Dynamic Braking Resistor (DBR) Connection Diagram with VFD

Dynamic Braking Resistor (DBR) is an electrical component that is used in various industrial applications to dissipate excess energy generated during the braking process of an electric motor or other electrical devices. When a motor is decelerating or stopping, it acts as a generator and produces back electromotive force (EMF). In such cases, the energy needs to be dissipated to prevent damage to the motor and the associated drive system.

The dynamic braking process is commonly used in applications like elevators, cranes, electric trains, electric vehicles, and other machinery that require frequent and controlled deceleration or stopping. The Dynamic Braking Resistor (DBR) is generally used with a motor-controlling system such as VFD to perform the Braking. In this article, we are going to see the Connection Diagram between VFD(Variable Frequency Drive) and Dynamic Braking Resistor.

Connection Diagram

Here, you can see the Dynamic Braking Resistor (DBR) Connection Diagram with VFD.

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Wiring Procedure

1. Identify DBR Terminals in VFD: Almost all the VFDs generally come with specified terminals or connections for DBR. Commonly, it will have at least two terminals: one for the input connection and another for the output connection. These terminals are typically labeled as "+" and "-" or "DC+" and "DC-". Here, in the above wiring diagram, our VFD has "DC+" and "DC-" terminals.

2. Connect the Input of DBR to VFD: Connect one terminal of the DBR to the "+" or "DC+" DC bus terminal of the VFD and the other terminal of the DBR to the "-" or "DC-" DC bus terminal of the VFD. This connection allows the DBR to receive the excess regenerative energy produced by the motor during braking.

3. Resistor Contactor or Brake Chopper: In some VFD systems, a resistor contactor or brake chopper might be needed to control the connection between the DBR and the VFD. A brake chopper is a solid-state device that controls the energy flow between the VFD and the DBR. If your VFD system includes a brake chopper, follow the manufacturer's instructions to make the necessary connections.

4. Configure VFD Parameters: To enable dynamic braking with the DBR, the VFD's parameters need to be properly configured. These parameters may include setting the dynamic braking mode, configuring the braking resistor value, and setting the braking torque or current limits. The specific parameters and their values will depend on the VFD model and the application requirements.

It is always recommended to follow the VFD and DBR manufacturer's guidelines and instructions when making these connections. Improper connections or incorrect parameter settings can lead to system malfunctions or even damage the equipment. Always refer to the user manuals and documentation provided by the VFD and DBR manufacturers for the specific installation and configuration guidelines.

Working Principle

When the VFD detects that the motor is decelerating or stopping, it switches into dynamic braking mode. In this mode, instead of just cutting off the power supply to the motor (as in normal stopping), the VFD routes the excess energy generated during braking to the DBR.

The excess energy generated by the motor is redirected to the DBR. The DBR is connected in parallel with the DC bus of the VFD, and it acts as a load that absorbs the excess energy from the motor.

The DBR is designed with a high-power rating and resistance to handle energy dissipation effectively. As the excess energy passes through the DBR, it is converted into heat to dissipate the energy.

To prevent overheating, DBRs are usually equipped with cooling mechanisms, such as heatsinks or fans, to efficiently dissipate the heat produced during braking.

Once the motor has completed the braking process the VFD switches back to its regular control mode, supplying the appropriate frequency and voltage to the motor.

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