Braking in DC motor is employed to make the dc motor to halt from operating condition by applying a brake. It is to be considered that significant difference exists between the words ‘braking’ and ‘breaking’, should not get confused. In dc motors we apply the brake to make the dc motor halt.
Different braking methods employed in the dc motor are listed below.
- Plugging
- Dynamic braking (Rheostatic Braking)
- Regenerative Braking
1. Plugging
This is the simplest type of braking method. In plugging the power supply given to the dc motor is made to reconnect so that it tends to drive the motor in the opposite direction. In simple the motor windings are connected in reverse direction of the rotation of the motor when the armature is still rotating in the normal operating direction because of the external torque or due to the inertia. This method is employed for the quick reversal or rapid stopping of the motor. It has some disadvantages such as consumption power during braking and heavy inrush currents into the motor during this mode of braking damages the motor.
2. Dynamic braking (Rheostatic Braking)
In this method, braking is provided to the motor by dissipating the energy to the resistance. In Dynamic braking, the power supply is removed to the motor and the kinetic energy of the rotating parts stored in the motor is converted to electrical energy which will be dissipated to the external resistance connected across the motor terminals at the time of braking.
3. Regenerative Braking
In regenerative braking, the motor remains connected to the supply and the braking energy generated is supplied back to the source. Some of the conditions required to apply regenerative breaking are supply voltage should be lower than induced emf, the motor should be operating in over-excited condition, and the speed of the motor should be more than the no-load speed of the motor. When the load connected to the crane is lowering or when the electric locomotive is moving downgrade in such cases regenerative braking can be applied.
