| General > General Technical Chat |
| The "All American Five", & more dangers!! |
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| TimFox:
--- Quote from: GlennSprigg on May 01, 2020, 12:33:34 pm --- --- Quote from: TimFox on April 30, 2020, 01:24:41 pm --- --- Quote from: Tom45 on April 30, 2020, 04:46:18 am --- --- Quote from: TimFox on April 29, 2020, 04:03:42 pm ---... Consolidated Edison in New York finally ceased DC distribution totally in 2007. ... --- End quote --- To be fair to Con Ed, I think they carried on with DC service for such a long time because there were a few elevators in NYC that used DC motors. Substituting AC motors and controls was apparently deemed to be a bigger problem than just continuing DC service to the few ancient DC installations. A search brought this article: https://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/ Apparently the hold outs haven't converted to AC. They just installed AC to DC converters on site. --- End quote --- Yes, the very late dropping of DC service in New York was related to elevators. However, before the War, there was a lot of DC distribution in New York and Boston, a big problem for transformer-operated equipment and the origin of AC-DC jokes (another topic). Around 1965, I visited the roundhouse of the Duluth, Missabe, and Iron Range Railroad in Proctor, MN, which still had one or two Yellowstone 2-8-8-4 simple articulated steam locomotives (the most powerful ever built, slightly more tractive effort than the more famous Big Boys of the Union Pacific). The big electric motors ran on 25 Hz power for historical reasons, which they could still obtain from Minnesota Power and Light Co., although the rest of us enjoyed modern 60 Hz power. --- End quote --- Wasn't the U.S. still using DC for some TRAMS for quite a while?? Also, until recently seeing a "Mr. Carlsons Lab" radio restoration video, where it had an extra large transformer, designed to work down to 25-hz supply frequency, had I ever HEARD of the use of 25-hz !! --- End quote --- Third-rail subway, elevated, and suburban trains in US are usually DC (about 600 to 750 V) and originally ran with DC brushed motors for speed control. Modern cars use inverters driving induction motors at variable frequency for speed control. Overhead wires are often higher voltage DC; the Illinois Central suburban line in Chicago uses 1500 V DC. For mainline service, the Pennsylvania RR electrified at 12 kV, 25 Hz, as a compromise between weight of control transformers in locomotives and DC motors driven by AC. (Similarly, the Swiss railways used 16-2/3 Hz, a subharmonic of 50 Hz.) |
| james_s:
--- Quote from: TimFox on May 01, 2020, 04:40:57 pm ---Third-rail subway, elevated, and suburban trains in US are usually DC (about 600 to 750 V) and originally ran with DC brushed motors for speed control. Modern cars use inverters driving induction motors at variable frequency for speed control. Overhead wires are often higher voltage DC; the Illinois Central suburban line in Chicago uses 1500 V DC. For mainline service, the Pennsylvania RR electrified at 12 kV, 25 Hz, as a compromise between weight of control transformers in locomotives and DC motors driven by AC. (Similarly, the Swiss railways used 16-2/3 Hz, a subharmonic of 50 Hz.) --- End quote --- Wasn't the low frequency AC used so they could run large rotary converters back before mercury arc and later solid state rectifiers capable of handling high power levels were developed? |
| jogri:
--- Quote from: TimFox on May 01, 2020, 04:40:57 pm ---Similarly, the Swiss railways used 16-2/3 Hz, a subharmonic of 50 Hz. --- End quote --- Actually, germany, denmark and austria also use this system... It's a relict from the early 20th century, but it still works (some german powerplants even have dedicated 16 2/3Hz generators for that purpose). Btw, we even have a 400V three-phase suspension railway over here, i'd like to know which engineer envisioned this monstrosity (he was probably bored and decided he needed a new challenge). |
| CatalinaWOW:
Whether totally factual or not, we were taught at university that all of the early power operating frequency decisions were actually fact based. The analysis was presented and variations given in homework problems and tests. They had a specific set of materials available at the time which set core losses in the transformers and also saturation levels. Each system had an expected distribution architecture which set line losses through capacitance. Set up the equations, take the derivative, find the zero point and you have the optimum frequency. And with the data available to us at the time it appeared that the calculations were done correctly. The difference between the European and North American solution is well with what would be expected from slightly different material costs and distribution arrangements. And you would expect the distribution arrangement to be very different in a dedicated rail power system, so the frequency is significantly different (as is the frequency chosen for airborn and ship power systems). Once a few were built the benefits of standardization outweighed the benefits of optimization and folk settled on just a few options. |
| Electro Detective:
--- Quote from: GlennSprigg on May 01, 2020, 12:33:34 pm --- Also, to rsjsouza, regarding Earthing. I don't know how 'Earths' are set up in the U.S., but here in Australia, it goes like this... The 'Earth' is not supplied to the property. An Earthing stake is driven into the ground close to the Switchboard/Meterboard. All the earth wires within the property (outlets/lights) go back to a dedicated earth-termination bar in the main switchboard. The Earth-stake in the ground is also connected to this bar. However, 'we' ALSO have a hefty cable link in the switchboard, linking that Earth-Bar to the Neutral-Bar, under what we call 'M.E.N.', meaning a 'Mains-Earth-Neutral' system. So that the Neutral is always referenced to Earth also! Often, old un-earthed circuits simply need the addition of a separate earth wire, (if not included in the cables), to bring it up to spec. And we 'virtually' have no power outlets without a built in switch, which obviously switches the Active. And our outlets are automatically 'polarized' due to the diagonal layout of the prongs. :) --- End quote --- afaik the incoming 'Neutral' is also earthed via the power pole transformer box to an earth ground in the soil below so the Neutral comes into the mains switchboard sort of 'pre-earthed' the premises 'earthing stake/copper plated rod' is wired to its own earthing buss bar which in turn is then linked via a thick wire/link to the Neutral buss bar If you lose the neutral, or any neutral, things still work via the earth return paths, but not safe :scared: Open for correction on this, stubborn humming coffee machine undergoing diagnosis, dis-assembly and blockage purge/clean :horse: |
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