Pennsylvania Trolley Museum has not just one, but two 500 kW rotary converters. Neither is presently in service, but we have very long term plans to use one of them (the “Thompsonville” machine) to recreate a classic Pittsburgh Railways Company substation. Both a substantial infusion of cash and a quieting down of our other capital projects will be necessary before that project can become a reality.

The Thompsonville rotary (the technical name is “synchronous convertor”) was built by Westinghouse in 1916 and was initially installed in a portable substation on PRCo’s Wilkinsburg-to-Verona suburban line. Around 1928 or 1929 it was installed in a new permanent substation at Thompsonville on the Pittsburgh-to-Washington interurban line, that event coincident with the introduction of new higher horsepower interurban cars. The Washington interurban was discontinued in August of 1953, but Thompsonville remained operable through the fall while PRCo work cars salvaged signals and other equipment. Thompsonville Substation was restarted one last time on February 7, 1954 to power the movement of our three original cars between the truncated end of the interurban line at Drake Loop and our nascent museum location at Arden. Hence this particular machine has a special connection to PTM’s history.

Thompsonville substation’s building was subsequently gutted and the rotary moved to the PRCo substation at West Library. The brick Thompsonville building is still there, repurposed for other use, and provides a three dimensional blueprint for our planned replica substation. We obtained the rotary machine, plus the associated switchgear, in 1984 when the West Library substation was replaced by a solid state rectifier installation as part of LRT upgrades to the remaining Pittsburgh trolley system.

The Thompsonville rotary is a 6-pole 500 kW compound wound 600-volt machine. We have most of the major parts to install it in a replica Thompsonville building. However, applicable codes are radically different now than they were back in the day. Since, for all practical purposes, this will be a “new” installation, much of the classic “Doctor Frankenstein” switchgear will be merely for show, as nothing can be “grandfathered”. The “New Thompsonville” design will therefore incorporate modern switchgear for safety, all discretely hidden behind the (disconnected) authentic switchgear panels.

PTM’s second rotary convertor is also a 6-pole straight shunt 600-volt Westinghouse machine that came from the Duquesne Light Company’s Stanwix Substation in downtown Pittsburgh. It supplied 550 volt DC to customers who required it for large elevators, etc. We obtained it in 2002 after DLCo persuaded their last direct current customer to upgrade their equipment. It is a much more modern and somewhat smaller physically than the Thompsonville machine. I do not know the exact date of build but would guess the very late 1920s or early 1930s. Duquesne (pronounced “Due-KANE” ) Light and Pittsburgh Railways were sister companies under the umbrella of the strangely-named Philadelphia Company, but the Stanwix substation was always independent of PRCo’s trolley power system. Both of our rotary converters have been stored indoors since acquisition. They're dusty, but dry.

There was also a second Westinghouse 500 kW convertor at Stanwix which fed the same commercial DC system. It was older than the Thompsonville machine and, like the rotary we obtained, had been well cared for. It was sent to the Baltimore Streetcar Museum, but I’ve no information of what became of it there.

There’s one other PRCo rotary converter in captivity. Around 1985, a 2000 kW Westinghouse rotary from the South Hills Junction substation was salvaged by a private individual who kept it at an industrial site near New Castle, Pennsylvania. When he cleared out that location, the rotary was sent to the Youngstown Steel Heritage group. Perhaps Rick Rowlands can pick up its story from there.

/s/ Larry
Lawrence G. Lovejoy, P.E.
Director of Engineering
Pennsylvania Trolley Museum, Inc.

Andy,

Thank you for the update on the Tandy rotary. The rotary was in use when I visited a few years before the subway closed. The original underfloor of the DC Transit "Winnebago" cars with DCTS shop markings on the running gear, plus the rotary in service gave the Tandy operation a certain trolley museum charm. I am surprised the whole thing lasted as long as it did.

Best,

Wesley

Wesley, you're welcome. I got to see one started and operating before it was removed. I wish we could have saved one.

Hi Larry. Thanks for your reply. Joe is trying to run down how many railway size operational rotary converters there are in the US today. Do you know of any that are currently operational now? Thanks. David Johnston

David. Joe, Ask Gary Baker next time he ties up at Rio Vista. He is the caretaker/tech and most knowledgeable person regarding the demand sensing auto start/stop, think 6-phase, 300 or 350KW General Electric synchronous converter substation equipment from Del Paso on the Sacramento Northern donated by Western Pacific to the S. Cal. Rwy Museum in Perris. It's complete and believe operable, set up in a period, classic steel prefab former gas station light structural steel building with large windows all around so visitors can see the machine, watch the sequencing drum controller start the rotor spinning up to synchronous speed, lower brush rigging on the DC output end commutator then close the line breaker that puts the machine on line automatically. The AC and DC switch gear, the breakers and meters were installed as they were on original slate panels behind the machine. The high speed overload circuit breaker trip surge buffer resistor grid banks are under roof outside in a chain link fenced area where the gas station pump island was. Since it consumes energy just spinning (windage) and the museum operation never lent itself to auto start/stop, once diode rectifier substation equipment was acquired and set-up, the converter became back up and primarily a static display. Somewhat ironic that it's housed in a former gas station if the future is to be battery electric vehicles that need charging stations not gas stations. (Sorry, electric vehicle charging isn't a service available at Del Paso) Anyway, a complete, operating synchronous converter is on display in full view, fitting for museum visitor experience.

Visicomm Industries will sell you a new, repeat NEW, 3-phase rotary converter, but it's an AC to AC frequency converter, 50 Hz to 60 Hz or vice-versa.

Amtrak has overhauled two PRR-era 60 Hz-25 Hz rotaries at its Lamokin Substation (Chester PA). I think they're 3-phase 60 Hz in and single-phase 25 Hz out.

Per Visicomm:
"Rotary frequency converters are more rugged and flexible in the loads they can handle aside from greater motor starting surge capacity. For example, SCR loads and welders are almost insurmountable problems when using a solid-state approach."

https://50hz.com/rotary-frequency-converter/

Phil Mulligan

Larry, from that same private collector, Branford has a 1000kW unit that weighs 12 tons. We have no intention of using it for power conversion, but it will ultimately be put on display.

The advantage of a rotary converter over a Motor driven Generator is that you are just turning a giant rotary switch which takes less effort than spinning a large capacity generator.

That's kinda true. The theory of the synchronous converter is pretty complicated, and I'd put everyone to sleep trying to go into it. But it is more than just a synchronously rotating switch. If we had just that, we'd have essentially a mechanical version of a mercury or silcon rectifier, with either 6 or 12 switches connecting between the AC phase leads and the DC output. The result would be crappy, ripple-ridden DC (which is exactly what you get out of rectifiers, btw).

The synchronous converter is essentially a synchronous motor and a DC generator sharing the same field structure and sharing either end of the same armature. But unlike a motor-generator set, you don't have the ability to independently change the DC side field excitation, so the ratio of phase-to-phase AC RMS input voltage and DC output voltage is fixed. Each armature coil is at a different phase so the resulting "rectification" by the commutator, just as in a pure DC generator, has as many "pulses" as there are commutator bars, which is a lot smoother than 6- or 12-puse rectifiers.

Like a synchronous motor, field excitation can be adjusted for load, to achieve a unity power factor, or even to create a leading power factor to compensate for the naturally lagging PF nature of the grid and induction motor loads.

The synchronous converter is going to be lighter and smaller than an equivalent capacity M-G set because of the shared field and shared armature. Both types of machine also have the advantage
over rectifiers that they have short-duration load smoothing ability because of the rotational inertia of the armature.

For typical museum use, M-G sets and rotary converters are a big money loser, because the standby costs of supplying the power to keep the machine turning are considerable. For a busy electric railway, where the load is almost constant, the efficiencies are actually comparable. But the reduction in size and weight, plus the elimination of maintaining moving parts, made it a no-brainer for railway companies to switch.

A rotary converter has the advantage over an MG set in that not all of the power must be converted to mechanical energy as it is on an MG. Some does stay in the electric domain.

Wiki has a good explanation.
https://en.wikipedia.org/wiki/Rotary_converter

Here are some photos of a rotary on display at IRM. Their explanatory sign said it was a motor and generator in one which is not quite true but my pics are from several years ago and perhaps it has been updated. I'll look next visit.

Might this be a booster converter? It's been a quite a while, but I recall something about boosters being able to vary the DC output voltage. All those deflectors on the commutator could be a sign of this being used on a 3rd rail operation.

Another museum that has a rotary converter is the Illinois Railway Museum; the equipment is from the Chicago, Aurora & Elgin Railroad. It is not operational. They also operate a complete C,A & E sub station to provide 600-volt power. There was an article in Rail & Wire about them, about ten years ago.

Ted Miles, IRM Member

the Electric City Trolley Museum in Scranton, PA has a very good electric equipment display.

Hershey Transit Lebanon Division substation report and photo.

The Illinois Railway Museum has a complete sub-station from the Chicago, Aurora & Elgin Railroad; the use it to make their 600-volts DC.

They also have a smaller rotary converter; I think it is from The Milwaukee Electric Railway & Light Company.

Ted Miles, IRM Member