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The "All American Five", & more dangers!!
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vk6zgo:

--- 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.

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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 !!

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.   :)

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The Melbourne trams (streetcars) use DC, as did the long extinct Sydney & Perth ones.
For many years, Perth had a sustantial network of trolleybuses, which also used DC.

In the Sydney CBD, several old buildings were an "island" of DC into the 1950s, one strangely, being the headquarters of Australia's then premium Electronics magazine "Radio & Hobbies", (later "Radio,Television & Hobbies", then "Electronics Australia").

To provide ac for their design lab, & for anything else that needed it, there were "rotary converters" in the basement.
Unfortunately, there were power outlets of both "species" of electricity in the lab, so they occasionally let large quantities of "magic smoke" out of something.

The main reason for retaining DC was for the "Lifts"(elevators)

Later, the setup was reversed, with AC to the building, but rectifiers in the basement for the lifts.
Later, still, it was becoming obvious that the old lifts couldn't meet modern safety standards, & parts were virtually unobtainable, so building management "bit the bullet" & replaced them with modern ones.



schmitt trigger:
I know that New York’s subway, Paris metro and others still use DC. But how about London’s tube?
TimFox:
I have not seen a reference to this, but I believe train cars with sliding power contacts to DC feed (third rail or overhead wire) use capacitors on the vehicle to mitigate rough connection.
Gyro:

--- Quote from: schmitt trigger on May 02, 2020, 04:29:12 pm ---I know that New York’s subway, Paris metro and others still use DC. But how about London’s tube?

--- End quote ---

Yes, 600V DC irrc. The London tube actually has a fourth (centre) rail. It returns current through this insulated rail, rather than the running rails, to prevent corrosion of surrounding metal structures, pipes, etc.

UK suburban 3rd rail systems are also 600V DC. They used to use mercury arc rectifiers, I don't know about these days.


In days gone past, the London underground had its own coal fired power station near the Thames, the coal was stored under water to prevent spontaneous combustion (funny how you remember little facts like that), but these days the supply is derived from the grid, with a gas turbine powered backup station.

P.S. There used to be nothing better than watching the 3rd rail slippers on a train sparking violently on a really cold, frosty morning (school day memories!). I suppose it's all VFDs these days, but back then, it was brushed DC motors and stepped resistor current controllers.
TimFox:
The Chicago Transit Authority retired the last 6000 series ‘L’ cars in 1992, after 42 years of service.  IIRC, there were three forward settings on the speed lever:  resistor, series, and parallel (fastest).  Until VF drives, DC motors were the practical choice for variable speed.
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