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

[John MacCallum <johnmac@MYlisp.com.au>]

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

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