What Are Braking Resistors?

The basic property of resistors is consumption huge energy and dissipate that consumed energy in the form of heat. When any mechanical system decelerates, the system acts as a generator and creates a large amount of electrical energy which is transferred back into the power circuit. This large amount of energy is consumed by the resistor, which is present in a power circuit. Resistor converts the consumed energy into heat and at the same instant braking effect is created. Hence, the resistor used in this process is known as a braking resistor and the process is called dynamic braking. Thus, the purpose of a braking resistor is to quickly stop or slow down the mechanical system by producing a braking torque. Braking resistors are designed with specifications such as resistance and average braking power. Braking resistors with smaller ohmic values help motors to stop faster and dissipate more heat. The braking resistors require less service and provide higher reliability. Therefore, braking resistors are preferred over friction brakes to decelerate motors.  

Speed control is very essential in cranes, elevators & lifts, electric locomotives, and wind turbines. Therefore, braking resistors are an integral part of these applications. Trains are expected to create opportunities for the braking resistors market. The rise in urbanization is increasing the use of trains for transport. Electric trains are largely accepted over diesel trains globally, as these are eco-friendly and regenerate energy. Electric trains generate large amounts of energy while slowing down or stopping. Hence, large amounts of energy are dissipated or regained. Therefore, a dynamic braking system is mainly incorporated for brakes in an electric train’s engine system. Conventional discs, which are used for brakes, require heavy maintenance. Hence, dynamic braking is used as an additional system. Kinetic energy is converted into the electric current at the traction motors of the engine in dynamic train braking. The generated current is dissipated under the train’s car body in onboard series of braking resistors. Also the demand for motor safety, reliability, and durability are important factors for the growth of the braking resistors market.

Principle of Operation

When braking, the motor fields are connected across either the main traction generator (diesel-electric locomotive) or the supply (electric locomotive) and the motor armatures are connected across either the brake grids or supply line. The rolling locomotive wheels turn the motor armatures, and if the motor fields are now excited, the motors will act as generators.

During dynamic braking, the traction motors, which are now acting as generators, are connected to the braking grids (large resistors), which put a large load on the electrical circuit. When a generator circuit is loaded down with resistance, it causes the generators to slow their rotation. By varying the amount of excitation in the traction motor fields and the amount of resistance imposed on the circuit by the resistor grids, the traction motors can be slowed down to a virtual stop (approximately 3-5 MPH).

For permanent magnet motors, dynamic braking is easily achieved by shorting the motor terminals, thus bringing the motor to a fast abrupt stop. This method, however, dissipates all the energy as heat in the motor itself, and so cannot be used in anything other than low-power intermittent applications due to cooling limitations. It is not suitable for traction applications.

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