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During my early days of learning about AC Traction technology, I was having a conversation with a gentleman about how the pre-production SD60MAC demonstrator locomotives did during performance testing while on the U.P.. When the subject turned to how they did on the high speed intermodal trains, his colorful comment on this was "They'll pull like hell, but they won't run like it." So once the garden variety versions of AC Traction locomotives (they are the ones in the 4000 to 4400 horsepower output range) began operating on the U.P.,
I felt the situations might arise in which these locomotives would be used outside of the turn and burn, heavy haul category of operations. So today, you will be reading my findings regarding how true or false that comment was.
For about one month, they had a testor consist of two SD90/43AC units with a C44-9DC locomotive in the middle of the consist (From the overall standpoint, the C44-9 units are very good intermodal train service performers). Because DC model locomotives can "turn it up" so well at the top end speed zones, my belief was that the DC unit was serving as a "kicker" to aid with top end acceleration once the two AC units were out of their low end, tractive effort horsepower mode in which their operating characteristics are designed.
Well, as it turned out, my guess on this didn't quite ring true: I observed during operating a 60 mph conventional format empty coal train having two AC units and one DC unit (The consist makeup: a C44AC, a C44/60AC and a C40-8), that once you hit the 35-40 mph zone, the consist would begin to lose its ability to "turn it up."
Once the train was up to speed, if the throttle was placed below Run 5, the deceleration rate was faster than it was with an all DC units consist in identical locations (The specific area, for those of who are familiar with it, that I targeted for this report was the gradual downhill run on the Choctaw Subdivision in Oklahoma between Caddo and Caney bottom).
Also among my research were visits with the engineers who had operated the two empty coal trains of the conventional format which were powered by the trio of SD90/43AC units, as well as with a gentleman who had a conventional format empty coal train which had as its power lashup two SD90/43ACs and a C40-8. All of them indicated that in this same area, the SD90/43ACs had a little more spunk to them; however, they still were not that top end responsive.
Like my experience, if they went below Run 5 throttle, the remaining horsepower output would cause a quicker deceleration rate of the train than it would with a mostly or all DC units consist.
When the throttle was increased, the locomotive's speed recovery was not as fast (I would find out as part of this study that the condition is due to the AC Traction units not having as high a compensated horsepower rating as their DC counterparts). We all agreed noting that once the train got up to its maximum authorized speed, they would hold their own.
1. The gear ratio application on the locomotive. With the current AC Traction units, the gear ratio setting is to allow the higher horsepower output to be used for low end tractive effort application. If this were changed to where you would now have the unit capable of putting greater emphasis on high end acceleration with the horsepower, the amount of generated low end tractive effort output would be reduced. In addition, the fuel usage economics now becomes a more critical factor, as the amount used to get the train up to speed and then maintain that speed would be greater (For you rail buff historians: These factors, in comparison to the cost of diesel fuel, was why the "Fast Forties" were regeared from 59:18 to 62:15 fleet standard).
2. The ability of the wheelslip control system to do what it does. In a wheelslip condition, you lose horsepower output while attempts to correct the situation are taking place. One interesting fact I was given about this: A two stroke engine will recover from a wheelslip condition quicker than a four stroke version.
3. This is a factor strictly to the AC Traction units: At the higher track speeds, the garden variety versions will to some extent experience horsepower loss as a result of the inversion process whereby DC is converted into AC for use by the traction motors.
This is due to the levels of heat generated by this process, and the heat being dissipated by the cooling air being blown across the inverters, in essence, produces the loss. This loss, however, is not to so major an extent that it will cause a significant depreciation in the horsepower output, but it is a factor nonetheless.
Also, due to the ability of the AC Traction motor to spin at a higher speed than the DC counterparts, it can gain more tractive effort and speed , so this factor also to some extent can offset the horsepower heat loss.
The jobs on which they were operated included intermodal trains along with heavy haul unit trains. Whereas the current versions of AC Traction units are designed mainly for low end tractive effort output service, the 6000 horsepower variety (along with to some extents the 5000 horsepower SD80MAC) are designed primarily for high speed service.
Under high adhesion, low speed, high throttle operating conditions, the testing showed that 6000 horsepower AC units are not really that good; however, what was a surprise to many was that in these situations, their tractive effort output was higher that was originally estimated.
The 6000 horsepower AC units are not ballasted; so a more important factor with how much tractive effort development they can produce will rest with it having a topped off fuel tank.
Yes, although for now, the appearance was brief: SD90AC prototype unit No. 8205 on May 15th was received in interchange onto the U.P. at the former Cotton Belt interchange at Herington, Kansas.
It was enroute to the AAR-TTC in Pueblo to undergo developmental testing (the interchange was made by job LVW50-18 off the U.P. at Avondale, Colorado). Between now and year's end, there will be a small group of prototypes appearing on the U.P. to undergo road testing; some of them will be outfitted with the Integrated Distributed Power system.
There were two other very
important issues on this which I was asked to pass along to you when an
individual is performing troubleshooting while aboard the remote consist;
(1).
If you are dealing with the isolation switch on the remote locomotive,
remember that you should not place the locomotive "on the line" while it is
under power or in dynamic braking, and (2).
If you are dealing with the
automatic brake, whenever the train or engine is moving, you do not make any
adjustments to the regulating (feed) valve on the controlling locomotive, nor
do you cut out the automatic brake valve on the controlling locomotive. All of
these no no's are stated in the current edition of U.P.'s Air Brake and Train
Handling rulebook.
The other item was a two part question concerning the tractive effort meter and control box console displays not matching up with one another, along with why the system cannot "tell" apart an AC Traction model locomotive from a DC model. Let's take the readings miscomparison portion first: The necessary modification requires only a hardware change; specifically, the correct type of current module I indicated in my response. These modules are manufactured by Pulse Electronics, a well known and respected vendor of locomotive products. So the units needing this treatment will soon be seeing this application.
Meanwhile, the newest deliveries of C44AC locomotives (the 6500 and 6600 series numbers) are outfitted with the correct type of module, so they show the right tractive effort. In the area of proper locomotive model/type identification, this irregularity is occurring with C44AC units in series number 6838 to and including unit 6887. This correction will require a hardware modification to the DP system module; specifically, a jumper will need to be added to the backplane of the system module so that it can "tell" the equipment that it is on an AC Traction locomotive.
2. In recent time, a number of new general orders have been issued which contain data pertinent to locomotive operations along with revisions to the air brake rulebook and timetable special instructions. Make note of these new issusances, and note that some of them contain the statement that you are to have copies of these documents available for reference while on duty.
3. Also make note of the general notice regarding the SD90/43AC locomotives which outlines how to properly condition them for consist operations depending upon their placements. 4. On July 1st, the new statutes take effect regarding two way E-O-T telemetry equipment requirements for trains. As more about what this requirement entails becomes available, I will pass that on to you. In the meantime, information on how to properly arm the various types of systems is available by way of a tape from the video services library, along with a job aid pamphlet available through your supervisor.
5. Lastly, remember that if you have on line of road a locomotive failure, notify the train dispatcher along with the road failure desk about this situation. Give to Mr. Goodwrench as much data as you can regarding the nature of the problem so that if you cannot revive the patient, that the locomotive hospital folks at the maintenance facilities will then be prepared with the right tools to cure the situation.