Railway Electrification
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In no way am I an expert here and I'll be interested if someone chimes in but historically, DC traction motors were used on railroads due to high starting torque requirement. The DC is generated by a diesel powered generator.
I believe but am not certain that as power semiconductor devices have improved, some of the new high speed passenger trains use AC (partly due to reduced torque reqmt's vs. freight trains) and essentially a VFD. I'm sure a quick web search would yield more details on the modern train propulsion systems.
I believe but am not certain that as power semiconductor devices have improved, some of the new high speed passenger trains use AC (partly due to reduced torque reqmt's vs. freight trains) and essentially a VFD. I'm sure a quick web search would yield more details on the modern train propulsion systems.
boboelectric
Senior Member
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- Eighty Four,Pa.15330
The transit system in Pittsburgh uses d.c. The can only have a circuit so many miles before they hand off to another substation.I guess d.c. is easier to control with the traction motors.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
With maybe a few exceptions, all local transit (trams, subways, etc) use between 600 and 800VDC. The control systems are easier and you can apply the line voltage directly to the motors. (BTW, I think the London Underground is the only system that uses a 4 rail system, with separate power and return rails.)
Virtually all currently operting long distance trains use AC, mostly 12-25kv at either 50 or 60 Hz. There are oddballs- in the US is Amtrak's Northeast Corridor is still 11kv 25Hz from WashDC to NYC and to Harrisburg PA, I think parts of SEPTA are, too, and there's at least one private coal hauler in the southwest that's 50KV. IIRC there are a few European systems at 16 2/3 Hz.
In the past there were also 1500 and 3KV DC systems, but AFAIK they've all been taken down long ago. Also, that some systems that were originally 25Hz have been converted to 60.
The next question is usually why 25Hz? When the systems were built, all before 1940, 25Hz was a common frequency for industrial use because the motor commutation was better at lower freqs (motor experts, please correct me), and most railroads generated their own power.
The Indian Railways Fan Club has a nice set of pages that describe their power distribution. http://www.irfca.org/docs/traction-schematics.html
Me? No, I'm not much of a train fan
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Virtually all currently operting long distance trains use AC, mostly 12-25kv at either 50 or 60 Hz. There are oddballs- in the US is Amtrak's Northeast Corridor is still 11kv 25Hz from WashDC to NYC and to Harrisburg PA, I think parts of SEPTA are, too, and there's at least one private coal hauler in the southwest that's 50KV. IIRC there are a few European systems at 16 2/3 Hz.
In the past there were also 1500 and 3KV DC systems, but AFAIK they've all been taken down long ago. Also, that some systems that were originally 25Hz have been converted to 60.
The next question is usually why 25Hz? When the systems were built, all before 1940, 25Hz was a common frequency for industrial use because the motor commutation was better at lower freqs (motor experts, please correct me), and most railroads generated their own power.
The Indian Railways Fan Club has a nice set of pages that describe their power distribution. http://www.irfca.org/docs/traction-schematics.html
Me? No, I'm not much of a train fan
.LawnGuyLandSparky
Senior Member
Zbang, Amtrak's catinaries are clearly marked 10-12 KV at 10,000 cycles here in NY.
The catenary at 10-12kV is fine. the 10,000 cycles - 10kHz though?
From the TGVweb.
RichB
Senior Member
- Location
- Tacoma, Wa
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- Electrician/Electrical Inspector
Used to work at a Loco rebuild facility--BNSF was just starting to use what we called ACMACs--they had AC traction motors--solved the motor-slip problem at start up some how--never got to work on one so I don't know how they did it.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Diesel-electric locomotives, until the last maybe 10 years, were always DC motors with a nominal 600v. There were all sorts of connections to match the speed & load. Once GTOs and IGBTs came along, builders started making AC drives. The motors are simpler and easier to maintain (no commutator), and they have much better controls, but they're also much more expensive due to those controls (think -really- big VFD that has to deal with vibration and crud). Some railroads use them only for specific purposes, like pulling coal trains.
Most transit now is AC motors with DC supply. AFAIK all 'high speed' trains are too.
The whole field of traction power and control, along with the signaling is fascinating. Some of the schemes seem mind-bogglingly complex until you look at what they have to deal with, like, say, AC track circuits with AC traction power.
Most transit now is AC motors with DC supply. AFAIK all 'high speed' trains are too.
The whole field of traction power and control, along with the signaling is fascinating. Some of the schemes seem mind-bogglingly complex until you look at what they have to deal with, like, say, AC track circuits with AC traction power.
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