New NY Dual Mode Discussion

Not saying it cant be done, but for Amtrak a couple of miles of third rail into and out of Penn, WHY??? Two control stands means twice the inspections as both would be counted as locomotives.Then you going to drag a power unit all the way to NFL for??? What if it has to go to TOR or MTR ??? Albany already has a hard time getting stuff fixed in a timely manner. If it were me and this well above my pay grade just put a pan on it and call it a day. Many years ago GE reps used to ride quite a bit when the dual modes were still relatively new and chatting with one he told me if GE had to do it again no third rail just a pan. AC voltage directly from the wire to the traction motors no giant AC to DC inverters.

If it were another company running service, or an agency without deep pockets, we would see a diesel up front and a third-rail (or AC) cab-equipped MU on the far end geared for 15 mph max under its own power. Not much, just enough to shove a train into NYP and pull it back out at walking speeds.

Railjunkie wrote: ↑Fri Jul 10, 2020 11:25 am Not saying it cant be done, but for Amtrak a couple of miles of third rail into and out of Penn, WHY??? Two control stands means twice the inspections as both would be counted as locomotives.Then you going to drag a power unit all the way to NFL for??? What if it has to go to TOR or MTR ??? Albany already has a hard time getting stuff fixed in a timely manner. If it were me and this well above my pay grade just put a pan on it and call it a day. Many years ago GE reps used to ride quite a bit when the dual modes were still relatively new and chatting with one he told me if GE had to do it again no third rail just a pan. AC voltage directly from the wire to the traction motors no giant AC to DC inverters.

The AC pan idea makes quite a lot of sense. I suggest the split-up two-unit method as an alternative to what's happening today and the continued determination to use third rail. I think that's perhaps because they can build enough between Amtrak and MN to make a larger order than just one carrier needs, which drives per-unit cost down.

Also, I can't say the "two control stands" argument has held much sway in the past. They have oodles of cab cars and cabbages laying around the system, ten more control stands cannot make or break the maintenance infrastructure.

Well... what's heavier? Diesel + third rail, or diesel + caternary?

STrRedWolf wrote: ↑Fri Jul 10, 2020 4:33 pm Well... what's heavier? Diesel + third rail, or diesel + catenary?

Latter. Take a look at the ALP45. Bulky and not high on fuel economy.

Early 1990's LIRR put together a train from some Japanese double decker cars and 2 of 3 on hand rebuilt and modernized FL9AC's. Ignoring how LIRR used one of the 3 as a parts source (meaning there were no spare locos if one of them died - which was frequent), there were some regular problems with the locos. At the top of the list were the inverters. Now I know it was 3rd rail, not cat, and I believe that while the 3rd rail power was DC, it had AC traction, hence the inverters. They frequently burnt out, supposedly because of inadequate ventilation. Metro North (using a variation of the same FL9AC's) would, once in a while, dole out a replacement inverter (they were very expensive). End result is that for many reasons, the 'BITANIC' was frequently out of service while awaiting parts. And with no backup loco, no way to deal with the problems. There were other issues. Dead storage batteries in the cars. Magnetic between car cable connections which didn't work well (eventually they were replaced by standardized connectors between cars. The locos where heavily computerized - described as bleeding edge.

IOTW, any way to avoid inverters sounds good.

Virtually everything is inverter driven these days , one way or the other. Even diesel locomtives. I'd say the problem is in the small batch and trying to mix and match , Once set up right they are very reliable.

R36 Combine Coach wrote: ↑Fri Jul 10, 2020 4:51 pm

STrRedWolf wrote: ↑Fri Jul 10, 2020 4:33 pm Well... what's heavier? Diesel + third rail, or diesel + catenary?

Latter. Take a look at the ALP45. Bulky and not high on fuel economy.

If you aren’t concerned with having a high-powered AC unit and mid-powered diesel like the ALP-45DP, but are content with the same or less power from the AC half, I bet you could make a much lighter dual-mode diesel/cat locomotive. Maybe the AC part would be light & compact enough to use the same prime mover with a half-size fuel tank.

David Benton wrote:Virtually everything is inverter driven these days , one way or the other. Even diesel locomtives. I'd say the problem is in the small batch and trying to mix and match , Once set up right they are very reliable.

Exactly. The FL9AC was the problem (the follow-on DM30AC isn’t great either), while the inverter-equipped GE P32ACDM has been pretty reliable until heavy use & age began taking its toll.

David is correct, plus you have thirty years of inverter development to count on. We use inverters in cranes every day and the difference from 1990 and 2020 is leaps and bounds. What was once the size of a refrigerator can now be the size of a shoebox.

Tadman wrote: ↑Fri Jul 10, 2020 8:02 pm David is correct, plus you have thirty years of inverter development to count on. We use inverters in cranes every day and the difference from 1990 and 2020 is leaps and bounds. What was once the size of a refrigerator can now be the size of a shoebox.

If you're doing Diesel AC, AC Catenary (NEC), and AC motive bogies, it makes sense to keep it all AC as much as possible. The whole system is kept simple. The only issue you'd have is the need for a frequency converter if the system is 60 Hz AC and you're pulling 25 Hz power. But if anything's DC, you'll need a rectifier and inverter.

That said, I bet that shoebox will shrink further. I don't know if the latest tech using gallium nitride (GaN) is what gets it down to shoebox size, or if it will let it go even smaller.

It doesn’t work quite like that, as far as I know anyway. I think the current standard is to take the high-voltage single-phase AC from either the traction alternator or catenary, rectify it into very-high-voltage DC, then invert & chop it into multi-phase AC which powers the motors (and is throttled via frequency modulation.) That is, the supply frequency and not the voltage or amperage dictates the motor speed - if the system is 60 Hz, the motor would only run at 3600 rpm (or would stall if not supplied with enough voltage or amperage.) Same with 25 Hz, the motor would only rotate at 1500 rpm.

I don’t know of a way to directly convert single-phase fixed-frequency AC to multi-phase variable-frequency AC without an intermediate DC step.

mtuandrew wrote: ↑Fri Jul 10, 2020 10:43 pm It doesn’t work quite like that, as far as I know anyway. I think the current standard is to take the high-voltage single-phase AC from either the traction alternator or catenary, rectify it into very-high-voltage DC, then invert & chop it into multi-phase AC which powers the motors (and is throttled via frequency modulation.) That is, the supply frequency and not the voltage or amperage dictates the motor speed - if the system is 60 Hz, the motor would only run at 3600 rpm (or would stall if not supplied with enough voltage or amperage.) Same with 25 Hz, the motor would only rotate at 1500 rpm.

I don’t know of a way to directly convert single-phase fixed-frequency AC to multi-phase variable-frequency AC without an intermediate DC step.

Wow, I was in the process of making a post about this exact thing! You beat me to it by three minutes.

Yes, there is no such thing as "keeping it all AC". This thread has some description of the intermediate DC link as implemented in the ACS-64. http://cs.trains.com/trn/f/743/t/217694.aspx

Also, as far as the FL9AC, don't forget that they used very early GTO thyristor based inverters, which were far less reliable than modern IGBT transistor based inverters. Only a select few thyristor AC traction passenger locomotives ended up being at all successful in the U.S., mainly the P32ACDM and original ALP-46 order.

Amtrak706 wrote: ↑Fri Jul 10, 2020 10:52 pmWow, I was in the process of making a post about this exact thing! You beat me to it by three minutes.

Yes, there is no such thing as "keeping it all AC". This thread has some description of the intermediate DC link as implemented in the ACS-64. http://cs.trains.com/trn/f/743/t/217694.aspx

Also, as far as the FL9AC, don't forget that they used very early GTO thyristor based inverters, which were far less reliable than modern IGBT transistor based inverters. Only a select few thyristor AC traction passenger locomotives ended up being at all successful in the U.S., mainly the P32ACDM and original ALP-46 order.

Thanks for confirming I got it right!

Is the AEM-7AC thyristor-based too?

mtuandrew wrote:

Amtrak706 wrote: ↑Fri Jul 10, 2020 10:52 pmWow, I was in the process of making a post about this exact thing! You beat me to it by three minutes.

Yes, there is no such thing as "keeping it all AC". This thread has some description of the intermediate DC link as implemented in the ACS-64. http://cs.trains.com/trn/f/743/t/217694.aspx

Also, as far as the FL9AC, don't forget that they used very early GTO thyristor based inverters, which were far less reliable than modern IGBT transistor based inverters. Only a select few thyristor AC traction passenger locomotives ended up being at all successful in the U.S., mainly the P32ACDM and original ALP-46 order.

Thanks for confirming I got it right!

Is the AEM-7AC thyristor-based too?

Nope, it is IGBT. I've been told it was actually the first locomotive with IGBT inverters for traction in the world.

Amtrak706 wrote: ↑Fri Jul 10, 2020 10:52 pm

mtuandrew wrote: ↑Fri Jul 10, 2020 10:43 pm It doesn’t work quite like that, as far as I know anyway. I think the current standard is to take the high-voltage single-phase AC from either the traction alternator or catenary, rectify it into very-high-voltage DC, then invert & chop it into multi-phase AC which powers the motors (and is throttled via frequency modulation.) That is, the supply frequency and not the voltage or amperage dictates the motor speed - if the system is 60 Hz, the motor would only run at 3600 rpm (or would stall if not supplied with enough voltage or amperage.) Same with 25 Hz, the motor would only rotate at 1500 rpm.

I don’t know of a way to directly convert single-phase fixed-frequency AC to multi-phase variable-frequency AC without an intermediate DC step.

Wow, I was in the process of making a post about this exact thing! You beat me to it by three minutes.

Yes, there is no such thing as "keeping it all AC". This thread has some description of the intermediate DC link as implemented in the ACS-64. http://cs.trains.com/trn/f/743/t/217694.aspx

Also, as far as the FL9AC, don't forget that they used very early GTO thyristor based inverters, which were far less reliable than modern IGBT transistor based inverters. Only a select few thyristor AC traction passenger locomotives ended up being at all successful in the U.S., mainly the P32ACDM and original ALP-46 order.

This is all correct. To oversimplify, you can't just feed AC out of the catenary into the traction motors, you have to control it (to control speed and pulling). With industrial voltage, you can't just feed it through a switch or rheostat like they once did. (this was a thing - early streetcars and cranes had the line voltage go right through the operator control - DANGEROUS!!)

The inverters take the line AC, translate it to the different AC that the motors require, and meter it out to control the motor power and vehicle speed.