wjstixBy 1930, engines were developed that were large enough to pull long trains, but had larger drivers so they could go much faster: 2-8-4s, 2-10-4s, 4-6-6-4s...'supersteam' engines. Those engines brought the end to the drag freight era.
Until the era of PSR, where except for 'primere' trains, all other trains are loaded down to the level that the trains will DRAG at minimum continuous speed over the ruling grade (and if stopped on that grade will need additional power to get the train restarted).
Never too old to have a happy childhood!
DR DENNIS GORDANI am late to the discussion, but note that all comments relate to diesel electrics, while "drag freight" started in the steam era, when there was no issue with overheating at low speed, so slogging along with the least power that kept things rolling was safe and economical.
The minimum continuous speed of 10-12 mph also conveniently translates into the lowest speed where the locomotive can use all its power without slipping excessively.
That unit I saw with the failed blower was a mid-train remote in a 220 car 30,000 ton grain drag. Not easy to replace if it failed completely, and as it was still making power I don't think the crew knew about the problem, as you only get a generic trainline alarm message without any details if something happens on a remote.
The Diesel Doc called them a few minutes later and asked them if it was giving any alarms or only putting out reduced power, apparently it had thrown a code when the blower failed. He told them to keep using it and to call back if it stopped pulling properly.
Greetings from Alberta
-an Articulate Malcontent
I could argue that the stator windings on an AC motor are equivalent to the field windings on the DC motor. In both cases, the duty cycle doesn't change...
The major difference is in the armature, where the windings of an induction motor are substantial copper bars that don't need insulation. Another difference is a much larger fraction of the bars are conducting current on the induction motor as opposed to the fraction of active windings in a DC motor. Finally, in a stalled induction motor, the field still needs to be rotating in order to induce the torque producing currents in the copper bars composing the "squirrel cage", and thus spreading out the heat.
As for number of windings on a DC motor: IIRC, modern traction motors can have up to 1500V applied to the terminals. DC machine practice is to limit potential difference between commutator bars to 20V, so we're looking at 75 bars (or more) between the positive and negative brushes. Each pair of bars corresponds to one winding, so under normal operation, each winding has a duty cycle of a few per cent. Running full current through a winding at 100% duty cycle is going to create some serious temperature rise.
Bottom line is that the switch to AC motors was done for good reason.
Erik_MagAC induction motor windings have varying current even when the rotor is not turning in conjunction with beefier windings help prevent stall burns.
I would have said this also applies to operations over the road, but that story about the GE making traction power with the TM blower disabled, and the hot-metal-and-grease smell, has made me profoundly nervous. I can see providing military equipment with the "RUN NOW -- no backchat" option, but not locomotives. On the other hand, in this era of PSR I can almost see the attractiveness of a Northstar-style limp-home power capability...
SD70Dude Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done ) can cause 'stall burns' inside DC motors.
Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done ) can cause 'stall burns' inside DC motors.
Stall burns presumably being a burned out winding on the armature. When the motor is turning, any given winding is only conducting current for a relatively small fraction of the time and this has a chance to cool down before conducting current again. My understanding is that DC locomotives often have a minimum continuous speed to prevent stall burns.
AC induction motor windings have varying current even when the rotor is not turning in conjunction with beefier windings help prevent stall burns.
cefinkjr The term "drag freight" brings to mind the similar "hold for tonnage", meaning a train's departure was to be delayed until maximum tonnage had been accumulated. Immediately after the NYC/PRR merger, "held for tonnage" was enough to send Al Perlman ballistic and could get you fired. He insisted that, if a train was scheduled to depart at 7:00, the dust was settling behind the markers at 7:01.
The term "drag freight" brings to mind the similar "hold for tonnage", meaning a train's departure was to be delayed until maximum tonnage had been accumulated. Immediately after the NYC/PRR merger, "held for tonnage" was enough to send Al Perlman ballistic and could get you fired. He insisted that, if a train was scheduled to depart at 7:00, the dust was settling behind the markers at 7:01.
Hmmm.. Hold for tonnage.. Geez thats sounds eerily similar to... Oh nevermind...
Lithonia Operator SD70Dude Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done ) Commenting for a friend, are you?
SD70Dude Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done )
Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done )
Commenting for a friend, are you?
It works very well in certain situations, or so I've been told.
AC motors seem relatively immune to this type of damage, as long as the traction motor blowers are working properly. I recently saw a newer GE unit with a failed TM blower still working away, it was giving off a very noticeable smell of hot grease and metal.
Paul of CovingtonI always liked the term "bird's nested" for overheated motors.
Overheating melts the insulation between windings, and likely produces a ground-fault or short long before the copper actually starts expanding enough to foul the stator poles.
When I was little I always thought about open spinning reels and how not to use them when I read about birdsnesting.
BaltACD 'melting down' from the excessive heat generated in the motor windings.
I always liked the term "bird's nested" for overheated motors. I can picture in my mind what the windings look like.
_____________
"A stranger's just a friend you ain't met yet." --- Dave Gardner
The reality is the Diesel-Electrics of generations upto the start of AC traction in the mid 1990's, had 'short time ratings' developed from the maximum amperage the traction motors could handle without 'melting down' from the excessive heat generated in the motor windings. The short time ratings come into play when the train is moving too slowly - as train speed increases amperage the traction motors require decreases.
Steam engines in 'drag' service, generally had small driving wheel diameters, faster steam engines had larger driving wheel diameters. The reality is that steam engines at maximum load in drag serice would maintain 5 MPH. The MCS of diesel-electrics in freight service range from 9 to 12 MPH and thus diesel-electrics 'could' haul the same amount of freight as a steam engine at roughly twice the speed and not have to stop for water during the trip.
jeffhergert oltmannd A drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there". So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight. Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s. Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton. However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) . Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish. UP switched from hp/ton to Tons per (equvilant) Powered Axle. That doesn't mean everything gets the same TPA requirement. Just as not every train had the same hp/ton requirement. Intermodals may have a 250 TPA while a coal train may have a 800 TPA over the same crew district. The lower the TPA, the faster a train should be able to go. Most of our coal trains have a 575 TPA on my district. Some, where they want to save fuel and lug around a isolated/dead engine on a train, get the 800 TPA. Jeff
oltmannd A drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there". So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight. Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s. Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton. However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) . Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish.
A drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there".
So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight.
Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s.
Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton.
However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) .
Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish.
UP switched from hp/ton to Tons per (equvilant) Powered Axle. That doesn't mean everything gets the same TPA requirement. Just as not every train had the same hp/ton requirement. Intermodals may have a 250 TPA while a coal train may have a 800 TPA over the same crew district. The lower the TPA, the faster a train should be able to go. Most of our coal trains have a 575 TPA on my district. Some, where they want to save fuel and lug around a isolated/dead engine on a train, get the 800 TPA.
Jeff
That's very different from NS. I didn't know! Thanks for explaining.
Going with TPA and varying it by train type on a route is kind of a backhanded way for getting to HP/ton - provided it's based on the locomotive with the lowest HP per (equivalent) axle.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
oltmanndA drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there". So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight. Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s. Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton. However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) . Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish.
CSX does NOT dispatch trains based on axles - they dispatch trains based on tonnage ratings - the tonnage ratings define the limits of drag tonnage on a territory. Tonnage ratings do not take into consideration helper districts. A HP/ton figure is included on CSX Train Documents, however, it is there for information only.
Where there are helper districts, trains are powered for for the adjoining less graded territories with the helpers supplying the necessary power to defeat the mountain grade.
The only trains CSX supplies 'extra' power to are intermodals. With the implementation of PSR and DPU on the intermodal trains - they are being dispatched at drag ratings for the power - longer trains with in train DPU's but drag tonnage ratings for the train as a whole.
How long the drag era lasted also depended on what was being "drug". Manifests normally picked up speed many years before mineral trains did.
Some railroads and engine types come to mind that operated beyond the time period you suggest: 2-10-0s on the PRR, 2-10-2s on many lines.
My grandfather was a 30+ year engineer/fireman on the VGN. He told me the term was from: dragging coal out of the hollers in WV.
To my knowledge the "drag freight" era was the period from roughly 1910-1935. Before that, engines were relatively small, like 2-8-0s for freight trains. Freight trains then were relatively short, unless you had double-(or triple-)headers.
When Mallet / Articulated engines came into use, railroads could run much longer trains using one big engine instead of running a long train with multiple smaller engines (thereby not having to pay multiple crews). Early Mallets had very small drivers, since that allowed them to start and pull long, heavy trains without slipping. This, however, limited their top speed - a USRA 2-6-6-2 would be limited to running at 20 MPH or less for example. Running faster was difficult in part because it was hard to counterbalance small drivers properly.
So you ended up with very long trains being pulled by very large steam engines, trundling along at 12-15 MPH. That would be a "drag freight".
When 'superpower' engines started to be built in the late twenties, railroads found they could have engines with larger drivers like 2-8-4s or 4-8-4s that could pull as long a train as a drag freight engine, but at a much faster speed.
ChuckAllen, TX
Thanks for the explanations, guys.
Juniata ManEd: In the PSR world we now inhabit; I believe drag freights like your old 177 are being reborn. I watched a southbound CSX freight crawl through Dalton, GA last evening with one motor as leader and a second single motor as mid train DP. No idea what car count or trailing tonnage was but, it took the entire train better than eight minutes to pass and I doubt he was moving much faster than 20-25 MPH. Back about 15 years ago, NS had train 177 which ran from Chicago to Ft. Wayne, did some yard work and then went to Chattanooga. It was my favorite train at that time. Why? It had just about everything except intermodal. Typically it was long (well over 100 cars) and heavy. One day I heard it call signals on the scanner and went down to watch it. If I recall, it had about 100 loaded grain cars on the front end with an assortment of gons with scrap steel for SDI in Columbia City, In., a few auto racks, boxcars, tank cars, etc. Total car count was 177 cars (note 177 cars for trains 177) and it crawled thru town at a slow speed. When you say "drag freight" that 177 comes to mind. In my mind, a drag needs to have gons with scrap...but that is my definition. Sadly 177 has been discontinued. Ed
In the PSR world we now inhabit; I believe drag freights like your old 177 are being reborn.
I watched a southbound CSX freight crawl through Dalton, GA last evening with one motor as leader and a second single motor as mid train DP. No idea what car count or trailing tonnage was but, it took the entire train better than eight minutes to pass and I doubt he was moving much faster than 20-25 MPH.
Back about 15 years ago, NS had train 177 which ran from Chicago to Ft. Wayne, did some yard work and then went to Chattanooga. It was my favorite train at that time. Why? It had just about everything except intermodal. Typically it was long (well over 100 cars) and heavy. One day I heard it call signals on the scanner and went down to watch it. If I recall, it had about 100 loaded grain cars on the front end with an assortment of gons with scrap steel for SDI in Columbia City, In., a few auto racks, boxcars, tank cars, etc. Total car count was 177 cars (note 177 cars for trains 177) and it crawled thru town at a slow speed. When you say "drag freight" that 177 comes to mind. In my mind, a drag needs to have gons with scrap...but that is my definition. Sadly 177 has been discontinued. Ed
Back about 15 years ago, NS had train 177 which ran from Chicago to Ft. Wayne, did some yard work and then went to Chattanooga. It was my favorite train at that time. Why? It had just about everything except intermodal. Typically it was long (well over 100 cars) and heavy.
One day I heard it call signals on the scanner and went down to watch it.
If I recall, it had about 100 loaded grain cars on the front end with an assortment of gons with scrap steel for SDI in Columbia City, In., a few auto racks, boxcars, tank cars, etc.
Total car count was 177 cars (note 177 cars for trains 177) and it crawled thru town at a slow speed.
When you say "drag freight" that 177 comes to mind.
In my mind, a drag needs to have gons with scrap...but that is my definition.
Sadly 177 has been discontinued.
Ed
CSX has been a Drag Freight railroad for at least 30 years. The only trains that had more power than was required for maximum tonnage were intermodals - they would have nominally 1 more unit than maximum tonnage per unit would allow.
A second aspect of assigning power to a specific merchandise or intermodal train is always what will be the power requirements at the other end of the line to handle trains in the return direction. Daily volumes vary on scheduled trains - sometimes you end up with a train that actually has more power than drag tonnage would indicate.
Ed:
My recollection of a drag is one that stopped at every station where there was local switching to be done. This was much more common in the mid 1900's with the sixteen hour on duty law. Now we have 'locals' when there is a need for this.
The drag era really was when you normally had only one engine, a steam engine, to pull a train. The train was built to the capacity of the engine, taking all the tonnage the engine's rating allowed.
They also seemed to switch trains at almost every division point yard. Blocking cars was rare or nonexistant. Cars moved in the general direction of their destination.
You build a train at yard A. Next division point is yard B. The train is built with maximum tonnage, "shorts"- those going to intermediate points between A and B and cars for B, might be first out on the head end. The rest of the train is in whatever order the track standings were for destinations beyond B. The maximum tonnage for an engine, may not reflect the worst grade to be encountered on the district. They may be able to handle 3500 tons out of A, but midway there might be a point where it can only handle 2750 tons. The train may be dispatched with 3500 tons, reduce at a point before the lesser rating begins and continue. If further on the tonnage rating again becomes higher, the train may fill at some point with any available tonnage heading it's way. Tonnage set out waits for available space on a future train heading that way.
Drag freights gradually became unpopular because of the slow handling, not just slow speeds but having to reswitch trains so often, and the cost of switching cars multiple times. Railroads started to block cars in trains for multiple destinations. They started expediting some, but by no means all, freight trains. They were trying to hold onto, or win back, business that they were losing to trucks. Reading old Railroad Magazine/Railroad Stories from the late 1930s, it was a concern back then. Many of the same things discussed now, were discussed then. The biggest difference was then they thought they had a future in many lines (not actual branch lines, etc but categories) of freight. Some of which has either been lost by the railroads or no longer wanted.
Our community is FREE to join. To participate you must either login or register for an account.