Prior to the development of the rectifier, streetcar and other DC electric railways used rotary converters to change alternating current into direct current. I wonder how many of these machines are preserved and, of those, how many are still in service. We have a working one at the Western Railway Museum (aka Rio Vista Junction) and I believe that the Southern California Railway Museum has one. (Ours is a Sacramento Northern "Automatic Portable Sub Station" designed to start automatically as a train approaches and shut down once the train is drawing current primarily from the next substation.)

To add a little to what Joe has said: the rotary substation at RVJ is the first automatic portable substation built for the electric railway industry, the principles and design of automation being developed by Bion J. Arnold for stationary substations a few years earlier. The one at RVJ was built (1920) because the SN was having low voltage problems about 5 miles north of Sacramento, in the vicinity of a station named Del Paso. Once they figured the needs of the situation, they installed a stationary substation of the same capacity at Del Paso. By the mid-1950s, the portable one wound up being the power supply for the short section of catenary at the WP's shops in Sacramento which was used to test the electric locomotives after shopping. After the discontinuance of the electrification in Marysville-Yuba City in 1965, the WP donated the portable to RVJ and the machinery out of the Del Paso building to SCRM. About 15-20 years later, WRM went up to Del Paso, dismantled the building and re-erected it to house the solid state substation acquired from the BART test track. WRM has a second rotary converter, but it hasn't been set up for use. WRM usually runs the portable sub on the first weekend of the month. Seashore has an M-G set, but I don't know how often they run it these days. I understand that SCRM hardly runs theirs anymore. East Troy no longer operates it's rotating conversion equipment, having scrapped all the HV switchgear and transformers quite a while ago.

As a youth, I used to remember members starting up the substation at the Ohio Railway Museum. Looking through old annual reports, in 1960, they report installing of a "motor-generator" to create the 600v DC (allowing them to retire gas-electric Erie 5012 from the service).

I guess this is different from a rotary converter, since sounds like an AC motor runs a DC generator. Is this correct?

Here's the annual report in question:

http://www.columbusrailroads.com/new/pdf/orm/orm%201960%20report.pdf

Bob

The progression of conversion equipment is approximately: 1880s-1890s, dyanmo driven by a stationary steam engine; latter 1890s the "M-G set", a generator (renamed from dynamo) driven by a separate motor which operates on some multiple of 3 phase AC; 1900-1910: synchronous converter, which is can be thought of as essentially an M-G set with only one set of field windings and and a single armature which has a commutator on the DC end and slip rings on the AC end -- this is also what is known as a "rotary converter"; mercury arc rectifier, water cooled and almost simultaneously developed with the rotary converter; "tungar bulb" glass bulb type mercury arc (I have no date for these; Ferrymead in NZ and a number of other COTMA members use them -- they a bit strange to observe in operation, like right out a science fiction movie); ignitron tube, a variation on the "tungar bulb" type and is water cooled, used in the first order of PRR E-44s; NH "jets" etc.; and solid state rectifiers, which is the present "state of the art".

Did most of the electric box cabs on the class have onboard M-G sets or rotary converters. N&W used rotary phase converters to convert single phase to three phase for the motors. I don't know about the Virginian, but their GE's from the fifties had M-G's.

What does RVJ, SCRM and WRM stand for?

WRM = Western Railway Museum, located at Rio Vista Junction on the old Sacramento Northern Railway. Rio Vista Junction was not a railroad junction, but was the transfer station for buses to Rio Vista, CA.

RVJ = WRM (see above)

SCRM = Southern California Railroad Museum, formerly Orange Empire Railroad Museum, located at Perris, CA.

General Electric developed the Tungar (Tungsten-Argon) bulb in 1916.
http://www.r-type.org/pdfs/tungar.pdf

> Did most of the electric box cabs on the class have onboard M-G sets or rotary converters.

Being DC, the MILW electrics were straight resistance control, all of them: the switchers, box cabs, bi-polars, the WH ones, and the Joes. Same is true for the BA&P. As far as I know, the MILW's substations all used M-G sets: one motor driving two 1500v generators connected in series. This had to do with suppressing ring fire on the generator commutators and minimizing flashovers between brush holder sets.

> N&W used rotary phase converters to convert single phase to three phase for the motors. I don't know about the Virginian,

The boxcabs on the VGN were the same. What was different is the configuration of the motors in relation to the jackshafts and axles.

> but their GE's from the fifties had M-G's.

as did the GN's single phase locomotives. All the single phase stuff north of Washignton DC (B&M, NYNH&H, PRR, RDG) were single phase AC using isolation type auto-transformers on the MU cars and locomotives (excepting things like the E-44s and NH Jets).

Note to our readers: we are talking about the equipment inside each locomotive and on each MU car, not what was/is in substations. Interurban railways which used AC are a separate topic of discussion.

> General Electric developed the Tungar (Tungsten-Argon) bulb in 1916.

Correct (anode was carbon), I was winging it and sort of misspoke. The principle of a mercury arc rectifier dates from 1880 (Austria), but they were not commercially developed until 1902 by Hewitt (US) when he invented the glass envelope type. Some models appear to have been housed inside a round steel tank, and somewhere there is a picture of one under development for RR use, mounted on a flatcar and being towed by a DC locomotive on GE's test track at Schenectady. The SN's substation at Valdez on the Holland Branch had one of these. "Tungar bulb [type]" was a reference to the glass envelope, which was a large slightly conical glass bulb 3-4 feet tall and 2 feet in diameter at its widest with arm-like protrusions for the electrodes. I watched one of them operating at Ferrymead, and with all the eerie bluish glow, it was like being in your own personal VR sci-fi movie watching a creature from Planet X-9. This was the 600v one powering their streetcar line; they also have a 1200v one for their suburban trackage.

The Northwest Railway Museum at Snoqualmie, WA had a rotary converter that came from Seattle Transit. I don't know what became of it.

The Fox River Trolley museum in South Elgin Illinois has a rotary converter from the CA&E Batavia branch. I believe it is currently out of service.

Iowa traction in Mason city Iowa has a rotary converter from the Chicago North Shore and Milwaukee in Highwood, IL

It would appear to follow that 'Tungar' rectifiers would have an argon-filled envelope and use tungsten heaters for the initial mercury vaporization. I don't think there is a major difference in the fabrication or sealing methods for glass envelopes between carbon-vacuum and tungsten-argon. It would be interesting to know the argon pressure used in these things.

There was a rotary converter of some type operational on the New York ex-IRT, just north of the tunnel at about 181st St, at least into the '80s. I recall this as being a motor-generator type, not a synchronous converter or single-frame machine. It would be interesting to see what became of it.

The GN electrics were motor-generator IIRC.

NTHT had two rotary generators(?) that were originally built for the Shreveport trolleybus system, then used for the original Leonard Subway and then backup for the Tandy Subway. The copper mice got into them and they were damaged beyond our ability to repair them and were scrapped.

At one time, Dallas MATA had a rotary convertor that I understand was off the deck of a 600 volt Texas Electric locomotive that allowed it to operate on the 1200v section. Not sure if that still exists.

A fun thing you could do with a mg set or just a generator if you have rotational power on hand, was to wire the windings in series with the rotor. As your car moved further down to line it would start sucking up more current due to voltage drop, since the current being drawn would first go through the windings this would cause the voltage the generator was making to go up making up for the voltage drop automatically. This would only work if you're using one car on that line however if another one was put on that line and it was closer to the power source it could get overloaded. On the subject of mercury are rectifiers here is a video from a tramway museum pulling some major power https://youtu.be/O7E4vNYuv4E

Also recommend reading https://play.google.com/store/books/det ... woAQAAMAAJ for more information about rotary converters and substations.

Toledo Lake Erie & Western has one, inherited from the Waterfront Electric group. Don't know if it works or what to do with it.