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Braking Effort

By on May 12, 2013

 Braking effort is the effort required to stop the train within safe braking distance. It has safety consequences. Braking effort is required to counter the kinetic energy of train running at a speed V and can be expressed as .

  •  frac{1}{2}times Wtimes V^{2}-(T_{r(avg)}pm T_{g}+T_{c})times Dtimes g=T_{b}times Dtimes g     where D is braking distance, Tr(avg) is average train resistance and Tb is braking effort.
  • Braking effort shall be such that it should be able to stop the fully loaded train on a prevailing ruling gradient section within Emergency braking distance governed by the signaling system prevailing on the territory. This governs the requirement of maximum braking effort.

Braking Effort is provided by means of

  • Mechanical brakes: In this system, the brake shoe binds with the tread of wheel, causing mechanical energy to be converted into heat energy through friction. It is the principle braking system.
  • Maximum braking effort is limited by adhesive weight for slide not to occur. Tbmax  = μ*W for skidding not to occur. Braking effort shall not exceed 750KN distributed over all axles for a train of 5000T when adhesion is at 0.15.  This gives the retardation of 0.15 m/sec. The time taken and distance travelled by the train if running at 50kmph or 13.8m/sec is

t=frac{13.8}{0.15}=92.6 sec ;

D=13.8times 92.6-0.5times 0.15times 92.6^{2}=634.6m

(Note: This excludes train resistance or any other resistance arising due to territory)

  • Empty freight trains are more prone to wheel skidding because of less axle load. In view of this brakes are adjusted to empty condition for reduced brake pressure.
  • Electric Brakes: Mechanical energy is converted to electrical energy by using the traction motor as a generator and  either fed back this energy  to OHE system (Regenerative Braking) or wasting across the resistor (Dynamic or Rheostat  Braking). This provides smooth braking, saving on wear of brake blocks.  and regeneration in specific class of locomotive.
  • Regeneration is not possible in Diesel Locomotive, but partly possible to use regenerated energy for head-on-generation or for auxiliary load of the locomotive itself.
  • Regenerative and rheostat braking of different class of locomotive is shown below

Railelectricd

 

Maximum electrical braking effort is limited by the weight of the locomotive multiplied with a coefficient of adhesion. Considering the widely varying conditions of adhesion, the braking effort is restricted to 25T only for 6 axle locomotive.

 

 

 

 

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