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Electrical Steel: The Material at Heart of the Grid [Hackaday]
When thoughts turn to the modernization and decarbonization of our transportation infrastructure, one imagines it to be dominated by exotic materials. EV motors and wind turbine generators need magnets made with rare earth metals (which turn out to be not all that rare), batteries for cars and grid storage need lithium and cobalt, and of course an abundance of extremely pure silicon is needed to provide the computational power that makes everything work. Throw in healthy pinches of graphene, carbon fiber composites and ceramics, and minerals like molybdenum, and the recipe starts looking pretty exotic.
As necessary as they are, all these exotic materials are worthless without a foundation of more familiar materials, ones that humans have been extracting and exploiting for eons. Mine all the neodymium you want, but without materials like copper for motor and generator windings, your EV is going nowhere and wind turbines are just big lawn ornaments. But just as important is iron, specifically as the alloy steel, which not only forms the structural elements of nearly everything mechanical but also appears in the stators and rotors of motors and generators, as well as the cores of the giant transformers that the electrical grid is built from.
Not just any steel will do for electrical use, though; special formulations, collectively known as electrical steel, are needed to build these electromagnetic devices. Electrical steel is simple in concept but complex in detail, and has become absolutely vital to the functioning of modern society. So it pays to take a look at what electrical steel is and how it works, and why we’re going nowhere without it.
Iron vs. Steel
The idea for a feature about electrical steel came from a story bemoaning delays plaguing renewable energy projects in the United States, mainly due to supply chain issues with the transformers needed to upgrade and expand the electrical grid. Building wind and solar farms is one thing; connecting them to the existing grid is another, one that often requires building completely new substations and refurbishing existing ones to gather the output of geographically dispersed generators and boost it to an appropriate voltage for long-haul transmission. Substations need transformers, often lots of them, and transformers are large, complicated devices that more often than not are custom-built. Lead times on large power transformers now routinely exceed 150 weeks!
The root cause of the three-year wait for large power transformers comes down to raw material supply chain problems, particularly with electrical steel. The electrical steel market is global both on the supply and demand side, so disruptions in one part of the world can ripple through the entire market. The electrical steel market’s current disruptions can be blamed on a host of factors: pandemic-era shutdowns of mines and factories, international sanctions, tariffs and trade disputes, off-shoring of manufacturing, and probably about a dozen other things. What it all means, though, is too little of this specialized material to go around.
So what is electrical steel? In some ways, the name is a misnomer; while electrical steel alloys are formulated specifically to change their electrical characteristics, these changes result in different magnetic properties, which is the key to understanding what they are and why they’re important. Electrical steel, which is used in the cores of nearly every device that uses magnetism, is probably better called “magnetic steel.” The material does have a few other monikers that better reflect this, such as “relay steel” and “transformer steel,” but the name “silicon steel” is perhaps most chemically descriptive, for reasons that will soon become obvious.
All steels are simply alloys composed primarily of iron and carbon, and electrical steel is no different. Pure iron is quite soft and ductile; the addition of carbon in just the right amounts serves as a hardening agent that gives the alloy its increased tensile strength and other desirable properties. Being primarily composed of a metallic element, steel is a good conductor of electricity. That sounds like it would be a beneficial property, and indeed it can be, as in the case of automotive electrical systems, which often use the steel body and chassis as a low-impedance return path.
Hysteresis Control
However, in electromagnetic assemblies like motors, generators, and transformers, carbon steel’s conductivity ends up causing problems that need to be solved. This has to do with the ferromagnetic properties of the iron in the steel, such as magnetic permeability and magnetic coercivity. Magnetic permeability measures the degree to which an external magnetic field, such as from a coil of wire carrying an electric current, induces a magnetic field in a material. Permeability is what makes steel stick to a permanent magnet — the magnet induces a temporary magnetic field in the high-permeability steel, causing the two to stick together. Coercivity, on the other hand, measures the degree to which a ferromagnetic material can resist becoming demagnetized by an externally applied field.
