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American Lit: 1920

American Lit: 1920

Washington, D.C., circa 1920. "Congressional Library power plant." 8x6 inch glass negative, National Photo Company Collection. View full size.


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Paralell Wired Lamps -

I would agree with Bunke and argue that the lamps in the overhead fixtures were wired in parallel as the lamp fixture over the operator and rotary converter have what appears to be a burned out lamp, i.e. only 4 appear to be illuminated.

The rotary converter most likely was for the operation of elevators as AC motors for this purpose did not appear until much later.

M-G Set

This plant's purpose was most likely to convert 60 Hz to 25 Hz via a motor-generator set.

In the 1920's, 60 Hz was already the standard in the US for power generation, but 25 Hz was widely used for motor drives requiring precise and variable speed control.

For instance an elevator drive motor that needs to accelerate slowly, then maintain a consistent speed, then decelerate slowly.

Later years saw better development of voltage control that would better allow precise motor speed control and 25 cycle disappeared from common use.

(Believe it or not, US Steel in Gary, IN had 25 Hz equipment in service until 1997. They used a M-G set just like this one for just that purpose, theirs was quite a bit larger in size and capacity.)

Series vs Parallel

In response to Sulzermeister: if the lamps were in series, one burned out bulb (of which there appear to be at least two) would cause the rest of the bulbs in the fixture to be dark as well. My guess is a parallel 110v arrangement.

Rubber mats don't work for AC

@landtuna - a rubber mat will only protect you from DC or low frequency AC.

AC at higher frequencies and/or voltages will treat you, the rubber mat, and the conductor beneath it as a capacitor (your feet are one plate, the conductor underneath the mat is the other and the mat is the dielectric). The capacitor will pass the AC current through you.

You said you were on a destroyer. Lots of salt air, and probably a light coating of salt on the rubber mat, too. That may also have been a conduction path to ground.

Not on the tour

I visited LOC last year. Seeing this install or any of its remnants would have been a highlight.

5-Lamps Burning

The light fittings (fixtures in US speak?) each have 5 lamps. I'd guess that they're 110V lamps in series across a traction voltage DC supply. The machine might be a rotary converter with its barring motor nearest the camera.

Rubber mat safety

In fact, if he stays on the rubber mat, he will be safe from touching any single conductor. If he touches a "hot" line, no consequential current will flow and he will "float" up to the conductor voltage. If he steps off and gets grounded, or touches the other conductor, then, that would be a problem.

Mr. Natural

Accustomed as we are to seeing people in period shots either frowning or maintaining rigid photo-poses, it's refreshing to see real life reflected on the face of a subject. "OK, pal, you done with that thing? I got work to do."

It's perfectly safe

See, you just stand on the rubber mat and you'll be fine.

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