A century ago, Dutch physicist Heike Kamerlingh Onnes cooled a ring made from mercury near the absolute zero [at 0 Kelvin (minus 459 F) the coldest possible temperature], sent through electrical current and removed the battery. One year later, the current was still flowing. The experiment helped Kamerlingh Onnes discover superconductivity, a physical phenomenon that drops electrical resistance to zero in extremely cold metals. It also helped him win the Nobel Prize.
Electrical resistance is why light bulbs, batteries and wires get hot. That heat, though, is waste. If our appliances and power plants were superconductive, they would become hugely more efficient, allowing us to use the same electricity over and over again.
The heat is on: GE engineers test high-temperature superconducting power generator.
But superconductive machines remain elusive. A century after Kamerlingh Onnes’ discovery, scientists are still struggling to make superconductivity work at balmier temperatures.
Last week, however, researchers at GE Power Conversion turned on the heat. The tested a new superconducting generator called Hydrogenie. The GE team replaced copper wires wound on the rotor inside the generator with a metal base covered with a superconducting ceramic layer. They made the machine work at 43 Kelvin (minus 383 F) and produce 1.7 megawatts of electricity.
Minus 383 F is still quite frigid, but for superconductivity researchers it’s like a trip to the tropics. They call the new technology “high temperature superconductors” for good reason. Until recently, superconductivity still shivered near 4 Kelvin, where Kamerlingh Onnes’ experiments left it. “This technology is a true breakthrough,”says Martin Ingles, GE Power Conversion manager for Hydrogenie. Ingles says that Hydrogenie could “radically improve” the efficiency of wind and water turbines, ocean ship propulsion, and other technology.
Because the ceramic and metal windings have virtually no resistance, their cross section could be as small as 2 percent of the copper wires used inside motors today. This could bring a new age of small, light, and extremely powerful motors and generators.
The GE researchers had to crack hard technical problems to design the new system. “It’s rather like trying to keep ice cubes frozen on a rotisserie in a very hot oven,” Ingles says. To keep the system cold, they pipe frigid helium gas into the machine rotor and then send it around the individual coils. Although they placed the rotor inside a vacuum for better insulation, it still has some direct contact, via its shaft, with the outside world. The temperature difference problem along the shaft – scientists call it temperature gradient – is a big problem. Imagine plunging your teeth into a scoop of ice cream, except hundreds of degrees colder.
But the GE team developed a patented method for dealing with the gradient and transferring torque from the cold coils to the rotor. They also designed “low resistance thermal joints and assemblies” that minimize the cooling power required to cool the coils.
GE says that “the machine demonstrates all of the technologies required” to make high-temperature semiconducting machines “a commercial reality.”
Electricity has never been this cool.