In the 9 December magzine section of the Jerusalem Post, a reporter said that use of ground contact as developed by Bombardier would have saved money be eliminating the need for the overhead wire, as well as improving esthetics next to the Old City Wall. I wrote the Post Letters Editor and the reporter with the correction, noting that ground contact systems are more expensive becuase of the complicaton in track construction, plus the need for maintenance and inspection of the automatic devices that power the segmented rail only when the rail vehicle is over the segment. I also pointed out that the system isn’t applicable to the area next to the Old City Wall, because this area is grassed, including over the ties between the rails, and there are trees as well. Wet grass and fallen leaves to not make good insulators! The track would have to be paved, with a net esthetic loss in my opinion. The reporter said she doesn’t claim to be an expert. But she did accept a freebe trip to Germany to see the new Israel Railways double-deckers under construction at a Bombardier plant there. So far, no correction has been printed.
Also, she has contributed for years to the magazine HaRakevet. I had planned to subscribe to this magazine, but came across a piece in issue No. 80 that affects me directly here in Jerusalem and again has some bad distortions of fact. I would like to subscribe, and if any reader wishes to help me, he or she can contact me at: daveklepper@yahoo.com. I will explain the problem, and then you can tell me if any correction should appear. Thanks…
Dave K’s comment about ground contact reminded me of the old Washington DC trolley system. Now that was a bit before my time, but the DC trolley system ran on ground contact, the contact being in a “trench” below the road, DC not permitting any overhead wires. What Dave said about the pitfalls of such a system is correct though, the DC system was on paved streets and not through grassy areas.
Trouble with paved streets and underground conduits is that, in most places in the US, they use salt in the winter. Salt’s really bad on under street conduits.
To Falcon48: Oh yeah, what you said about salt and underground contacts is totally correct. I suppose what made the DC system workable was the fact that winters in Washington are usually prettty mild, snowfall and ice typically aren’t much of a problem. Of course, the DC trolleys have been gone for decades so it’s a moot point anyway. I’m not aware of any other city in the US that used that kind of a system.
From the sounds of it, the ground contact system may not be the same thing as the conduit system used in DC. The “segmented rails” seems to imply the running rails are powered as in a scaled up version of two rail power for model trains (I may be way of on this), where the rails are only energized when a train is in the segment.I don’t see this or the conduit system as having any initial or operating cost advantages with respect to overhead wire.
FWIW, there was a book published in the mid-70’s titled YV88, an Eco-fiction (eco-fantasy was more like it), that described what I think is the ground contact system. The authors had proposed spring supported rails above feeder conductors, where the weight of the electric railcar would compress the springs and initiate contact between the feeders and running rails. The book did get a couple of things right, fiber optics for communications and computer bulletin board systems.
Several cities in Europe and USA had underground electric vaults built in the early 1900’s into the center or along side of the rail lines for the collection of power to move the streetcars. These vaults were like the cable car vaults except that the electric wire or rails were attached to the side walls of the vault with one side the positive and the other the negative source of power. Each car had a “Plow” which extended from the car into the vault with spring loaded “shoes” pressing against the power wire or rails. The power was transfered to the controls of the car from one shoe then back to the ground with the other shoe. These systems were more expensive to build and maintain than overhead wire systems, but were required for clear views and esthetic reasons in many capital cities, Berlin, Paris, Washington DC and others.
As with many underground systems where electric is exposed to the weather and wet conditions they did not function well without much repair, maintenance and most were removed after a very short time. The system in Washington DC lasted until 1950 when the streetcars were removed and replaced by bus transportation.
That’s what I was referring to as the conduit system - which was the term used by the transit industry 100 years ago. (look at any electric railway engineering textbook or handbook from that era). The conduits were often re-purposed cable car slots.
But if anyone reading this is currently a subscriber, and has read or has issue No.80, please contact me. Thanks!
The system referred to by the Jerusalem Post was not the conduit system but a surface contact system with the conducting strip about two milimeters above the pavement surface and control boxes that sense when a rail vehicle is directly above and that powers the segmant only when the car is directly above.
Thanks for the description of the surface contact system. While it does sound cheaper (well, maybe) to install and operationally more flexible than the conduit system, it also sounds like a royal maintenance headache. I think you are right on the money in saying it is not compatible with grass.
Dave the reporter may have misunderstood the system that Bombardier was proposing. The Bombardier sytem “Primove” uses contactless inductive power transfer rather than a underground contact rail
The “Primove” system would work better with grass (and be generally safer) than an exposed contact conductor. The initial cost is likely to be much higher than overhead wire and be less efficient as well.
What might make sense is a hybrid approach, overhead wires in most areas, with the “Primove” used in esthetically sensitive areas.
New York also had a conduit system in Manhatten. But I don’t think salt was as widely used during most of the trolley era as it is today. I know, for example, that Milwaukee WI didn’t start using it extensively until the last years of the North Shore Line. Unfortunately for NSL, the salt impregnated the 3rd rail pickup apparatus and caused problems on the ‘L’ in Chicago when the trains switched to 3rd rail pickup. Apparently, NSL had to deal with this after snowstorms by hosing down the trucks of southbound trains at Harrison Street in Milwaukee, just after they left the streets.
Cinders, not salt, was the curse or the saving grace on snow and ice for most of the 19th and half the 20th Centuries. As the use of coal fell, so did the availablity of ashes or cinders. And the increased reliance on salt and salt products. I don’t think D.C. had that much snow and ice that salt had that much use in the city. Salt became much more prevelant as it was found in more accessble pockets than before.
Thanks, Dave. I got around to looking the root up in my biblical Hebrew lexicon, and found that the derivatives of the root occur quite often–and the noun “Rekev” is usually translated “chariot.” Is “Rakevet” properly a feminine plural? Of course, all readers of this[:)] thread are waiting breathlessly for the answer.[:)]
The route is the verb Rokhave (present tense) or Rakhav (past tense) or lirrkhove. infinituve, to follow. The chariot “rachba” or rachva comes from the fact that the chariot follows the horse or horses. (Soos, soosim) Thus horse and rider were thrown into the sea (The Exodus story) Sus virakhba samu baYam. And Rakevet is a faminine noun. The plurel is Rakevot. Kal is masculine for light and Kala feminine.
Still waiting for someone who had read Issue 80.
There would seem to be some loss in efficiency by tranformer-like inductive coupling. At one time in my life I worked for Mystic Transformer Co., Winchester, MA, and we designed transformers to have as close coupling as possible between the primary and secondary coils. Even then, 98% was about the best we could manage. Close coupling is not possible with one coil on the vehicle and the other buried below ground. I’d say about 80% efficiency is about the best that could be obtained, and this means sufficient power loss.
What was the size range produced by Mystic? And how much of the typical loss was due to core loss (eddy current and hysteresis) versus conductor loss? I have a recollection of reading about distribution transformers attaining 99+% efficiency at rated load by using tape wound hypersil or metglas to reduce core losses. I would assume that the tape wound core would have a lower reluctance (higher effective permeability) than a laminated core. The 98% efficiency agrees with what I’ve read and have been told about conventional transformers.
I did come across a Westinghouse article from 1918-19 where the author claimed over 99% efficiency with a power transformer. They went on to explain that this was an autotransformer…
Power transformer design is easy when compared to designing an audio transformer capable of covering 20 Hz to 20 kHz.
The 80% figure may be optimistic.
It is possible to get good power transfer with loose coupling by having a low loss source of reactive power (e.g. really good capacitors), see the section on coupled resonators in the ARRL Handbook (formerly The Radio Amateur’s Handbook). this efficiency is very sensitive to disturbances in the resonant circuits such as caused by the changes in i
None of the power transformers I designed were large than 1kW. So 98% was about the best we couild do. This was 1952-1954, when some of the more exotic metals and techniques were still in the future. Alos, we produced pulse transformers requiring extremely high hihg-fruency response, and we deliberately introduced loss–producing air-gaps to linearize the frequency response. Also, conventional, but very high-quality, high-fidelity audio transformers for the tube-type power amplifiers of the time.
The high fidelity audio transformers were really works of art, trying to get a high magnetizing inductance for the low frequencies and low leakage inductance for the high frequencies. Direct coupled outputs are so much easier.