Diesel Locomotive Multiple Unit Operation

[CastroPuss]

It is understood that when diesel locomotives are coupled together to form a multiple unit configuration (excluding remote/distributed power units), the multiple unit electrical cables are connected as well as all the air hoses.

The lead locomotive becomes the "master" unit which controls the other connected locomotives. The other connected units power and braking settings mimic the power and braking settings in the lead locomotive. So if the lead locomotive is running at run 4, for example, all of the other locomotives should be running at run 4 also. Similary if the lead locomotive is in dynamic braking mode, the other locomotives should be running in dynamic braking mode as well. And so on. Correct?

Is it possible to have some or all of the other locomotives operate only in power or run mode (and not use dynamic braking), or operate only in dynamic braking mode (and not run in power mode)?

This question is asked because I recall a situation in an article where five locomotives (all connected and running as far as I know; no "dead" units) at the head end of a consist had an issue with (minor) fire occurring in the second locomotive. There was a mention that the second unit was used "exclusively for braking". That was basically all that was said.

How can one (or more) locomotives operate semi-independently from the lead unit while connected in multiple unit configuration?

[CSSHEGEWISCH]

The only braking that would be utilized in an otherwise isolated unit would be the air brakes through the trainline and possibly the independent brake.  Dynamic braking would not be used.

[ndbprr]

A train can have too much dynamic braking. IC limited it to 16 axles. THere is a switch in the cab to lock out dynamic brakes or at least There was

[BaltACD]

The capabilities of today's main line locomotives would make steam era operating people minds explode.  Too much power and too much braking available for trains that are approaching 2 miles or more in length or coal trains approaching 20K tons.

[jeffhergert]

CSSHEGEWISCH

The only braking that would be utilized in an otherwise isolated unit would be the air brakes through the trainline and possibly the independent brake.  Dynamic braking would not be used.

 

Some engines, and I think they were a batch of EMD SD70ACe units, had a position on the isolation switch that allowed the unit to be isolated (off line) for power but left the dynamics operable.

Engines have the capability to have the dynamics cut out.  We have rules on how much dynamic braking force may be on line.  Units that are in excess of the limit are to be cut out.

Jeff  

[CastroPuss]

Thanks for the comments. Ah yes! I now vaguely recall something about dynamic brakes being able to be cut out in units. However. This is the first time that I'm aware of that (some) units seem to have the option of having their power cut out (and with engine running; ie not "dead"). This is a bit unusual! So it seems the second (and maybe other) unit(s) were either ordered with the power cut out feature added, or it may have been a retrofit modification? Presumably these units also have the option of dynamic brake cut out as well power cut out(?)

[Jackflash]

Confirm what Jeff said, I have seen this option too,  not very often I have only seen it a few times, cant remember what engines

[Wizlish]

jeffhergert

Engines have the capability to have the dynamics cut out. We have rules on how much dynamic braking force may be on line. Units that are in excess of the limit are to be cut out.

Exactly how is that done at present?  Does the procedure vary with type of unit?

I'm presuming that it is done when the train is being made up, and cannot be changed via any setting of a control system like LEADER.  On the other hand, I can see a potential advantage if one of the DB-enabled units should suffer a road failure en route and another unit could be commanded to 'take its place' without having to stop the train or walk the consist to make the settings.

[zugmann]

It's a switch.  Sometimes in the computer screen, other times just somewhere in the cab.  Nothing too involved. And please leave that LEADER out of the important stuff like dynamic braking.  That thing is going to make engineers even dumber.

[groomer man]

Jeff what are the drawbacks or problems that could arise from excessive dynamic braking?

[BigJim]

groomer man

Jeff what are the drawbacks or problems that could arise from excessive dynamic braking?

 

Too much braking effort localized right at the head end of the train could send excessive force to be transmitted through the train to cause the cars to jack-knife and derail.