Edith Clarke

1883-1959

The first woman employed as an electrical engineer in the US and the first female EE professor, whose Clarke transform reduces messy three-phase power math to a clean, computable form still used in motor control today.

Edith Clarke was born in 1883 in Howard County, Maryland, one of nine children, and orphaned at twelve. She used her inheritance to study mathematics and astronomy at Vassar, graduating with honors in 1908. The path into engineering was anything but open to her. She taught, briefly studied civil engineering, then took a job as a human computer at AT&T (a person who did calculations by hand), studying electrical engineering at Columbia at night. In 1919 she became the first woman to earn a master's in electrical engineering from MIT.

Even with that degree she could not find work as an engineer, so General Electric hired her to supervise a team of women computers calculating mechanical stresses in turbines. Frustrated by lower pay and status, she even left for a year to teach physics in Turkey. When she returned in 1922, GE finally hired her as a salaried electrical engineer, making her the first professionally employed female electrical engineer in the United States. In 1926 she became the first woman to present a paper at the American Institute of Electrical Engineers, showing how to calculate the maximum power a transmission line could carry before going unstable.

Her signature mathematical tool is the Clarke transform. Three-phase power systems involve three currents and voltages that are constantly shifting and interacting, which makes the equations cumbersome. Clarke's transformation re-expresses those three coupled quantities in a simpler set of components (often called alpha-beta) that decouple the problem and make it far easier to compute. She also invented the Clarke calculator, a graphical device patented in 1925 that solved transmission-line equations with hyperbolic functions ten times faster than the methods of the day. Her 1943 textbook, Circuit Analysis of A-C Power Systems, trained power engineers for decades.

Clarke's math is alive every time a modern motor spins under precise control. Field-oriented control, the technique that runs the brushless motors in drones, electric vehicles, and robots, starts by applying the Clarke transform to collapse three phase currents into a two-axis frame, then controls torque and flux separately. The US Department of Energy has called her work the first step toward smart grid technology and dubbed her the smart grid's founding mother. In 1947 she became the first female professor of electrical engineering in the country, at the University of Texas at Austin.

Fun facts

Before she could be an engineer she had to be a computer, the human kind. Clarke spent years doing calculations by hand at AT&T and GE, directing teams of other women doing the same, before GE finally let her hold the job of engineer in 1922.
Her 1925 patent was for the Clarke calculator, a simple graphical instrument that solved power-line equations involving hyperbolic functions about ten times faster than existing methods. It was a hardware shortcut for math no one wanted to grind through by hand.
Asked about being a woman in engineering, she said there was no special demand for women engineers as such, but there was always a demand for anyone who could do a good piece of work. She also lent her expertise to the turbines installed at Hoover Dam.