Discussion related to commuter rail and rapid transit operations in the Chicago area including the South Shore Line, Metra Rail, and Chicago Transit Authority.

Moderators: metraRI, JamesT4

  by Tadman
 
Any reason the geeps don't have dynamic brakes? I know the MU's have 'em, and I think the electric motors had them. Further, doesn't C&O have dynamics on their mountain-going fleet?

  by MikeF
 
My guess would be that since the South Shore is, for the most part, flat, the railroad just decided to save a few bucks on the 38's by ordering them without dynamic brakes.

  by dinwitty
 
dyanmic brakes idea came from, where else, but electrified lines...

by using the motors as generators it applied braking power without using up the brake shoes. Going downhill the power boosted trains going uphill.

Unfortunately for diesels they gotta dissipate that power thru large resistor arrays and thats the big lump you see on diesels.

I don't believe the CSS has any huge grades to worry about regenerative braking..

  by MikeF
 
Dinwitty's comments bring up a separate point -- the difference between dynamic and regenerative braking.

In dynamic braking, which is used on diesel locomotives and most modern electric equipment (including NICTD's fleet), the energy generated by the traction motors during braking is dissipated in the form of heat through braking resistance grids.

In regenerative braking, the energy is transferred back into the catenary or third rail to help power other trains. This form of braking is used on some rapid transit equipment and on some of the electric commuter trains out East, and was also employed on some older electric locomotives. Regenerative braking will also be employed by GE's new hybrid diesel locomotive, but the energy will be sent to batteries to power the traction motors at low speed.