Re: 82's Leading Patricks West. - Where are they now?

[mauried@commslab.gov.au (Maurie Daly)]

In article <37B89F53.C13A6C1C@MYlisp.com.au> John MacCallum <johnmac@MYlisp.com.au> writes:
>From: John MacCallum <johnmac@MYlisp.com.au>
>Subject: Re: 82's Leading Patricks West. - Where are they now?
>Date: Mon, 16 Aug 1999 23:33:35 GMT

>Maurie Daly wrote:
>> 
>> In article <37B4BA32.83DAD935@MYlisp.com.au> John MacCallum <johnmac@MYlisp.com.au> writes:
>SNIP

>> What seems to be inconsistant with the 82 load ratings is the continuous
>> tractive effort of the traction motors.
>> Bearing in mind the the 90 class have exactly the same motors and the SRA
>> rate the 90s at 1700 tonnes up 1:40 at 15.4 km/h,if we assume that the motors
>> are running at 100% capacity under these circumstances,then in the 82 case
>> allowing for the lighter axle load and lower HP we should be able to get
>> around 1250 tonnes up 1:40 at 15 km/h , with the motors running at only 70%
>> capacity , ie the ratio of 4000 to 3000 HP , but as you indicate they are
>> rated at no more than an 81 .
>> If the 82s are adhesion limited then we should get 1475 tonnes or in the case
>> of HP limitation we should get 1275 .
>> The fairly common occurrance with trains slipping in the Adelaide Hills is
>> just about always the non super series locos that ASR uses,ie the CLP/CLF/ALFs
>> etc.
>> The BLs dont seem to show the problem , although given the way that NRC
>> underload their trains its not likely to ever happen anyway.
>> 
>> cheers
>> MD
>Yes Mauire , I was somewhat puzzled by the difference in the Tractive
>effort between 81 and 82 classes but I was even more surprised about the
>lack of tractive effort available from NRs.

>It was when pondering this and some other information I had
>read on the subject that it occurred to me that adhesion is the
>main reason for the difference in tractive effort between these
>engines. 

>I can't comment much about the NR class because I don't have much data
>available for them but with the 81s and 82s have a very high
>adhesive ability. The 82 class because it weighs more has more
>adhesive weight and therefore can provide more tractive effort.

>Traction motor heating is still a problem however because as the
>speed falls off Back EMF falls and therefore traction motor currents
>rise dramatically. An example from memory is an 81 class which
>at around 20 kph has about 900 amps of traction motor current.
>If the speed drops to 15 kph the current rises to about 1100
>amps and the engine is in the time limited load range. If the
>engine was able to continue to slow down without losing adhesion
>it will either have an Alternator over current or overheat the
>traction motors and have a ground relay at the very least.

>The 82 class produces similar currents ,although the traction
>motors are slightly higher geared. If the loading was increased
>to take advantage of the higher tractive effort then the speed
>will fall below that of an 81 and the traction motor currents
>would be considerably higher than that of an 81 class.
>The continuos current rating for the Main alternator on an 82
>class is 7020 amps. Thus as its traction motors are in parallel
>this gives 1170 max available to the traction motors. So as you
>can see from this somewhere just below 15 kph the available
>current from the Alternator will be exceeded and the unit will
>have a Alternator over current and shed the load.

>When next I have a look at an 82 class loadmeter I will check to
>see at what current the time de-rating starts.

>-- 

>Pope

>Alias   John MacCallum

>remove MY from MYlisp to get the real email address.


OK a bit of info on the NRs which may explain some of the mystery.
Digging back thru a couple of articles , the NRs are fitted with GE793 series 
traction motors , not the GE752 series as indicated by Railpage.
The 793 motors are a lightweight version of the 752 , about halfway between 
the 761s as used on the ELs and the 752s as used on the BHP CM40s.
The reason for this was the 23 tonne axle load limit which couldnt be exceeded
and the bigger motors would have gone over the limit.
A consequence of this is that the continuous rating of the NRs is not very 
brilliant ,minimum continuous speed is around the 22-24 km/h mark .
Pity really as with the bigger motors you would get the mind numbing pulling 
power of 485 kn , whether with only 23 tonnes you could use it is another 
question.
On a similar issue I read somewhere that the organization that bought the ELs 
is going to overhaul and regear them for freight work,no specifics but the 
logical solution would be to replace the lightweight 761 motors with the big 
752s and you would get a loco like the 82.

On the 82 load issue and why the SRA rate them so poorly ,its possible that 
its a practicality issue.
Most of the lines over which the 82s run in NSW which have 1:40 grades
also have many other lesser but not insignificant grades like 1:50,1:66 which 
would mean that a fully loaded 82 pulling 1200 tonnes will make for a very 
slow journey , schedule C4 as its called.
Dont see many trains running to this schedule anymore.

On the Melb - Adelaide line however its a totally differant story as we have 
850 kms of line of which only 20 km at one end is 1:40,all the rest is 
basically flat with one short 1:50 at Diapur and the similar short 1:66 at 
Stawell.
If you can get up the hill from Goodwood to Mt Lofty or Callington to Mt Lofty
even at 15 km/h ,then for the rest of the trip a single 82 with up to 1300 
tonnes can for the most part run at full line speed, (2hp/tonne) is more than 
enuf to maintain 100 km/h on the flat.
Locos like 82s would be excellent for ASR to run on this line.


MD