In this article we shall discuss about the types of electrical braking in a DC motor. There are various types of electrical braking used for DC motor. Electrical braking is preferred to stop a DC motor over the mechanical braking because it has many advantages. In electrical breaking, we stop the motor by electrical energy rather than stopping using the mechanical friction brakes.
Types of Electric braking in a DC motor
There are three types of electrical braking we use for DC motor.
- Regenerative Braking
- Dynamic braking
Now, we shall discuss the above electrical braking techniques.
1.Regenerative Braking in DC motor
DC motor works as a generator if the motor speed is more than the no load speed of the motor. This condition happens when;
- DC motor shaft experiencing an external force which also rotate the motor and it cause the speed of the motor is more than the no load speed of the motor.
- When motor speed does not reduce when its speed set point is reduced. This may happen due to load inertia.
In above cases, the motor work as an generator. The motor converts kinetic energy to electrical energy, and it return the electrical energy to power supply system. During regeneration, the back EMF(Eb) is more than the armature voltage(V) and armature current flows from motor to supply side.
When Eb>V, the motor feeds electrical energy to supply till supply voltage becomes greater than the back EMF of the motor.
During motoring the armature current is,
|Ia = (V-Eb)/Ra|
During regenerative braking the armature current is,
|Ia = (Eb-V)/Ra|
Though regenerative braking is not used for braking, the regenerative braking is used to maintain the constant speed of the motor.
The plugging is simplest type of braking. The armature voltage polarity is reversed at the time of plugging to stop the motor. During plugging the back EMF supports the armature voltage, and thus the total voltage across the motor terminal is (V+Eb). In this condition, the armature current reverse its direction and exerts counter torque,which brings the motor to stop. The plugging method is highly inefficient because at the time of braking the source also supplies current which gets dissipated in the braking resistor(Rb) and armature resistance(Ra).
2. Dynamic Braking
The DC motor keeps on rotating after switching off armature power supply because of inertia. To immediately stop the motor, a braking resistor(Rb) is connected across the armature. In this condition, the motor acts as an generator and converts kinetic energy into electrical energy. The electrical energy dissipates in the braking resistor(Rb) and armature resistance(Ra) and motor stops. This method of braking is also known as Rheostatic braking.
The dynamic braking is also an inefficient method of braking because the energy is dissipated as heat in resistance(Ra+Rb). However, it is more efficient than plugging because in dynamic braking supply source does not supply current in the armature circuit.
These are the three types of braking methods used in industrial applications.