Braking of DC Motor: Either mechanical braking or electrical braking can be used to quickly stop a running motor. Mechanical break shoes are used to apply mechanical braking. Therefore, the surface and physical state of the brakes affect how smoothly mechanical braking occurs. Electric braking can be used to stop a motor smoothly.

Electrical braking of dc motor (Braking of DC Motor)

There are three types of electric braking of a DC motor 

(i) Rheostatic or dynamic braking,

(ii) Plugging or reverse current braking  and

(iii) Regenerative braking.

(i) Rheostatic or dynamic braking

For DC shunt motors, the armature is connected to a rheostat (variable resistor) and is then disconnected from the power source. The supply is still connected to the field winding. Naturally, the armature is now propelled by inertia, and the machine begins to function as a generator. The connected rheostat will now receive current from the machine, and heat will dissipate at the rate of I2R. By changing the resistance connected across the armature, braking effect can be adjusted.

In case of DC series motor, motor is disconnected from the supply and field connections are reversed and a rheostat is connected in series. The field connections are reversed to make sure that the current through field winding will flow in the same direction as before.

(ii) Plugging or Reverse current braking

This method causes the motor to run in the opposite direction because the armature connections are reversed. The armature terminals being reversed causes the applied voltage V and back emf Eb to start acting in the same direction, exceeding the total armature current. A variable resistor is connected across the armature to limit this armature current. This applies to both the series and shunt wound approaches.
When compared to rheostatic braking, plugging provides more braking torque. Typically, this technique is used to control elevators, machinery, printing presses, etc.

(iii) Regenerative braking

Where there is a very high inertia load on the motor, Regenerative braking is used (e.g in electric trains). The Armature current Ia and Armature torque are obviously reversed when the applied voltage to the motor is reduced to less than the back emf Eb. So, speed decreases. Regeneration occurs when power is returned to the line because the Generated emf is greater than the applied voltage (the machine is acting as a DC generator). As speed continues to decrease, back emf Eb also does so until it is lower than the applied voltage and the direction of the Armature current once more changes to the opposite of Eb.