BNSF has joined the majority of Class I railroads by ordering nothing but AC drive locomotives, that leaves only CN among the Class I railroads as still buying DC drive mainline locomotives with DC traction motors. How long will that last. Sean Graham-White has reported that this years BNSF order for 227 locomotives will consist entirely of GE ES44C4s.
beaulieu BNSF has joined the majority of Class I railroads by ordering nothing but AC drive locomotives, that leaves only CN among the Class I railroads as still buying DC drive mainline locomotives with DC traction motors. How long will that last. Sean Graham-White has reported that this years BNSF order for 227 locomotives will consist entirely of GE ES44C4s.
Could you explain briefly to someone who is not an engineer or technician the advantages and disadvantages of an AC vs DC locomotive? Thanks!
AC traction is more expensive and better for prolonged pulling at low speeds.
Sam1: there are actually three possibilities, and BNSF is the only RR so far to choose the third one. Other RRs have some six-axle engines with six AC motors (best pullers but expensive) and also some cheaper six-axle engines with six DC motors. BNSF apparently thinks if you want a cheaper engine the best choice is six axles and four AC motors; us fans have no idea how much cheaper they are, or how well they pull.
I have no idea of BNSF locomotive strategy....
My carrier exclusively bought AC's for a number of years....for several years in the middle of this decade the only locomotive orders were for ES44DC's that have been down rated to ES40DC's, the subsequent orders have been exclusively for AC's.
People making such decisions change over time and the ideas of what is 'right' change with the personnel. Any comptent top level manager can make any set of facts prove any bias he may have on a particular point....both for and against.
Never too old to have a happy childhood!
Sam1 Could you explain briefly to someone who is not an engineer or technician the advantages and disadvantages of an AC vs DC locomotive? Thanks!
DC the only advantage is the initial purchase price.
AC advantages
1) Either a lighter motor for a given amount of power or a more powerful motor for a given amount of weight
2) The potential to reduce the amount of unsprung mass. The greater the unsprung mass the greater the hammering of the track.
3) inherent advantage with both the 3-phase asynchronous and permag synchronous motors for superior traction control. The motor will rotate at a speed determined by the frequency of the power supplied, and will resist turning either faster or slower.
4) no need for brushes and commutators with their limitations and maintenance requirements.
5) Greater rotational speed range for the traction motors.
The price differential has been decreasing since the introduction of the SD70MAC in 1994. I expect that within a couple of years DC motored locomotives will cost more due to low production levels. It is almost certain that the only DC locomotives produced this year will be the already completed CN order for SD70M-2s.
beaulieu DC the only advantage is the initial purchase price. AC advantages 1) Either a lighter motor for a given amount of power or a more powerful motor for a given amount of weight 2) The potential to reduce the amount of unsprung mass. The greater the unsprung mass the greater the hammering of the track. 3) inherent advantage with both the 3-phase asynchronous and permag synchronous motors for superior traction control. The motor will rotate at a speed determined by the frequency of the power supplied, and will resist turning either faster or slower. 4) no need for brushes and commutators with their limitations and maintenance requirements. 5) Greater rotational speed range for the traction motors. 6) I'll add the advantage of operating in snow and other "foreign" materials. Amtrak's dismal flashover rate this past winter on snow bound routes with their DC P-40, 42s is an example. Next AMTRAK order is already specified AC for both electric motors and for the future diesel orders. Also when UP broke out the rotary plows on Donner they used AC locos to push the rotarys and as far as I know had no traction motor failures?? All RRs snow plow extra have been notorious for traction motor failures in the past. The price differential has been decreasing since the introduction of the SD70MAC in 1994. I expect that within a couple of years DC motored locomotives will cost more due to low production levels. It is almost certain that the only DC locomotives produced this year will be the already completed CN order for SD70M-2s.
6) I'll add the advantage of operating in snow and other "foreign" materials. Amtrak's dismal flashover rate this past winter on snow bound routes with their DC P-40, 42s is an example. Next AMTRAK order is already specified AC for both electric motors and for the future diesel orders. Also when UP broke out the rotary plows on Donner they used AC locos to push the rotarys and as far as I know had no traction motor failures?? All RRs snow plow extra have been notorious for traction motor failures in the past.
I think DC-traction, C-C mainline diesels are going the way of DC-generator-equipped diesel locos in the 60s and 70s and spartan cab mainline locos in the 90s. Even NS is buying brand-new AC motive power from GE and EMD.
beaulieu [snipped; emphasis added - PDN] Sean Graham-White* has reported that this years BNSF order for 227 locomotives will consist entirely of GE ES44C4s.
*Author of a 2007 book on "GE Evolution Locomotives" - see:
http://www.amazon.com/GE-Evolution-Locomotives-Sean-Graham-White/dp/0760322988
timz [snipped; emphasis added - PDN] Sam1: there are actually three possibilities, and BNSF is the only RR so far to choose the third one. . . . BNSF apparently thinks if you want a cheaper engine the best choice is six axles and four AC motors; us fans have no idea how much cheaper they are, or how well they pull.
This almost overlooked point is almost as significant as the move to AC motors - namely, that after almost 2 years of experience with the original order of 25, BNSF is now jumping in for them in a big way, with over 9 times as many in this order. To be clear, these locomotives ride on essentially A1A trucks, but hey are quite different from those trucks of old. In particular, the center unpowered axle has GE's "Dynamic Weight Management System" to transfer up to 25% or so of the weight on it to the adjoining powered axles when needed for additional tractive effort. Although this concept was greeted with considerable skepticism when it was first unveiled 2 years ago, BNSF is now "putting its money where its mouth is" with this large follow-on order, so I have to presume that the experience with them has been satisfactory enough to justify the repeat order, which speaks volumes to me.
See article titled "GE Unveils new Evolution Series Locomotive" datedlined May 20, 2009 at:
http://www.gizmag.com/ge-evolution-series-locomotive/11748/
- Paul North.
beaulieu Sam1: Could you explain briefly to someone who is not an engineer or technician the advantages and disadvantages of an AC vs DC locomotive? Thanks! DC the only advantage is the initial purchase price. AC advantages 1) Either a lighter motor for a given amount of power or a more powerful motor for a given amount of weight 2) The potential to reduce the amount of unsprung mass. The greater the unsprung mass the greater the hammering of the track. 3) inherent advantage with both the 3-phase asynchronous and permag synchronous motors for superior traction control. The motor will rotate at a speed determined by the frequency of the power supplied, and will resist turning either faster or slower. 4) no need for brushes and commutators with their limitations and maintenance requirements. 5) Greater rotational speed range for the traction motors. The price differential has been decreasing since the introduction of the SD70MAC in 1994. I expect that within a couple of years DC motored locomotives will cost more due to low production levels. It is almost certain that the only DC locomotives produced this year will be the already completed CN order for SD70M-2s.
Sam1: Could you explain briefly to someone who is not an engineer or technician the advantages and disadvantages of an AC vs DC locomotive? Thanks!
Now I know or at least I have a good idea of the differences. Thanks for your excellent response.
What about the minority builders (MPI, NRE, Progress, Railpower, etc)? It appears that they're still pretty big on DC traction motors.
Ulrich AC traction is . . . better for prolonged pulling at low speeds.
But some have questioned the usefulness of that attribute as a practical matter, because a train at very low speeds is clogging up the main line and not making the best utilization of the more expensive and capable AC-motored locomotive. The DC-motored locomotive would have to keep moving at 15 MPH or so to avoid overheating, and that also keeps the main line more fluid. So the real advantages of the AC motor might be in the factors listed above by others - this one is just '"the frosting on the cake", another useful but not primary benefit.
In situations that would 'kill' a DC engine and leave it's train DEAD looking for additional power, the AC engine could keep the train moving to a point of clearance. That is the practical difference on a day to day basis of AC traction in today's railroad enviornment. There is nothing worse that a DC powered train to have Ground Relay issues that require a traction motor or two to be cut out on the ruling grade and the train then being 'dead in the water' until additional power can be secured to get the 'cork' out of the bottle and let traffic move again.
Paul_D_North_Jr But some have questioned the usefulness of that attribute as a practical matter, because a train at very low speeds is clogging up the main line and not making the best utilization of the more expensive and capable AC-motored locomotive. The DC-motored locomotive would have to keep moving at 15 MPH or so to avoid overheating, and that also keeps the main line more fluid. So the real advantages of the AC motor might be in the factors listed above by others - this one is just '"the frosting on the cake", another useful but not primary benefit. - Paul North.
beaulieu The price differential has been decreasing since the introduction of the SD70MAC in 1994. I expect that within a couple of years DC motored locomotives will cost more due to low production levels. It is almost certain that the only DC locomotives produced this year will be the already completed CN order for SD70M-2s.
An AC induction motor is almost invariably cheaper to make than DC motor of the same capacity and synchronous motors aren't much more expensive than induction motors for a large enough motor size. On the other hand, it may have taken s short while for economies of production to ramp up for AC traction motors, but I suspect that happened several years ago.
I think it is safe to say that the inverters are responsible for most of that price differential. A lot of progress has been made in large scale power electronics in the last 20 years. When EMD and Siemens first collaborated on AC drives, the only suitable component for the inverter were GTO's (Gate Turn-Off thyristors), which were a bit clumsy to work with. GE entered the market when suitable IGBT's came into production, which are much easier to work with. The price of these components has been coming down.
- Erik
[Edit] Note that all of the production electric cars use AC traction motors.
That is not true that BNSF has gone to all AC traction units. They are still ordering ES44DCs and ES44C4s (a A1A version of the ES44DC), along with of course the ES44ACs. The ACs are supposed to stay on coal trains while the DCs and C4s are supposed to be on intermodals.
EJE818 That is not true that BNSF has gone to all AC traction units. They are still ordering ES44DCs and ES44C4s (a A1A version of the ES44DC), along with of course the ES44ACs. The ACs are supposed to stay on coal trains while the DCs and C4s are supposed to be on intermodals.
BNSF's entire locomotive order for 2011 consists of GE ES44C4s, which is an A1A version of the ES44AC not the ES44DC. These locomotives have 4 AC traction motors on a six axle locomotive. They have AC motors to enable them to produce the same amount of tractive effort as a ES44DC with six DC traction motors.
While I can't speak to BNSF's plans (I'd say this order is strong anecdotal evidence that they're considering leaving DC orders behind despite very recent purchases of them, but only time will tell), it simply isn't true that only Canadian National is still in the DC camp.
Norfolk Southern is still firmly committed to DC traction and has ordered plenty of modern DC power in recent years with clearly no plans to change when they discuss their recent foray into modern AC power. So it's incorrect to assume such a thing just because they've concluded that AC power is advantageous enough to justify the higher price tag in some specialized situations finally. And CSX has also made significant orders of the latest DC power in recent times.
The only Class 1 carriers clearly committed to AC exclusivity for new purchases are Union Pacific, Kansas City Southern, and Canadian Pacific. BNSF has bought over 700 ES44DC units in very recent times and Canadian National and CSX have both bought large numbers of the latest DC units.
Just because there might be no order on the books currently for DC units is hardly evidence that a line has decided to focus exclusively on AC purchases in the future. Things always change, it wouldn't even be shocking to see a line like Union Pacific even start buying DC power again after buying extremely large numbers of SD70M's a few short years ago. They might've just felt like their large fleet has been adequate for their needs for a few years so we might all be wrong to assume they've taken an all AC course for future purchases.
Leo_Ames Norfolk Southern is still firmly committed to DC traction and has ordered plenty of modern DC power in recent years with clearly no plans to change when they discuss their recent foray into modern AC power. So it's incorrect to assume such a thing just because they've concluded that AC power is advantageous enough to justify the higher price tag in some specialized situations finally. And CSX has also made significant orders of the latest DC power in recent times.
NS has ordered 25 SD70ACe and 25 ES44AC locomotives each for 2011, 2012, 2013, and 2014. They may place supplemental orders, but they have no DC motored locomotives on order at all. I would say that also makes them now AC only. Like all the other Class I railroads they are nervous about Tier 4 coming in 2015.
No, it only makes them AC Only if they only have AC locomotives. Thats like calling the Apache Railway "EMD Only" because they only have EMD's on order, not ALCos.
Mechanical Department "No no that's fine shove that 20 pound set all around the yard... those shoes aren't hell and a half to change..."
The Missabe Road: Safety First
What are you going to claim when there is a day when Norfolk Southern doesn't have a locomotive order announced or under construction? That they're ceasing buying new locomotives and will be sticking with their current fleet or second hand purchases permanently?
It's the same logic you're using to make that claim.
Several top individuals in Norfolk Southern's mechanical department have stated otherwise. Norfolk Southern isn't going to just be placing orders for AC locomotives in the future. That they don't currently have anything on order is lousy evidence to make such a bold claim.
Come back when there is some evidence to support such a thing (For example, a period of several years since they last bought a DC locomotive, a word from an official at the company, or just something instead of the nothing you're basing it off now). Right now, their huge DC orders in recent years, their slow testing of the waters with AC orders, and their statements all point to continued investment in new DC locomotives in the future for the bulk of their orders.
beaulieu Leo_Ames: Norfolk Southern is still firmly committed to DC traction and has ordered plenty of modern DC power in recent years with clearly no plans to change when they discuss their recent foray into modern AC power. So it's incorrect to assume such a thing just because they've concluded that AC power is advantageous enough to justify the higher price tag in some specialized situations finally. And CSX has also made significant orders of the latest DC power in recent times. NS has ordered 25 SD70ACe and 25 ES44AC locomotives each for 2011, 2012, 2013, and 2014. They may place supplemental orders, but they have no DC motored locomotives on order at all. I would say that also makes them now AC only. Like all the other Class I railroads they are nervous about Tier 4 coming in 2015.
Leo_Ames: Norfolk Southern is still firmly committed to DC traction and has ordered plenty of modern DC power in recent years with clearly no plans to change when they discuss their recent foray into modern AC power. So it's incorrect to assume such a thing just because they've concluded that AC power is advantageous enough to justify the higher price tag in some specialized situations finally. And CSX has also made significant orders of the latest DC power in recent times.
Why would the Tier IV emission regs. dictate what kind of traction motors are specified on a locomotive order?
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
carnej1 Why would the Tier IV emission regs. dictate what kind of traction motors are specified on a locomotive order?
It doesn't affect the type of traction motor. What I meant was that NS has locked in orders through the end of Tier 3 production to assure themselves of having a continuing supply of new locomotives. They believe that there will be a rush to lock in order slots as the deadline approaches and some companies may not be able to get as many locomotives as they want. What they are concerned about is that reliability of early Tier 4 locomotives will be significantly less than current models, also operating costs may be higher as a result of perhaps needing Urea aftertreatment of the exhaust, or if EGR is chosen through failures of that system. Tier 3 which becomes effective 1/1/12 is a very minor upgrade from Tier 2 so no serious problems meeting those standards is expected. Inspite of the manufacture's assurances railroad CMOs are nervous about the ability of the builders to meet Tier 4 with locomotives that are as reliable as current models, and have reasonably similar operating costs. Especially in the first year of production. They are expecting serious teething troubles.
Leo, the last new DC powered locomotive for NS was ES40DC 7719 built in February 2008, since then (3 years) NS has taken delivery of 116 AC drive locomotives (91 ES44AC and 25 SD70ACe). NS has placed further orders for 150 more AC drive locomotives with delivery spread over three years 2012 - 2014 (50 per year). I expect that baring a big run up in rail traffic that is all the new locomotives that NS will buy in that time period. I agree it is possible that NS could still place additional orders before 2015, but I would not bet on it. BTW they bought 350 DC motored Tier 2 locomotives (220 ES40DC and 130 SD70M-2) between 1/1/02 and 2/08.
beaulieu [snipped and rearranged] . . . bought 350 DC motored Tier 2 locomotives (220 ES40DC and 130 SD70M-2) between 1/1/02 and 2/08. February 2008, since then (3 years) NS has taken delivery of 116 AC drive locomotives (91 ES44AC and 25 SD70ACe). . . . 150 more AC drive locomotives with delivery spread over three years 2012 - 2014 (50 per year).
February 2008, since then (3 years) NS has taken delivery of 116 AC drive locomotives (91 ES44AC and 25 SD70ACe).
. . . 150 more AC drive locomotives with delivery spread over three years 2012 - 2014 (50 per year).
350 DC locomotives / 6 years = 58 per year, on average.
116 AC locomotives / 3 years = 39 per year (slow economy)
50 AC locomotives per year on order (I'd be surprised if there isn't an 'option' to add more units to each year's delivery.)
In short: For recent past years and for the next several years on NS, the "indicated replacement rate" of locomotives has been and apparently will continue to be all AC locomotives.
Nevertheless - and, although these figures seem low for a system of NS' size* - for each period add to them the products of Thoroughbred Mechanical Services' in Altoona - all DC, as far as I know - for a more complete picture of what NS is doing. See http://www.nstms.com/index.html and http://www.altoonaworks.info/ for mroe info.
*"Over 3,300 locomotives" per the TMS link above. If we assume a 30-year service life, that would mean replacing about 110 locomotives each year - about twice what NS has been doing. Will they continue to let the locomotive fleet gradually age ? Rebuild more units to keep the average age about the same ? Buy more new units ?
Well, now we know part of the answer to the questions I posed above: Buy more used units ! (and perhaps rebuild them ?) Apparently word was out today that NS will buy 20 ex-C&NW/ UP SD60's from Helm Leasing. See this webpage for a few more details: http://www.nsdash9.com/rosters/6530.html
With regard to this thread - obviously these are DC motors, which partially contradicts the recent string of NS' all-AC new purchases . . .
Leo_Ames ...CSX have both bought large numbers of the latest DC units.
...CSX have both bought large numbers of the latest DC units.
Without getting into the internal politics of that order, I'll just say that as of now there is a lot of second guessing on CSX about the logic of it. Especially since all the ES44DC have now been downrated to 4000 hp. You should note that all the orders since have been for AC traction only.
AC traction is a superior technology for locomotives, pure and simple.
I look at things this way when BNSF First tried out the EVO44C4's I knew that they were going to be a Winner. Why First off Ac Traction Motor reliability for a DC motor Price. GE figured out a way to get the power down at low speeds and the first 25 Worked BNSF reupped for 50 More. Now they went Big time for 200+ this year. I think we have the Replacement for their DC motors Look for the Dash-8s and 40-2s that they have left and Dash-9's plus the SD-70-75's to be hitting the bricks real soon.
One great thing about AC power is it flows from the generator through the traction motors and back through the generator in a loop. With DC it flows from the generator to the traction motors and ends there. With AC power you can stall a train at full throttle on a hill and just sit there. With DC power you would be burning up the traction motors. Burned up traction motors will be a thing of the past with AC power.
Thomas 9011 One great thing about AC power is it flows from the generator through the traction motors and back through the generator in a loop. With DC it flows from the generator to the traction motors and ends there. With AC power you can stall a train at full throttle on a hill and just sit there. With DC power you would be burning up the traction motors. Burned up traction motors will be a thing of the past with AC power.
What are you talking about? - All current flows back to the starting point. The hot lead of the generator produces the 'potential' and it flows back to the 'ground' of the generator via the traction motor. There is not just one cable/wire to the traction motor(AC or DC). The copper 'windings' in a DC traction motor will overheat and become 'soft' - sooner or later they will touch the traction motor case and produce a 'ground short'. BTW, AC traction motors are not 'indestructible' - They can fail from abuse....
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
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