Hey all,
I did a search on this in the forums and didn't find anything so if someone knows of a post with regards to this, please point me in that direction. Anyway I was sitting at a crossing on the Donner route at about 3800 ft and watching a stack train go by going uphill, slowly....slower and slower then stop. The lead units were 3 GE ACs of mixed types and a SD70M. The tail unit was a ES44AC. I was wondering if it is common in a mixed consist AC/DC that a train might slow enough to drop below the minimum speed of the DC unit causing the traction motors to overheat and stall the train? I thought that the train might just by slowing/waiting for a meeting with another train but I finally had to get going (on company time) and in trying to get around the train I passed the end unit and it sounded like it was still running in notch 8.
Thanks for the insight.
Eventually the DC engine will DErate itself to avoid a meltdown. The AC's will be like SO WHAT and keep on LUGGINE. IIRC correct there was a story in Trains in the mid-late 90's about the Ac4400 of the SP that they were on Tennesee pass moving UPhill at something like 0.5 MPH and did no damage to the TM's in Notch 8.
edbenton Eventually the DC engine will DErate itself to avoid a meltdown. The AC's will be like SO WHAT and keep on LUGGINE. IIRC correct there was a story in Trains in the mid-late 90's about the Ac4400 of the SP that they were on Tennesee pass moving UPhill at something like 0.5 MPH and did no damage to the TM's in Notch 8.
I read the story about the AC's working that SP train and no doubt, DC motors would have stalled and fried the traction motors prior to the computer controlled diesels.
The Union Pacific has a bad habit of mixing AC and DC units on most trains. The DC units will protect themselves to some degree, but the use of the DC motors mixed with AC units for heavy trains is not a good practice.
CZ
That's one of the reasons Warren Buffett, and I, sold our UP (and NS) stock. As far as NS goes, the cost of toilet paper is outrageous!
Hays -- in DC country.
broncoman a crossing on the Donner route at about 3800 ft
http://maps.google.com/?ie=UTF8&ll=39.200392,-120.795268&spn=0.003417,0.006856&t=h&z=17
broncomanit sounded like it was still running in notch 8.
Great detective work. I was at Alta Bonny Nook Rd crossing. The train kept inching it never stopped. Its double tracked through there and I think all the way to near Nyack so I don't think that it would have had to stop to wait as that is still probably about 5-10 track miles to the point were the track goes to single track at Emigrant Gap....I think. Anyway its what you think about when you are watching/thinking at a crossing, but still on work time.
Union pacific also had a bad habit of mixing GE and EMD locomotives on trains.EMD's load up pretty quick.GE's load up typically a lot slower.If you have one EMD on the front and 4 GE's following,that one EMD will be trying to pull the entire train while those other GE's are still loading up.Trains work best when they have matching units.
As far as burning up traction motors.I heard with the AC motors you can go as slow as you want(including stalling at any throttle position)and you won't burn anything up.They say the electricity runs in a loop from the generator,through the traction motor,and back into the generator.DC traction motors can only take so much power and heat before they start to smoke and burn up wires.
Its interesting though that UP mixes AC and DC units on all trains except grain unit trains. All the ones I have seen that pass westbound through Auburn are AC only (the EMD units are SD90s).
timz broncoman a crossing on the Donner route at about 3800 ft Here? http://maps.google.com/?ie=UTF8&ll=39.200392,-120.795268&spn=0.003417,0.006856&t=h&z=17 broncomanit sounded like it was still running in notch 8.While it was stopped?
Standard rule on the NS when your traction motors are over heated your movement will stop and all brakes applied reverser centered then the throttle will be placed in notch 8 for maximum cooling.for 15 minutes
Finally, thanks to Edbenton, I know why and what for this "derating" feature is for.
New question: Do AC units ever need to derate themselves?
what is derated?
First of all, my understanding is that UP is not buying new DC road power at all anymore. Only AC. So that means that unlike BNSF, AC is not restricted only to heavy haul applications, when it's part of the total fleet for all trains, then it will have to run with DC engines as well.
Thomas 9011 Union pacific also had a bad habit of mixing GE and EMD locomotives on trains.EMD's load up pretty quick.GE's load up typically a lot slower.If you have one EMD on the front and 4 GE's following,that one EMD will be trying to pull the entire train while those other GE's are still loading up.Trains work best when they have matching units.
This may be true that the difference in loading will do this, but if mixing power is a bad habit, then its one that's been going on since the U25B,
Shots from the Santa Fe, UP and even SP mixing GE and EMD units be they U boats, super 7s mixed with SD40s or Superfleet Dash 8s and 9s mixed with GP60Ms.
I'm watching a video from 1988 of the San Diegan with and F40 on one end and a Dash 8 32BWH on the other as it passes Santa Fe freights with all sorts of mixed GE and EMD power.
Ever since the development of the standard 27 pin MU Cable the carriers have been mixing and matching all forms of power that was capable of being controlled by the MU Cable. Baldwin was the only manufacture that did not use a control system that did not accept the 27 pin MU cable as they uses a pneumatic throttle control system.
On the large carriers, Power Managers give little regard for the operating characteristics of the various engines when planning power consists for trains....they see Train A that needs power for 10000 tons to be hauled between A & Z and they will put together a engine consist that to their ideals has 10001 tons of tonnage rating between A & Z...to the Power Manager that is effective power management. Whatever the combination of engines is that comes up with the 10001 tons of tonnage rating is of no consequence....GE - EMD - AC - DC they are all engines with tonnage ratings and to the Power Manager they all operate together. Case Closed!
Never too old to have a happy childhood!
The very very bottom line is this is basically a true statement. The fact of the matter is that it is not a big deal at all. And far from being a "bad habit"!
Do any of you railbirds remember the "Tug-of-War" analogy?
.
Our community is FREE to join. To participate you must either login or register for an account.