Most of you reading this owe your lives to the phenomenon described in this post. Therefore, it is worth understanding precisely how grid power is generated, and what it looks like. And of course, you will not find this anywhere else.
Rant topics are inspired by reader comments. At AESP National, a young gentleman approached me to say the Rant provides good information that is easy to understand and read. He referenced a Greentech Media Energy Gang podcast, which explained as much. At the ~50 minute mark of the podcast, they explain that learning how things work, and being able to explain it, is the key to success. Here it goes…
I cannot think of a goofier scenario between what we do and our collective knowledge of electricity. Nearly everyone reading this owes their career to the electric utility industry, but no one, including me, understands electricity very well. For example, early in my career, I discovered how complex it is to evaluate electric motor efficiency and power. Short of the incandescent light bulb (essentially a toaster coil), a motor is the simplest, but major, load in existence.
I have a lot of expertise in the machines that motors drive and how to reduce their energy consumption. These include compressors, fans, pumps, and blowers. We focus on reducing the power required to produce shaft power. If it is strictly an electric load with internal magic, like that of an LED and the circuitry that makes it illuminate, I guarantee almost no one, if anyone, reading this knows how that works.
We live in a world of alternating electrical voltage and current supplied by spinning rotors in a generator at a power plant. The spinning rotor is powered by prime movers, including gas and steam turbines, or in rare cases, internal combustion engines (diesels).
The physics of generation involve current flowing through electric coils (think a spool of sewing thread). This produces a magnetic field, a magnet. You should have generated an electromagnet in 7th grade science class.
Make a loop of conductive (copper) wire as shown in Figure 1 and connect the ends to a small (AA, etc.) battery, and you will have an electromagnet.
Just as we can make magnets with electric current, we can make electricity using magnets.
Whether you move a wire quickly through a magnetic field from north to south or vice versa, or spin a north/south magnet past wires, you produce electrical current. This is the easy part, but magnets can be the permanent variety, with which everyone is familiar, or an electromagnet. The question is, what type is used for power generation? The answer was very difficult to find, but PJM delivers.
It seems to me that huge hulking permanent magnets would be very expensive for power generation. At the same time, we already know current must be supplied to a loop of conductive (copper) wire to produce an electromagnet.
Wouldn’t you know it? I was right on both counts. Both types are used. The permanent magnet type, known as the salient three phase generator, is shown in Figure 2 below, as viewed from the end. It is used for slow speed generation (hydro and maybe wind turbines).
Figure 3 depicts the cylindrical rotor generator. As shown, electromagnets are produced by direct current to windings embedded in the rotor. Figure 4 provides a cartoon of the full rotor.
In all cases, rotor magnets spin past coils in the stationary stator of the generator to produce electricity. Isn’t it beautiful?
Sine Waves and Alternating Current
Did you know the length of sunlight throughout the year, when plotted, forms a sine wave? You do now because I just said so. This is due to the earth’s axial tilt (23.5 degrees), its 24-hour spin, and its annual orbit around of the sun. Figure 5 shows hours of sunlight at various latitudes north of the equator. For reference, Minneapolis and the Portlands are about 45 degrees north. For north latitudes, 12 hours shown is the first day of spring and the first day of autumn.
Earth itself is an electromagnet, generating a magnetic north and south pole. Consider the right-hand rule which applies to magnets and current flow. Make a thumbs up with your right hand, fingers pointing in direction of spin (which is counterclockwise for earth). Your thumb points north for both earth and an electromagnet. Magnets and earth each have north and south poles.
Guess how a compass works. A compass consists of a small magnet on a disk with nearly frictionless rotation. The magnet finds the earth’s north pole, which isn’t just a home for Santa Claus.
Three Phase Power
Our electric grid provides three phase power derived from the red, yellow, and blue coil loops shown in the stator cartoons above. The power they produce is 120 degrees out of phase, as shown in the Figure 6 sine waves of voltage and power. Those colors, black, blue, and red, are universal for North America.
We will dig into the significance of three-phase, alternating current power next week.
 Except on the equator where the length of daylight is the same all the time.