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Old 13th January 2017, 22:07   #331
Sunbird24
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Quote:
Originally Posted by captainbigun View Post
An AC generator? You mean alternator, which is brushless....
I copied the manufacturers data from here http://www.newag.pl/wp-content/uploa...MOTIVE-6Dg.pdf
Maybe a failure of their translations but quite a few countries do use the term AC generator and I worked for an American company for many years so picked up a lot of their terminology.
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Old 14th January 2017, 01:33   #332
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It should be noted that some early electric and diesel electric locomotives (especially the early AC stuff on Southern) used repulsion motors instead of brushed DC motors.
That would mean you would have an alternator coupled to the motor field windings and the brushes would only carry low voltage armature current - with the attendant reduction in sparking and brush attrition.

Repulsion Motors are also rather easy to control, and you can do the drivetrain without rectifiers, which was important before they existed and your only real alternative was the universal motor - however they have serious problems attempting to do dynamic braking, it can get a bit hairy as the voltage across the alternator climbs rather alarmingly.

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Old 15th January 2017, 17:06   #333
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Several 88s in the yard this afternoon (15-Jan) including 3, 4, 8 & 10. Also a low loader tractor unit, so maybe the low-loader is inside to have a locomotive lifted onto it.
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Old 15th January 2017, 22:32   #334
ac6000cw
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The thermal efficiency of diesel engines is irrelevant to a discussion of the relative haulage capabilities of diesel locos i.e. how heavy a train they can start/accelerate/maintain a given speed with. The engine power ratings are normally power at the crankshaft i.e. where the alternator/generator is attached - if the engine is less thermally efficient it just means it burns more fuel to produce the same power into the traction system.

The video below is quite a good demonstration of the relatively small amount of power needed to start a train on a 2% gradient, versus that needed to keep the train moving at a reasonable speed on it. The locos are probably in power notch 1 or 2 (out of 8) when starting, then slowly notched up to full power by about 2 minutes into the video - there is a bit of wheelslip being corrected in the middle part, you can hear the engine note varying. The lead loco is a DC-drive EMD.

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