What do you think is more powerful?

[Rail1435]

the big boys were pretty masssive and powerful at 4-8-8-4 wheel arrangement.

Very massive: YES 541 t with tender.

Powerful? With only 4,3 MW as a 80t electric BoBo! 

[Rail1435]

See one of the 3 powerful biggest one-body locomotive: the Alstom-Datong version:

More information:

http://www.railcolor.be/international/viewtopic.php?f=5&t=23

 

[Texas Zepher]

Well why don't we just settle this discussion and make up 2 trains that have identical weights & lengths.  We'll hook up an SD70ACe to one and the GG-1 to the other.  We'll time them and monitor speeds and train control performance.

That would be one scientific way of gathering data.  The results might not be as straight forward as one would think.  For an example take the Santa Fe's dynometer car measurements of the various diesel locomotives vs their steam locomotives.  The PAs have far more impressive drawbar horsepower than even the famed 2-10-4, but we didn't see the Santa Fe running out and purchasing PAs in bulk, because the 2-10-4 had far more drawbar pounds of pull.  The PAs numbers were by a small margin generally better than the Fs, but the Santa Fe choose the Fs for OTHER reasons.

If the GG-1 was that great...wouldn't they still be in use?

Find another piece of industrial equipment that was built in 1934 that is still in use.  The guts of Hoover Dam have had more face lifts than Joan Rivers.  I can think of two more fair ways to compare the two locomotives.   1.  Wait until 2050.  Compare the SD70ACe to whatever the most modern locomotive is at that time and ask if they were so great why aren't they still in use.   2.  Wait until the last SD70ACe is retired and compare its service life to the 45 years of the GG1s.   The final question would be why the SD70ACes were retired.  As I understand it, the GG1s weren't retired for performance reasons but because the frames had cracks due to long service life.   Neither do I know how long the EPA would have contiued to let them run with all those PCBs in the transformers.  It is simple economics that says why replace a transformer if one also has to replace an entire frame. Stuff wears out.

Wouldn't straight-electric freight engines be rampant if they were that great?

Has nothing to do with the locomotive.  It is too expensive to string and maintain overhead wire, to dangerous (to stupid people) to run 3rd rail.  Even the extensions of the modern light rail here in Denver is being planned with DMUs instead of the overhead wires just for this reason.

I think that the bottom line is that for its time and even after the GG1 was a truely awsome locomotive.  It is sad that the final steam locomotives didn't get to live out their natural service lives so they could be compared in this same manner.  Just another example that shows $ are more important than raw performance.

[oltmannd]

Neither the PCBs nor the truck frame cracks were the death knell for the GG1s. The cracks were a long time problem and were fixed by welding and stress relieving.  They could have gone on forever like that.  You reset the fatigue live by heating the castings up in an oven.  Cast couplers and other draft equipment pieces go thought this now as part of being reclaimed.

The GG1s were running on mineral oil, not Pyranol at the end, much like the E44s, Jersey Arrows and Silverlinters.  There was still a problem with residuals in the transformers, so spills were still reportable.

What killed them was cost of ownership, performance and looming change in catenary power (which only partly happened).

AEM7s and E60s were more powerful, simpler and (supposed to be) faster. 

[Stevo3751]

The only problem with the turbines were that they used just as much fuel idling as they would while operating.

[passengerfan]

SUPERMAN

Al - in - Stockton

[bakupolo]

We're comparing apples and oranges. The electrics can draw on a humungous amount of energy produced miles away by a turbine and generator the size of a city block, burning a ton of coal every few seconds. They're only half a locomotive anyway - the lower half. Power distribution being equal, the electrics should pull the drawbars out of almost any deiesel.

Best to compare the SD70 to other self-contained locos - in looks it beats them all and I'm a shallow railfan that likes to look primarily at beautiful engines. Yes, yes, the SD70 beats them all! 

 

[erikem]

The only problem with the turbines were that they used just as much fuel idling as they would while operating.

Not quite true - the 4500HP turbines burned 450 gal/hr at full throttle and something like 200 gal/hr at idle. You weren't completely off the mark as a 4400 HP diesel burns a bit over 200 gal/hr in run 8. 

[HarveyK400]

Powerful seems to be used commonly to describe starting tractive effort and effective limit of adhesion.  Powerful in that sense should not be confused with power.  It is the horsepower that produces tractive effort inversely proportional to the speed and limited by adhesion.  Power must be controlled at low speeds to avoid tractive effort exceeding adhesion, around 25% weight on drivers, resulting in wheel slip.

As I recall, the GG1 and SD70ACe have roughly the same horsepower.  The difference is the significantly greater weight on drivers and wheel slip control of the SD70ACe that gives greater starting tractive effort.  This allows starting and moving a much "heavier" train, a combination of weight, journal, and track modulous factors, at low speeds; but it will not attain more than 13 mph where horsepower-generated tractive effort falls below maximum adhesion.  You can get a more exact number with the fundamental engineering formula Tractive Effort=308xRated Hp/Mph (the better efficiency of a modern locomotive will make some small difference).  Above 18 mph, assuming 4300hp for both, there is no difference in performance with the same smaller train.

It takes 7.7 hours to travel 100 miles at 13 mph; and 5.6 hours at a continuous 18 mph without delays in route.  This does not account for grades that adds 20 lbs lifting resistance per ton per each percent rise.  Only a train a third the size of the one that could be started by an SD70ACe could attain 40 mph and take only 2.5 hours for 100 miles, discounting grades and delays in route. 

Take the same heavy train that could be started by one SD70ACe and add two more like units combining for 12,900 hp and you can make 40 mph over the road and deliver the load before you turn grey.  What good is the 321,000 lb starting tractive effort when you have only 99,300 lbs tractive effort at 40 mph?  Three GG1s have more than enough tractive effort to start the same train and still make 40 mph.  Three SD70ACe's = three GG1's.

Would you consider an 8,800 hp, 215,000 lb electric locomotive with only 53,600 lbs starting tractive effort to be less powerful?  It would take two such units to start the same heavy train as a lone SD70ACe.  However, only two electrics would be needed to haul the train at 50 mph instead of only at 40 mph for three SD70ACe's.

The UP three-unit (cab-traction control, turbine-generator, and tender) 8,500 hp gas-turbines were the all-time highest rated horsepower single locomotive in the U. S. until the Acela power cars, basically underemployed TGV's.  

 

 

[Alan Robinson]

We are talking about too may different things here. The conversation isn't all that complicated. There is one answer to the question of "most powerful" and that is which locomotive delivers the most horsepower at the rail. All else is fluff.

Now, what do we do with that horsepower is a different matter.

Starting tractive effort is important because you can't pull a train you can't start, but it isn't everything. Suppose I built a multi drive wheeled, one million pound, rock filled sled and then hooked all the drive wheels together (through suitable gearing of course) to a 3 horsepower lawnmower engine. Starting tractive effort would be about 250,000 pounds, but I don't know of any railroad that would want one. Not even for switching.

Starting tractive effort really has little to do with power and is mostly determined by weight on drivers with other influences such as anti-slip technology and factor of adhesion. Simple steam locomotives had a form of anti-slip control known as side rods. All drive wheels were locked together so that one axle couldn't run away. Geared engines had the same advantages. Articulated locomotives didn't as one engine could slip and not the other. They behaved more like double headed locomotives. Steam locomotives tended to be characterized by the ability to pull any train they could start. But how fast? That depended on boiler horsepower, the ability to turn the heat in coal or oil into high pressure, superheated steam. By overfiring, steam locomotives could be overloaded, sometimes to twice their rated boiler horsepower. It affected starting tractive effort not a whit, but it did everything for tractive effort at speed.

Diesel electrics have high starting tractive effort available IF THEY HAVE ENOUGH WEIGHT ON THE DRIVERS to use what they can produce. Early diesels were generally underpowered for their weight and were not so limited. Modern diesels are more likely to be weight limited (as was most steam) but some of this is made up for by anti-slip technology and synchronous AC drive systems that limit slip as with the side rods of a steam engine. All axles are forced to turn at the same rate.

Any electric drive system, either diesel electric, gas turbine electric or straight electric has two tractive effort limits. One is the starting, or short term, rating. This is the maximum current limit of the motors and controls combined with the gear ratio to produce torque at the rail. It is available for a short time only before something overheats. This limit is large, but it can only be used if there is enough weight on drivers to keep the locomotive from slipping.

The continuous tractive effort is the limit the locomotive can produce continuously without overheating the traction system. There is a minimum speed where this tractive effort can be maintained for any given locomotive. At any speed below this, the continuous tractive effort stays the same. The power from the prime mover (diesel or turbine) or the power from the overhead (electric) must be limited as train speed falls below this speed to avoid destruction of the traction gear. So, a well designed locomotive for normal purposes will usually have the continuous tractive effort located at the same operating point the prime mover reaches maximum power output. Above this speed, tractive effort for a typical diesel or turbine falls because the prime mover can't generate additional power to maintain both tractive effort and speed, too. (The product of tractive effort and train speed is the power at the rails, and must be less than the prime mover's power, as diesels and gas turbines can't be overloaded.) These characteristics combine in diesel electric and gas turbine locomitives to give the ability to start a train the locomotive can't necessarily pull.

Many straight electric passenger locomotives have been designed so there is no starting tractive effort limitation. The locomotive slips due to lack of weight before the continuous tractive effort limit set by the electrical gear is reached. This would be done because for passenger service, horsepower at high speed is what counts. Yes, there had to be enough starting tractive effort to start the train (seldom a problem for high speed service, as trains are short and light) and the required tractive effort increases as train speed goes up due to higher air and rolling resistance. But it usually takes plain old horsepower to move a really high speed train, not tractive effort. Witness the French TGV high speed test recently where a pair of locomotives each produced about 25,000 horsepower. They would be worthless for moving freight, not enough weight and not enough tractive effort, but they could really fly. Another example was the Hudson type 4-6-4. Often less starting tractive effort than the Pacific 4-6-2 they replaced, but lot's more horsepower at speed. Again, not much of a freight engine.

I'd say the TGV locomotives probably win the test in terms of horsepower at the rail (although there may be others I don't know about), but in a very specialized service. More normal freight service would require much heavier locomotives such as we see in current US diesel electric practice or in earlier heavy steam days.

[Rail1435]

...

I'd say the TGV locomotives probably win the test in terms of horsepower at the rail (although there may be others I don't know about), but in a very specialized service. More normal freight service would require much heavier locomotives such as we see in current US diesel electric practice or in earlier heavy steam days.

A TGV-A powerhead has only 5,2 MW on four axles, with 68 t weight and 100 kN starting effort, max. speed 300 km/h (190 mph).

A Prima 6000 has 6 MW with 88 t on 4 axles and develop a starting effort of 320 kN, maximal speed 140 km/h (90 mph).

There were French examples from Alstom, but German examples have more or less the same values.

Note that the values for electrics are given in continuous power. At "high" speed a greater power can be required for a short time (~140 % for 15 min.) , which is not possible for diesels, limited by the engine power.

[Alan Robinson]

Please check out the information on the latest high speed test of the TGV at http://travel.timesonline.co.uk/tol/life_and_style/travel/article1608769.ece wherein you will notice each of the two powerheads were drawing 19.6 megawatts. This would be about your 5.2 megawatts, but on each of four axles. This test achieved a sustained speed of 310 miles per hour and a top speed of 353 miles per hour. The powerheads for this test were equipped with larger wheels and everything, locomotives, cars, track, were carefully adjusted. Even the voltage on the overhead wire was raised temporarily. Clearly, this will not be the normal operating speed or conditions.

The power draw of 19.6 megawatts converts to a little over 26,000 horsepower. Not all of this will appear at the rails, but about 90% of it will. Even this works out to about 23,600 horsepower.

Remember, work is force times distance. The force (tractive effort) may be modest, but the distance is large. Also rember that kinetic energy is proportional to the square of the velocity. Double the velocity while keeping the force constant and you require four times as much power. This is why, when looking for horsepower at the rail, it helps to examine high speed locomotives. This is also how a very moderately sized turbojet aircraft engine with a relatively small static thrust of 10,000 pounds or so (equivalent to starting tractive effort) can produce a horsepower of more than 10,000 when operating at cruise speed of 550 to 600 miles per hour.

[Stevo3751]

That depends on the voltage of the catenary system. The average modern diesel produces about 4,000 horsepower. If you are willling to make the catenary draw about 25,000 to 30,000 volts like the TGV, you can make 12,000 horsepower. That however is probably a big expense. It's really just a matter of how much technology and money you're willing to put in to create a high horsepower locomotive.

[Rail1435]

Please check out the information on the latest high speed test of the TGV at http://travel.timesonline.co.uk/tol/life_and_style/travel/article1608769.ece wherein you will notice each of the two powerheads were drawing 19.6 megawatts.

 

19.6 magawatt: yes, but on 12 motor-axles (2 powerheads with induction motors and one central unit with sychronous motors, now installed on AGV new train).

[mdainsd]

Hello, just visiting from the classic toy train forum.

On three rails, an ACe drags a GG1 wherever it wants.

Sorry, i couldn't resist.

Cheers.