Crossing the 6,000-hp threshhold - locomotive engine design

Railway Age, July, 1996 by Gus Welty

The benefits of higher horsepower--unit reduction capability, superior tractive effort--are clear. How basic railroad operating practices will be affected remains to be seen.

As the number of a.c.-traction locomotives in service increases and as two roads prepare to receive 6,000-hp locomotives from General Motors' Electro-Motive Division and from GE Transportation Systems, several questions may be worth exploring:

* How will railroads be using this new power in order to get maximum benefits from the inherent advantages of both a.c. and high horsepower?

* What impact will this new generation of motive power have on basic rail freight operations?

* What comes next?

Burlington Northern Santa Fe has had more experience with a.c. traction than any other U.S. road. BN began testing three SD60MAC prototypes in mid-1992 and followed up less than a year later with a $675-million order for 350 4,000-hp a.c. units from EMD, breaking new ground not only with a.c. but also with EMD's radial track and its advanced microprocessor control system.

The SD70MAC production units had a few bugs to be worked out, but nothing serious, and BNSF says they've performed up to expectations.

Meanwhile, while EMD's plunge into a.c. grew from a partnership with Siemens Transportation Systems dating back to 1984, GE came to the rail freight market with a system developed out of its own experience with a.c. in the rail transit market. Both builders found ready markets, with all of the largest U.S. carriers except Norfolk Southern (and Santa Fe before the BNSF merger) climbing aboard the a.c. bandwagon.

At about the same time, the horsepower race was also heating up. Top numbers had been in the 4,000-to-4,400-hp range, but both EMD and GE jumped to 6,000 with just a passing flirtation with anything in between. The first of the 6,000-hp units will be delivered later this year, but in the meantime both builders have been delivering lower-horsepower locomotives that can be retrofitted with the more powerful engines.

All of the new systems contribute to a package that includes such benefits as lower maintenance costs, lower emissions, and improved fuel economy. Importantly, a.c.-plus-higher-horsepower allows a railroad to use fewer units to get the job done. And it's this unit-reduction capability that raises certain questions.

For example, when BN placed its initial order for SD70MACs, the point was made that three such units could replace up to five d.c. locomotives. In other words, unit coal trains that had been powered by five 3,000-hp SD40-2 locomotives could be operated with three 4,000-hp SD70MACs.

That meant a reduction of 3,000 hp per train, and while the a.c. units could demonstrate superior tractive effort and adhesion, there would be a certain penalty in terms of speeds that could be attained or maintained with lower total horsepower. And, while high speed may not be a primary goal in the operation of coal trains, a speed reduction can exacerbate line-capacity problems and perhaps increase load/empty cycle times, two conditions that do not produce good equipment utilization.

In any event, the two roads getting the first 6,000-hp a.c. locomotives will be looking very carefully at their performance to determine exactly what unit-replacement ratios can be for various types of service.

* CSXT and 6,000 hp. CSX Transportation will be getting its first three high-horsepower units from GE Transportation Systems by mid-summer, out of an order for 53 such locomotives with the remaining 50 units scheduled for delivery next year.

CSXT says the performance of lower-horsepower a.c. locomotives already in service has exceeded expectations, and it will be exploring a number of options with the first three 6,000-hp units. They're scheduled for testing on intermodal trains and coal trains and possibly on general merchandise trains. Depending on the tonnages involved and the ruling grades to be traversed, CSXT is looking at single- and two-unit power consists, with two-for-three or one-for-two replacement ratios, as specific situations may permit.

For CSXT, there's interest in the speed factor for intermodal operations, but in general the big thing seems to be the tractive-effort advantage provided by the new power. At this point, CSXT believes the 6,000-hp units will be a good fit, providing speed where it's needed and making it possible to handle ruling grades with fewer units.

* UP's test program. Union Pacific will be getting 6,000-hp locomotives from both builders, with the first 10 due from GE by August and with EMD planning to have at least six high-horsepower units on UP by the middle of next year, with 25 locomotives to be built as 6,000-hp units; UP also has an extensive retrofit program involving both GE and EMD in which in-service lower-horsepower locomotives will go back to the manufacturers for replacement of existing engines with 6,000-hp power plants.

UP will be testing the new power in coal service, but the 6,000-hp units are mainly intended for service on long-distance intermodal and manifest trains. Here, UP is looking at replacing four 3,000-hp locomotives with two higher-horsepower units and at using two of the new locomotives to replace three later-model units with higher horsepower ratings than the workhorse SD40-2.