This month's column is part two of my update on the AC Traction models of locomotives. From the comments I have heard so far, operating crews who have had the opportunity to work with them are impressed with their performance. Certainly, AC technology for locomotives has developed into a success story most of us thought would not happen. However, as you continue to read this feature, the past present and future of this story's development will come through.
Among the first AC Traction prototype units to undergo field testing in revenue train operations were a pair of F69PH-AC four axle locomotives constructed by General Motors for Amtrak. They performed quite well in passenger train service, but their success in the area of high speed operations left many in the industry to believe that AC technology would not work in low speed, heavy haul freight service.
Well, I'd now like to share with a true event in which an unintentional circumstance would lead to no doubts that it could live up to that expectation. Three of the SD60MAC prototype units will pulling a 17,000 ton unit coal train up a steep grade near Trinidad, Colorado on the Burlington Northern railroad. Also with this train was a business car transporting the top management for their company; they were along to see first hand a demonstration of these locomotive's capabilities. The train speed held steady at 12 mph until a problem surfaced with one of the three units ( it shutdown due to a turbo failure).
The remaining two units then gradually increased their output to the maximum rating of 175,000 lbs. of tractive effort, and held the train speed to 6.3 mph for over an hour . At that point, the traction motors were detected to be approaching overheating conditions, leading to the protection system gradually starting cutback of the locomotive's output. The train still kept moving for another 20 minutes before finally stalling out 300 feet short of the crest.
Shocked yet? If not, then the next fact will grab your attention: had the temperature cutback threshold been just 10 degrees lower, this train would have made it all the way to the crest, even with the locomotive's output in the cut-back state of motor overheat protection.
If there are any of you who have seen or read a critic's review of a given subject, you may have noted at times their remark in some form of "Well, that's okay, but....". So there might be someone looking at this now thinking (to finish that question) "how well can this work if you have an AC-DC mixed consist versus an AC exclusive consist?" The next story is another actual event in which a non-staged event occurred, but the ending was a successful one. It occurred in the Power River Basin area of Wyoming with a CNW loaded coal train comprised of 115 cars.
Each car was carrying 132 tons. The power consist was a C44AC leading two Dash-8 DC locomotives. While going upgrade, one of the Dash-8 units shutdown due to a failure. The train speed dropped to 2 mph and held steady. The leading AC unit, with its greater enhanced wheelslip control system, put out very high and stable adhesion conditions. Also of valuable assistance was the traction motor thermal protection program used in the Dash-8's software program. The end result: the train made it all the way to the crest of the hill.
Like any other electrical control system, the high voltage portions of the AC Traction locomotive requires some form of protection to avoid be subjected to potential damage from over-voltage and over-current conditions. To do this, AC locomotives are outfitted with a feature called the inverter protection system . The GM MAC locomotive, with its inverter per truck arrangement, uses a version called crowbar fault operation.
This feature is contained within the inverter control system. The crowbar comes after the fault has happened; when the crowbar is fired, the inverter control system notifies the locomotive control computer of this situation. What occurs is a cutoff of the inverter output by way of the inverter system and the DC Link gear being shorted out. After a 10 to 15 second period of no-load, should the self analysis program locate and correct the cause for the fault condition, the locomotive will begin to gradually load back up to the output of the throttle setting.
There are two types of crowbar fault firings in use on the MAC unit: soft ,and hard. The soft crowbar places on-line resistors which will allow for a slow bleed down of the AC current. However, should this process not occur quickly enough, the system will then fire a hard crowbar. The hard crowbar triggers a shorting out condition, which results in a complete and rapid unloading of the locomotive.
The operator will receive a message on the display screen notifying him of a crowbar firing. Should the cause for this be determined as being a bad inverter, the locomotive control computer will then automatically cutout that device, and a condition message to that effect will be shown on the display screen.
The GE AC unit, with its inverter per axle arrangement, employs a different form of process correction in the event of an inverter problem. It works in the following sequence of events:
A. The computer control system will isolate that inverter.
B. A verify test is done on it.
C. If the test result shows a bad inverter, it will be cutout automatically by the computer. This action will be reflected by a message on the display screen. In the likelihood that the unit is about to have an overall major system condition, a protection feature will then become active which will "turn off the switch" to the main generator, resulting in a rapid unloading of the locomotive.
Now under development are AC Traction model locomotives which will be capable of producing 6000 tractive horsepower. The type of engines they will be outfitted with are 16 cylinder dual turbo, "H" series models; the turbos will be small in size, enabling the units to be able to load up at a fast rate (keep in mind that the loading rate can be modified by way of the computer program requested by the customer).
In order to be able to apply the larger size fuel tanks they are equipped with, the units are not ballasted; therefore, an important factor in determining their tractive effort amounts depends on how fuel is in the tank. They will be capable of producing under power throttle conditions up to 200, 000 lbs. of tractive effort output , and up to 115,000 lbs. of dynamic braking effort.
The 8000 series SD90MAC units, along with the 7000 series C60AC which are presently operating with the 4300 and 4400 horsepower engines also introduced to the industry the convertible platform, allowing for an easy changeover to the 6000 horsepower engine. So you might be wondering are there any actual 6000 horsepower engines constructed? Yes, there are. On March 29th of this year, two C60AC prototype units came onto the UP at the Proviso yard facility in Illinois. They were involved with various testing exercises, the purposes of which are part of a process that looks for weak links and , when they are discovered, are corrected before the manufacturer goes to the full scale production model program.
Among the test results: it was found that these locomotives can get more of their 6000 horsepower output down to the rail than what was thought they could. However, under high adhesion, high throttle-low speed operations, they were not as well suited for heavy haul freight service, whereas on intermodal trains, they did quite well. The units left UP property on April 17th back to Proviso for GE to do some fine tuning , and are slated to return to the UP later this year.
As far as the 10 unit UP order of C60AC prototypes, once they arrive on the property, they will most likely spend their time operating on intermodal trains between Chicago and the west coast. It is also being proposed to run two of them as the sole power on a unit coal train test down to Texas.
Is there a possibility that there will also be some 6000 horsepower SD90MAC prototypes coming onto the UP? Could be -- in the third quarter of this year, the UP might be welcoming a pair of them. They might also be wearing UP cosmetics, but as yet, nothing has been finalized on this. There has already been lab testing done on this engine at the GM facilities, and a display model is slated to appear at the LMOA show in Chicago this fall.
A newer ruling has now been handed down with regards to the inverter cutout portion of the locomotive daily inspection rules for the AC Traction locomotives. In the last issue, it stated that for a GE locomotive, in order for it to pass this inspection, that only one inverter could be cutout.
The new guideline now permits a GE unit to still be able to pass a daily, regardless of the number of inverters there are in the cutout position. The guideline for the MAC unit's inverter per truck, however, still is in effect (on them, if one of them is cutout, it cannot pass a daily). There are investigations and procedure reviews taking place on this matter which might permit this to be changed.
The next part of this series will focus on the E-Brake and integrated display screens systems.