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1940–1949 · TWIN BRANCH'S HIGH-PRESSURE DECADE
The frontier: For one decade the steam plant at Twin Branch was a place where the country's power engineers were pushing a genuine frontier, and — unlike most local firsts — this one is documented in the profession's own journal at the time. The Electrical World of 18 October 1941 devoted its lead coverage to the plant: "Twin Branch Innovations Discussed by Designers," with Philip Sporn, the system's engineering chief, writing "Twin Branch Extends High-Pressure Economies" about his own project. The unit the designers described was built for steam at 2,500 pounds' pressure and 940 degrees, with reheat to 900; within the first twenty-four hours of starting, Sporn's colleagues recorded, the operating pressure was brought to 2,700 pounds at the popping valves. The claims that ride on that record are printed here at their carriers' strength, which is the discipline of this section. Of the plant's third unit, added in 1940–41, the city's history writes: "according to a company publication, 'the world's first generating unit to utilize steam pressure as high as 2,400 pounds per square inch in the commercial production of electric power'" — the carrier is the utility's own publication, and the claim stands as its claim. Of the fifth unit, online in 1949, De Kever's sentence carries its attribution inside it: it "held the world's record for operating efficiency by a single unit," I & M later touted. The settled strength of the matter is the trade record: the frontier itself is documented by the engineers who built it; the first and the record are the operating company's words, printed beside it, unmerged.
Sources: the Technology section of this history — Electrical World, vol. 116, no. 16, 18 October 1941, the Twin Branch lead coverage and Sporn's account (2,500 psi, 940°F, reheat 900°F; 2,700 psi at the popping valves within twenty-four hours); De Kever, Mishawaka: A History — the third unit's "world's first… 2,400 pounds" as a company publication's claim; Unit 5 (1949) and the efficiency record as I & M's touting.