Electrification costs 600v DC vs 25 kV AC

Does anyone have info on the cost per mile of 600V DC third rail vs 25kV AC catenary?

I can't comment on the costs other than to say for a long stretch of track the cost of DC would climb significantly. DC does not travel well. There would need to be a large high-voltage AC infrastructure with multiple converter sites to put DC on the third rail.

The advantage of 600V DC over 25kV AC is that the 600V lines can be closer to just about anything than the 25kV lines, but the disadvantages are twofold: more expensive per mile than 25kV and lower maximum operating speed ("161 km/h (100 mph) is considered the upper limit of practical third-rail operation" per Wikipedia. However, if building a primarily underground system, the savings of a smaller tunnel bore (using 600V DC) may be greater than the difference in costs between 600V DC and 25kV AC.

Although I can find estimated costs per track mile of $4.8 million per mile in Los Angeles in 2012 for 25kV AC, and $18 million per mile in Long Island in maybe 2022 for 600V DC (I don't know if LIRR estimate includes other capital costs), I can't find any more generalized comparisons.

There is a reason that electric utilities use high Voltages to transport power over longer distances, up to 765,000 Volts AC. The higher the Voltage, the lower the resistance line losses, hence greater efficiency and less wasted energy. Because of resistance losses, the conductors for lower Voltages must be very large diameter, hence much more costly including support structures, to carry the same amount of energy as higher Voltage lines.

Everyone - It would be interesting to get a direct comparison between 25 KV AC and 600/700 volt DC per mile...

LIRR third rail electrified routes ON Long Island require a substation every 2-3 miles - and most importantly a substation near any railroad station - trains draw the most current/amperage starting up from a station...
Higher voltage AC needs far fewer substations - If I am correct 11 KV AC requires a substation 10-15 miles apart - and 25 KV AC less than that...

Some of the best examples for comparison can be found in the UK specifically the southeastern area...
If anyone is unaware the London area has the largest third rail electrification known - and there are many routes in the UK that are electrified with 25 KV AC such as the East Coast and West Coast Main Lines...

The UK has some MU car classes that are dual mode AC with pantograph(s) and DC with third rail shoes...
These car types serve lines that run predominately north and south through London - overhead wire north, third rail south...There are also some London Overground rail routes using dual-mode MU cars...

One of the world's busiest rail stations - Clapham Junction (just south of London) - is (almost) entirely served by third rail MU trains - the exception is some DMU trains - Southwestern Rail is the largest train operator there...
MACTRAXX

MACTRAXX wrote: ↑Mon Jul 18, 2022 7:28 pm The UK has some MU car classes that are dual mode with AC pantograph(s) and DC third rail shoes.
There are also some London Overground rail routes using dual-mode MU cars.

The only "Dual-Mode" AC/DC electrics in North America are the MNCR/ConnDOT M-8s (and the M-2/M-4/M-6 and New Haven MUs before them). They can also run straight DC, even up to Croton and White Plains from time to time.

As you can gather, most of the time 600v DC is used for subways and their ilk as third rail power, VS 25 kV AC used in caternary power for electric trains.

Also many light rail installations use 600 - 1200 volts OCS. That may be because the danger of higher voltage in most locations not isolated from the public.

Thank you all on the AC/DC primer. I am really just looking for cost comparison s

It looks like you have a job assignment. This page is an enormous font of information , but would hardly count as a source for comparing installed costs of the two systems. Even among the individual systems, the price difference between NY and CA are radically different.

I think you can safely assume the cost of 3rd rail is the same as catenary, except for the cost of the catenary itself, PLUS the cost of stepdowns/converters every few miles and the cost of the installed rail itself.

I'd think third rail will always work out to be cheaper to install and maintain over time. It's not prone to ice or storm damage, plus the material used (steel rail) is something already procured in large volumes. Lifespan of the wear wire is 15-20 years, while rail can last 100+ years... Only downside is the limits it places on speeds.

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Costs vary by the number of trains operation at the same time, tension on the w8res, length of train line, etc. As a general rule, it takes around 1000 volts ac to push electrons a mile. So in theory, one 25kV power station could reach out 25 miles in both directions, or a total of 50 miles of track. At best, 600 Vdc may reach out 1 mile, or a track distance of 2 miles when another power feed is required. Other parameters can change the general rule of thumb, like the frequency (Hertz) of the ac line.

electricron wrote: ↑Sun Aug 07, 2022 5:00 am As a general rule, it takes around 1000 volts ac to push electrons a mile. So in theory, one 25kV power station could reach out 25 miles in both directions, or a total of 50 miles of track.

Excellent point. Which is why USA electric utility companies' major backbone transmission systems are at 500,000 to 765,000 Volts nominal. Also, at the retail customer level, in significant part the reason for house wiring nominal Voltages changing from years ago 220/110 Volts to present day 240/120 Volt nominal.