Every electrical engineer who works in the field of alternating current (AC) systems should be familiar with the Clarke Transformation concept. It is a fundamental concept used for control, monitoring, and analysis of electric motors, generators, variable speed drives, electric grids, AC power converters, etc.
What not so many engineers know is that Clarke is a (pioneering) woman engineer called Edith, who managed to find a place for her talent in one of the biggest masculine industries in the first half of the 20th century.
Throughout her career, Clarke was often the first in her endeavors, whether the first professionally employed female electrical engineer in the United States, the first female full voting member of the AIEE (that would become IEEE), or the first full-time female professor of electrical engineering in the US. She had substantially contributed to the development of mathematical methods that simplify the design and analysis of AC power systems (equivalent circuits, graphical analysis, etc.).
Life and Career
Clarke was born in Howard County, Maryland, in 1883 and was orphaned at a young age. She studied mathematics and astronomy at Vassar College in Poughkeepsie, New York, USA, and received a bachelor’s degree in 1908. Then after 3 years as a teacher (in mathematics), in the fall of 1911, she enrolled in the civil engineering program at the University of Wisconsin, but left after a year to become a computing assistant to George A. Campbell at American Telephone and Telegraph (AT&T), where she could acquire good knowledge about the transmission lines and electrical circuits.
From MIT to GE
Edith Clarke enrolled in electrical engineering at Massachusetts Institute of Technology (MIT) in 1918, to earn an M.S. degree in 1919, and was the first woman to receive an electrical engineering degree at the school. She then joined General Electric (GE) in Schenectady in 1920, where she trained and directed a small group of women computers doing calculations of mechanical stresses in turbine rotors. In 1921, she filed a successful patent application on a graphical calculator to be used in solving transmission line problems, and it was published in her first technical paper in the GE Review in 1923.
Being a female engineer, she could not have the same status or salary of an engineer at GE. She left GE in 1921 to accept a one-year teaching job at a women’s college in Turkey. The following year, she returned to the US to become a salaried electrical engineer in the Central Station Engineering Department at GE.
University of Texas and Retirement
Clarke retired from GE in 1945 and joined the electrical engineering faculty at the University of Texas in 1947. In 1948, she became the first woman to be elected a Fellow of the AIEE. She retired to her native town in Maryland in 1956, where she died in 1959 at age 76.
Contributions and Publications
In February 1926, Clarke became the first woman to present an AIEE paper that was later published in the Transactions of the AIEE. In the paper, she explained how equivalent circuits could be used in calculating the stability of power systems.
In March 1931, she presented an AIEE paper on the method of symmetrical components. This method, developed earlier by C. L. Fortescue and others, facilitated the analysis of unbalanced three-phase circuits by converting a problem into equivalent symmetrical circuits that were simpler to analyze. Clarke went on to contribute to the development of the method of modified symmetrical components and published a tutorial paper on the subject in 1928.
She co-authored several papers with Charles Concordia, known for the Concordia Transformation, an equivalent power conserving form of Clarke Transformation.
In 1943, Clarke published a book titled Circuit Analysis of A-C Power Systems, based on her notes for lectures to GE engineers, and intended for use as a textbook in engineering schools or as a reference book for power engineers. The principal focus of the book was on the use of symmetrical components to solve problems related to polyphase power generation and transmission. She later published a second volume on the subject in 1950.
Some of Clarke’s technical papers
- K. J. Cox and E. Clarke, “Performance Charts for 3-Phase Transmission Circuits under Balance Operation,” in Transactions of the American Institute of Electrical Engineers. Part III: Power Apparatus and Systems, vol. 76, no. 3, pp. 809-817, April 1957.
- W. C. Duesterhoeft, M. W. Schulz and E. Clarke, “Determination of Instantaneous Currents and Voltages by Means of Alpha, Beta, and Zero Components,” in Transactions of the American Institute of Electrical Engineers, vol. 70, no. 2, pp. 1248-1255, July 1951.
- E. Clarke, “Impedances Seen by Relays During Power Swings With and Without Faults,” in Transactions of the American Institute of Electrical Engineers, vol. 64, no. 6, pp. 372-384, June 1945.
- E. Clarke and S. B. Crary, “Stability Limitations of Long-Distance A-C Power-Transmission Systems,” in Transactions of the American Institute of Electrical Engineers, vol. 60, no. 12, pp. 1051-1059, Dec. 1941.
- E. Clarke, H. A. Peterson and P. H. Light, “Abnormal Voltage Conditions in Three- Phase Systems Produced by Single-Phase Switching,” in Transactions of the American Institute of Electrical Engineers, vol. 60, no. 6, pp. 329-339, June 1941.
- E. Clarke, S. B. Crary and H. A. Peterson, “Overvoltages During Power-System Faults,” in Transactions of the American Institute of Electrical Engineers, vol. 58, no. 8, pp. 377-385, Aug. 1939.
- E. Clarke, C. N. Weygandt and C. Concordia, “Overvoltages Caused by Unbalanced Short Circuits Effect of Amortisseur Windings,” in Transactions of the American Institute of Electrical Engineers, vol. 57, no. 8, pp. 453-468, Aug. 1938.
- E. Clarke, “Three-Phase Multiple-Conductor Circuits,” in Transactions of the American Institute of Electrical Engineers, vol. 51, no. 3, pp. 809-821, Sept. 1932.
- E. Clarke, “Simultaneous Faults on Three-Phase Systems,” in Transactions of the American Institute of Electrical Engineers, vol. 50, no. 3, pp. 919-939, Sept. 1931.
- E. Clarke, “Steady-State Stability in Transmission Systems Calculation by Means of Equivalent Circuits or Circle Diagrams,” in Transactions of the American Institute of Electrical Engineers, vol. XLV, pp. 22-41, Jan. 1926.
- J. E. Brittain, “From Computor to Electrical Engineer: The Remarkable Career of Edith Clarke,” in IEEE Transactions on Education, vol. 28, no. 4, pp. 184-189, Nov. 1985.
- J. Brittain, “Edith Clarke and power system stability,” in IEEE Industry Applications Magazine, vol. 9, no. 1, pp. 9-10, Jan.-Feb. 2003.
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