What is known as dynamic braking in DC motor?

When an electric motor rotates, a kinetic energy is stored in its rotating mass. If the motor is disconnected from the supply it continues to rotate for a period of time until the kinetic energy is totally dissipated in the form of rotational losses or frictional loss. The faster the dissipation of the kinetic energy, the more rapid is the braking.

During the dynamic braking the kinetic energy of the motor is converted into electrical energy. This energy is dissipated in resistive elements. The rate of dissipation can be increased by the design of the braking resistance. When the motor is connected to source, the power flows from source to motor. If it is connected from the source, and the ends are connected to braking resistance which is connected across the motor terminals.

In braking condition, motor acts as generator and braking current flows motor to resistor, by which the kinetic energy is dissipated by heat. If we are using smaller resistor, then the energy dissipated is faster and the motor brakes also faster.

For DC motor, there are two cases

1. DC shunt motor

2. Dc series motor

Dynamic braking in DC shunt motor can be obtained by disconnecting the armature from supply and connecting an external resistance across the armature terminals. The field winding is cleft connected across the supply and it is undisturbed. This method is also called rheostatic braking. The braking effect is controlled by varying the braking resistance.

In DC series motor, both armature and the field winding are disconnected from the supply and shunt across a braking resistor.

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