AC locomotives

Does anyone know why Canadian National and Norfolk Southern have not purchaced any AC locomotives, while the other big roads (UP, BNSF, CSX, and CP) have plenty?
P.S I am aware of Sorfolk Southern's ownership of those ex-Conrail SD80MAC's (their only AC locos). NS would not have these units if The Big Blue had not been split between NS and CSX.

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RE: AC locomotives, kevarc, Feb-14-03, 11:17 AM, (1) RE: AC locomotives, rdamon, Feb-14-03, 11:30 AM, (2) RE: AC locomotives, plainsman, Feb-14-03, 11:51 AM, (3) RE: AC locomotives, JonN, Feb-14-03, 12:26 PM, (4) RE: AC locomotives, whockin, Feb-14-03, 02:02 PM, (5) RE: AC locomotives, xlspecial261, Feb-15-03, 03:29 AM, (6) RE: AC locomotives, plainsman, Feb-15-03, 05:50 AM, (7) RE: AC locomotives, xlspecial261, Feb-15-03, 06:24 AM, (8) RE: AC locomotives, plainsman, Feb-15-03, 11:15 AM, (9) RE: AC locomotives, xlspecial261, Feb-15-03, 11:52 AM, (10) RE: AC locomotives, sd70mac666, Feb-16-03, 12:48 PM, (11) RE: AC locomotives, westerngy, Feb-16-03, 02:48 PM, (12) RE: AC locomotives, jtr1962, Feb-17-03, 00:44 AM, (13) RE: AC locomotives, xlspecial261, Feb-17-03, 02:40 PM, (14) RE: AC locomotives, jtr1962, Feb-17-03, 03:28 PM, (15) RE: AC locomotives, kyleh24, Feb-17-03, 04:03 PM, (16) RE: AC locomotives, xlspecial261, Feb-17-03, 04:12 PM, (17) RE: AC locomotives, AKM103, Feb-17-03, 04:24 PM, (18) RE: AC locomotives, xlspecial261, Feb-17-03, 04:26 PM, (19)

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Ns couldn't see the benefits for their system for the additional costs.Kevin Arceneaux
It is time for Amtrak to become a fallen flag!

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Maybe if EMD made a SD70AC with a High Short Hood???

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I agree with Kev, NS has always taken a very conservative approach to their power pool. You will note they also use the downgraded 4,000 HP Dash 9 instead of the 4,370 HP version everyone else has chosen. They feel they get more from sligtly extended life and reduced fuel consumption than the extra horsepower would benefit on their typically more curvy hill routes, where high speed is not often the consideration. The 4,000 HP version will start and pull just as heavy a train up to their typical track speed.
The AC locomotives are much more expensive to purchase than the DC types. For roads like UP and BNSF with lots of coal trains on typically straight high speed routes, the cost is quickly recouped in additional tonnage. I am not as familiar with the NS cargo profile, but I would guess it involves less need for high speed or crowded unit coal on fast mainlines, the major areas which AC would benefit? If the unit coal running on their system is not impeeding the flow of traffic, they can move it more cheaply with the lower horsepower and/or less less expensive equipment. They also have lots of high horsepower 4 axle equipment for moving their intermodal freight. Some roads have put 6,000 HP AC on this service, but high HP 4 axles work just as well, and cost much less. The answer to if their thinking is correct will be if they make money and stay in business?
Bob

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LAST EDITED ON Feb-14-03 AT 12:28 PM (EDT)

Thanks for clearing up my confusion about NS, but my question about Canadian National still stands. They run heavy coal trains through moutainous territory (the location and task for which AC traction seems best suited), but have not a single AC locomotive in their locomotive pool. Canadian Pacific, on the other hand, has embraced AC traction wholeheartedly. Since 1995, they have purchaced 360 AC4400s, 60 SD90/43MACs, and 4 SD90MAC-H IIs. These locos account for close to 40% of their motive power pool, the highest ratio of any North American freight railroad.

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CN already has a large fleet of sd70 and 75's, and some 50, 60's where CP still had their fleet of aging sd40-2's. CN does not have the 2.4% grades to deal with on their mainline as the grade over Yellowhead pass is much more forgiving at 1%. CN Also has double track main where CP has single. The coal reserves where CN services are dwindling and not as much heavy tonnage is being moved as CP. CN has more "hot trains" running at higher speeds. Two completely different Railways.

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Bob,AC power is actually most useful in low speed drag service, not in high speed mainline service. AC's show little or no benefit in the higher speed ranges, HP being the same. Actually, in my experience, AC is a detriment in high speed service in equally powered locomotives.Once, I was actually able to confirm my suspicions with an impromptue drag race. First a little background;At Rondout IL we still pick up orders on the fly (Possibly the last place in the country this is done?). As the older locomotives have a lower cab height than the newer safety cabs, the order hoops can be set to two different levels. The train in front of me, an intermodal train with two SD60's missed their orders as the operator put them in the high hoop. As we were right behind, with two AC4400's on a junk train, we were told to stop at the tower and pick up their orders and run down alongside them on main 1 and hand em over.Well, I stopped next to them and handed the orders over to 183's conductor out the window. Then, the race was on. The two AC4400's pulled out a lead of about three engine lengths up to about 25MPH after getting left out of the hole by two lengths (I was still kicking off the brakes when he started pulling, so he got a bit of a jump on me). After stabilizing up to about 30 MPH, the SD60's started pulling the AC's and passed us like we were standing still at about 34MPH still accelerating hard while the AC's were already laying down.The two trains were of similar weight and length. Two things should be noted. CP's AC4400's derate to 4000HP at 24MPH, so the horsepower between the SD's and AC's are pretty close above that speed. And, it should be noted that an intermodal train generally has more wind resistance than a general freight. This doesn't really begin to come into play until speeds above 40 (Unless it's got a lot of double stacks, then it's lower). Even with that, the other train was well over 40MPH when his rear end went by us.These characteristics, along with the much higher cost, have often caused me to question CP's strict diet of AC only power since 1995. Many trains that we run over the Soo District do not require the low speed lugging power provided by AC locomotion. I'm sure many of the train's running over the network east of the Rockies, north of the border, are similar. While it might require a segregation of power, AC's on unit/bulk trains only for example, going the way UP has with it's huge SD70M order would seem to make more financial sense. UP uses AC's in coal, unit train service, while the 70M's are in general freight service and intermodal.Using the biggest, most expensive hammer, isn't always necessary to do the same job. And doesn't always make financial sense.(btw-I wrote down the HP figures by notch last trip, but then left em on the engine. *argh* I'll try and get em next time. Going from memory, run1=300, run2=600, run3=900, run4=1500, run 5=2000HP, 6=2500, 7=3400, 8=4000/4400. Don't take these as gospel as my memory is as leaky as the Titanic.)Best,
Todd

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Hi Todd,
Very interesting story! As to the higher speed AC units, I was really thinking about the 6,000 HP versions that are used by some roads on their intermodal stuff (including UP on some AC6000s). I know the AC4400 and SD70Macs are almost completely coal drags on roads I see, but won't those still get a unit coal train up to 25-30 mph faster than a DC of same power, thus keep the mainline moving more with heavy traffic? It is interesting that the 6,000 HP versions have not taken off in sales. I know some have reported reliablity problems on the few out there. Maybe they are not performing to expectation either??
Thanks for the HP data, I will get it from you when you get a chance, I appreciate the help.

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It's hard for me to compare a DC to an AC below 20MPH or so because we don't have any Dash 9's. Since there is a HP variance in the power I use, it is harder to tell what the difference may be.However I will venture out and say that from what experience I do have that an AC will accelerate a heavy train faster up to about 10-13 MPH, HP being equal. The reason for this is the fact that AC can put more/all of it's power down at low speed. Above this speed, the DC locomotive shouldn't be traction limited. For the modern stuff, Dash 9's and 70's/75's for instance, the difference may be less.Since the rate of acceleration and top speed is a function of Horsepower, it should make no difference as long as the locomotive is not traction limited. As stated above, there does seem to be a difference once you get moving faster than 25MPH or so. The AC's simply do not seem to like speed for some reason. They are real dogs above 45MPH or so unless you have a very light train. This is surprising to me as they have very good transmission efficiency, around 93% I have heard. But then, I'm not an electrical engineer, so I do not know why this phenomenon occurs.Hope this helps,
Todd

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Hi Todd,
Thanks for the reply. I forgot to ask before, do all AC4400s derate at 24 mph or just the CP version? I had not heard this mentioned before. It won't help much with the physics models, as the sim does not allow derating or transition or power limiting, maybe in version 2 or 3??
Bob

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As far as I know, only CP's do.They were not built as such, except the last two orders. The earlier units were built with a switch for either 4400 or 4000 HP that the engineer could select. (I honestly have to say, I haven't noticed if the 8600's have this or not. Haven't seen a 9700 yet.)A couple years ago, the software on these earlier units was changed to include the automatic derating. They derate at 24 MPH an go back to full power at 17MPH. Supposedly this for fuel conservation and engine longevity. The diesel doctor told me the extra 400HP adds a lot of stress to the prime mover, so derating them makes them much more reliable. (Quite possibly another reason NS's units are 4000HP, to address the original question)An interesting side note; Back when we had the HP switch to play with, oftentimes we would drop it back to 4000HP to cut down on the vibration. It's a really big difference in the cab.Best,
Todd

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Switches are fun to play withI think CNR and NS haven't justified the extra expense of AC power, but who knows
The Ragged they come and the ragged they kill
Down in the Cool air I can see
Superbeast; Rob ZombieI dragged your big-assed dirty robbed car out of that ditch

I Took Your Name: R.E.M.

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CN has no need for the AC's low speed drag service as their route even through the Rockies has no grade over 1%.In the whole system coast to coast then run a fairly level railroad.
Just Rollin Down The Tracks Dale

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>(btw-I wrote down the HP figures by notch last trip, but then left
>em on the engine. *argh* I'll try and get em next time. Going from
>memory, run1=300, run2=600, run3=900, run4=1500, run 5=2000HP,
>6=2500, 7=3400, 8=4000/4400. Don't take these as gospel as my memory
>is as leaky as the Titanic.)I've modified my throttle notches to give something similar in MSTS. For the Dash9 I used the percentages as follows:1=4.4%
2=11%
3=23%
4=34%
5=50%
6=65%
7=81%
8=100%I got the numbers from Al Krug's website, IIRC. My question to you is, at low speeds, does the locomotive develop the same proportion of it's maximum tractive effort in each notch? For example, you said in run1 you have 300HP, which is 6.8% of 4400 HP. Let's say that the loco can develop 170,000 lbs TE maximum(don't know the exact figure offhand). In run1 will you get 6.8% of 170,000, or ~11500 lbs, up until the speed reaches 9.8 MPH, at which point you would be HP limited, or will you get something higher? If you remember offhand the starting TE in all the notches that would be great. I'm trying to get my locos as real as possible. I can use the Adheasion and Numwheels parameters to limit my maximum TE, and then bump the MaxContinuousForce parameter as high as needed to get the correct TE in the lower notches. The idea does work well on older equipment, I'm just looking for hard numbers for newer stuff since the locomotive computers can be programmed to do just about anything, unlike older equipment. I'm also curious why modern equipment has notches instead of just a continuously variable throttle. It must make holding at the speed limit a pain. In MSTS I usually need to oscillate between two notches to do that.>Since the rate of acceleration and top speed is a function
>of Horsepower, it should make no difference as long as the
>locomotive is not traction limited. As stated above, there
>does seem to be a difference once you get moving faster than
>25MPH or so. The AC's simply do not seem to like speed for
>some reason. They are real dogs above 45MPH or so unless you
>have a very light train.
>
>This is surprising to me as they have very good transmission
>efficiency, around 93% I have heard. But then, I'm not an
>electrical engineer, so I do not know why this phenomenon
>occurs. I'm wondering about that as well. If anything, for a given prime mover horsepower an AC locomotive should put more power to the rail at high speeds. Perhaps they all start to derate as the speed increases to save wear and tear on the engine. I would certainly assume that they do once you get past the locomotive's maximum speed when running a short train(since you obviously don't need 4400 HP to move a 10-car train at, say, 75 MPH), but no reason why they should do so to any great extent before that.Electrics definitely do this sort of "derating". I used to ride Arrow III EMUs on the NEC to college. The power seemed to peak at about 80 MPH, and then started dropping off after that. 0 to 60 took about 37 seconds, 0 to 80 about 60 seconds, 90 took another half a minute, and then another minute or so to creep up to 100. Some of them crept all the way to 115 after about 6 minutes. I figured each EMU unit developed about 1000 HP under about 80 MPH. After that, the power had to drop off sharply based on the acceleration rates and the final top speed of the train(usually in the 95 to 105 MPH range).

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I only recall the TE for the first two notches at very low speed. ie; below 3 MPH. Run 1 is 14K and run two is 54K. Oh yeah, just rememebered. The most TE I have observed was 164K in run 8 at 1MPH. That was bouncing between 154 and 164.TE is a bit different compared to HP as it varies due to speed. The faster the armatures spin, the less torque they put out. In run1 at 10 MPH you may only have 1K of TE. In 8 at 45MPH, 28-30K or so comes to mind. It drops off very rapidly.The modern locos have notches as they must be backwards compatible with the older power. I doubt we will see the notched throttle go away due to this. Also, the notches do not really cause any problems as you would have to vary the throttle anyhow due to slight grade changes and curves. Generally, a train changes speed fairly slowly as it reacts to changes, so you don't really need to vary the throttle constantly.The locomotives do not derate, other than the aformentioned drop of 400HP at 24MPH due to fuel conservation and maintenance reasons.. At 60MPH it is still putting out the full 4000HP as shown on the locomotive monitor. And you may very well need 4400HP to pull a 10 car train at 75MPH. There are a lot of variables, but the faster you want to go, the more HP you need.Hope this helps,
Todd

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>I only recall the TE for the first two notches at very low
>speed. ie; below 3 MPH. Run 1 is 14K and run two is 54K. Oh
>yeah, just rememebered. The most TE I have observed was 164K
>in run 8 at 1MPH. That was bouncing between 154 and 164. So TE does increase in a different proportion than HP as you run up the notches. Very interesting. I'll see if I can do something close to this in MSTS. Probably impossible to duplicate exactly, though, as the percentages differ from the HP percentages between those notches. For example, in run 1 HP is 6.8% of maximum, TE is 8.5%, in run 2, the numbers are 13.6% and 33%, respectively. Run 2 gives you double the HP but almost 4X the TE as run 1. Offhand, do you know what notch you need to be in before you reach maximum starting TE? Based on the way it's going up, it looks like you'll get there by run 4. I'll probably just try to match the notch you reach maximum starting TE in. The rest will probably be off by a bit, but I can't do any better given the limitations of MSTS.>TE is a bit different compared to HP as it varies due to
>speed. The faster the armatures spin, the less torque they
>put out. In run1 at 10 MPH you may only have 1K of TE. In 8
>at 45MPH, 28-30K or so comes to mind. It drops off very
>rapidly.That makes sense. At some point you'll definitely be horsepower limited.>The locomotives do not derate, other than the aformentioned
>drop of 400HP at 24MPH due to fuel conservation and
>maintenance reasons.. At 60MPH it is still putting out the
>full 4000HP as shown on the locomotive monitor. And you may
>very well need 4400HP to pull a 10 car train at 75MPH. There
>are a lot of variables, but the faster you want to go, the
>more HP you need. I would imagine you might need 4400 HP to move a 10-car TOFC or double stack at 75 MPH. Those definitely have a lot of air drag. I'm still wondering why the ACs are such dogs acceleration-wise, as you say. Perhaps because they take longer to load than the older DC units?Thanks for the help, Todd. I'll see how much of this I'm able to duplicate in MSTS. It's nice having someone who actually drives these things to ask questions.

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The best explanation of speed and traction I ever read came from Al Krugs web site. I've read it numerous times. I'm sure some of you will be most interested in it...
http://www.vcn.com/~alkrug/rrfacts/hp_te.htmKyleH

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Another interesting thing is the fact that GE and EMD are different in how TE relates to throttle postion.An EMD SD9043MAC goes like this;Run1=20K
Run2=40K
Run3=60K
Run4=80K
Run5=100KI do not have the numbers for the other notches, but I would assume they are also proportional. Also, our 90's are not set up to display HP, so I cannot get those numbers.Once again, these fall off as speed increases. The run5 figure was obtained at about 7 MPH.I do not know all the ins and outs of the sim and how it processes HP and TE. However, they do seem to be handled seperately and on curves. As they should be.I have been trying to get this info together for Bob B, but things have not been working out at work. Been catching UP 70M's, Soo 60's, SD90's, etc instead of the more common AC4400's of late. When I get all the figures together, I will try and get them out for Bob, you, and the other physic boys to play with.Best,
Todd

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Norfolk Southern does have another AC...the GP38AC. Saw it on a site b4...here is a pic:

Marcus James MJ

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http://www.train-sim.com/dcforum/User_files/3e5152f455e1197f.jpg

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The GP38AC does not have AC traction motors. They do have a main alternator versus a main generator.This was an option on that particular locomotive.The Dash 2 series all had main alternators.Note-The MP15AC is the same idea.Todd

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