Small steam turbines as used on railway engines, how are they controlled?

[ericmark]

In the UK in the main railway tracks were fenced so steam engines did on often have lights as they would reduce the drivers vision in most cases to see a couple of miles ahead.

But the slower narrow gauge often restricted to 15 MPH and engines used in other countries often had steam turbines to run electric head lights. This one has a pair of head lights OK not a British engine, but picture taken near Welshpool in Wales, engine on loan.

So how is the output regulated? And what sort of speed control? From the whine it seems quite high speed, here is another example. this one Welsh Highland Railway.

 

[bernardgreen]

With variable mechanical speed the generator could control the output voltage ( or in some cases the output current ) by varying the current in the generator's field windings.

 

[ericmark]

With variable mechanical speed the generator could control the output voltage ( or in some cases the output current ) by varying the current in the generator's field windings.

I had considered that, however unlike the dynamo or alternator with a car or coach, the steam input could also be varied as likely a dynamo so speed does not matter, and the steam turbine only drives the one item, so not sure if steam input regulated, which is why I asked.

 

[bernardgreen]

I know on fairground showman's locomotives the speed of the generator was controlled by a bob weight governor controlling the steam valve. The very large flywheel smoothed out any transient fluctuations in the steam flow.

 

[SUNRAY]

I know on fairground showman's locomotives the speed of the generator was controlled by a bob weight governor controlling the steam valve. The very large flywheel smoothed out any transient fluctuations in the steam flow.

It also went a long way to preventing the engine stalling.

 

[big-all]

on older coaching stock you have axle mounted generators and batteries
trains in the uk until around the 80s have only ever had marker lights often just paraffin lamps similar to semaphore signals and others would be perhaps 15-90w depending on number off markers or if a head code box off 2 or 4 digits

 

[ericmark]

Coaches clearly need to have some sort of electrical regulation, one can't control the speed, however in the main coaches need to get to around 20 MPH for the dynamo to cut in, and since the legal limit on narrow gauge is 15 MPH this is a problem.

Also the whole reason for having narrow gauge is tight curves, so most coaches are on boogies, so not much room to mount a dynamo, I note lights built into carriages, but no dynamos, so I assume where they came from originally they were powered from the engine?

With this engine

The turbine is very visible, Zillertal was one of two U-Class 0-6-2T locomotives built in 1900 for the opening of the Zillertalbahn in Austria by Krauss & Co. The Zillertalbahn runs nearly 32km from the mainline at Jenbach to its terminus at Mayrhofen. The locomotive arrived in Wales on hire from the Zillertalbahn on 13th August 2019 and entered service on 30th August, so not designed for the Line. Joan and the Countess however were, but some of the original features are now missing, originally it went through the streets at Welshpool and had a bell as well as the whistle, which there is no sign of now, and today they do not run at night, so no need for lights.

Christmas Santa specials we use lead acid batteries for lights and these are recharged off the train with no way to charge them while running.

Away from railway generators I have worked on have been in the main AC, and the frequency was important, so the engine speed was fixed, but these I assume are DC so no frequency to worry about, so suppose it could be controlled by how much steam is supplied. I think Joan and Countess did have a steam turbine, but not where it can be so easy seen as with Zillertal.

 

[Jackrae]

Since the life of a tungsten filament lamp is highly dependent upon its supply voltage, might the loco lamps in question have been of the carbon-arc variety.

See : https://tonupboys.com/the-history-of-the-railway-locomotive-headlamp/

 

[ericmark]

After @Jackrae post I was able to find this PDF instruction set and it seems it was a permanent magnet AC generator and the speed governor was set using a special high frequency volt meter.

So it seems there was no electrical regulation, it was all done by the governor.

Not really what I expected, but does make sense.

 

[Jackrae]

After @Jackrae post I was able to find this PDF instruction set and it seems it was a permanent magnet AC generator and the speed governor was set using a special high frequency volt meter.

So it seems there was no electrical regulation, it was all done by the governor. View attachment 263116Not really what I expected, but does make sense.

That really comprehensive maintenance book was obviously written by someone who knew what they were on about - unlike some of today's efforts.