Electrical Braking of DC Motor

DC motors are extremely important and found in a wide range of industrial devices and uses. Regardless of the business you work in, a DC motor is most likely used somewhere. A DC motor can be stopped or brought to rest by cutting the supply using a variety of methods. Please note that electrical braking, not mechanical braking, is the preferred method of stopping a DC motor. 

To put it another way, the circuit's voltage and current action, not the rotor's mechanical friction brakes, stops the motor. It's very likely that your DC motor needs new brakes if you're reading this. The good news is that DC motors are very efficient at converting direct electrical energy into mechanical energy. DC motors can be braked using a variety of techniques. Let's take a closer look at the various forms of DC motor braking.

Table of Contents

• What Does Braking Mean in DC Motor?
• Electrical vs Mechanical Braking
• What is Electrical Braking in DC Motor?
• Types of Electrical Braking
• Regenerative Braking
• Advantages of Regenerative Braking
• Disadvantages of Regenerative Braking
• Dynamic Braking
• Advantages of Dynamic Braking
• Disadvantages of Dynamic Braking
• Plugging or Reverse Current Braking
• Advantages of Plugging
• Disadvantages of Plugging
• Conclusion

What Does Braking Mean in DC Motor?

In motors, braking is the process of lowering or halting the motor's speed. In order to bring the motor and related machinery to a controlled stop, this crucial procedure is necessary. Process control is enhanced, worker safety is guaranteed, and mechanical damage is avoided with proper braking.

Electrical vs Mechanical Braking

One of the following techniques can be used to halt the DC motors:

1. Electric Braking
2. Mechanical (Friction) Braking

Friction between the motor's moving parts and the break shoe stops the motor in mechanical breaking. Mechanical breaking has a number of drawbacks, including not stopping smoothly, wearing down moving parts, wasting breaking power as heat, and taking longer to stop, among other issues. In electric breaking, the motor's moving elements transform their kinetic energy into electrical energy, which is then either returned to the supply source or dissipated in a resistance.

What is Electrical Braking in DC Motor?

Instead of use mechanical friction to halt a DC motor, electrical braking regulates voltage and current.

Types of Electrical Braking

There are three electrical braking methods of a DC motor

• Rheostat Braking or Dynamic Braking
• Regenerative Braking
• Plugging or Reverse Current Braking

Regenerative Braking

In regenerative braking, the motor functions as a generator, transforming the kinetic energy of its moving components into electrical energy. After then, the electrical source is reconnected. The motor slows down as a result. With a constant field excitation, regeneration braking is only feasible when the driven load compels the motor to operate at a speed higher than the no-load speed. The motor's armature current reverses under these circumstances because the back EMF (Eb) is greater than the supply voltage. 

The electrical energy produced by the motor is therefore transmitted to the supply source, and the motor now starts to function as a generator. Regenerative braking requires that the motor's back EMF be higher than the supply voltage in order to reverse the armature current and switch the motoring action to the producing operation. The primary purpose of regenerative braking is to regulate the speed of DC motors that power loads like electric trains, elevators, cranes, hoists, etc.

Advantages of Regenerative Braking

Energy Recovery: It transforms the kinetic energy of the motor into electrical energy that can be utilized again.

Increased Efficiency: In applications where energy conservation is essential, this approach is quite effective.

Smooth Deceleration: Ensures a smooth stop by offering smooth control over deceleration.

Disadvantages of Regenerative Braking

High Cost: Because of its complexity, regenerative braking systems can be costly to implement.

Requires Special Equipment Not suited for all applications because it necessitates a power supply capable of processing returned energy.

Dynamic Braking

In dynamic braking, a DC motor's armature is linked across a braking resistance (Rb) and detached from the power source. The field winding is still attached to the supply, though. As a result, the motor produces a braking torque and functions as a generator. Since an external resistance Rb is placed across the armature for the electric braking, this technique is sometimes referred to as rheostat braking. 

Since all of the energy produced is lost as heat in the resistance, dynamic braking, also known as rheostat braking, is an inefficient braking technique. When the motor functions as a generator during dynamic electric braking, the kinetic energy of its moving elements is transformed into electrical energy and released as heat in the armature circuit resistance Ra and the braking resistance Rb. This causes the motor to come to a rapid stop. Since all of the energy produced is lost as heat in the resistance, dynamic braking, also known as rheostat braking, is an inefficient braking technique.

Dynamic Braking
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Advantages of Dynamic Braking

Widely Used: Suitable for a wide range of applications, particularly if energy recovery is not required.

Simple and effective: It's easier to implement than regenerative braking and requires fewer components.

Cost-Effective: The system is cheaper because it does not require putting energy back into the power source.

Disadvantages of Dynamic Braking

Energy Loss: Energy is lost as heat rather than recovered.

Heat Management: The heat created must be dissipated using a cooling system or enough ventilation.

Plugging or Reverse Current Braking

In reverse current braking, also known as plugging, the armature connections are switched, causing the motor to revolve in the opposite direction and producing the required braking effect. If the power source is not unplugged when the motor reaches rest, it will begin to rotate in the opposite direction. The supply voltage and the back EMF will act in the same direction when the armature connections are switched. As a result, the voltage across the armature during the braking will be equal to (V + Eb), or almost twice the supply voltage. Because of the armature current being reversed, a strong braking torque is generated. A current limiting resistor is connected in series with the armature to keep the current flowing through it within a safe range. Plugging is a very inefficient way to break because resistances consume both the power from the source and the power from the moving parts. Printing presses, machine tools, elevators, rolling mills, and other equipment are mostly controlled by plugs.

Plugging
Image used curtesy of Tutorialspoint 

Advantages of Plugging

Plugging is the fastest technique to halt a DC motor.

Simple Control: Implementation is as simple as reversing the motor's polarity.

Disadvantages of Plugging

High Energy Consumption: Plugging consumes a large amount of energy as heat.

Wear and Tear: The rapid reverse torque caused by frequent plugs might wear out the motor components.

High Current: Can result in significant inrush currents, which can harm the motor if not managed.

Conclusion

Electrical braking is typically used to stop a motor-driven unit in a precise location or to regulate the driven unit's speed appropriately while it decelerates. Applications requiring frequent, precise, fast, or emergency stops use electrical brakes. Passengers may stop smoothly and without any hassle thanks to electrical braking. Electric brakes maintain a laden hoist's speed within safe bounds while it is lowered. If not, the drive or machine speed will increase to risky levels. When active loads are relevant, electrical braking is utilized more frequently. Despite electronic braking, mechanical brakes can also be used to generate braking force.