ELECTRIC BRAKING
Electric braking is the process by which a running motor can be brought to rest smooth braking of the motors can be achieved by the electric braking it uses the electric current or magnetic actuating force to reduce the speed of the rotating device. It is used in industrial and vehicular braking applications which need fast response time and tension control. There are two types of electric brakes magnetic brakes and Electrically actuated friction brakes
Electric braking of DC motor is of three types
• Rheostatic or dynamic braking
• Plugging or reverse current braking
• Regenerative braking
RHEOSTATIC OR DYNAMIC BRAKING
In DC shunt motors armature will be disconnected from the supply and a rheostat is connected across it. The field winding is connected left across the supply the machine will act as a generator. due to the inertia which drives the armature and current will be feed by the machine to rheostat and heat will be dissipated braking effect is controlled by varying the resistance which is connected across the armature
PLUGGING OR REVERSE CURRENT BRAKING
Armature connections are reversed in this method and by this motor tends to run in the reverse direction the applied voltage and EMF will act in the same direction due to the reversal of the armature terminals and by this total armature current will increase to reduce this armature current a variable resistor is connected across the armature Plugging gives greater braking torque when compared to rheostatic braking this type of braking is used in printing presses machine tools and controlling elevators
REGENERATIVE BRAKING
This type of braking is used when the load on the motor has very high inertia if applied voltage to the motor is reduced to less than back emf the armature current will be reversed and the torque of the armature is reversed and the speed will reduce when the generated emf is greater than the applied voltage and the power will be returned to the line and this process is called regeneration speed is reduced and the back emf falls until it is lower than the applied voltage and armature current direction will again become opposite to back emf