AC vs. DC traction

[Anonymous]

I have seen the BN burn up alot of DC motors on pushers at Crawford Hill.
Allan.

[edbenton]

Yes they can but when they are mue'd use lose they low speed advantage of the ac units.

[daveallisonpe]

Godd Answers! Question: Can AC & DC be MU'd?

[Anonymous]

Yea, thank you all, good readings.

So then, if you had a bunch of AC's and bunch of DC's in your fleet, how would you assign jobs to them? I mean it seems to me like AC's would get all the job, cause they are good for both high speed trains and for slow heavy crawls.

[daveklepper]

Good explanations

[tree68]

I read an account in TRAINS some time ago that said that an AC was in run 8 at about a half mile per hour, pulling a sizeable train up a grade. Can't do that with DC. (Would have been interesting to see the result when they broke a drawbar, which I believe the story said they did).

[oltmannd]

Tony-

Good answer. I'll just add:

AC: better wheelslip = higher adhesion = more tractive effort, which is the stuff you need to haul heavy trains such as unit trains

The reason you don't see 6000 HP DC locomotives is that about the most the frt RRs ever need from a locomotive with 100,000 to 120,000# TE is 4000 - 4500 HP. More than this and you're just wasting fuel. A six axle AC and do 150,000 to 175,000# TE which is a good match for 5000 - 6000 HP.

[owlsroost]

In general terms:

DC drive
--------

Good : Cheaper (currently), simpler, well understood, generates less interference with signalling etc

Bad : Not as good performance as AC for really heavy-haul freight or for high-speed passenger use. Motors have brushgear which needs maintenance and is a weak point if abused.

AC drive
--------

Good : Better wheelslip control than DC so ideal for really heavy-haul freight (also better dynamic braking), and AC traction motors can withstand abuse that would wreck DC motors. AC motors are lighter and smaller than DC so it's possible to get more power in the same space (which is probably why the GE/EMD 6000hp units are AC drive only) - this is also important for for high-speed passenger trains.

Bad : More expensive than DC (but getting cheaper) due to complex electronics, can create interference problems with signalling etc.


The railway world in general is going AC drive, so as soon as the cost of AC drives matches that of DC the DC drive will become obsolete for new rolling stock (my prediction [:)]). We've pretty much reached that stage in Europe, certainly for electric locomotives/multiple units.


Tony

[Anonymous]

Can someone explain to me what are the pros and cons of each of the traction systems, and for what kind of jobs would it be preferable to use one over the other?