Overview
A magnetic track brake (Mg brake) is a brake for rail vehicles. It consists of brake magnets, pole shoes, a suspension, a power transmission and, in the case of mainline railroads, a track rod. When current flows through the magnet coil, the magnet is attracted to the rail, which presses the pole shoes against the rail, thereby decelerating the vehicle.
While brakes such as disc brakes or shoe brakes depend on the frictional connection between wheel and rail, the magnetic track brake acts directly on the rail. Therefore, its brake effect is not limited by wheel-rail contact. Thus, environmental factors such as wetness or contamination of the rail have less influence on the brake force.
Usage
Magnetic track brakes are used on rail vehicles in addition to the primary, wheel-effective brake systems. As an additional brake system, they help to ensure that the prescribed brake distances of rail vehicles can be complied with.
Since magnetic track brakes always act unregulated and at their maximum brake force, they are only used as safety and emergency brakes. They can be used at speeds of up to 280 km/h. With the usage of special friction materials they can be used up to speeds of 350 km/h.
From Wikipedia (CC BY-SA 4.0).