What is Rheostatic Braking?

Rheostatic Braking is a form of electrical braking where the traction motors act as generators. The electricity generated by the moving train is fed into onboard resistors, where it is converted into heat and dissipated into the air.

What is the difference between Rheostatic and Regenerative braking?

The main difference is energy usage. Regenerative braking returns the electricity to the power supply line or battery for reuse. Rheostatic braking wastes the electricity by converting it into heat via resistors.

Why do diesel locomotives use Rheostatic Braking?

Diesel-electric locomotives are not connected to an external power grid (catenary). Therefore, they cannot regenerate power back to a source. They use rheostatic braking to dissipate braking energy safely as heat.

Burning the Energy: Rheostatic Braking Systems Explained

Understand how trains stop without friction. Rheostatic Braking converts kinetic energy into heat via resistor grids, providing reliable braking for diesel locomotives.

December 10, 2025 12:14 pm

Rheostatic Braking is a type of Dynamic Braking used in electric and diesel-electric trains. In this system, the train’s Traction Motors are switched to act as generators during deceleration. Instead of feeding the generated electricity back into the power supply (as in Regenerative Braking), the energy is directed into large banks of onboard resistors where it is dissipated as heat.

How It Works: Turning Motion into Heat

The principle relies on the conservation of energy. To slow the train down, its kinetic energy must go somewhere.

Generation: The electrical connections to the motors are reconfigured so that the turning wheels drive the motors. The resistance to turning creates a braking torque on the axles.
Dissipation: The resulting electrical current is channeled to Resistor Grids (often mounted on the roof of the train or locomotive).
Cooling: These resistors get extremely hot. Large cooling fans, powered by the braking current itself, blow air through the grids to vent the heat into the atmosphere.

Comparison: Rheostatic vs. Regenerative Braking

While both methods use the electric motors to stop the train (saving wear on mechanical brake pads), the destination of the energy differs.

Feature	Rheostatic Braking	Regenerative Braking
Energy Destination	Onboard Resistor Banks	Overhead Line / Third Rail / Battery
Efficiency	0% (Energy is wasted as heat)	High (Energy is reused)
Primary Use Case	Diesel Locomotives, DC lines with no receptive load	Modern Electric Trains (EMUs), Metros
Infrastructure	Self-contained (Independent of grid)	Requires receptive grid or storage

Why Use Rheostatic Braking?

In the age of energy efficiency, wasting power as heat seems counter-intuitive. However, Rheostatic Braking remains essential in specific scenarios:

Diesel-Electric Locomotives: Since these trains generate their own power onboard and are not connected to an external electric grid, they cannot “push” energy back anywhere. The only option is to burn it off via resistors.
Non-Receptive Grids: In some DC electric systems, if no other trains are nearby to consume the regenerated power, the line voltage rises dangerously high. The system effectively “dumps” the excess energy into rheostatic resistors to protect the equipment.