Why is it that when diesel trains don’t use electric pickup even though they could?

Question

If the trains are diesel/electric then surely they could have a pickup to collect electricity from the wire/third rail, where I live there is a railway line which for half of its way is diesel, but the other half is electric (it joins to an electric one) why doesn’t this train use both sources? (It’s the Uckfield – London Bridge Line). I have seen it on French, Dutch, German and Czech railways. Surely the cost of diesel is higher than electricity?

okay, I mean a train using diesel as a fuel EVEN THOUGH it is on a track with electrical pickup avaliable

and that the train is a diesel/electric one; so it uses electric current anyway, apparently the trains on the railway line near to me are "Turbostars"

Answer 1

could be a number of reasons for the diesels operating in diesel on an electric line. first question, how far does the train go OUTSIDE of electrified territory? it may be easier for the railroad to operate the diesel over the whole run, despite having access to wire/3rd rail part of the way. some diesel are equipped (at least here in the usa) with combination equipment, that is, they operate as pure diesel where there is no wire or 3rd rail, and once they get into electric territory, they can switch over and operate as an electric. the big reason for this is to cut down on engine emmissions in congested city areas.

Answer 2

Its using it because it doesn't have electric motors. The relatively small diesel engine drives the wheels though something similar to an automatic gearbox.

Diesel Electric starts to become unefficient under around 700hp.

There were experiments in hybrid locomotives in the 1960s - the problems were the small diesel engine wasn't really powerful enough for mainline use, there wasn't room to install anything bigger because of the electrical equipment and the diesel engine was dead weight when not in use. You can see one usually parked in the sidings at Woking

Turbostars are Diesel Hydraulic - They have a 450hp Mercedes Benz MTU engine driving the wheels through a Voith fluid drive, it is not possible to convert them to electic drive

Answer 3

It already be designed and has been since 1957... New Haven Railroad EMD FL-9's... Electric-Diesel-Electric units... EMD 567 diesel engine, and external 3rd Rail pick-up shoes to operate into Grand Central Terminal NYC. 60 units built (30 in 1957 30 in 1960)...some still in service for MN per CDOT equipment pool as straight diesel electrics, albeit with numerous rebuilds..

GE came out with the same design to replace the FL-9's in the early 1990's, called a P32AC-DM built on the Genesis frame... Same idea - main diesel-electric system powered by a diesel engine, and external 3rd rail pick-up...along with the system required to operate off 600vDC third rail..

LIRR has a newer one called the DM30AC (I think that is what its called)... again same premise...

Its a sound design, and works fine.. Original units, the FL-9's were made to eliminate the need for an engine change at New Haven where diesels from Boston were swapped for an electric motor to abide by pollution laws in NYC...

Before the NEC was fully electrified, Boston-New Haven had no overhead wires, though pre-WWI and depression plans existed to do it... The wires ran from New Haven-Park Avenue on the GCT route (and on the Hell Gate Bridge route to Washington DC) from 1907 on with the New Haven having the first stretch completed on the line then.. The HGB route branches from the GCT route at New Rochelle NY..

The FL-9's ran on diesel from Boston-Park Ave NY on GCT bound trains... there they shut down the prime mover (or idled it) dropped the third rail shoes, turned a switch or two and drew power from the 3rd rail... Simple as that from the engineers perspective... The third rail gear and electronics take up more space and add weight however.

As impractical as running diesels under wire may be, its not... Plenty of good reasons to do it and not having a diesel messing around with overhead pantographs for wires...

The New Haven, Penn Central, Conrail, Amtrak, LIRR, Metro North...etc... all used FL-9's this way and the last 3 I mention get along just fine now with P32AC-DM's... They can use both under-running (NYC) and over-running (LIRR) third rail and draw their propulsion and HEP current from there....

Answer 4

The man above is right on.

There is one drawback to electrification for freight operations, and that is the brute horsepower needed for heavy haul operations, primarily. We are talking serious current at medium high voltage. Extreme in any circumstance.

Now, consider the problems with transmission of this power. I am not talking about issues with overhead wires or third rails, but the physics involved with pushing this massive current greater and greater distances, while the fall-off in decibels increases exponentially. This means relay stations, and a lot of them.

It is much more economical, as well as practical, to carry your electricity around with you, hence, the diesel electric locomotive.

Way to go, Ace. The way I see it, you've got ten points coming your way.

Answer 5

In a single word, COMPLEXITY....
....a locomotive that runs off both diesel/electric and (external) electric power has to carry all the normal diesel/electric equipment, as well as a major portion of the equipment needed for a straight electric loco.
This adds significantly to it's aquisition cost, as well as to the cost, and complexity, of its maintenance.

Why does it need all that additional equipment?
A diesel/electric loco is throttled by governing the output of the diesel engine, while an electric loco must use invertors, "chopper" controls, tranformer tap changing, or a resistance bank to throttle its power.

In simpler terms, a diesel/electric is throttled at the engine, and it's electric generator simply passes all the power thru, while an electric loco must throttle in its "transmission".

Answer 6

Here in the US that would be impractical. Imagine laying an additional 10,000 miles of highly charged rail through cities, countryside, etc. Diesel is much cheaper to buy vs reto fitting an entire rail system. At least here, anyway.

Answer 7

The cost to run those wire thousands of miles is mind boggling

Answer 8

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