Millikan-Sorensen Vacuum Switch
Dublin Core
Title
Millikan-Sorensen Vacuum Switch
Description
Transmission of power is dangerous when high voltage drives immense amounts of current. When Big Creek finished construction, ultra-high voltage (up to 220 kV) was generated and ready to be transmitted [7]. Thus, significant safety challenges arose, specifically in regards to interrupting electrical arcs. The traditional oil circuit breakers that relied on oil to quench arcs faced growing problems such as fire risk, large size, and high maintenance [7]. Recognizing this, in 1923, Southern California Edison partnered with Caltech to build a high-voltage laboratory [4]. The photo above depicts all three switches that were developed and tested [8]. The bottom center shows the first prototype followed by the second on the left and the third prototype on the right. The large metal caps apart of the second and third switch were used to create vacuum-tight joints for the lead-in conductors [8].
The second vacuum switch was a larger version of the switch Sorensen and Mendenhall first tested [8]. From a 1926 paper by Sorensen and Mendenhall titled “Vacuum Switching Experiments at California Institute of Technology,” high success is reported as “the switch was operated as a single-pole switch to open and close this circuit more than 500 times without showing any burning of the switch contacts” [8]. It was even tested at the Torrence substation of the Southern California Edison Company where it was able to interrupt currents as high as 600 amperes at 12,780 volts [8]. Subsequently, the third switch was brought to Laguna-Bell substation where it was able to interrupt 926 amperes at 41,500 volts [8]!
Works Cited
[1] “100 Years Young: Big Creek Hydroelectric Plant Still Going Strong.” Edison International | Newsroom, https://newsroom.edison.com/stories/100-years-young:-big-creek-hydroelectric-plant-still-going-strong. Accessed 17 Mar. 2026.
[2] “Power Lines Around Los Angeles: Isolation, Interconnection, and Aesthetics.” Boom California, 21 May 2020, https://boomcalifornia.org/2020/05/21/power-lines-around-los-angeles-isolation-interconnection-and-aesthetics/.
[3] Fox, Donna, Robert J. McEliece, and Babak Hassibi. “An Electrifying Century: An Early History of the Caltech EE Department.” ENGenious, 8 Oct. 2010, engenious.caltech.edu/articles/history-EE-Department-century. Accessed 5 Feb. 2026.
[4] Heilbron, J. L., and Robert W. Seidel. Lawrence and His Laboratory: A History of the Lawrence Berkeley Laboratory, University of California Press, 1990. UC Press E-Books Collection, https://publishing.cdlib.org/ucpressebooks/view?docId=ft5s200764&chunk.id=[section
identifier]. Accessed 5 Feb. 2026.
[5] Millikan, Robert A., and Royal W. Sorensen. Brief for Millikan and Sorensen. Robert A. Millikan and Royal W. Sorensen v. Talma T. Greenwood, Interference No. 56557, United States Patent Office, [Year, e.g., 1928], [Collection Name, e.g., Royal W. Sorensen Papers], [Box 3], Caltech Archives, Pasadena, CA.
[6] Ornelas, Gabriela. “Big Creek’s Powerhouse 8 Marks 100 Years of Hydroelectric Power.” Energized by Edison, 8 Oct. 2021, energized.edison.com/stories/big-creeks-powerhouse-8-marks-100-years-of-hydroelectric-power. Accessed 5 Feb. 2026.
[7] Record, Historic American Engineering. Big Creek Hydroelectric System, East & West Transmission Line, 241-Mile Transmission Corridor Extending between the Big Creek Hydroelectric System in the Sierra National Forest in Fresno County and the Eagle Rock Substation in Los Angeles, California, Visalia, Tulare County, CA. Still image. California -- Tulare County -- Visalia, https://www.loc.gov/pictures/item/ca3976/. Accessed 17 Mar. 2026.
[8] Sorensen, Royal W., and Hallan E. Mendenhall. “Vacuum Switching Experiments at California Institute of Technology.” Transactions of the American Institute of Electrical Engineers, XLV, Jan. 1926, pp. 1102–07. Semantic Scholar, https://doi.org/10.1109/T-AIEE.1926.5061306.
The second vacuum switch was a larger version of the switch Sorensen and Mendenhall first tested [8]. From a 1926 paper by Sorensen and Mendenhall titled “Vacuum Switching Experiments at California Institute of Technology,” high success is reported as “the switch was operated as a single-pole switch to open and close this circuit more than 500 times without showing any burning of the switch contacts” [8]. It was even tested at the Torrence substation of the Southern California Edison Company where it was able to interrupt currents as high as 600 amperes at 12,780 volts [8]. Subsequently, the third switch was brought to Laguna-Bell substation where it was able to interrupt 926 amperes at 41,500 volts [8]!
Works Cited
[1] “100 Years Young: Big Creek Hydroelectric Plant Still Going Strong.” Edison International | Newsroom, https://newsroom.edison.com/stories/100-years-young:-big-creek-hydroelectric-plant-still-going-strong. Accessed 17 Mar. 2026.
[2] “Power Lines Around Los Angeles: Isolation, Interconnection, and Aesthetics.” Boom California, 21 May 2020, https://boomcalifornia.org/2020/05/21/power-lines-around-los-angeles-isolation-interconnection-and-aesthetics/.
[3] Fox, Donna, Robert J. McEliece, and Babak Hassibi. “An Electrifying Century: An Early History of the Caltech EE Department.” ENGenious, 8 Oct. 2010, engenious.caltech.edu/articles/history-EE-Department-century. Accessed 5 Feb. 2026.
[4] Heilbron, J. L., and Robert W. Seidel. Lawrence and His Laboratory: A History of the Lawrence Berkeley Laboratory, University of California Press, 1990. UC Press E-Books Collection, https://publishing.cdlib.org/ucpressebooks/view?docId=ft5s200764&chunk.id=[section
identifier]. Accessed 5 Feb. 2026.
[5] Millikan, Robert A., and Royal W. Sorensen. Brief for Millikan and Sorensen. Robert A. Millikan and Royal W. Sorensen v. Talma T. Greenwood, Interference No. 56557, United States Patent Office, [Year, e.g., 1928], [Collection Name, e.g., Royal W. Sorensen Papers], [Box 3], Caltech Archives, Pasadena, CA.
[6] Ornelas, Gabriela. “Big Creek’s Powerhouse 8 Marks 100 Years of Hydroelectric Power.” Energized by Edison, 8 Oct. 2021, energized.edison.com/stories/big-creeks-powerhouse-8-marks-100-years-of-hydroelectric-power. Accessed 5 Feb. 2026.
[7] Record, Historic American Engineering. Big Creek Hydroelectric System, East & West Transmission Line, 241-Mile Transmission Corridor Extending between the Big Creek Hydroelectric System in the Sierra National Forest in Fresno County and the Eagle Rock Substation in Los Angeles, California, Visalia, Tulare County, CA. Still image. California -- Tulare County -- Visalia, https://www.loc.gov/pictures/item/ca3976/. Accessed 17 Mar. 2026.
[8] Sorensen, Royal W., and Hallan E. Mendenhall. “Vacuum Switching Experiments at California Institute of Technology.” Transactions of the American Institute of Electrical Engineers, XLV, Jan. 1926, pp. 1102–07. Semantic Scholar, https://doi.org/10.1109/T-AIEE.1926.5061306.
Source
Caltech Archives and Special Collections, High Voltage Research Laboratory
Date
1924-1926*
Still Image Item Type Metadata
Original Format
Photograph
Physical Dimensions
4" x 6 "
Citation
“Millikan-Sorensen Vacuum Switch,” Electrifying Los Angeles, accessed July 2, 2026, https://www.electrifying.collopy.net/items/show/3.