• When a Train Stalls...

  • General discussion about locomotives, rolling stock, and equipment
General discussion about locomotives, rolling stock, and equipment

Moderator: John_Perkowski

  by Denver Dude
When a locomotive (or series of them) can't pull the grade, I am under the impression that it's mostly about adhesion, weight on the drivers, trailing weight, grade percent, etc.

But is it possible that that the prime mover, generator/alternator, and traction motors are just maxed out and can't turn at all?

Also, I found the video below. Some commenters are saying that the locomotives can overheat and will de-rate if in run 8 for too long, at too low of a speed. I don't think that's true. I am guessing that the AC traction motors are fine either way, and it's all the same to the diesel engine when in full power, whether the locomotive is moving 70 miles per hour or 12.


https://www.youtube.com/watch?v=rFnNFuCOxZM" onclick="window.open(this.href);return false;
Last edited by Denver Dude on Tue Dec 23, 2014 11:13 am, edited 1 time in total.
  by Desertdweller
You are correct in that AC locomotives are less prone to damage under those circumstances.

But locomotives do not "stall out" in the sense that the drive system "stops turning".

You have to consider that there is no direct mechanical link between the engine/generator and drive wheels. Locomotives will always encounter wheel slip before they "stall out". Modern locomotives have a wheel slip device that cuts amperage to the traction motors when wheel slip begins. Otherwise, the amperage draw will quickly drop when the wheels begin to slip. An engineer can control wheel slip by noting the amperage draw when slip starts, and staying below that level.

There are situations that would cause the drive system to lock up, but this involves mechanical failure in the traction motor or gears. A failed armature shaft bearing could cause the armature to seize, or maybe drop and come in contact with the field. A pinion gear could break and jam, or foreign material could get between the pinion and spur gear, jamming the drive. But adhesion exceeding tractive effort, and causing a stall, no.

Trains can stop moving when load exceeds tractive effort, but the drive system will not lock up. The locomotive will simply stop and spin its wheels.

  by litz
Actually, any modern locomotive with proper wheelslip detection won't even stop/spin ...

It'll just slowly crawl down in speed, until it's no longer moving.

The locomotive's control circuitry will engage and either throttle down, or disengage long before either powerplant damage, generator damage, or wheelslip damage occurs.

Presuming everything is working correctly, that is.