This posting was originally published with Sustainable West Seattle in June 2010
War of the Currents: Round 1
Before there was HD-DVD vs. BlueRay, Mac vs. PC, or Beta vs. VHS there was AC vs. DC. And if you think that Steve Jobs and Bill Gates had a rivalry, check out Edison and Tesla, two of the greatest innovators ever and bitter foes in the War of the Currents. This posting will be a bit more technical than I usually get, but I won’t assume you know anything about electricity and there will be no math.
Electricity is the flow of subatomic electrons through a conductor, like water through a river. We use two values to describe the flow: voltage and current. Voltage is comparable to the speed of the water. If you know the voltage you know how much energy each electron is carrying (the actual speed doesn’t change). The current tells you how many electrons are flowing past a point. The total energy carried by the electrons is the Voltage X Current (does that count as math?).
Two Systems – AC & DC
There are two kinds of electrical systems: Alternating Current (AC) and Direct Current (DC). In DC the electrons and energy both flow in one direction. It’s a pretty straightforward system, like a river. In Alternating Current the electrons just move back and forth, but energy flows. It’s like an ocean wave, where energy moves across the ocean’s surface and finally crashes on the shore, but the water just moves a short distance back and forth. One more key bit of physics; the energy loss through transmission (getting the electricity from where it’s generated to where it’s consumed) depends on the voltage: for a given amount of energy higher voltage means less energy loss.
In the late 1800 Edison and his company, General Electric, built DC generation systems. There was no simple way of changing the voltage, so transmission was at the same voltage as was needed by the device that was being powered (at this time it was mainly for lighting). If you needed more than one voltage, then you would need extra wires. This meant that the transmission losses were significant and the power plants needed to be close to the demand, within a few miles. This ruled out the use of renewable energy sources (i.e. hydropower) since those weren’t close enough to the demand.
In 1884-1885 the invention of a simple AC transformer allowed power to be converted easily, cheaply and efficiently from one voltage to another, but only for AC power. This allowed generation at one voltage, transmission at another and use at any voltage that the device required.
Edison & Tesla Propose Different Systems
For about 10 years there was an intense rivalry between DC (Edison and General Electric) and AC (Westinghouse and Tesla). Edison claimed that AC was much more dangerous, since at lower voltages the AC electricity going through a person can disrupt the heart rhythms. He even encouraged the use of AC electricity for executions to discredit the technology. Imagine the current climate change deniers working to have executions performed by hypothermia to prove the climate wasn’t warming.
An AC system was put into operation in 1896 taking power generated at Niagara Falls to Buffalo, NY. This system’s success in transmitting electricity (over what seems like a short distance today) basically ended the War of the Currents. There were some skirmishes, but any real interest in DC ended.
AC Grid Goes Continental
In the ensuing 114 years the AC grid has gone from transmitting energy 20 miles to transmitting power across half the continent. Some have described the North American Grid as the most complicated machine on the planet. It connects dams in the Northwest to homes in Los Angeles and coal-powered plants in Ohio with factories in Tennessee. With a few interesting exceptions where DC is used, it’s three giant AC grids. One grid connects the Western US and Canada, another grid for the Eastern US and Canada and a third grid just for Texas.
Now to mention some of ACs downsides: as I described above the electrons move back and forth. How much time it takes the electrons to move back and forth is their frequency (how fast they move) and their phase is at what point are they in moving back forth. Think of pushing a child in a swing. If you push forward while he’s moving back, then you’ll slow him down (out-of-phase). If you push forward while he’s moving forward he’ll speed up (in-phase). If you’re at different frequencies then sometimes you’ll be in phase and sometimes you’ll be out-of-phase. The implications for the grid is that every power plant has to synchronize its output in frequency, phase and voltage or the grid becomes unstable. This is very difficult. The loads (e.g. air conditioners, elevators, and everything else) must exactly equal the sources (e.g. dams, nuclear power plants, wind farms) every second of every day. This is how a problem in Ohio in 2003 caused a loss of power across much of the Northeastern US and Southeastern Canada.