# Catenary Question



## Amfleet (Aug 1, 2003)

This has always puzzled me, but where does the overhead catenary get its power. Does it draw from local power plants along the NEC or does Amtrak own power plants to produce the electricity? I take it the wires need a lot of power.


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## battalion51 (Aug 1, 2003)

The power is drawn from substations near the right of way (I'm not quite sure how far the substations are spaced). Back at the early part of the last century Railroads owned their own powerplants to produce the electricity. As the overhead rose to maintain and operate these plants the railroads began contracting out the power supply to outside companies. The same probably still holds true today.


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## AMTRAK-P42 (Aug 1, 2003)

I thought I had heard it was about every 50-75 miles..?


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## battalion51 (Aug 1, 2003)

You guys would know better than me. Although I know that substations are required more often for third rail pick up than they are for overhead catenary.


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## AlanB (Aug 2, 2003)

First, B51 is correct, originally the New Haven made it's own power. At the moment I'm not sure if the Pennsy did, I'll have to go and look at the article on that, but I don't think that they did. Today all power is simply purchased from the local power companies and Amtrak simply provides the transformers to get the correct voltage.

Off the top of my head I'm not sure how far apart the substations are. Battalion is correct again though, that third rail substations are much closer together. The reason for this is that third rails use DC power, while the catenary uses AC power. AC power can travel much further distances with out loosing its power.

That's why your home uses AC power and all high-tension wires in this country carry AC power. Anyone needing DC power simply converts AC to DC right where they need it, as it's far too costly and far too hard to transmit DC power more for more than a very short distance. Even you guys who run model trains convert AC power to DC. That's what your transformer does.

Now just imagine that you could get permission and the money to expand your layout to fill the entire basement. You would need several transformers to power that entire track, because you are using DC power. If model RR's ran on AC power, you wouldn't need nearly as many transformer to run a layout that large.

Now the wires do carry a lot of power, more than enough to fry someone who touches one. Oddly enough the NEC actually uses several different voltages along the way. There is one voltage from Boston to New Haven, then a different one down to basically the Bronx, and then another from there to DC.

I think that the Morris & Essex uses still another voltage for their wires.


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## PRR 60 (Aug 2, 2003)

A real short primer on the PRR catenary.

The PRR, in the early 1900’s, selected 11kV, 25 cycle (hz) AC overhead catenary as its power supply for electric train operation. This selection was based on in-depth study of the pros and cons of various electric traction systems and was the first such design in North America. The original overhead electrification, built in the Philadelphia area, was expanded to the entire NY to Washington corridor in the 1930’s (along with Harrisburg and commuter lines).

The PRR was also unique in providing it’s own high-voltage transmission system to feed the catenary system. The 11kV catenary is supplied from a series of step-down substations located every 20 to 30 miles along the right-of-way. A railroad-owned network of 132kV, 25hz, single-phase (two wire) transmission lines was built to connect the step-down substations with the sources of the railroad’s power. Those lines still exist today. They are the two, or sometimes four wires (two circuits) at the top of the catenary structures (except where utility transmission lines have leased space above the RR lines). It was a tripping (short circuit) of two of those lines that disrupted the NEC at rush hour a couple of weeks ago.

The PRR purchased its power from the local utilities. Of course, utility power is 60hz, not 25hz, so that presented a complication. This incompatibility was solved in a couple of different ways. One way was for the utility to dedicate special 25hz generators for the PRR. Safe Harbor Dam, located south of Harrisburg on the Susquehanna, was one such facility. The dam had two dedicated hydro generators producing 25hz power. Another way was for the utility to provide power at 60hz and for the PRR to convert that power to 25hz. Richmond Generating Station in Philadelphia is an example of a location where the PRR had conversion equipment.

Today, Amtrak still purchases power from the local utilities. Safe Harbor’s two generators are still in service and the dam supplies to Amtrak at Perryville, MD and via the old PRR transmission lines to Philadelphia. PECO Energy still supplies Amtrak at Richmond Station (Philadelphia) via two 69kV, 60hz transmission lines that Amtrak converts to 25hz.

One significant technical advance in recent years is the ability to convert 60hz power to 25hz. In the olden days, this was accomplished by a gigantic motor-generator set. The 60hz utility power would drive a huge electric motor that would, in turn, spin a 25hz electric generator. 60hz in; 25hz out. It worked, but it was an inefficient and maintenance intensive facility. Today, conversion is accomplished solid-state. A new Amtrak frequency converter station in Philadelphia is a perfect example. It takes the PECO-supplied 60hz power and first rectifies it to direct-current (DC). Then a solid-state converter artificially imposes a 25hz alternating wave-form on the DC current creating power that for all intent and purposes is 25hz. No moving parts, much easier to maintain, and much more efficient that the big machines.

Back in the office I have a copy of a technical article that appeared in a 1930’s edition of Railway Age describing the engineering details of the PRR electrification project. If I find that my memory has failed me in any of the data I stated above, I’ll add a correction. One thing is certain. Those folks in the 1930’s did a sensational job with that project. Nearly 70 years later, essentially that same electrical system is powering the busiest rail line in North America. Amazing!


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## Chris Brock (Dec 30, 2008)

Hmmm..a lot of concepts described in the message quoted below are incorrect....

First of all, the ability of electrical power to move great distances with high efficeincy has nothing to do with AC vs DC. It has everything to do with, and only to do with, VOLTAGE!.

100Kv DC can be transmitted just as as far as 100Kv AC. There is a reason why most high voltage systems are AC instead of DC. To convert between high and low voltages, you need only a simple, relatively inexpensive and reliable passive device: a transformer. This device converts electricity to magnetism and back to electricity. The new voltage is set according to the ratio of wire turns between the primary and secondary wire turns inside the transformer.

To change DC to a different voltage requires a relatively expensive active device that has the added challenge of making it reliable. The technology to change AC voltage has existed for about a century. DC voltage conversion technology has existed only since about 30+ years ago.

A principle of physics is that every time you double the operating voltage of a wire, that wire can carry four times the power. The higher the operating voltages, the greater the spacing between substations, the smaller diameter catenary wire can be and the higher amount of power that can be delivered to a locomotive.

There is a long distance electrical power transmission line that goes between Oregon and California that is DC. It operates at 1 million volts. The two end points are very expensive, however, that cost is offset by the much lower transmission line cost. Instead of running three cables (for 3 phase AC) , only two are needed. Less wire and insualtors, and smaller, cheaper towers are used.

Amtrak would love to have all of its catenary operate at 25Kv 60 Hz, and tried very hard to make it happen. However, it would take spending a lot of money to change out transformers and insulators. For now, it's cheaper to have the locomotives accommodate different voltages and frequencies.



AlanB said:


> First, B51 is correct, originally the New Haven made it's own power. At the moment I'm not sure if the Pennsy did, I'll have to go and look at the article on that, but I don't think that they did. Today all power is simply purchased from the local power companies and Amtrak simply provides the transformers to get the correct voltage.
> Off the top of my head I'm not sure how far apart the substations are. Battalion is correct again though, that third rail substations are much closer together. The reason for this is that third rails use DC power, while the catenary uses AC power. AC power can travel much further distances with out loosing its power.
> 
> That's why your home uses AC power and all high-tension wires in this country carry AC power. Anyone needing DC power simply converts AC to DC right where they need it, as it's far too costly and far too hard to transmit DC power more for more than a very short distance. Even you guys who run model trains convert AC power to DC. That's what your transformer does.
> ...


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## Dutchrailnut (Dec 30, 2008)

Ok lets answer where power comes from, not how its distributed.

From gate (near sunnyside) to Boston, power comes from regular 60 hz powergrid.

From gate to Washington DC the power is converted or generated at 25 hz.

at westfarms in bronx power converters transfer commercial 60 Hz poweer to 25 Hz 12.5 Kv

In New jersey most power is obtained from a Hydro powerplant which generates 25 hz power some newer inverter based units supliment the power from Commercial grid.


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## PRR 60 (Dec 30, 2008)

Wow! Here's an oldie but goodie. And its about electric power transmission: my dream come true!



Chris Brock said:


> ...First of all, the ability of electrical power to move great distances with high efficeincy has nothing to do with AC vs DC. It has everything to do with, and only to do with, VOLTAGE!.


That is not quite correct. AC power transmission is less efficient than DC for two primary (and a few secondary) reasons.

First, high voltage AC transmission induces reactance into lines. This reduces a line's ability to transmit real power. Second, electric transmission conductors have a higher resistance to high voltage AC power than they do to high voltage DC power. This due to "skin effect": the property of AC current to be more densely concentrated near the surface of the conductor than at the core. Both reactance and skin effect are not issues with DC power transmission. So, all things being equal - conductor size and voltage - a DC power transmission line will carry more power more efficiently than a AC power transmission line.

As you correctly pointed out, the problem with DC power transmission is the terminal costs. It is very expensive to convert between AC and DC at high voltages and high current levels. Only when the savings realized by the more efficient DC power transmission offset the higher terminal costs, is DC a viable alternative. As a rule of thumb, unless a line is extra-high voltage (EHV) and very long, DC transmission is not economic.



Chris Brock said:


> ...A principle of physics is that every time you double the operating voltage of a wire, that wire can carry four times the power.


That is not correct. It is proportionate to the voltage. Simplistically, a wire rated at 10A at 100V can carry 1000VA power. At 200V, that same wire can cary 2000VA power. In the real world, a three-phase, AC transmission line with conductor rated at 500A per phase operating at nominal 69kV (phase-to-phase) can carry 60MVA power. That same line and conductor operating at 138kV can carry 120MVA power.

Welcome to Power Transmission Unlimited!


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## AlanB (Dec 30, 2008)

I'm just trying to figure out why we're revisting a 5+ year old topic. :unsure:


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## GG-1 (Dec 30, 2008)

AlanB said:


> I'm just trying to figure out why we're revisting a 5+ year old topic. :unsure:


Lightning?  heck it shut Oahu down Friday night/Saturday morning. And I would say also very few people understand "Electricity"

Eric


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## Joel N. Weber II (Dec 30, 2008)

PRR 60 said:


> One significant technical advance in recent years is the ability to convert 60hz power to 25hz. In the olden days, this was accomplished by a gigantic motor-generator set. The 60hz utility power would drive a huge electric motor that would, in turn, spin a 25hz electric generator. 60hz in; 25hz out. It worked, but it was an inefficient and maintenance intensive facility. Today, conversion is accomplished solid-state. A new Amtrak frequency converter station in Philadelphia is a perfect example. It takes the PECO-supplied 60hz power and first rectifies it to direct-current (DC). Then a solid-state converter artificially imposes a 25hz alternating wave-form on the DC current creating power that for all intent and purposes is 25hz. No moving parts, much easier to maintain, and much more efficient that the big machines.


Given that the long term goal seems to be to get the entire railroad running on 60 hz, what advantages does the solid state 60 hz to 25 hz converter have over simply converting that section to 60 hz?


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## PRR 60 (Dec 30, 2008)

Joel N. Weber II said:


> ...Given that the long term goal seems to be to get the entire railroad running on 60 hz, what advantages does the solid state 60 hz to 25 hz converter have over simply converting that section to 60 hz?


Going to 60hz electric traction was Amtrak's goal thirty years ago (with the NECIP), but times have changed. The cost and efficiency of 60hz to 25hz conversion has come down, and the cost of converting the entire 25hz system to 60hz is high - too high. With no great operational advantage to 60hz, Amtrak made the decision to keep the NYC to WAS and HAR former PRR corridor at 25hz for the foreseeable future. The new Richmond (Philadelphia) solid-state static frequency converter station was installed in 2001 at a cost of about $70 million. It, at least at the time, was the largest converter station in the world. With upgrades taking place at other converter stations, Amtrak has invested heavily in modernizing the 25hz system and is committed to retaining 25hz power for the lower NEC catenary system.


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## PRR 60 (Dec 30, 2008)

AlanB said:


> I'm just trying to figure out why we're revisting a 5+ year old topic. :unsure:


I think because someone must have had a very good grasp of the site search function. :lol:

This may be the oldest resurrection from the dead in site history.


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## AlanB (Dec 30, 2008)

PRR 60 said:


> AlanB said:
> 
> 
> > I'm just trying to figure out why we're revisting a 5+ year old topic. :unsure:
> ...


If it's not the oldest, it certainly ranks up in the top 5.


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## Joel N. Weber II (Dec 30, 2008)

PRR 60 said:


> Going to 60hz electric traction was Amtrak's goal thirty years ago (with the NECIP), but times have changed. The cost and efficiency of 60hz to 25hz conversion has come down, and the cost of converting the entire 25hz system to 60hz is high - too high. With no great operational advantage to 60hz, Amtrak made the decision to keep the NYC to WAS and HAR former PRR corridor at 25hz for the foreseeable future. The new Richmond (Philadelphia) solid-state static frequency converter station was installed in 2001 at a cost of about $70 million. It, at least at the time, was the largest converter station in the world. With upgrades taking place at other converter stations, Amtrak has invested heavily in modernizing the 25hz system and is committed to retaining 25hz power for the lower NEC catenary system.


You've said that, but that doesn't really explain why converting to 60 hz would be too expensive.

Are there any technical problems that would occur if, at the existing 25 hz to 25 hz phase breaks in the catenary, they started having multiple switches between 60 hz and 25 hz along the WAS to NYP route? It's clearly possible to have a train go from 25 hz to 60 hz and vice versa, given that it happens somewhere along the WAS to BOS route.

Does converting one segment to 60 hz require any changes to the infrastructure fed by the substation, or does it simply require replacing a substation that converts 60 hz to 25 hz while changing voltage with a new substation that does the voltage conversion without the frequency conversion?

Wouldn't eliminating all 25 hz in the entire system also allow lighter locomotives to be used? Does that have some potential benefit, especially in places where dual mode (diesel and catenary) locomotives are desired, or does the weight savings from removing 25 hz compatibility turn out to not be all that much?


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## George Harris (Dec 30, 2008)

PRR 60 said:


> Joel N. Weber II said:
> 
> 
> > ...Given that the long term goal seems to be to get the entire railroad running on 60 hz, what advantages does the solid state 60 hz to 25 hz converter have over simply converting that section to 60 hz?
> ...


A few years ago I rad across a paper by Uli Hertzel elplaining the advantages of DC for railroad overhead power. Being as I am neither electrical engineer nor electrician, there was a lot I did not understand, but apparently much can be gained by regenrative braking on a DC line which is not practical with AC. Also, some of the phase imbalance problems were supposed to go away. Anyone able to clarify?


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## Joel N. Weber II (Dec 30, 2008)

I wonder if DC would introduce additional safety problems, though.

IIRC, once a current starts to flow between two points, you can move those points away from each other, and the current has some tendancy to continue to flow. With a DC current, it can continue to flow for a good long time, whereas with an AC current, the next zero crossing (zero crossings will happen 120 times a second with 60 hz power) will cause the power to stop flowing unless the points are close enough for the voltage involved for a current that is just starting up to flow between those points. I have been told that this is why DC light switches apparently were designed to open up a physical gap much more quickly than a modern AC light switch does.

I can't quite put my finger on a concrete example of why DC catenary would definitely end up being a bad idea because of this, but I also don't really feel like I'd want to be the one to get the blame if someone discovered an example in a way that got someone seriously injured or worse.


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## PRR 60 (Dec 31, 2008)

Joel N. Weber II said:


> ...You've said that, but that doesn't really explain why converting to 60 hz would be too expensive.


Everything that is a part of the Amtrak power transmission and distribution system on the former PRR portion of the NEC is designed for 25hz, single-phase operation. That includes the six 25hz power sources (three of which are less than 20 years old), the high voltage transmission system, the step-down substations, the catenary feeders, and the systems for electric power protection, control and operation. From big items like transformers to simple items like metering, relays and control software, it would all have to go and be replaced with like items designed for 60hz, three-phase. Despite the conventional wisdom, much of that stuff on Amtrak's ET system is reasonably modern. And, it would all have to be replaced in such a way that the trains keep running throughout the change over. That alone would be a neat trick. Lest we forget, commuter rail operations like SEPTA also use the Amtrak 25hz system. They would have major costs as well.

Even utility 60hz power supply to Amtrak is an issue. Right now, the utilities supply Amtrak (PRR) at five injection points (the sixth being a dedicated turbine at Safe Harbor Dam). Back in the late 1970's during the Northeast Corridor Improvement Project, Amtrak looked seriously at going to 25kV, 60hz for the PRR catenary. They asked the affected utilities to assess the impact of providing 60hz power to Amtrak at multiple additional points. Since the existing single-phase Amtrak 132kV transmission system could not be used for three-phase power, Amtrak would have to have additional points of supply over and above the five existing ones. The cost to the utilities to add those supply points was in the tens of millions (in 1980 dollars). Since Amtrak is a commercial customer, the utilities’ cost of providing that new service would have to be paid by Amtrak. From the utility perspective, Amtrak would not be buying more power, only changing how and where it wants to get its power. So if Amtrak wants it their power a different way and in different locations, Amtrak pays. This is all to point out that conversion to 60hz, three phase is not in any way, shape, or form an easy matter. The more you dig into the problem, the more problems you find, and the more it costs.

So then the issue becomes the advantage of using 60hz, three-phase. While it permits use of standard equipment, and has perhaps some power advantages, those were not found to be sufficient to justify the changeover. There is nothing wrong with 25hz ET power except that is unique. But today, unique does not mean bad or even un-economic. The trains run just fine on 25hz. Given that, would you not agree that the multiple hundreds of millions that would be spent to convert to 60hz would be better spent on high-speed catenary or additional high-speed trainsets?


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## transit54 (Dec 31, 2008)

While we're on this topic, how does metering work on lines that Amtrak shares with commuter railroads? Does each locomotive have a meter in it? How does Amtrak bill commuter railroads for the electricity they use? By the same token, how does Metro-North, for instance, bill Amtrak for their energy use?


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## PRR 60 (Dec 31, 2008)

rnizlek said:


> While we're on this topic, how does metering work on lines that Amtrak shares with commuter railroads? Does each locomotive have a meter in it? How does Amtrak bill commuter railroads for the electricity they use? By the same token, how does Metro-North, for instance, bill Amtrak for their energy use?


I do not know specifically, but I believe the billing is done on a calculated formula basis, not direct metering of usage.


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## HP_Lovecraft (Dec 31, 2008)

Chris Brock said:


> First of all, the ability of electrical power to move great distances with high efficeincy has nothing to do with AC vs DC. It has everything to do with, and only to do with, VOLTAGE!.


Right and Wrong.

AC has the ability to run a much higher voltage, which gives it the much extended range, produced more effeciently.

Still, I got lost in most of this thread. Is the catenary AC or DC?


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## PRR 60 (Dec 31, 2008)

HP_Lovecraft said:


> Chris Brock said:
> 
> 
> > First of all, the ability of electrical power to move great distances with high efficeincy has nothing to do with AC vs DC. It has everything to do with, and only to do with, VOLTAGE!.
> ...


AC: 25hz.


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## access bob (Dec 31, 2008)

PRR 60 said:


> HP_Lovecraft said:
> 
> 
> > Chris Brock said:
> ...


25hz South of a point just North of New York

60hz New York to Boston

and just to add to the fun it is

11kv DC to New York

25kv New York to Boston.

so three automatic engine input changes DC to Boston

Bob


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## George Harris (Dec 31, 2008)

access bob said:


> PRR 60 said:
> 
> 
> > HP_Lovecraft said:
> ...


I recall seeing somewhere that the ex-New Haven electrification was changed to 60Hz, but the voltage only went to 12.5kV, not to 25 kV due to insulation and clearance issues. Onely the new overhead east of New Haven is at 25kV.

By the way, we are not the only ones in the world with strange overhead power. The overhead line on the German Railways is AC at 16 2/3 Hz. Don't remember the voltage right now. 16 2/3 was selected as being 1/3 of the normal European house current frequency of 50Hz.


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## Joel N. Weber II (Dec 31, 2008)

PRR 60 said:


> Going to 60hz electric traction was Amtrak's goal thirty years ago (with the NECIP), but times have changed. The cost and efficiency of 60hz to 25hz conversion has come down, and the cost of converting the entire 25hz system to 60hz is high - too high. With no great operational advantage to 60hz, Amtrak made the decision to keep the NYC to WAS and HAR former PRR corridor at 25hz for the foreseeable future. The new Richmond (Philadelphia) solid-state static frequency converter station was installed in 2001 at a cost of about $70 million. It, at least at the time, was the largest converter station in the world. With upgrades taking place at other converter stations, Amtrak has invested heavily in modernizing the 25hz system and is committed to retaining 25hz power for the lower NEC catenary system.


When I first read this, I was assuming that that $70 million frequency converter would have output 11 kV to feed the catenary directly. But it's now seeming to me that a lot of what you are saying would make a lot more sense if that frequency converter's output is at 132 kV. Could you clarify which is the case?

Is there anything that would prevent a single phase 132 kV system from being able to run at 60 hz?


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## Chris Brock (Jan 1, 2009)

PRR 60 said:


> Wow! Here's an oldie but goodie. And its about electric power transmission: my dream come true!
> 
> 
> Chris Brock said:
> ...


Thanks for the reply. I didn't think anyone would see a reply I wrote to to five year old post.

I agree that reactance tempers the full potential of high voltage AC. I like the way you explained it. The lower the AC frequency, the lower the reactance issues. Also, one big disadvantage to very high voltage AC is that the high slew rate of voltage change causes radio frequency interference. EMF exposure to people is another.

One apparent advantage of AC is that insulators are less prone to flashovers, or maybe this is easily mitigated by just using slightly higher voltage rated insulators than you would otherwise use if on an AC circuit.

The "wire carrying four times the power for every doubling of voltage" includes distance; it comes from this:

When you double the voltage, only half the current is needed to transmit the same amount of power. At the same time, the distance in which the voltage drops to the same amount you had before also doubles. 2 X 2 = 4. I'm not making this up; a lot of dry text books describe this.

Do you know of any effective practical way to step down very high DC voltages that could be used in a locomotive? If that problem could be solved, this would make the case for the implementation of a very high voltage DC catenary infrastructure the next time a new rail line is converted to electric traction.

On the power source side, stepping up to high DC voltages is easy. Start with AC, use transformers and use rectifiers at the highest voltage. (This is easy for me to say since I've never had to do any of this).

If a DC system could be deployed, good bye EMF, RFI, power factor and other issues.

Happy New Year,

Chris


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## battalion51 (Jan 1, 2009)

Wow, memories of when Jon used to be on the system. Man that's been a while. Time sure does fly when you're having fun.


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## John S (Jun 14, 2014)

What was the original reason for PRR selecting 25 Hz current instead of 60 Hz like everything else?

AC was chosen as the national standard (pretty much everywhere) primarily because of its ease in changing voltage and allowing higher efficiency transmissions at high voltages. But AC current has drawbacks as well, including inductance and the need to keep everything in sync. With modern technology, changing DC voltages has become much less expensive, and conversions between AC/DC are much more efficient too.

Underground AC transmission lines are less unsightly and have less damage from storms and lightning strikes, but can be very inefficient. DC does not have have this disadvantage underground.

Perhaps hundreds of years from now, houses will be supplied with DC if Mr. Fusion doesn't prove successful in the home.


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## Guest (Jun 14, 2014)

Note from above: The issue with underground AC line loss is primarily due to capicitance.


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## jis (Jun 14, 2014)

access bob said:


> 25hz South of a point just North of New York
> 
> 60hz New York to Boston
> 
> ...


Well now that this has popped up into my attention.....
It is

11kV 25Hz from Washington DC to Gate (just east of Harold in Sunnyside, Queens NY)

12kV 60Hz from Gate to Mill River (roughly, actually slightly short of Mill River, between New Haven State Street, and Mill River)

25kV 60Hz from Mill River to Boston


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## neroden (Jun 14, 2014)

John S said:


> What was the original reason for PRR selecting 25 Hz current instead of 60 Hz like everything else?


I believe the US had not standardized on 60 Hz at the time. There were a lot of 25 Hz commercial operations in the late 19th century, including most of the Niagara Falls power, and a bunch of these were still operating as late as 1946.


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## Trogdor (Jun 15, 2014)

Is this a new record for oldest thread dug up by a guest?


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## Acela150 (Jun 15, 2014)

Trogdor said:


> Is this a new record for oldest thread dug up by a guest?


LOL!!


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## ehbowen (Jun 16, 2014)

Joel N. Weber II said:


> PRR 60 said:
> 
> 
> > Going to 60hz electric traction was Amtrak's goal thirty years ago (with the NECIP), but times have changed. The cost and efficiency of 60hz to 25hz conversion has come down, and the cost of converting the entire 25hz system to 60hz is high - too high. With no great operational advantage to 60hz, Amtrak made the decision to keep the NYC to WAS and HAR former PRR corridor at 25hz for the foreseeable future. The new Richmond (Philadelphia) solid-state static frequency converter station was installed in 2001 at a cost of about $70 million. It, at least at the time, was the largest converter station in the world. With upgrades taking place at other converter stations, Amtrak has invested heavily in modernizing the 25hz system and is committed to retaining 25hz power for the lower NEC catenary system.
> ...


(Yes, I know this is a 5-1/2 year old post. I still wanted to answer it, since it looks as if nobody else has.)

Disclaimer: I am not an electrical engineer.

As far as I am aware there is no reason that a single phase 132 kV system at 60 Hz would not work. However, there are still some problems. The small problem is that transformers and other electrical equipment are designed specifically for the frequency at which they will operate. You can run 60 Hz equipment on 50 Hz for a time (I have, in a foreign port in the Merchant Marine) but you have to watch it for overheating and other signs of distress. (Plus, none of your clocks work!) I assume that 50 Hz equipment on 60 Hz would be similar. But 50 cycles and 60 cycles are fairly close together, relatively speaking. I'm pretty certain that operating the 25 Hz NEC equipment on 60 Hz simply would not work properly, even in the short run, and so you would still be looking at replacing all of the transformers and other distribution equipment. That's the small problem.

The big problem is that standard electrical power supply is three-phase. The voltage oscillates with each leg 120 degrees out of phase. Part of the big trick of designing an electrical system is balancing the load between the phases. You definitely do not want to have a commercial building pulling 100 amps on phase A, 135 amps on phase B, and 420 amps on phase C. The electric meters, particularly the new smart meters, would pick that up in a flash and the utility would hit you HARD. Now you propose supplying the NE Corridor with a thousand times that much single-phase electricity. Where are you going to get it?

The proposed design for the NY-Washington NEC, like the actual 60 Hz section north of New York, would use all three phases to balance the load. You would have three miles or so fed from phase A, then another three miles fed from phase B and so on...with an unpowered "phase break" between the phases. That's very important! Since the phases are all at different (instantaneous) voltages at any given point in time, a loco with both pantographs up and the front pan in contact with A and the rear pan in contact with phase C has just shorted the phases. At 25,000 volts the results would be spectacular! So you have to have an isolated, unpowered phase break longer than the longest locomotive which will ever run on your track for safety.

If you use three phase, that is. But you have proposed using single phase, just at a different frequency (60 Hz). Well, after you've replaced all your 25 Hz transformers and distribution equipment, then where are you going to get ten thousand amps of 25 kV single-phase power? From the utility? They'd laugh you out of town; their system simply couldn't supply it without massive structural changes...which they would expect you to pay for. Convert the three-phase to single-phase yourself? Well, now you're now on the right track...but aren't you doing that already, only at 25 Hertz? Then why not just stay at 25 Hertz?!


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## neroden (Jun 16, 2014)

ehbowen said:


> ...but aren't you doing that already, only at 25 Hertz? Then why not just stay at 25 Hertz?!


Because you have to buy non-standard equipment on all the locomotives and EMUs, handle dual frequency conversions on the locomotives and EMUs, use a lower voltage (and so use larger-diameter catenary wire), and buy piles of non-standard equipment for everything from insulators to switches.

Using a frequency which is *popular* is extremely valuable in terms of parts acquisition.

If you switch to 60Hz, you could theoretically do the conversion using phase shifters rather than frequency converters.


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## PRR 60 (Jun 16, 2014)

neroden said:


> ehbowen said:
> 
> 
> > ...but aren't you doing that already, only at 25 Hertz? Then why not just stay at 25 Hertz?!
> ...


There are very few non-standard parts required to accommodate 25hz supply. Insulators are the same, switches are the same, circuit breakers are the same (sized for 25hz), power control and protection is the same (with software set for 25hz). The size of conductors is dependent on current, and voltage matters with that, but not frequency. 25hz vs 60hz is not a big deal from a maintenance and parts standpoint.

Modern electric traction uses three-phase AC motors for maximum efficiency. Obviously, a single catenary wire can only deliver single phase power. So, regardless of the frequency of the power in the catenary, it is necessary for a modern electric locomotive to first rectify the single-phase AC to DC, then invert the DC to three-phase AC. That is the only way. A phase shifter can only shift the phase angle of the AC, but cannot turn single phase to three phase, and it certainly cannot change the AC frequency. Since the AC goes to DC then back to AC, the supply-side frequency is of very little consequence. Solid-state rectifiers handle 60hz and 25hz easily. The high-side power transformers for 25hz are a little larger than those for 60hz, but that is about it as far as the impact of using 25hz. Almost all the other stuff are off-the-shelf items that are interchangeable regardless of frequency.

Just to elaborate a little more, modern AC traction use variable frequency to control motor speed. The only way to vary the AC frequency is to take the fixed-frequency AC supply, rectify it to DC, then invert it to AC with the ability to control the output frequency. Once again, the high-side frequency does not matter.

Conventional wisdom would suggest that the use of an odd frequency like 25hz would create lots of issues. With modern solid-state equipment, the conventional wisdom is wrong.


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## neroden (Jun 17, 2014)

In that case, why do NJ Transit, SEPTA, and Metro-North have locomotives/EMUs which can't handle both 60 Hz and 25 Hz? I await your answer.

If you are correct, it is a matter of no consequence -- and next to no cost! -- to modify them to handle multiple frequencies on the fly. But from what I've read, that isn't actually true, and it is a pain to modify them. Please tell me I'm wrong and it costs nothing to make Metro-North's M-8s switch to 25 Hz on the fly, or to make SEPTA's Silverliner Vs switch to 60 Hz on the fly.



> Solid-state rectifiers handle 60hz and 25hz easily.


Then why don't Silverliner Vs or M-8s handle both? Because apparently they don't.


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## Green Maned Lion (Jun 17, 2014)

From what I understand from a former director of planning of the LIRR who is often wrong, the difference between a NJT Arrow III 25hz and 60hz is the position of a switch that is not motorman accessible. He also insists that it would be very easy to make them able to be shift on the fly.

He further insists that the reason NJT does not do it is simply because they want to waste money buying new MLV power cars. I don't know if any of this is true. I have always been skeptical about a Manhattanite Texan who cares about how New Jersey wastes it's money.


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## jis (Jun 17, 2014)

Neorden, as they say the "answer is blowing in the wind" The answer to your question is sitting in the original material from PRR that you are reacting to. An equipment that is equipped with a 25Hz transformer will work fine in 60Hz. OTOH an equipment that is equipped with a 60Hz transformer will not work with 25Hz. This is because as a matter of Physics, to transform the same amount of power at a lower frequency you require more metal in the transformer core, hence require a "heavier transformer" (to quote PRR). OTOH, if you already have enough metal in the transformer to work with 25Hz it will work fine with 50 or 60Hz. And the rectifiers don't care much which of those frequencies are thrown at it.

Now to address the specific issues raised....



neroden said:


> In that case, why do NJ Transit, SEPTA, and Metro-North have locomotives/EMUs which can't handle both 60 Hz and 25 Hz? I await your answer.


In case of NJ Transit (Arrows) they can operate on the fly in 25Hz and 60Hz. In case of new SEPTA equipment they will operate fin under 60Hz if they can find any such in SEPTA territory. There isn't. In case of MNRR M-8s they will not operate in 25Hz because they have 60Hz transformers. So part of your premise is incorrect, and where it is correct it is explained above why that is the case.


> If you are correct, it is a matter of no consequence -- and next to no cost! -- to modify them to handle multiple frequencies on the fly. But from what I've read, that isn't actually true, and it is a pain to modify them. Please tell me I'm wrong and it costs nothing to make Metro-North's M-8s switch to 25 Hz on the fly, or to make SEPTA's Silverliner Vs switch to 60 Hz on the fly.


No. M-8s cannot because they were manufactured with 60Hz transformers to save weight. As explained above you cannot operate a 60Hz transformer at 25 Hz and still expect not to produce fireworks. Silverliner Vs will work fine under 60Hz. They just don't have any in SEPTA territory. They will not work fine under 25kV unless they have been built with 25kV tap changing transformer. So cost will be zero for Silverliner Vs provided voltage is not changed. Moderate cost upgrade to tap changing transformer if not already so equipped, provided the installed transformer has the capability to take such an add on. Pretty much exorbitant cost if not. M-8s are essentially unmodifiable at this time without spending a huge sum of money. 


> > Solid-state rectifiers handle 60hz and 25hz easily.
> 
> 
> Then why don't Silverliner Vs or M-8s handle both? Because apparently they don't.


Again Silverliner Vs should have no problem with 60Hz, if they could find any in SEPTA territory. M-8s don't because their transformers are not built with enough metal to handle 25Hz. That is a weight saving decision and has nothing to do with rectifiers. Rectifiers really don't care whether they are given 25Hz or 60Hz to rectify. There are certain optimizations that can be designed into a rectifier bank to handle both more efficiently, but even without that they will work fine.



Green Maned Lion said:


> From what I understand from a former director of planning of the LIRR who is often wrong, the difference between a NJT Arrow III 25hz and 60hz is the position of a switch that is not motorman accessible. He also insists that it would be very easy to make them able to be shift on the fly.


If he indeed said that he is wrong. NJT Arrows can operate fine in both 25Hz and 60Hz and can change on the fly. They used to do that all the time when they traveled from New York to Long Branch before the voltage south of Matawan was raised from 12kV to 25kV. The new electrification from Matawan to Long Branch is capable of operating at either 12.5kV or 25kV, but both at 60Hz since it uses feed from commercial power.
Initially it was switched on at 12.5kV 60Hz so that Arrows could continue to operate to Long Branch, presumably since at that time NJT did not have enough ALP-44s to handle all Long Branch trains. When they got enough of those they flipped the voltage to 25kV which is more efficient.

What they cannot do is change on the fly from 11/12kV to 25kV because they don't have the automatic transformer tap changer on the HV side.



> He further insists that the reason NJT does not do it is simply because they want to waste money buying new MLV power cars. I don't know if any of this is true. I have always been skeptical about a Manhattanite Texan who cares about how New Jersey wastes it's money.


That is also a bit of a stretch, since the original decision not to put in the tap changer itself was a short sighted money saving exercise and pre-dates any decision to get MLVs by many years. Post facto it might look like that to someone who is not familiar with the history of NJ Transit. Interestingly those two decision were not even made by the same regime. They were made by two regimes that were separated by another one between them!


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