IMHO the solution should be a long term operation. One way would be to gradually remove the 25 Hz equipment in a section at a time with new 60 Hz equipment. Move the 25 Hz equipment that still has some life left to in service 25 Hz locations that needs replacing. That way no new 25 Hz equipment would be bought ? Maybe even some given to SEPTA ?
consideration would be needed to convert those lines where all in service rolling equipment can use 60 Hz.
1. The primary generators for 25 Hz is at Safe Harbor with the transmission lines from there to Harrisburg, Perryville, and Atglen ( on to Trenton & PH). That may be the last section feeds to be converted.
2. Newark - Trenton is going to be the first to get a rebuilt constant tension CAT by 2017 so maybe that line along with continuing to NYP & Sunnyside might be first especially since the voltage would go from 12.0 Kv to 12.5Kv. That would give a silght increase of power capability carried by the CAT for the higher speeds that have already been tested. AMTRAK also want to abandon the 25 Hz primary that runs along the PRR old Trenton cutoff.
3. Harrisburg - ATGLEN might be another shorter segment
4. Perryville - WASH might be a good segment as all MARC electric can use 60 Hz either 12.5 Kv or 25 Kv.
Don,
I am not entirely unfamiliar with the difference between alternating current and direct current as they are applied to motors. However, in April of 2010 Don Graab wrote an essay for Trains. He argued that asynchronous motors produced high torque at low speeds and were particularly valuable for pulling long heavy trains. However, at high speeds there was little or no advantage and, since the electronics were more expensive, many freight railroads used DC motors for that job. Of course technology can change fast these days so what was true 2 1/2 years ago may no longer be true today.
Here is a link to the essay: http://trn.trains.com/en/Railroad%20Reference/Locomotive%20Profiles/2010/04/AC%20traction%20a%20motive%20power%20bosss%20perspective.aspx
John WR But Dave, don't asynchronous motors have a drawback in that the electronics needed to convert AC to DC and then back to AC again requires a certain amount of maintenance that a single conversion to DC with series wound DC motors does not need?
But Dave, don't asynchronous motors have a drawback in that the electronics needed to convert AC to DC and then back to AC again requires a certain amount of maintenance that a single conversion to DC with series wound DC motors does not need?
With the AC to DC machine, you need to control the voltage to control the power and speed. This was typically done with tap switches on the transformer - so you have lots of high power switch gear and a control system to operate it. With the AC-DC-AC machine, the DC buss is maintained at a constant voltage and it's chopped back into variable frequency AC by inverters. Much less mechanical machinery involved.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Meanwhile another nor'easter is predicted for the middle of next week although it is not predicted to be as strong or cold as the last one. It could cause problems over Thanksgiving.
Wed. Nov 14th AMtrak news release with co sponsor NJT, says they feel the Kearny Substation will be online and in service on Friday...this will increase catanary power as well as signal and switch power. Therefor there can be an increase in the number of trains being handled on both the Corridor and trhough the East river tunnels to Sunnyside Yard. No new schedules posted...but MNRR is complete, LIRR is busing the Long Beach Branch and east of Riverhead and still modified schedules (reduced services) on most lines, especially east to Montauk., NJT has modified (reduced) schedules on all lines except the NJCL which is hoped to have some kind of service by this weekend..
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The inverters and their controls are electronic devices that require the sort of maintenance that a high quality stereo or tv set requires. The DC motors running off an ac catenary required tap-changing transformer contactors or the same sort of electronic control on the voltage output of the rectifier system that the inverter control requires. So there is absolutely no cost advantage in maintenance for dc motors over ac regarding the control system and considerable maintenance saving for the motors.
The inverters usually don't require much maintenance beyond keeping the cooling system working. There is nothing mechanical to wear out, where DC series motors have commutators and brushes that wear. An AC induction or synchronous motor is typically cheaper for a given power output than a DC motor as well as being smaller, lighter and more rugged. We may soon see DC motors as an extra cost option on locomotives as opposed to being a lower cost option.
- Erik
I'll leqve it to Dave Phelps to answer the above question accurately, but my understanding is that the new M-8's cannot run on 25Hz, because in design it was decided that the transformers would occupy too much space and be too heavy. They can, I believe, switch automatically between 12,500 and 25,000 volts.
But a major correction to an earlier posting is required. The first big step in chaning ac locomotives was moving to rectivication and using pure dc motors instead of 25Hz (or 16.5Hz in Europe) ac commutator motors. Thus the "Jets" (NYNH&H EP-5's), the Virginian and PRR post-WWII electric freight locomotives, the Washboards (4400's), and the early Silveliners, possibly up to Silverliner-4's. But now all modern electric railway equipment, from streetcars to European freight electrics have a development paralleling that of the most efficient diesels, and use ac non-synchronis, slanted bar (as opposed to the bars in squirel-cage) hysterisis motors. As on ac diesels, this eliminates brushes and commutators and their wear. The ac is rectified to dc, then converted back to ac at the Hz corresponding to the speed of the motor plus slippage. The M-8's use such motors and so do the latest Silverliners, and of course Acela and Bombardie Amtrak locomotives, the NJT dual-modes, etc. Some of the Amtrak Swedish Meatballs or Toasters have been converted. Indeed, Metro North and LIRR even had some FL-9's upgraded with such motors!
Phelps Now, again as someone pointed out, the changeover on the EMUs is made, if necessary, by manually cranking the changeover shaft from one position to the other (the power contacts are inside the transformer tank). The "M-(even number)" series cars on MN (ex NH lines) have a 60 Hz-rated transformer that is designed not to saturate at 25 Hz, but only one primary winding, so they can't operate at 25 kV. The exception is the newest, the M-8s, which are dual voltage. Dave Phelps
Now, again as someone pointed out, the changeover on the EMUs is made, if necessary, by manually cranking the changeover shaft from one position to the other (the power contacts are inside the transformer tank).
The "M-(even number)" series cars on MN (ex NH lines) have a 60 Hz-rated transformer that is designed not to saturate at 25 Hz, but only one primary winding, so they can't operate at 25 kV. The exception is the newest, the M-8s, which are dual voltage.
Dave Phelps
Dave; thanks for the info. a few questions about the silverliner - IVs / arrow - IIs since they were specified somewhat earlier than the -Vs.
1. where do the outputs of the transformer go ? Rectifiers or do some go directly to auxilaries ?
2. type traction motors ?
a. any difference in acceleration?
3. did lighting look different on the different frequencies ?
4. NOTE; All AMTRAK reports etc now specify the 25 Hz as 12.0 Kv.
5. There has been some debate whether the M-8s could operate on 25 Hz but you suggest they could ?
6. Of course the M-8s can also operate on the under running DC out of grand central terminal.
7. if the earlier Ms are not retired first could they be retrofited for dual voltage ?
Lots of people have very nicely given the theory and history of the use of 25 Hz; I don't need to repeat it. However, discussion of SEPTA (and to some extent NJT) seems to overlook a bit of history that, as it happens, I personally participated in.
At the time the cars that became the Siverliner IVs and Jersey Arrow IIs were being specified, there were firm plans to convert the former Reading lines to 25 Kv, 60 Hz, and the eventual use of 12.5 kV, 60 Hz in various places was pretty well established. Accordingly, the specifications required that those two fleets be capable of operating on any of the three possible combinations - (then) 11 kV, 25 Hz, 12.5 kV 60 Hz, and 25 kV, 60 Hz. Those Silverliners that were to run on the (converted) Reading lines had to have "on the fly" changeover capability. The main transformers were designed with two primary windings, to be connected in parallel at the lower voltages and in series for the higher voltage. The greater losses at 60 Hz were compensated for by the higher nominal voltage (the change to higher nominal at 25 Hz came later, as one commenter pointed out).
By the time the cars were actually delivered, the plans to make the Reading 25 kV had fallen through, but GE did develop and test on one car the automatic changeover system. Yours truly, together with one other GE engineer, received a patent for the system (which has long expired; the system now in use on the NEC works generally the same way as the GE system, with some refinements made possible by the evolution of technology since the early '70s). Now, again as someone pointed out, the changeover on the EMUs is made, if necessary, by manually cranking the changeover shaft from one position to the other (the power contacts are inside the transformer tank).
The folks who explained the history of 25 Hz did a great job, by the way, thanks!
Not really a typo, Mike, but when I said Amtrak electrified the line in the 1960's I guess I was confused. Amtrak did not even exist in the 1960's. I went back and changed my original statement. Thanks for pointing out this error.
TIMZ, I presume you are talking MidTown Direct. Which, yes, are locomotive driven, or push pull, trains. BUT, trains from Matawan and South Amboy can be either push pull or EMU as all trains from Trenton. BUT ALSO, there are several EMU sets on the Hoboken Division (normally) for runs Hoboken to Montclair, Summit, Gladstone and Dover but not for Mid Town Direct Service.
Which is why NJT doesn't use EMUs on those trains.
MidlandMike I'm guessing the equipment can handle 60 Hz, but the EMUs might have problems with the on-route voltage change from 12.5 Kv to 25 Kv. I believe NJT has a similar problem on the North Jersey Coast line
I'm guessing the equipment can handle 60 Hz, but the EMUs might have problems with the on-route voltage change from 12.5 Kv to 25 Kv. I believe NJT has a similar problem on the North Jersey Coast line
NJT has to change power from Morristown/Montclair line trains at Kearny Jct to the Corridor and at Matawan on the NJCL to Long Branch..
henry6 MidlandMike blue streak 1 MidlandMike I get the impression Amtrak would like to upgrade the entire system to 60 Hz to avoid future problems like this emergency compatibility, but (according to another railfan forum) SEPTA is the final holdout. SEPTA may / should not be a big problem as the silverliner - 5s are being built to work on both 25 and 60 Hz... SEPTA might not object to ATK modernizing the lines they both run on, however, wouldn't SEPTA also have to modernize their own suburban lines as all the operations are integrated? But SEPTA Rail already has integrated their electric operations so all equipment seems to run on former PRR and former RDG tracks.
MidlandMike blue streak 1 MidlandMike I get the impression Amtrak would like to upgrade the entire system to 60 Hz to avoid future problems like this emergency compatibility, but (according to another railfan forum) SEPTA is the final holdout. SEPTA may / should not be a big problem as the silverliner - 5s are being built to work on both 25 and 60 Hz... SEPTA might not object to ATK modernizing the lines they both run on, however, wouldn't SEPTA also have to modernize their own suburban lines as all the operations are integrated?
blue streak 1 MidlandMike I get the impression Amtrak would like to upgrade the entire system to 60 Hz to avoid future problems like this emergency compatibility, but (according to another railfan forum) SEPTA is the final holdout. SEPTA may / should not be a big problem as the silverliner - 5s are being built to work on both 25 and 60 Hz...
MidlandMike I get the impression Amtrak would like to upgrade the entire system to 60 Hz to avoid future problems like this emergency compatibility, but (according to another railfan forum) SEPTA is the final holdout.
I get the impression Amtrak would like to upgrade the entire system to 60 Hz to avoid future problems like this emergency compatibility, but (according to another railfan forum) SEPTA is the final holdout.
SEPTA may / should not be a big problem as the silverliner - 5s are being built to work on both 25 and 60 Hz...
SEPTA might not object to ATK modernizing the lines they both run on, however, wouldn't SEPTA also have to modernize their own suburban lines as all the operations are integrated?
But SEPTA Rail already has integrated their electric operations so all equipment seems to run on former PRR and former RDG tracks.
MidlandMike John WR ... But in the 1960's when Amtrak electrified the line between New Haven and Boston ... I'm not sure if this was a typo, the line was converted in the late 1990s. The following link has a review of early RR electrification supply systems, recent electric system conversions, and some thoughts for the future: http://www.ltrc.lsu.edu/TRB_82/TRB2003-001318.pdf
John WR ... But in the 1960's when Amtrak electrified the line between New Haven and Boston ...
...
But in the 1960's when Amtrak electrified the line between New Haven and Boston ...
I'm not sure if this was a typo, the line was converted in the late 1990s. The following link has a review of early RR electrification supply systems, recent electric system conversions, and some thoughts for the future:
http://www.ltrc.lsu.edu/TRB_82/TRB2003-001318.pdf
activated
John WR Thanks for your explanations, Erik. If I understand you correctly the Pennsylvania choose 25 Hz because it was available at the time and needed only a step down transformer to directly power it traction motors. At 60 Hz back emf is a real problem but at 25 Hz it is not. DC was rejected because of the expense involved in converting AC to DC. But in the 1960's when Amtrak electrified the line between New Haven and Boston solid state electronics made it much easer and cheaper to convert AC to DC. In fact the conversion could be done on board the train itself. And a 25 Hz motor may be run on DC. At the same time 60 Hz uses much smaller transformers and is converted to DC as easily as 25 Hz is. So Amtrak chose 60 Hz at high voltage and step it down and convert it to DC on the train to run DC motors. The reason Amtrak has not converted to 60 Hz and DC motors south of New Haven is because opponents in the Congress will not grant Amtrak the funds it needs to modernize.
Thanks for your explanations, Erik. If I understand you correctly the Pennsylvania choose 25 Hz because it was available at the time and needed only a step down transformer to directly power it traction motors. At 60 Hz back emf is a real problem but at 25 Hz it is not. DC was rejected because of the expense involved in converting AC to DC.
But in the 1960's when Amtrak electrified the line between New Haven and Boston solid state electronics made it much easer and cheaper to convert AC to DC. In fact the conversion could be done on board the train itself. And a 25 Hz motor may be run on DC. At the same time 60 Hz uses much smaller transformers and is converted to DC as easily as 25 Hz is. So Amtrak chose 60 Hz at high voltage and step it down and convert it to DC on the train to run DC motors.
The reason Amtrak has not converted to 60 Hz and DC motors south of New Haven is because opponents in the Congress will not grant Amtrak the funds it needs to modernize.
Blue Streak,
Phase balancing is most definitely an issue with commercial frequency electrifications. A couple of things come to mind, the first having different sections of the track connected to different phases, and the second being that electrification loads would be a relatively small portion of the total utility load.
I would guess that power factor would be an issue as well, though switchable capacitors should be able to take care of reactive power problems. Most of the wiring diagrams for rectifier locomotives show use of a smoothing reactor (choke input filtering), so the line current will look more like square waves than the spiky current typical of capacitor input filtering. I wouldn't be surprised to see power factor correction applied to locomotives - note that this is to keep the line current a close approximation to a sine wave in phase with the voltage - might even be simplest using an IGBT H-bridge for for handling power transfer between the AC on the catenary and the DC bus on the locomotive.
It's getting uncomfortably close to 40 years since I took power systems, electrical machinery and power electronics courses at Cal and there have been a LOT of new devices that have come down the road since then (e.g. IGBT's, SiC diodes and SiC MOSFET's).
But in the late 1990's (or early 2000's) when Amtrak electrified the line between New Haven and Boston solid state electronics made it much easer and cheaper to convert AC to DC. In fact the conversion could be done on board the train itself. And a 25 Hz motor may be run on DC. At the same time 60 Hz uses much smaller transformers and is converted to DC as easily as 25 Hz is. So Amtrak chose 60 Hz at high voltage and step it down and convert it to DC on the train to run DC motors.
Eric; reallly appreciate the primer. It has been way too long from my electrical courses to remember all of this and many of the advances and revelations that now are commonplace today were not even conceived.
One item you may want to address as there is much confusion among our posters and myself is how phase balancing is accomplished from the 3 phase grid to a single phase CAT and return thru regeneration. That definitely was not covered in my courses as there seemed to be no need ?
also are there any power factor problems with large installations of electric traction? Power factor problems seem to have disappeared from residential areas in this country.
My first thought was "Why would anyone want to build a brand new locomotive or MU car with AC motors running solely at line frequency?". An AC series motor is inferior to a DC series motor and the rectifiers for the DC motor would be less than the costs differential between the AC and DC motors. A single phase induction motor doesn't make any sense as a traction motor with fixed speed and torque pulsations - it would make a bit more sense to us a phase converter to produce three phase for the traction motors. Fixed frequency synchronous motors don't make any sense - the wheel diameters would have to be kept within a small fraction of an inch - and this would apply to any locomotives running in MU. Using a variable voltage, variable frequency drive makes a lot more sense for an induction motor and is the only practical way of using a synchronous motor.
There are a few advantages to running at 25 Hz or less. One is that circuit breakers will work better as there is more time for the arc to clear around the zero crossing point for the current. Flashovers may be more likely to self-clear for similar reasons. Another advantage is that skin effect is less of an issue, which is particularly important for the track return as the skin effect is far more pronounced in the rails than in the catenary (rails are ferromagnetic). The final advantage is that phase loading on the grid will be better balanced.
There are a couple of corresponding advantages to using 50/60 Hz. The first is that the only conversion equipment needed is a transformer - just hook it up to the grid and go... The second is that the transformer will be smaller, lighter and cheaper compared to 16 2/3 or 25 Hz.
So if you were building a new electric RR today, powered by AC catenary, and for some reason you wanted the locomotives and cars to use AC motors-- constant-frequency-AC motors, not variable-freq powered by inverters powered by DC-- you would still use 25 Hz or less?
John WR Thanks for the detailed explanation of why the railroads stuck to 25 Hz for AC motors instead of just using 60 Hz. However, no good deed shall go unpunished so please accept a couple of questions. 1. Why is a lower electric frequency (i.e. 25 Hz) more suited to powerful motors than a higher one? 2. You say that 25 Hz was used up to the 50's. Were new technologies developed at that time to allow the use of 60 Hz?
Thanks for the detailed explanation of why the railroads stuck to 25 Hz for AC motors instead of just using 60 Hz. However, no good deed shall go unpunished so please accept a couple of questions.
1. Why is a lower electric frequency (i.e. 25 Hz) more suited to powerful motors than a higher one?
2. You say that 25 Hz was used up to the 50's. Were new technologies developed at that time to allow the use of 60 Hz?
Answer to #1:
A couple of reasons. The inductive reactance of the field and armature windings becomes a significant part of the overall voltage drop across the motor - in an ideal series motor, the voltage drop is solely due to "back EMF". This is why my uncle's razor ran faster on DC than AC. The more serious reason has to do with commutation. On a DC series motor, the interpole compensates for armature reaction and thus allows the motor to be operated at a wide range of currents without having to adjust the brush position. An an AC series motor, the interpole does a poorer job of compensating for the combined effects of armature reaction and inductive reactance - where the inductive reactance increases with frequency.
Commutation problems increase with increasing terminal voltage, the motors on the GG1 were rated at 235 to 250 volts, where similar sized DC motors could be rated up to 1500 volts. The PCC's used two motors in series to allow use of 300 volt motors in the interest of better commutation. The downside of lower voltages is that the current increases - on the GG1, each motor was drawing over 2,000A when operated at its short time rating.
AC series motors need to be built with a laminated frame to reduce problems with eddy currents.
Answer to #2:
The mercury ignitron was developed to the point where it was practical to use in on-board RR service - mercury arc rectifiers where used on the South Shore Line in 1926 when it was converted to run on 1500VDC for compatibility with the Illinois Central commuter electrification - the rectifiers were in substations. Ignitrons work just as well at 60 Hz as they do at 25Hz. The use of ignitrons on locomotives and MU cars allowed those vehicles to be equipped with DC traction motors, which were smaller, lighter, more efficient and cheaper than AC series motors.
Silicon rectifiers became available about halfway through the E-44 production run, which made operation off of 60 Hz even more practical.
Further comments:
For a given power rating (actually volt ampere rating), the weight of a transformer is inversely proportional to the lowest design operating frequency. A 25 Hz transformer will need roughly 2.4 as much iron as a 60 Hz transformer (60/25 = 2.4). 400 Hz transformers will require 60 to 7 times less iron than a 60 Hz transformer, which is why aircraft power systems run on 400 Hz.
The size of an AC induction or synchronous motor is roughly proportional to its torque. Since the shaft power of a motor is the product of motor speed and torque, a high speed motor of a given size will almost invariably produce more power than a low speed motor. That's why a 400 Hz motor can produce more power for a given weight than a 60 Hz motor.
AFAIK, even now German Rail uses 15 kV, 16 2/3 Hz. Seems to work fine for freight and high speed ICEs.
C&NW, CA&E, MILW, CGW and IC fan
John, Blue Streak,
CERA Bulletin B-118, Westinghouse Electric Railway Transportation has an article on the the development of the single phase system where it specifically mentions using a lower frequency to improve performance of AC series motors. 25 Hz was chosen as it was already a standard frequency first used in the Niagara Falls hydroelectric plant. The European standard was 16 2/3 Hz and the Visalia Electric used 15 Hz.
With the exception of the N&W and VGN phase converter locomotives (not to mention the PRR's Big Liz), the GN and VGN motor generator locomotives and a handful of experimental rectifier locomotives, all single phase electric railway equipment in the US prior to 1950 used AC series motors. As mentioned above, these motors required 25 Hz or lower to operate satisfactorily.
[Edit: Note that the GG1 used two traction motors per axle (not a big deal with geared quill drives) as two smaller AC series motors will be more efficient than a single larger motor. Another advantage was the smaller motor was was used elsewhere on the PRR.]
My uncle showed me a rectifier module for electric razors and demonstrated that the razor ran a bit faster on DC than AC.
FWIW, 25 Hz was widely used pre-WW2 for industrial processes that needed large quantities of DC power, e.g. aluminum smelters. This was because the rotary converters were typically more efficient running off of 25 Hz than 60 Hz. It was also widely used for feeding substations for trolleys, interurbans and third rail railway electrifications as well as the DC districts in many downtowns. The last of the 25 Hz converters used on the Grand Central electrification were taken out of service ca 1990.
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