The Current War: Why Did Westinghouse (AC) Beat Edison (DC)?

October 31, 2019 | 9:37 am
A chromolithograph print of the 1893 World's Fair in ChicagoLibrary of Congress, no known restrictions on publication.
Mark Specht
Western States Energy Manager/Senior Analyst

As communities across California face widespread power outages and the debate over how to keep the grid reliable rages on, I decided to go to the movies for some historical context on our electric grid, seeing The Current War: Director’s Cut on opening night. With a big-name cast, my hopes were high, but the movie was just OK.

It’s a shame the movie wasn’t more compelling, because this is a fascinating story that deserves much more attention. The movie portrays the late 19th century “war” between George Westinghouse and Thomas Edison that would ultimately determine which technologies were used to build the foundation of the electric grid we use today. While Edison championed direct current (DC) systems, Westinghouse promoted alternating current (AC) systems, and the competition between the two was fierce.

While walking out of the theater, I couldn’t stop wondering: why exactly did Westinghouse’s AC systems triumph over Edison’s DC systems?

After doing a little digging, I found the answer.

Warning: This post contains spoilers, if there is such a thing for a historical film.

AC vs. DC

The fundamental difference between AC and DC electricity is that DC flows steadily in one direction (hence “direct” current) and doesn’t change over time, while AC oscillates back and forth (hence “alternating” current) and constantly changes with time.

AC electricity alternates back and forth over time, while DC electricity stays constant.

The film explained that the major challenge for Edison’s DC electricity was that it couldn’t be transmitted long distances. As a result, Edison’s system required a power plant every mile or so. While that works fine in densely- populated areas like New York City (which was the location of the United States’ first power plant, built by Edison), that model was extremely expensive and impractical in more rural areas.

But I also knew that today, some of world’s longest transmission lines use DC electricity.

So what gives? If DC electricity is a great option for modern long-distance transmission lines, why couldn’t Edison transmit his DC electricity further?

Transformers made AC the winner

The answer actually has less to do with differences between AC and DC and much more to do with a little-known component of our electric grid: transformers.

No matter what you do, transmission of electricity involves energy losses. (Unless you have a superconductor!) But you can minimize those losses by transmitting electricity at higher voltages. Voltage can be thought of as the “push” that moves charged particles and creates electrical current – the harder you push, the less energy you lose. Transformers are the key technology used to change voltage so you can push harder (and lose less energy) when transmitting electricity.

Electricity generation and consumption all happen at lower voltages, and transformers are used to increase the voltage before transmission (to reduce energy losses) and decrease the voltage back down before the electricity gets consumed.

You can think of high voltage transmission lines as an empty highway where cars cruise along at high speeds, and you can think of low voltage lines as side streets where cars go much slower. The transformer is the connection between the high voltage and low voltage lines, or in the highway analogy, it’s the highway on and off ramps that connect the side streets to the highway.

Transformers are an essential part of the grid – they increase the voltage (“step up transformers”) before long-distance transmission and decrease the voltage (“step down transformers”) before distributing electricity to customers for use. Transmitting electricity at higher voltages helps minimize energy losses.

Inventors of the late 19th century understood how to make transformers, but the kicker here is that transformers only work on AC electricity. Going back to the fundamental difference between AC and DC electricity that I explained earlier, transformers require a time-varying voltage to function, and since direct current is constant and alternating current is time-varying, transformers only work with AC electricity.

At the time, there wasn’t any easy method for changing the voltage of DC electricity, and this is what (temporarily) doomed DC electricity. Since there was no way to increase the voltage of DC electricity before transmission, DC electricity couldn’t travel very far without major losses, making DC systems inferior to AC systems.

High-voltage DC transmission lines carry electricity between the Washington/Oregon border and Southern California via the Pacific DC Intertie.

But DC has made a comeback

It wasn’t until much later that engineers developed the technology that could be used to efficiently convert AC to DC, which helped usher in the era of high-voltage DC transmission lines. Since high-voltage DC transmission has lower energy losses than AC over very long distances, the world’s longest transmission lines use DC electricity. For example, the US has an 846 mile high-voltage DC transmission line connecting the Washington/Oregon border to Southern California.

Westinghouse for the win

The climax of the film comes when Westinghouse is playing pool with Nikola Tesla (yes, the inventor for whom the electric car company is named). The phone rings, and Westinghouse learns that his bid to power the 1893 Chicago World’s Fair was accepted.

At this point, it’s game over for Edison. Westinghouse and his AC electricity systems have won.

Confession: I was rooting for Westinghouse the whole time

Before wrapping up this post, I must admit that I was rooting for Westinghouse throughout the entire movie. It just so happens that my grandfather worked at Westinghouse Electric Corporation for his entire career. My grandfather even patented numerous inventions (many of which were new technologies for transformers), and Westinghouse Electric Corporation held those patents.

But to complicate things even further, my wife’s grandfather worked for General Electric (which is the Edison successor company). So I guess it’s a good thing my wife didn’t come see this movie with me!

Posted in: Energy

Tags: California, energy

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Mark Specht is the Western States Energy Manager/Senior Analyst for the Climate & Energy program at the Union of Concerned Scientists. In his role, he leads research and advocacy efforts in California and other Western states to advance the transition to a less polluting and less carbon-intensive energy system.