BaltACD JPS1 oltmannd Which even my "back of the envelope" calculation showed is what likely happened. Getting to L/V is tougher to do and you can't reasonably determine it for every car in every location under every possible circumstance. There are trains built and run that will just plain derail if the go into emergency at the right spot. But, they don't, so no news is good news... How long did it take from the beginning of the railroad era for engineers to work out the mathematics to explain all the forces impacting operations? Or is it still a work in progress? Still a work in progress as they try to maximize tonnage and minimize costs.
JPS1 oltmannd Which even my "back of the envelope" calculation showed is what likely happened. Getting to L/V is tougher to do and you can't reasonably determine it for every car in every location under every possible circumstance. There are trains built and run that will just plain derail if the go into emergency at the right spot. But, they don't, so no news is good news... How long did it take from the beginning of the railroad era for engineers to work out the mathematics to explain all the forces impacting operations? Or is it still a work in progress?
oltmannd Which even my "back of the envelope" calculation showed is what likely happened. Getting to L/V is tougher to do and you can't reasonably determine it for every car in every location under every possible circumstance. There are trains built and run that will just plain derail if the go into emergency at the right spot. But, they don't, so no news is good news...
Getting to L/V is tougher to do and you can't reasonably determine it for every car in every location under every possible circumstance. There are trains built and run that will just plain derail if the go into emergency at the right spot. But, they don't, so no news is good news...
How long did it take from the beginning of the railroad era for engineers to work out the mathematics to explain all the forces impacting operations? Or is it still a work in progress?
Still a work in progress as they try to maximize tonnage and minimize costs.
I would think they would have a program that would predict the stringline potential of any given train, based on makeup, gradient, power, and curvature. Maybe it could also take over and prevent the stringline event from happening.
Never too old to have a happy childhood!
How long did it take from the beginning of the railroad era for engineers to work out the mathematics to explain all the forces impacting trains operations? Or is it still a work in progress?
petitnj Stringlining occurs when the pull of the locomotive at the curve angle exceeds the gravity pull.
Which even my "back of the envelope" calculation showed is what likely happened.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Just to add some physics details to the issue. What keeps trains on the track is the ratio of lateral to vertical force. Lateral is velocity squared/radius toward the outside of the curve and pulling times the sine of the car angles for pull inside the curve. Vertical is gravity. Safe speeds are designed to keep L/V less that 0.5 and some specify less than 0.3. The accident in Seattle last year exceeded L/V to about 1.0 and the train flew off the track. Stringlining occurs when the pull of the locomotive at the curve angle exceeds the gravity pull.
timz Wonder what the superelevation is -- maybe 2 inches? Think that has much effect? (The 2008 chart says four inches -- page 34 of the PDF) http://multimodalways.org/docs/railroads/companies/NS/NS%20Track%20Charts/NS%20Pgh%20Division%20Track%20Chart%202008.pdf What was the tonnage?
Wonder what the superelevation is -- maybe 2 inches? Think that has much effect?
(The 2008 chart says four inches -- page 34 of the PDF)
http://multimodalways.org/docs/railroads/companies/NS/NS%20Track%20Charts/NS%20Pgh%20Division%20Track%20Chart%202008.pdf
What was the tonnage?
Probably still four inches. That'll help things along a bit. Tonnage around 8000? 140+ cars? Train resistance balanced out at ~10 mph
BigJim oltmannd BigJim So, did you amend the rule book/timetable to limit trailing tonnage on said car? Yes. Headed axle limit on trains ascending HSC w/o helpers. Also tonnage limit. Was this before or after the fact? And, what particular rule number and tonnage rating? I ask because as I have said before, in my time there was no restrictions on centerbeam flat cars.
oltmannd BigJim So, did you amend the rule book/timetable to limit trailing tonnage on said car? Yes. Headed axle limit on trains ascending HSC w/o helpers. Also tonnage limit.
BigJim
So, did you amend the rule book/timetable to limit trailing tonnage on said car?
Yes. Headed axle limit on trains ascending HSC w/o helpers. Also tonnage limit.
Was this before or after the fact? And, what particular rule number and tonnage rating? I ask because as I have said before, in my time there was no restrictions on centerbeam flat cars.
If there were only two unit on line and the train was pushed from the rear, the derailment doesn't occur. Car length becomes irrelevant.
.
Excerpt from CSX Baltimore Division Timetable in 2015
CSX Batltimore Division Timetable No. 1 April 1, 2015 4466 PLACING EMPTY CARS IN TRAINS Empty Car Placement Train Classification Instructions for Manifest Trains: Empty cars 80 feet and longer (other than a box car) must be placed in the train in such a location that the trailing tonnage behind these empty cars does not exceed the amount listed below. In territory where helper locomotives are used on the rear of the train, their tonnage rating should be subtracted to the trailing tonnage listed below when determining the location for the restricted car(s): Between Direction TonnageHyndman & Sand Patch Westward 3,500Connellsville & Sand Patch Eastward 5,100Connellsville & New Castle Eastward & Westward 13,300
4466 PLACING EMPTY CARS IN TRAINS
Empty Car Placement Train Classification Instructions for Manifest Trains:
Empty cars 80 feet and longer (other than a box car) must be placed in the train in such a location that the trailing tonnage behind these empty cars does not exceed the amount listed below. In territory where helper locomotives are used on the rear of the train, their tonnage rating should be subtracted to the trailing tonnage listed below when determining the location for the restricted car(s):
Between Direction TonnageHyndman & Sand Patch Westward 3,500Connellsville & Sand Patch Eastward 5,100Connellsville & New Castle Eastward & Westward 13,300
SD70Dude oltmannd BigJim So, did you amend the rule book/timetable to limit trailing tonnage on said car? Yes. Headed axle limit on trains ascending HSC w/o helpers. Also tonnage limit. Looks like NS 'forgot' your instructions. Oops.
BigJim So, did you amend the rule book/timetable to limit trailing tonnage on said car?
Looks like NS 'forgot' your instructions. Oops.
NS forgot their Institutional Knowledge from those they let go putting in PSR.
Greetings from Alberta
-an Articulate Malcontent
oltmannd All weather adhesion rating for AC units is around 35%. For DC units with computer based wheel creep control, about 27-28%. Non-wheel creep (Dash 2, 7 Series), 18-21%.
All weather adhesion rating for AC units is around 35%. For DC units with computer based wheel creep control, about 27-28%. Non-wheel creep (Dash 2, 7 Series), 18-21%.
The 18-21% is in line with the 16% dispatchable factor adhesion given in the 1968 MR article on grades with a bit better control. The 35% available with AC could be done with DC motors with separately excited field windings and pole face windings, but motors with these features would be more like the traction motors in the PRR DD1's.
One other figure from the 60's was a 33% factor of adhesion for the KM desel hydraulics, with the combination of smooth torque and the three axles on a truck running off a common Cardan shaft. Demonstrator testing of the U25B's gave a 25% factor of adhesion on clean dry "western" rail. Durng one dynamometer test, the GE Little Joe demonstrator achieved 35% factor of adhesion - I've seen a few comments about traction current enhancing adhesion by burning away contaminants.
You want to dispatch trains on what you can count on, day in and day out.
oltmanndYou ever had a full tonnage train with three 4000 HP locomotives running in notch 8 at 10 mph on a 9 degree curve with an 80' empty head out? Where and when?
BigJimWell, that is your mind talking, not the mechanical dept. Can you prove that even a 73' centerbeam was in the derailment?
17 years in Conrail Mechanical Department - staff engineering position. Did a lot of locomotive application work, some derailment analysis work and testing.
https://www.mrc-rail.com/project/centerbeam/
https://www.bnsf.com/ship-with-bnsf/ways-of-shipping/equipment/pdf/73Centerbeam.pdf
https://www.csx.com/index.cfm/customers/resources/equipment/railroad-equipment/
https://www.up.com/customers/all/equipment/descriptions/centerbeams/index.htm
Standard centerbeam cars are 73' between the bulkheads. A 73' centerbeam car is 80' 6-1/2" between pulling faces. There are 61' centerbeam cars still rolling around, but these are not the current standard.
BigJimHas NS said anything about the cause of the derailment or are we to just take your word for it?
They haven't and probably won't say much. Your choice if you want to beleive what I've laid out or not.
You ever had a full tonnage train with three 4000 HP locomotives running in notch 8 at 10 mph on a 9 degree curve with an 80' empty head out? Where and when?
BigJimCan you prove that even a 73' centerbeam was in the derailment?
They were definitely centerbeams, although the length could be debated.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
oltmanndThe 73' centerbeam I found to use for my estimate is 80' over the pulling faces, which is what counts in this case.
Erik_MagThe two chief advantages of an AC induction motor is a much more rugged rotor (conductors are uninsulated bars vs insulated wires) and inherent almost constant speed operation (DC series motor speed can increase dramatically with loss of load). The former is good for higher continuous tractive effort and the latter is good for better adhesion.
My 2 cents on the AC versus DC.
The two chief advantages of an AC induction motor is a much more rugged rotor (conductors are uninsulated bars vs insulated wires) and inherent almost constant speed operation (DC series motor speed can increase dramatically with loss of load). The former is good for higher continuous tractive effort and the latter is good for better adhesion.
A further advantge of modern AC locomotives is indivdual control of the motors, so power reduction could be limited to the motor that is slipping as opposed to reducing power to the whole locomotive.
Response time of the DC series motor is limited by the inductance of the field winding limiting how fast the the motor current can be varied, a DC shunt motor (e.g. original AEM-7) can respond faster. Ultimate limit for response time for an AC motor is roughly the period of the highest frequency that will provide full power output of the motor.
Overmod BaltACD ... note CSX derated the 4400 HP the engines were purchased with to 4000 HP for fuel economy savings Interesting that NS seems to have done just the opposite. As I recall it, their dash-9-40W locomotives were delivered from GE with the 4000hp nominal rating 'for fuel savings', but with a simple override switch that would let them develop the 4400hp on demand; NS subsequently uprated quite a few of them between 2013 and 2015, but I believe kept the -40 designation on the cab to maintain the class distinction for parts and support. Did CSX adopt the same electronics for their derating program as GE provided in the NS C40-9Ws, and can the derating be 'overridden' as easily if wanted?
BaltACD ... note CSX derated the 4400 HP the engines were purchased with to 4000 HP for fuel economy savings
Interesting that NS seems to have done just the opposite. As I recall it, their dash-9-40W locomotives were delivered from GE with the 4000hp nominal rating 'for fuel savings', but with a simple override switch that would let them develop the 4400hp on demand; NS subsequently uprated quite a few of them between 2013 and 2015, but I believe kept the -40 designation on the cab to maintain the class distinction for parts and support.
Did CSX adopt the same electronics for their derating program as GE provided in the NS C40-9Ws, and can the derating be 'overridden' as easily if wanted?
According to http://www.nsdash9.com/roster.html all of NS' Dash 9's were uprated to 4400 HP and reclassified as D9-44CW's between 10-2013 and 09-2014. However, not all of the units have had their external model designation lettering updated to reflect the internal changes. If I recall correctly, this was done during NS' 2014 meltdown in an effort to boost their system velocity numbers. NS uprated their DC GEVO fleet and reclassified them as ES44DC's at the same time.
JPS1 caldreamer I ran some calculations for the tractive effort algorythm. It is pretty close for DC engines, but is way off (too low) for AC engines. Why would the tractive effort of a DC locomotive be different than that of an AC locomotive?
caldreamer I ran some calculations for the tractive effort algorythm. It is pretty close for DC engines, but is way off (too low) for AC engines.
Why would the tractive effort of a DC locomotive be different than that of an AC locomotive?
Well, it is and it isn't. It depends on how fast you are going, for the most part.
At 20 mph, there wouldn't be any difference. It's just force x speed = power since you are nowhere near the adhesion limit and thermal limit (DC only) of the propulsion system. The AC locomotive might give a bit more since it's electrical transmission system probably has less losses (I think...).
At low speeds, the AC unit can give you full HP down to lower speeds because it's adhesion is better (35% you can count on). Best you might get from DC is 27%. AC adjusts the frequency to match speed. DC has to react to slip by backing down main generator excitation which is slower due to the nature of the machine (inductive windings resist current change)
DC motors also have thermal limits which stop high TE levels from being produced for very long even when available adhesion is good.
zugmann oltmannd A three unit consist of SD70ACes operating in notch 8 at 10 mph makes about 400,000# TE. (you can get the speed by timing the Virtual Railroading youtube video and TE = HP x 308/speed) Actually, it was two 70aces and one 70m-2. Still a lot of TE, but a little less than 3 ACs.
oltmannd A three unit consist of SD70ACes operating in notch 8 at 10 mph makes about 400,000# TE. (you can get the speed by timing the Virtual Railroading youtube video and TE = HP x 308/speed)
Actually, it was two 70aces and one 70m-2. Still a lot of TE, but a little less than 3 ACs.
I should have caught that. Actually my 10 mph speed estimate is probably off by more than the TE difference...
BigJim oltmannd An 80' centerbeam car Can you prove to me that there was actually an EIGHTY FOOT centerbeam car in the consist? I've never seen one that long and I definately am not seeing one in the published videos.There was a stringline derailment like this years ago on the Hagerstown Dist. without any long cars involved. If I am not mistaken, it was due to an undesired emergency brake application back near the rear of the train.
oltmannd An 80' centerbeam car
Can you prove to me that there was actually an EIGHTY FOOT centerbeam car in the consist? I've never seen one that long and I definately am not seeing one in the published videos.There was a stringline derailment like this years ago on the Hagerstown Dist. without any long cars involved. If I am not mistaken, it was due to an undesired emergency brake application back near the rear of the train.
The 73' centerbeam I found to use for my estimate is 80' over the pulling faces, which is what counts in this case.
JPS1Why would the tractive effort of a DC locomotive be different than that of an AC locomotive?
Several reasons, the most important of which is that there can be essentially zero derating of the motors both right down to 'locked rotor' zero-speed operation and to avoid wheelslip above the 'microslipping' that gives best creep control. DC locomotives would require wildly more capable cooling arrangements, probably including sprayed coolant in the blown air, even to approximate what a good induction motor fed a properly-synthesized waveform can do.
The matter of adhesion limit is also a bit different, although I'll leave it up to Erik to make the electrical arguments comprehensible in English. DC motors typically 'cut power' in some way to accomplish creep control; AC drive can react in different ways that keep full nominal excitation strength active but keep wheelslip from propagating.
We can discuss the pros and cons of larger wheels if those aren't already known to you.
The why's require the expertise of a electrical/mechanical engineer - that I am not. However, the AC's have a more effective wheelslip control set up than to DC's.
The reality is that DC's have less tractive effort than AC's of the same power and axle configuration. On CSX's Baltimore Belt Line grade (Howard Street Tunnel) a CW44AC is rated for 4900 tons, a CW40DC (EVO's) is rated 3600 tons (note CSX derated the 4400 HP the engines were purchased with to 4000 HP for fuel economy savings).
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