (Volts)

where,  E =  Induced EMF (Volts)

            B =  Flux density (Wb/m^2)
            l  =  length of the conductor (m)
            v =  velocity of the conductor (m/s)

2.THUMB RULE

It states that "If the fingers of the right hand are placed around the wire such that the thumb points in the direction of current flow, the fingers will be pointing in the direction of the magnetic field produced by the wire."

3.