Topic: BR-220 (Voyager) Gear

[Carl]

In line with other diesel vehicles, the Class 220 in Pak 128 Britain-ex has a gear rating of 50%. However, I've noticed in my research that this train in fact has electric transmission for increased acceleration, and as such should probably be given a gear rating in line with electric vehicles -- i.e. 80.

The electric transmission is referenced here by Bombardier:
http://www.bombardier.com/en/transportation/products-services/rail-vehicles/intercity-trains/multiple-units/voyager---united-kingdom?docID=0901260d800128b6


(Incidentally, I discovered this after noticing that a Voyager with the stats given in pak128-ex was unable to keep up with the real-life timetable on my Great Britain map. After upping the gear to 80, the train's performance matched the timetable. Though this is hardly irrefutable evidence, it is at least some indication that the higher value represents real-life performance. Additionally, it is notable that vehicles in my map tend to be more likely to out-perform the timetable than underperform it, so that a vehicle which cannot meet the timetable represents a serious outlier.)

[jamespetts]

Many diesel locomotives and units have electric traction: most of the early BR diesels were diesel-electric. Electric traction is no more efficient than hydraulic traction (indeed, it might be a little less efficient), so the transmission losses are not reduced by electric traction. The gear value is intended to represent transmission losses between the engine and the forward thrust actually exerted by the locomotive/unit so that we can put in real values for the power and get realistic performance out of the units. That transmission loss will always be much higher with diesel than electric locomotives, as we have to take into account the transmission loss between the prime mover and the alternator/generator (in a diesel electric) as well as the transmission loss between the electric motors and the wheels.

What might account for your timetabling anomaly, however, is tractive effort: tractive effort values are not available for these multiple units, so I had to guess. Tractive effort affects acceleration, which can make a large difference to timetabling. It would be helpful if you could revert the gear to 50 and experiment with different tractive effort values to see which ones produce realistic performance.

[ӔO]

since this is a newer diesel-electric train, it might be using a newer, more efficient, power controller.

VFD/VVVF is the latest design and it offers substantial improvements in traction over IGBT, GTO, thyristor and chopper.

I'm not sure which type of motor it uses, but AC motors have also gone through a major improvement over the years.

[jamespetts]

I still very much doubt that efficiency is as high as 80% - even 50% is on the high side for diesel, really.

[Carl]

Thanks for the reply, James; very informative.

I've played around with tractive_effort a bit whilst holding gear fixed at 50. I am somewhat unsure what would be the range of realistic values for the tractive_effort value, but it seems that one needs to raise it to around 400 to match the real performance of a Voyager. It seems that changes in tractive_effort make very, very little difference unless the numbers involved are quite large.

One question: elsewhere on the forums, it is noted that Experimental can automatically calculate tractive_effort given a power value. Is this a default value that can be overridden by an alternative value stated in the dat file, or is there supposed to always be a proportional relationship between power and tractive_effort?

[ӔO]

just to be sure, did you give each car 560kW, for a total of 2240kW per 4-car set?

[Carl]

I've been running a 5-car set with 560kW in each car. So it's a 221 rather than a 220, but these trains all run to the same timetables in the hands of XC).

There is some weight variation among these classes and I have been using the 221 weights as described here:

http://www.therailwaycentre.com/New%20DMU%20Tech%20Data%20/DMU_220_221.html

But again, I'd these routes are presumably timetabled for 221s, so the weight can't explain the difference. (I gather that this weight difference is explained by the tilting equipment which 221s carry but 220s don't.)

However, I note that the pak128.Experimental Class 220 weighs less, which will probably mitigate the problem I'm describing here. This is probably only a concern for the heavier 221, so it's only a problem for me, and not for the pakset.

But is there any reason to think that the 221 has greater engine performance/tractive effort than the 220, to compensate for its weight?

[ӔO]

I found some obscure info about the motor used, which is an Alstom ONIX 800.
I'm not 100% sure if it uses IGBT.
IGBT would give it better performance compared to older types of power controllers.

http://www.uic.org/cdrom/2001/wcrr2001/pdf/sp/1_11/555.pdf

I don't notice anything particularly special about these onix 800 motors or the cummins diesel engine.
From my understanding, IGBT can handle Voltage droop better by upping the amperage, so that total power sent to the motors remains unaffected, but it can't pull more power than is supplied by the engine. Conversely, that means the unit can pull more power than it is rated for, if it is on external power.

Since these voyager trains only have 2 driving axles per car, which makes it 1 Motor, 1 Trailer, it shouldn't have particularly good acceleration. Although, for an express train, it's better than average or the class-43 that it replaced.

compared to the electrostar family of trains, which are 4M1T, 3M1T or 2M1T, voyager series should not out accelerate them.

[jamespetts]

May I ask - have you tried altering the rolling resistance?

[Carl]

I will give this a go - but the value is already only 13, so not very high. But I suppose Voyagers are more streamlined than most trains. Worth a try!

[jamespetts]

Yes, actually, what is your air resistance value?

[Carl]

I don't think I've set that value in the dat file -- an oversight on my part -- so it will be whatever the default is. I shall borrow the pak128br-ex value and see if that makes any difference, too.