Understanding Braking Resistors: Their Working Principles and Applications

1. What is a Braking Resistor?

A braking resistor is a type of power resistor that is used to dissipate energy in a system. It is typically designed to handle high power levels and is often used in applications where the kinetic energy of a moving object or the stored energy in an electrical system needs to be dissipated quickly and safely.

2. Working Principle of Braking Resistors

• In an electrical drive system such as a motor drive, when a motor is decelerating or braking, the motor acts as a generator. This is due to the principle of electromagnetic induction. As the rotor of the motor rotates in a magnetic field during deceleration, it induces a voltage in the motor windings. This generated voltage can cause a current to flow back into the power supply or the drive circuit.

• If this regenerative energy is not dissipated properly, it can lead to over - voltage conditions that can damage the components of the drive system. The braking resistor comes into play here. The resistor is connected across the DC bus of the drive system (in a variable - frequency drive, for example). When the motor is braking and generating a back - EMF (electromotive force), the braking resistor provides a path for the current to flow through.

• 
  

3. Applications of Braking Resistors

• Industrial Motor Drives:

• In industrial automation, braking resistors are used in conveyor belt systems, crane motors, and other heavy - duty motor applications. For example, in a large - scale conveyor belt system used in a manufacturing plant, when the conveyor needs to stop quickly, the motors driving the conveyor generate a significant amount of regenerative energy. Braking resistors are used to dissipate this energy and bring the conveyor to a smooth stop. This not only protects the motor and drive system but also shortens the stopping time, increasing the overall efficiency of the process.

• Elevators:

• In elevator systems, braking resistors play a crucial role. When the elevator car is descending and needs to slow down or stop, the motors generate regenerative energy. The braking resistor dissipates this energy to prevent over - voltage in the motor control system and to ensure a safe and smooth stop. This is especially important for high - rise elevators where the kinetic energy of the moving car is considerable.

• Electric Vehicles:

• In electric vehicles, braking resistors are sometimes used in addition to regenerative braking systems. While most of the energy during braking is usually recovered and stored back in the battery in a well - designed regenerative braking system, in some cases (such as during emergency braking or when the battery is full and cannot accept more charge), the braking resistor provides an alternative way to dissipate the energy. This helps to maintain the stability of the vehicle's electrical system and prevent damage to the motor and battery due to over - voltage.