As mentioned, they were cow-calf sets, model TR1. This was in the early days of dieselization and railroads were still using the steam practice of tailoring locomotives to a specific task. The TR1’s may have been intended as low-speed road locomotives (they were on Blomberg trucks) for transfer service within the Chicago Switching District.
NS has produced 4 axle road capable slugs with dynamic braking. Some of them were built as much as 20 years ago. They were built at the Roanoke East End Shops from retired GP9’s/18’s.
Most of those slugs have since been retired. NS has an ongoing road slug program (NS 700 series) which are rebuilds of retired GP38’s and are similar to CSX road slugs.
I know that when someone mentions slug, we all think of a 4 axle unit, but what about making a 6 axle slug? I’m thinking something along the lines of perhaps a SD38 or SD40 that has reached the end of its “normal” life and would be retired, theoretically could you not strip the prime mover and use it as a slug, or in the concept of AC power remove the prime mover, and use that space to install the inverters and microprocessor controls needed for such?
I also understand about the slug only being able to with stand a certain speed before it is cut off from the mother electrically, but if you were to mount the slug between two “mothers”, could you not potentially break through the 25 to 28 mph “barrier” that currently exists?
Are there lists anywhere of slugs currently in usage (2011) in North America? I never thought of slugs being particularly common, but after reading this thread, apparently they are.
If no list, can anyone provide a guess of numbers - dozens?, hundreds? All running on Class Is, or are there a few on Class IIs (or even shortlines?)
OK, thanks.
A few more questions;
This one regarding the mentioned 25-28mph cutoff: did the slug simply cut itself out at that speed, or was it done under control of the engineer?
Was the cut off abrupt, or did the slug gradually power down?
Did the slug retain the circuitry such that it still went thru transition steps? (And IIRC, the GP30 had about 20+ transition phases throughout it’s operational speed range)
Six-axle slugs do exist, BNSF and BRC have them on their rosters. They are plugged into six-axle mothers and the sets generally serve as hump pushers.
I didn’t know that about BNSF and BRC using 6-axle slugs…all right, well, check one thing off the list of my previous post.
Not being a Engineer I am not conversant in the specifics. The Mother is able to generate X amount of electical energy for traction…at low speeds this is more than the 4 traction motors of the mother can effectively transmit to the rail, the slugs extra 4 traction motors are able to use this excess electrical energy and turn it into effective traction…as speed increases the electrical energy requirements for each traction motor increase … at some point in the speed curve, the 4 traction motors of the Mother are using all the available electical power and depending on the grade the locomotive and its load can go no faster…at the ‘2’ unit tonage rating of the mother-slug combination this speed is approximately 25 MPH…I don’t know how electical
[quote user=“BaltACD”]
zardoz:
BaltACD:
CSX Road slugs retain the operational cab…they are coupled back to back with the Mother and allow operation from either cab. The prime mover in the slugs has been replaced with a equal weight cement ballast. At one time there was fuel sharing apparatus allowing the Mother to draw fuel from the slug’s fuel tank…I think this proved more trouble than it was worth and has been scrapped over the years. Most of the slugs started out life as GP30’s or GP38’s.OK, thanks.
A few more questions;
This one regarding the mentioned 25-28mph cutoff: did the slug simply cut itself out at that speed, or was it done under control of the engineer?
Was the cut off abrupt, or did the slug gradually power down?
Did the slug retain the circuitry such that it still went thru transition steps? (And IIRC, the GP30 had about 20+ transition phases throughout it’s operational speed range)
Not being a Engineer I am not conversant in the specifics. The Mother is able to generate X amount of electical energy for traction…at low speeds this is more than the 4 traction motors of the mother can effectively transmit to the rail, the slugs extra 4 traction motors are able to use this excess electrical energy and turn it into effective traction…as speed increases the electrical energy requirements for each traction motor increase … at some point in the speed curve, the 4 traction motors of the Mother are using all the available electical power and dep
The traction motors are in permanent parallel? I would think that would inhibit it’s starting tractive effort, compared to being in series. I know that the Metra F40PHs are in permanent parallel, and when we went from being used to starting a train in series (F7&E8s), it took a while to get used to the difference The train would get up and go so much quicker than the F40’s, although admittedly the F40’s did slip a lot less, which usually mand up for the difference in get-going speed.
When the slug does cut out, it must be quite the sensation for the Engineer in the lead unit.
Presumably if, say, 1200 amps are going thru each motor at a given speed, the total TE the unit is exerting will be the same, whether the motors are in parallel or series-parallel?
So you’re figuring in series-parallel they could run more amps thru each motor? More than 1500?
Pretty much all 4-axle EMDs with AC main gens are wired in parallel, no transition. They just keep pulling. Doesn’t seem to affect starting tractive effort, as they will slip if the power applied is too much.
At around 12-14 mph, the curves switch to being horsepower dependent. Above that speed, if you don’t have the horsepower, you aren’t going any faster. Below that speed, the GPs put out more power than 4 traction motors can use. Either the wheels slip, or traction motors start to smell, stink, let out factory smoke, provide a light show, etc. The slugs allow a GP40 to dig in better, like 2 GP7s would. But you’ll only go as fast as 2 GP7s pulling the same load.
1050 amps is the continuous rating on EMD D77 motors (pretty much the standard since 1965). Running more amps than that for longer than a half-hour or so will melt things.
I’ve had a GP38-2 load up 1500 amps, maybe a bit more. I don’t think a slug set would get near that, not enough horsepower.
On the AC slug vs the new BNSF A1A locomotives. The physics are the same, just in opposite directions.
For the AC slug, as mentioned above, the diesel engine can make more horsepower than can be transmitted to the rails at low speed. The slug woud be able to absorb more of this power and produce extra tractive effort with it. This is pretty much the same justification as DC slugs.
For the A1A locomotives just the opposite result is desired. AC motors are more compact and easier to cool than DC motors of the same horsepower… A higher horsepower AC motor can be fit in the same space as a DC motor. With a 4400 HP AC locomotive it is possible to absorb all of this horsepower through four traction motors at low speed, but the wheel to rail adhesion between the wheels and rail is the limiting factor. On the other hand, at high speed the four AC motors are more than capable of absorbing and transmitting all of the horsepower available from the prime mover to the rail without slipping…
To get more tractive effort at low speed, you have to improve wheel adhesion . The only practical way to do this beyond sanding the rail is to increase the weight on the drive axles. If you had two axle trucks, this could be done at low speed, but the weight on each axle is too high to prevent damage to the rail at high speed.
On the new locomotives the weight on the middle axles is relieved at lower speeds putting more weight on the outer drive axles. This gives almost as much tractive effort as a comperable six axle lccomotive. At higher speeds more weight is put on the center axle, decreasing the weight on the drive axles where it is no longer needed. This keeps the weight per axle down to the point where it will no longer damage the track structure.
The net result is you get a locomotive with only four traction motors instead of six that can perform like a 6 axle locomotive at low speeds, yet run li
You seem to be saying a four-motor locomotive pulls better than a six-motor at high speed, even if they’re the same total weight. Why would it?
3000HP/4 traction motors = 750 HP per traction motor
3000HP/6 traction motors = 500 HP per traction motor
More HP per axle = more speed
Depending upon wheel slip control - more HP per axle at slow speeds = more wheel slip potential.
If the engine had only two powered axles it would have even “more speed”? Would a one-motor AC44 pull harder at 70 mph than a six-motor?
Wheel slip control - it is still not a perfected science … AC wheel slip control is more effective that DC at the present time. The BNSF 4 traction motor AC’s manage to handle 1100 HP per axle and I understand their primary mission is handling intermodal trains on the Trans-con - long miles and high speeds.
Observations are that when you begin to exceed 750 HP per axle with DC engines they tend to become very slippery when used in heavy tonnage situations.
It sounds like you are switching cause and effect. Power = force * velocity. If drag is neglected, it will take twice the power to move a train twice the speed, but the force required will be about the same. Let’s say moving a train at 30 mph requires 2 AC4400CWs. If they decide to move the train at 60 mph and add two more AC4400CWs, then (neglecting increased drag) the train will have twice as much force available than needed. A larger fraction of the total power goes into speed. Assume the tractive effort (force available to pull the train) for an AC4400CW is 1.5 times the tractive effort of an AC4400C4. If you replaced the AC4400CWs with AC4400C4s, you have 1/3 less traction motors and associated equipment and still adequate force to move the train with probably little affect on the train’s performance (assuming it does not have to stop often). Therefore, it is not less traction motors means the locomotive can go faster; rather it is locomotives that will going faster may not need as many traction motors.
I suspect that eventually there will be some application of AC traction to low-to-medium horsepower locomotives for switching and similiar work in the North American RR industry. There are already AC motored switchers at work in Europe and elsewhere. Republic locomotive in South Carolina is marketing a small industrial “critter” type unit with AC motors which they claim produces the same tractive effort as an EMD SW1000/1200:
http://www.republiclocomotive.com/rx500_industrial_locomotives.html