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SEPEX DC Traction.

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SEPEX DC Traction.
Posted by Tubby Lunchbox on Friday, March 31, 2023 6:55 AM

Does anyone here know anything about SEPEX DC in Diesel Electric Locos?

So far I only know two: British Rail Class 60 buy Brush Traction & Goninan-GE Cv40-9i NR Class.

SEPEX is a big improvement over the old fashioned Series DC, it gets you halfway towards the effectiveness of AC Traction.

The BR Type 60 has 3100BHP, is 129 tonnes & can start a 3100 tonne train on a 1:100 Grade.

The Goninan-GE Cv40-9i has 4250BHP, is 132 tonnes & can start a 4000 tonne train on 1:100.

Any others out there? Would seem no in North America.

Cheers,

Tubby Lunchbox.

 

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Posted by Erik_Mag on Friday, March 31, 2023 10:44 PM

I'm assuming SEPEX DC refers to SEParately  EXcited DC. You are corrct that it does give some significant advantages over series motors in that a slipping axle will cause a dramatic reduction intorque generated by the motor and thus providing some inherent anti-slip. What it doesn't give is the inherent ruggedness of a three pphase induction motor.

As far as I know, SEPEX control for motoring in gas or diesel electric locomotives pretty much disappeared after the Lemp control system was developed. It is pretty much the standard method used for dynamic braking.

SEPEX DC was used on some of the GN's motor-generator locomotives used on the Cascade Tunnel as well as Amtraks AEM-7s.

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Posted by M636C on Saturday, April 1, 2023 5:12 AM

I have never seen any reference to separately excited traction motors in any description published about the Cv40-9i. I did obtain a glossy brochure (one page, two sided) in colour from the then Goninan Bassendean. It didn't even mention the type of traction motor used on the locomotive. I asked specifically about this and was told GE 793. I think this was the only appliucation of the 793 motor, which was described to me as an upgrade of the GE 731 switcher motor, standard gauge width but smaller in diameter than the GE 752 motor used on US Domestic locomotives. The GE 752 could not be used if the weight was to be kept to 132 tonnes.

I understand the GE793 soon proved a failure. I recall seeing NR 1 stopped at Yass Junction with at least one failed GE 793. The motor was improved as the GE 793A1 which weighed a little more, around 400 pounds more. This was adopted as standard in most of the 120 units from new and the original 793s replaced. This did reduce the fuel capacity to 11500 lires from the intended 12500 litres.

Although much was made about the variable horsepower setting of these units, including down rating of the engine on long grades to protect the DC motors, I've heard nothing about separate excitation.

The Swedish Rc electric locomotives had separate excitation of the motor fields, these wold be the most numerous group of locomotives fitted with separately excited traction motors. The British Rail APT-P was fitted with Swedish power equipment from the Rc series, as was the Swedish X2000 high speed power car.

Peter

BDA
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Posted by BDA on Tuesday, April 4, 2023 8:52 PM

Ok Peter , I think I understand why you think the way you do .

Most of the locomotive technology in Australia comes from the US , but the application here suffers greatly because of our piddly loading gauge - but mostly from our (approx) 2/3rds of USD axle loads .

The huge advantage USD locomotives have is that they can often hold their feet and pull (in run 8) right down to virtually a stand in overload situations . This is why operators of them have to pay close attention to short time ratings . It is quite easy to burn traction motors , in DCs anyway , when you have 30 plus tonne axle loads . Here in Australia we have more like 22 tonne axle loads so with the same as USD 4000 - 4500 Hp on tap our locos can't hold their feet anything like as well . When they do slip the control system current limits the traction motors to limit slip and also reduces the diesel engines output . No point the traction control system fighting excess horsepower - that achieves nothing . So with current limiting of traction motors they won't generate as much heat as they would if there was no wheel slip . 

Back when NRs first arrived (late 1996) I think I remember reading that Dash 9 tech could current limit traction motors if they were overheating . I challenge anyone to get these units to hold their feet full load full roar at very low speeds - enough to over heat their traction motors . As I've said before , how did I get 2000 tonnes up Demondrille with one leading a failure when committed ? 13 km/h 1300 amps never missed a beat . Went under the bridge at the top at 7 km/h . Obviously this is not something they can all do under all conditions .

Something you may or may not know is that the down fall of 90 classes is their weight vs traction motors . 167 tonnes on 6 D87s . They are heavy enough to hold on long enough and slow enough to fry their D87s . Probably the limitations of any similar weight SD60 variant . Obviously this was a Ready Power bean counter thing - common spares between 82s and 90s . They should have had D90s or better .

I don't know where you get this derate to protect traction motors bit on long grades with NRs . We used to regularly pull 4000-4200 tonnes up the Cullerin ranges with two of them and never got much under 21 - 22 km/h . These are the sorts of speeds you'd expect to be doing with an 81 or G class with around 1500 tonnes per engine . 

 

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Posted by timz on Wednesday, April 5, 2023 11:15 AM

Tubby Lunchbox
The Goninan-GE Cv40-9i has 4250BHP, is 132 tonnes & can start a 4000 tonne train on 1:100.

91000 lb tractive effort just to overcome gravity -- wonder how much more it has to come up with. Do they have TE meters?

BDA
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Posted by BDA on Thursday, April 6, 2023 5:10 AM

NO TE , they have an amp meter .

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Posted by Tubby Lunchbox on Wednesday, April 19, 2023 4:46 PM

521 kN Starting Tractive Effort @ timz.

As I said in a previous post I put brushes in them & they have Slip Rings not a Commutator, ruling out classic SERIES DC. This also means they have TWO ways to control torque BUT they don't deliver the torque of Series DC Traction Motor. To compensate, the Cv40-9i is geared 24% faster which is made possible by slip rings.

Another bonus is better Dynamic Brakes, that's why Goninan put the huge grids on it & they save a lot of brake shoes when compared to the oppositions alternative because the dynamics works smoother and to a lower speed.

They did bust a few pinions, but that wasn't a big problem. The fuel tank is 13500 litres, but limited to 12500 litres to get to 132 tonnes.

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Posted by Erik_Mag on Wednesday, April 19, 2023 10:21 PM

FWIW, 521kN equals 117,000 lbf for us Yanks.

Mucho kudos for using kN instead of kilogram force.

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Posted by Tubby Lunchbox on Friday, April 21, 2023 10:55 PM

Erik_Mag

FWIW, 521kN equals 117,000 lbf for us Yanks.

Mucho kudos for using kN instead of kilogram force.

Thanks! In wiki pages people are using MW for Loco HP, it's painful.

FWIW the BHP figures I quote are UIC standard, as in electricity output of all the alternators added up with their efficiency factor folded in. THP figures I quote are what the manufacturer says, GE in Austraila give an exact number, while Progress Rail everywhere seems to just subtract 200 from there BHP. I've seen a great video of a QES-3 panel in use in a 3000BHP GT26C-3 & it shows Main Generator amps & volts totalling 2825HP for the Traction Motors while in N8, so 175HP is lost to the rest of the Loco.

Tubby Lunchbox.

 

 

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Posted by Overmod on Saturday, April 22, 2023 10:10 AM

Tubby Lunchbox
Thanks! In wiki pages people are using MW for Loco HP, it's painful.

Speaking as an English user (and frequent mocker of SI shortcomings and contradictions) -- what's wrong with using MW as a metric equivalent of horsepower?  They're in nominally convertible units, and not very weird ones either -- use 750W for one HP as an approximation, that's only 4W out per horsepower.

Using horsepower instead of something like starting TE or continuous rating... and then metricizing that to KW... now that had better be newtons instead of kgf, even though I certainly used kilograms as a slot-in conversion for lb. drawbar pull in the past.  That is probably because I grew up interchangeably using, but knowing the difference, between lbw and lbf; did anyone actually use 'slugs' consistently in real work?

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Posted by Erik_Mag on Saturday, April 22, 2023 12:17 PM

One other weird imperial metric conversion is that 1 lbf of tractive effort at 1 MPH is equal to 1.99 watts. Another imperial meaurement, the foot, is 1.6% less than the distance light travels in one nanosecond in a vacuum.

The one annoying feature of using SI units for tractive effort with respect to grades is the need to use "g" to convert mass to weight. The equivalent annoyance with imperial units is converting weight to mass for tractive effort required for acceleration.

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