- Braking of DC Motor Definition: Electrical braking stops a DC motor by controlling voltage and current instead of using mechanical friction.
- Regenerative Braking: This method returns the motor’s kinetic energy to the power supply system but does not stop the motor.
- Dynamic Braking: Known as rheostatic braking, it disconnects the motor from the supply and uses a braking resistor to dissipate energy as heat.
- Plugging: Also called reverse current braking, this method reverses the armature terminals, producing high braking torque and wasting energy.
- Industrial Applications: These braking techniques are used in industries like elevators and printing presses.
Among the usual types of motors, a DC Motor is slowed by regenerative, dynamic or plugging torque. Plants usually apply Electrical Braking for that torque, not Mechanical Braking pads on the rotor. The torque comes from armature voltage and current, not from friction.
A DC motor uses these three types of electrical braking:
- Regenerative Braking
- Dynamic Braking
- Plugging
Regenerative Braking
Kinetic energy of the rotating mass is returned to the supply. That happens when an overhauling load drives the motor above no-load speed at constant field flux.
Back emf Eb then exceeds supply voltage V, so armature current reverses and the machine generates into the line.
Regenerative braking does not bring the shaft to rest. It only holds speed above no-load on a descending or overhauling load. Friction or another method is still needed at standstill.Dynamic Braking
This method is also called rheostatic braking. The armature is taken off the supply and a braking resistor Rb is connected across it. The field of a shunt or separately excited machine usually stays energised. The machine generates into Rb and that current produces braking torque.
Stored kinetic energy in the rotor and load is converted to electrical energy and dumped as heat in the braking resistor (Rb) and armature circuit resistance (Ra).
Dynamic Braking dumps that generated energy as heat in the resistances when the supply cannot accept regenerated power.
Plugging
This method is also called reverse-current braking. On a running separately excited DC motor or shunt DC motor, the armature terminals (or the armature supply polarity) are reversed while the field is left as it is. Supply voltage V and back emf Eb then add, so the voltage across the armature is V + Eb, about twice the line voltage. A series resistor is used to limit that current.
Armature current reverses and braking torque is high. Both the kinetic energy and energy drawn from the supply are dumped in resistances, so plugging is the least efficient of the three. A zero-speed detector must disconnect the supply or the motor will run up in reverse.
Plugging is used on lifts and printing presses where a fast stop is required.
Those three types of braking techniques are the electrical methods used on DC motors. A friction brake is still needed if the shaft must be held at rest.
