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DYNAMIC BRAKING

                             DYNAMIC BRAKING 

DYNAMIC BRAKING (OR) RHEOSTATIC BRAKING :
                        Dynamic braking is also called rheostatic braking. In this method of braking, a motor is disconnected from the supply and operated as a generator driven by the kinetic energy of the rotor. The kinetic energy of rotation is converted into electric energy, which is dissipated in the external resistance connected across the motor at the braking instant. The advantage of this type of braking is that no energy is required from the supply to brake the motor. This method of braking can be applied to brake the D.C motors, synchronous motors and induction motors.

DYNAMIC BRAKING TO INDUCTION MOTOR :
                     
                                           fig 1.1
               In 3 phase squirrel cage induction motor, the stator is disconnected from the A.C supply mains and D.C supply is given to the stator winding as shown in fig. 1.1(b). A steady flux is produced. The short circuited rotor cuts this steady flux and an emf is induced in these conductors. This provides the necessary braking effect. In the case of 3 phase slip ring induction motor the braking torque is controlled by adding the resistance in the rotor circuit. 

DYNAMIC BRAKING TO SYNCHRONOUS MOTOR :
                          In synchronous motor, the D.C excitation is maintained and the stator is disconnected from A.C supply. Then the stator is connected across three resistance in star or delta.Now the machine operates as an alternator and the kinetic energy is dissipated in the resistance and braking will occur.

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