What is the primary purpose of dynamic braking?

The primary purpose of dynamic braking is to slow down the train without using air brakes. This braking system utilizes the electric traction motors of the locomotive, which are switched to generator mode when the operator engages the dynamic brake. In this mode, the energy generated by the motors is converted into electrical energy, creating a braking force as it dissipates as heat within the electrical resistance grid.

Dynamic braking is particularly advantageous because it allows the train to reduce speed efficiently while simultaneously conserving air brake system resources, which is especially important during long descents or when repeated braking is necessary. Additionally, it helps save wear on the mechanical components involved in traditional air braking.

While other options may touch on aspects of train operation, they do not accurately capture the main function of dynamic braking in slowing the train effectively and promoting safety in train handling.