Why is it called Park’s, not Blondel’s, Transformation?

The History of the DQ Transformation

Park’s transformation can be considered to be the single theoretical contribution that triggered the development of advanced design, control, and analysis of electrical machines (motors and generators). To most practicing engineers and researchers in this field, the story goes like this:

Robert H. Park (1902–1994)
André-Eugène Blondel (1863–1938)

After Nikola Tesla invented the AC machine in the 1880s, it took the electrical engineers over 3 decades of struggling with AC circuits analysis before Robert H. Park (1902–1994) published his seminal paper, in 1929, “Two Reaction Theory of Synchronous Machines”. In that paper, the brilliant young engineer solved the problem mathemagically by introducing the dq0-transformation that has been called after him, the Park’s transformation, which transforms the natural 3-phase AC reference frame into a fictitious 2-circuit rotating reference frame.

The Park’s transformation is a brilliant idea indeed, except that it was not invented by Park… Have you ever heard of André-Eugène Blondel (1863–1938)? Here is the complete story.

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Electric Motors Should be More Fun

We encounter mechanical phenomena all the time. We see things move, fall, spin, oscillate, break, etc. Electrical phenomena, on the other hand, are not always visible. Therefore, it has become a common practice to use mechanical analogies to explain and teach less visible concepts.

Classical analogy. Source

We compare electrons to water when explaining voltage, current, and Ohm’s law. The inductor is often compared to a spring, and the capacitor to a mass/inertia. The electrical resonance can then be compared to the mechanical resonance.

Even control engineers use mechanical analogies to illustrate their concepts; the proportional-derivative controller is nothing but a mass-damper system in that sense.

The theory of AC motors involves many difficult concepts, often explained with mathematical formulas and graphs. This is an obstacle to effective teaching and vulgarization. In this post, I propose 3 ideas to make the teaching of AC motors more fun. My goal is to stimulate more ideas and analogies; if you have some, please share them.

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Edith Clarke – a Pioneering Woman Engineer

Edith Clarke (1883-1959)

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.

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