Why a generator

Ask a real train driver or fireman questions about how engines work, railways operate or anything else. If we do not know the answer, we will find out!
Post Reply
User avatar
allanroy
Posts: 286
Joined: 04 Jan 2009, 21:02
Location: Simon's Town

Why a generator

Post by allanroy »

On a recent trip on the Shosholoza Meyl I noticed that at the back of the train we had a generator coach. Now that would need to have diesel to power it. Why can the train not get its power from the overhead lines instead of the extra cost of the generators?
User avatar
Steve Appleton
Site Admin
Posts: 3605
Joined: 23 Jan 2007, 14:14
Location: Johannesburg, South Africa

Re: Why a generator

Post by Steve Appleton »

In SA, each passenger coach used to get its power individually from an axle-driven alternator or generator located under the vehicle. This fed a charger-regulator to charge a bank of expensive, heavy, deep-cycle batteries. The lights and a water pump were usually fed at low-voltage DC directly from the batteries. Small inverters were often fitted to provide low-power 220V AC to the shaver sockets. Later main-line coaches are equipped with hot water facilities and originally had an under-frame electric water heater fed from an AC alternator, also axle-driven (off the other bogie). Similarly, the air conditioning in dining and lounge cars was also powered from an axle-driven alternator.

Needless to say, this arrangement is expensive to maintain. A multitude of alternators and generators need regular servicing and the batteries deteriorate and have to be replaced at intervals (when not stolen). Centrally-supplied industry-standard 380V 50Hz AC 3-phase enables the use of industry-standard lighting and appliances, including ultimately air-conditioning throughout. Rovos Rail adopted that approach many years ago and this has recently been followed by PRASA. The question is how to produce that power.

Providing train power from the locomotive would be one solution. It's done in Europe. At present to my knowledge, no SA locos (electric or diesel) are equipped to supply any train power. Obviously there is no point in equipping those locos used for goods services. But, assuming some were equipped for passenger-train use, given the way locos are swopped and changed in SA there would be a good chance of a non-equipped loco being coupled-up and the train then becoming powerless.

In parts of Europe (Germany and Switzerland, I think), there are (or were) some restaurant cars that had a pantograph to draw power from the overhead. That is fine, so long as the train is always under catenary. What about SA where there are two different systems (actually given wire theft, 3 voltages: 3kVDC, 25kVAC and 0 volts!)? What when the train is on an non-electrified section hauled by diesels?

Theoretically 220V AC single-phase could be derived from an on-board transformer from the 25kVAC OH supply. However, 3-phase is better and, given the fact that the catenary voltage can vary significantly, this on-board supply would be more likely need to be derived from an expensive transformer-rectifier-inverter (effectively a UPS) system with batteries to bridge the gaps. Similarly, the 3kV OH would have to be electronically chopped and treated similarly (alternatively, a 3kVDC to 380VAC motor-alternator would have to be fitted).

Rather than going to all that trouble, a diesel 3-phase alternator is cheaper and easier to install. They need no transformers, inverters, chargers, etc. These machines are available off-the-shelf, are reliable, work continuously and even work where there is no OH traction supply! What could be simpler?
"To train or not to train, that is the question"
User avatar
allanroy
Posts: 286
Joined: 04 Jan 2009, 21:02
Location: Simon's Town

Re: Why a generator

Post by allanroy »

Steve thank you for such a wonderful reply. Did not reliase just how complex it can be.
User avatar
Steve Appleton
Site Admin
Posts: 3605
Joined: 23 Jan 2007, 14:14
Location: Johannesburg, South Africa

Re: Why a generator

Post by Steve Appleton »

Incidentally, Allan, FOTR has also replaced all the axle-driven generators and batteries in its fleet of 4M2 suburbans with 220V AC electric fluorescent lighting, fed through the train from a single 6 kVA diesel-driven alternator located under the frame of a "lounge" car which is normally placed near-centrally in the consist. Besides powering the lights, this generator also supplies power for a few other appliances, including a bar-fridge and hot-water urn in the lounge car.
"To train or not to train, that is the question"
Aidan McCarthy
Posts: 263
Joined: 13 Aug 2007, 15:44
Location: Boskruin

Re: Why a generator

Post by Aidan McCarthy »

Reefsteamers has also been using a generator to supply power to our trains for a long time. The wiring on the railway coaches was a mis-match of non-standard systems 24 V DC 110 V AC, etc. Much easier and cheaper to use off the shelf parts. We now have two generator coach now.
Aidan McCarthy

See more of my railway photos at http://mccarthyam.rrpicturearchives.net/
User avatar
Andreas Umnus
Posts: 479
Joined: 06 Jun 2008, 00:38
Location: Lingen (Ems), Germany

Re: Why a generator

Post by Andreas Umnus »

Steve Appleton wrote: In parts of Europe (Germany and Switzerland, I think), there are (or were) some restaurant cars that had a pantograph to draw power from the overhead. That is fine, so long as the train is always under catenary.
That is / was correct Steve.
But the pantograph was only in use when the train stopped in a station. When the train was on the run then the panthograph of the restaurant car was down.
Jacob Ossebaar
Posts: 15
Joined: 26 Aug 2012, 13:49

Re: Why a generator

Post by Jacob Ossebaar »

I would to explane ,the energie delivery on the Europe Railway system to the cariages .
Old systeem , heating by steam or electric by the engine from the pantograaf 1000 v-1500 v or 25 kV ; ventilation or lightning via alternator or battery .
New systeem , heating , charching battery delivery electricity 380/220 volt by transformation of the high voltage /380/220 volt , from the electricitiecabel from the engine pantograph .
The pantograph on the german/swiss restaurants are ONLY avelebel when the electricitycable from the engine are 0 volts ,and deliverd only the retaurant .
User avatar
Philip Martin
Posts: 102
Joined: 24 Aug 2014, 17:51
Location: Pennsylvania, USA

Re: Why a generator

Post by Philip Martin »

My impression of North American practice is that in the old days some railroads had axel generators and storage batteries on passenger cars; others had generators on the locomotives. Axel generators are a thing of the past over here now, i believe. When electric trains on the line I work for in New Jersey loose power now, as in a phase gap for instance, the lights and air conditioning go out, and the emergency lights come on.
The idea of a pantograph on a dining car surprises me. Some of our diners had or have diesel generators. I remember the diesel diners stinking up Penn Station in New York when I worked there fifty years ago.
I saw a photo of a European steam engine with a pantograph. It sounds like a joke, but the signal system on that road was actuated by the overhead wire.
User avatar
John Ashworth
Site Admin
Posts: 23606
Joined: 24 Jan 2007, 14:38
Location: Nairobi, Kenya
Contact:

Re: Why a generator

Post by John Ashworth »

Philip Martin wrote:I saw a photo of a European steam engine with a pantograph. It sounds like a joke, but the signal system on that road was actuated by the overhead wire.
See http://www.friendsoftherail.com/phpBB2/ ... =257&t=252, although this one is about power rather than signalling.
Image
Post Reply

Return to “Railway Operations - ask a question about how railways work..”