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Re: NT Class again
Aus loco discussion mailing list
Tim, thanks very much for providing the details on the NT control system.
It's much appreciated. You're right that it's a bit different to what I
expected, and I'm now wondering whether the (scant) information I have on
the BRCW/Sulzer system apparently applied to the NSUs is entirely accurate.
If I may ask an additional question, does the manual you have indicate
whether the air pressure control to the engine governor is trainlined for MU
purposes? That would seem to be the simple way to signal notches 6 through
18 to trailing units, but it's also possible that there could be a matrix of
trainwires for these, with translation to air pressure taking place
individually on each unit using some kind of air-to-electric transducer. In
any event, notches 1 through 5 would need to be signaled electrically by
trainwires, as throttle line pressure would logically remain at zero across
The spring loading on notch 18 seems most likely a device to limit
continuous operating at full power. At a guess, I'd say it reflects the
fact that the Sulzer LDA28 engine, at its "C" rating, was a bit
overstressed, and running at 800 rev/min for any length of time could
adversely affect its durability. Notch 17 probably dropped it back to
around 750 rev/min.
Anyway, the NT control system appears to be a blend of electric and
pneumatic techniques. The net effect, firstly increasing generator
excitation at minimum engine speed, then steadily increasing engine speed
(presumably under automatic load control) is similar to that of the EE
pneumatic system. But the latter uses air pressure to control both phases.
I.e., the initial increase in throttle line pressure (to around 15 lbf/in2
for a Mark II engine, I believe), increases generator excitation at idle
speed. Then further increase of throttle line pressure progressively moves
the engine through its speed range under automatic load control.
Looked at another way, it seems that the NT control system is like a finer
version of the MV system used on the WAGR X /XA/XB classes. There, notches
1 through 3 progressively increase main generator excitation at minimum
engine speed, notches 4 through 10 increase the engine speed in 7 steps to
maximum, in this case electrically signaled for MU purposes.
This idea of incrementally increasing power output at the lowest engine
speed during initial controller (throttle) operation seems to be a British
one. As far as I know, the American 8 notch control schemes go straight
into automatic load control at the lowest engine speed on notch 1, which
then allows the engine fuel system to go to full rack (or to the notch 1
fuel limit setting in the case of Alcos.) Notch 2 then brings the first
increment in engine speed.
Since the NTs were designed to MU with the NSUs, one would expect them to
have similar control schemes, which is why, as mentioned above, I'm now
wondering whether the information I have, that the NSUs had a CP/AW version
of the Sulzer/BBC type continuously variable pneumatic throttle, is entirely
accurate. I guess the two systems could still work together after a fashion
if the NT does have a trainlined throttle air pipe. A quick analysis
indicates that with the NT leading, the NSU would stay at minimum power
until the NT moved to notch 6. The other way around, the NT would likely
start in notch 5, which seems a bit rough and ready. I suspect that the
NT/NSU coupling has to be more complex and sophisticated than this!
On the other hand, the origin of the NT control scheme is probably found in
the MCW/Sulzer/AEI Zambezi type locos supplied to several African railroads,
from which the NT is said to derive. And although I've not seen it
confirmed, the Zambezi likely has some connections to the solitary BTH
"Explorer" class loco supplied to Kenya. Although I understand that some of
BRCW diesel loco design staff did migrate to MCW when the former shut up
shop, essentially the NT and NSU have different ancestries. Therefore one
might expect then to have different control systems that are not necessarily
perfectly compatible in an MU sense.
Thanks again, Tim.
And if any correspondent has comparable information from NSU class manuals,
I'd sure appreciate their posting it!
----- Original Message -----
From: Timothy Parsons <email@example.com>
Sent: March 22, 2000 05:16 AM
Subject: NT Class again
> Aus loco discussion mailing list
> Hello again to Ausloco'ers from the other side of the world.
> I was following with interest the thread on this list back around
> regarding the CR/AN NSU/NT/NJ loco's. I think it was Steve Palmano who
> trying to get to the bottom of the control systems on NSU's and NT's.
> After some long overdue tidying up at home (including unpacking some boxes
> that had not been unpacked since I came over here from Australia several
> years ago!), I came across a copy of the "Control Apparatus and Electrical
> Machines" Maintenance Manual for the NT class (Book No. 1050/1 jointly
> published by Sulzer, Tulloch and AEI). Steve I think was suggesting that
> the NT's had a continuously variable EP throttle based on the Sulzer/BRCW
> design and asked for confirmation if this was so.
> The Maintenance Manual in fact confirms that this was not quite the case.
> To quote from the manual:
> "Engine Control - 18 power notches controlled, the lower 5 by fixed steps
> exciter battery field adjustment and the remainder by variation of air
> pressure to the diesel engine governor."
> The manual also contains a lot of detailed cutaway diagrams showing the
> notch number indicator plate and the cam operated master controller
> etc. The maintenance procedures also state that the spring in the master
> controller handle should be set so as to return the handle "smartly" from
> notch 18 to notch 17 and keep it there. Would this indicate that you
> not normally run the loco in notch 18?
> I cannot answer the question about MU capability with NJ's, but the manual
> confirms that NT's were able to run with up to 3 units (of either NT or
> class) in multiple, but that when running in multiple with NSU's, the
> lubricating oil priming procedure would require special attention (no
> details given). The manual also states that the auxiliaries on the NT's
> indeed operated at 110 volts as Steve suggested.
> I hope this is of some help in answering some of the outstanding points on
> this old thread!
> By the way, many years ago, I was told (tongue in cheek), that the class
> designations should really stand for the following:
> NSU = Non Serviceable Unit
> NT = Not Trafficable
> NJ = Not Junk
> I'll let others decide on their appropriateness...
> All the best,
> Tim (in England and starved of Alco's) Parsons
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