25 kV Single-phase

[Open Neutral]

So I'm in a discussion elsewhere re: Amtrak's 25 Hz/12KV system along the DC-NYC Northeast Corridor. It delivers ~65MW averaged over time, but has 350MW in generation/conversion capability. (An Acela train draws about 5MW/car.) The 25 Hz sources are a mix; some solid-state ones that I infer are 3phAC->DC->AC, some ancient but now newly rebuilt rotary ones (Lamokin Rotary Converters), some hydroelectric 25 Hz generation, and a cycloconverter at the DC end.

The 25 Hz is carried by a 138KV system overhead & stepped down at ~55 substations.

For decades, they have wanted to upgrade the c.1920s Pennsy system they inherited to 60Hz/25kV. North of NYC towards Boston, it is mostly that now, with some chunks of 60/12.5 as well.

For the northern leg, they have frequent "phase breaks" gaps in the catenary where it switches from one source to another to somewhat balance the situation. To move to 60Hz on the south of NYC trackage, they'd have to do likewise, a major project with lots of dollars and downtime.

But someone claims 25Kv single phase is frequently used in industry & it would be no problem for Amtrak to just buy same. If true, one can consider just feeding Amtrak 60Hz.

That's the first I've ever heard of such. Comments?

 

[zbang]

Oh, boy. This can be a can of worms. (I'm going from memory here, the books with the details are at home.)

Amtrak DC-NY is 25Hz 11kv, then there's a section of 60Hz 12.5kv, then 60Hz 25kv up to Boston. One of the transitions is at Hell Gate Bridge, can't recall where the other is. There's also the line to Harrisburg, which is also 25Hz.

The main problem with converting to 60Hz on the southern section is that all the controls, transformers, relays, impedance bonds, etc etc are built for 25Hz. Last study I read said that about the only reusable parts of the transmission system were the transmission lines. There's also the problem that no power company likes large single phase loads, this was an issue when designing the northern part electrification.


Industrial use-
Did you mean 25 Hz, not 25Kv? It was a common industrial frequency, and some large plants probably still generate their own for existing huge motors. IIRC Bethlehem Steel Sparrows Point was making their own 25Hz into the 1990's, for the old hot strip mill and the plate mill.
BTW, there are "phase" breaks in the southern section, too, but not as close as up north. Mostly they're block isolation, not separating different phases as we use that term.

Where are you reading about this? I'm curious.

(Trivia- the original New Haven RR electrification used three-phase wye connected.generation, with a grounded-B phase.)

 

[Open Neutral]

Oh, boy. This can be a can of worms. (I'm going from memory here, the books with the details are at home.)

Amtrak DC-NY is 25Hz 11kv, then there's a section of 60Hz 12.5kv, then 60Hz 25kv up to Boston. One of the transitions is at Hell Gate Bridge, can't recall where the other is. There's also the line to Harrisburg, which is also 25Hz.

It is a mess, but thanks to smart EE's {& retirement of antiques}, the revenue equipment is now multi-voltage/multi-frequency. The lower voltage may well be still used in some tunnels where clearance is tight.

The main problem with converting to 60Hz on the southern section is that all the controls, transformers, relays, impedance bonds, etc etc are built for 25Hz. Last study I read said that about the only reusable parts of the transmission system were the transmission lines.

I have to wonder why 100-odd 25Hz 5MVA transformers aren't usable at 60Hz. The other way around is sure to make smoke, but.... It could be they are to be scrapped merely for being a century old.

There's also the problem that no power company likes large single phase loads, this was an issue when designing the northern part electrification.

That was what I thought.

Industrial use-
Did you mean 25 Hz, not 25Kv? It was a common industrial frequency, and some large plants probably still generate their own for existing huge motors. IIRC Bethlehem Steel Sparrows Point was making their own 25Hz into the 1990's, for the old hot strip mill and the plate mill.

Another party was claiming 25Kv 50/60Hz single phase was common, 50 in EU, 60 here. I questioned that. He also claimed that the required standoff/insulator distance goes down with increasing frequency, but I can't recall that at all & am seeking cites. {I called my old power/machines prof last year on something else but it was obvious he was no longer fully with it, sigh....}

BTW, there are "phase" breaks in the southern section, too, but not as close as up north. Mostly they're block isolation, not separating different phases as we use that term.

My memory is one phase break near Perryvillle MD. Until you get to NYC area.

Where are you reading about this? I'm curious.

(Trivia- the original New Haven RR electrification used three-phase wye connected.generation, with a grounded-B phase.)

It's a discussion I'm in -- I'll date myself and say: Usenet. {most folks here won't have a clue...).

BTW, you might enjoy MY scheme for solving the issue.

1. Replace the existing scheme with on-board switcher supplies to take the cat voltage and provide ~2800VDC to power the VFD's in each prime mover. Saving: $$$ of copper in each.
   
2. Replace the fifty five odd 25Hz 12.5Kv substations with: 3ph in, 17KVDC out switcher supplies. More copper salvaged. You can bump up in voltage since with DC, RMS == peak. Higher voltage; lower losses.
   
3. Sub outputs will all be in parallel along the cat, as contemporary 750VDC transit systems third-rails are. Not only are each sub's POCO demand balanced across all three phases, but they won't go from zero to ~15MW and back to near zero 56 seconds later as the Acela goes through your sector.

You don't need a slew of phase breaks, as they did toward Boston. The switcher-fed rolling stock can also work on the northern 12.5/25KV AC as needed.

It's too audacious to get serious attention but is fun to ponder.