>David Johnson (trainman@ozemail.com.au) wrote:
>>Maurie Daly wrote:
>>
>>> This leads to various differant HP ratings that can be delivered to the
>>> traction motor sets at differant speeds and for differing times.
>>> Ideally it would be nice to be able to increase the number of traction motors
>>> from the usual 6 to 8 as engine HP increases,but loading and curve radii
>>> prevent this.
>>
>>A couple of observations I'd like to share. We ran a 105 wagon coal train from
>>Kooragang Island to Ulan and return. On the return, we did a test lift on
>>Whittingham Bank with three 90 class locos and 11670 tonnes hanging off the
>>back. At 0.5 km/h, the locomotives were exerting about 300 horsepower at 1900
>>Amps. At 2 km/h, the locomotives were exerting about 900 horsepower at 1800
>>Amps. At 25 km/h, the locomotives were exerting about 3830 horsepower at 900
>>Amps.
>Do you happen to know what the tractive effort at the same speeds was?
>Cheers
>David
The numbers which David has posted here , ie the traction motor amps are the
result of protection circuitry in the loco reducing alternator output to
prevent burnout of the motors as the speed reduces.
The other factor which I forgot to mention is the fixed gear ratio between the
axle and the rotor of the traction motor.
This ratio is usually a compromise , as on the one hand a high ratio allows
for a high tractive effort for the same maximum motor current , whilst a lower
ratio allows higher maximum speeds.
Ideally if the main usage of the locomotive is known before purchase,then the
motor gearing can be chosen to maximise the tractive effort for that use.
As an example the SRA 90 class are geared for 115 km/h running but the SRA
wont allow them to run faster than 80 km/h.
If this fact had been known when they were being built , then the motors could
have been geared for 80 km/h running which would have increased their max
tractive effort , and the loads they could pull by 115/80, ie a considerable
increase.
AN made the reverse mistake when it originally purchased the CL classes, which
were geared for 160 km/h running but of course were never allowed to run at
this speed.
Whilst this made them good for passenger trains , at the time AN didnt run
enough passenger trains to utilise all the fleet ,so they were pressed into
service on heavy freights where they were a total flop, fortunately the MK
rebuild seems to have regeared them all for 115 km/h running, a lot more
useful.
Here are some comparisons of tractive efforts at various speeds for a couple
of common US locos, SD-40s & SD-60s.
SD-40 3000HP 6 axle loco , axle load 32 tonnes.
speed TE
0 135000
4 115000
7 97000
11 78200
15 60100
20 46200
30 31600
40 23700
60 14900
70 11400
SD-60 4000HP 6axle loco,axle load 32 tonnes.
speed TE
0 150000
4 147000
7 142000
11 115300
15 80000
20 62000
30 42400
40 31800
60 19800
70 15500
As you can probably see, as the speed rises,the tractive effort also rises and
more closely comes to equal the figures which Geoff quoted in his equations
relating tractive effort & speed, however at very low speeds , the SD-40 is
almost as good as the SD-60, ie the extra HP is simply lost.
The above figures will exceed the max tractive effort for all Aus Govt locos
due to the lighter axle loads, however they would be correct for the locos of
the Pilbara which utilize these sorts of axle loads.
Theres an old axiom which basically says that nothing beats tonnes if you want
pulling power.
(The figures above are in MPH and pounds.)
cheers
Maurie Daly
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Maurie Daly
Department of Communications Lab.
Canberra
Australia
mauried@commslab.gov.au
ph 6 2791331
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