Superconductors promise powerful and compact electric motors to drive the propellers of ships, and compact generators for airborne defense. For commercial power components—that is, generators, transformers, and transmission lines—superconductors would avoid resistive heating and the associated power losses (inefficiencies) presently found in these devices. Or superconductors could allow us to build more compact components with enhanced capabilities. But the biggest demand for the development of superconductors and superconductor windings over the years has been from funding to develop and build superconducting magnets for huge experimental devices in particle physics. I briefly first mention two such devices and their latest accomplishment.
BIG SCIENCE—PARTICLE ACCELERATORS
Superconducting magnets are essential parts of modern particle accelerators. More than “atom smashers,” these huge machines are creating particles mainly out of pure energy. And they employ tens of thousands of tons of superconducting particle-beam-bending magnets, as for example in the building of the Tevatron at Fermilab near Chicago and the Large Hadron Collider (LC) near Geneva, Switzerland, the latter of which is described in some detail in Chapter 9, Part IV (C).
ADVANCED SUPERCONDUCTORS
Large-scale commercial success for power applications depends on our being able to make superconducting devices low enough in cost and sufficiently reliable that they will pay for themselves on the long term. That means that the cost of refrigeration to keep superconductors operating below their critical temperatures must be less than the dollars that are saved by replacing conventional devices to eliminate the inherent resistive heating in their copper windings and their associated power losses. And superconductors are absolutely essential if the tokomak fusion reactors under development are to generate more power than is consumed by the magnets that confine the fusion plasma, as described in Chapter 20.
Superconductor operation at higher temperatures tends to improve overall economic performance because refrigeration equipment is much smaller, less complicated, less expensive and more reliable for higher temperatures and because refrigeration costs increase in more than inverse proportion to the absolute temperature at which the superconductors operate. So, for example, refrigeration for superconductors that can operate in liquid nitrogen1 at its boiling point of 77 Kelvin degrees (above the absolute zero of temperature) will cost less than one twentieth as much as refrigeration for superconductors that operate in liquid helium at about 4 Kelvin degrees. (Note for reference that a normal room temperature of 72 Fahrenheit degrees = 22 Celsius degrees = 295 Kelvin degrees above the absolute zero of temperature. So, liquid nitrogen boils at a temperature a bit more than a quarter of the way from the absolute zero of temperature toward a normal room temperature, and liquid helium boils at a temperature just a little less than 1/50 of the way to room temperature.)
Refrigeration becomes particularly important for AC power generation and delivery applications. This is because superconductors, though they have no resistance if kept below their critical temperatures, do generate some hysteresis and eddy-current losses (i.e., generate heat) when operated in changing magnetic fields. Superconductors used in the generators, transmission lines, and transformers operate in the presence of changing magnetic fields. So the savings that might be made by using superconductors to get rid of resistive losses in these devices must be weighed against the cost of refrigeration to expensively remove the relatively small amount of heat that is still generated.
New, so-called high-temperature superconducting materials (HTS materials), and even second-generation HTS materials, have been developed that can be used in relatively inexpensive liquid nitrogen.
The most commonly used so-called first-generation HTS material is Bi2Sr2Ca2Cu3O10+x (bismuth-strontium-calcium-copper oxide, BSCCO for short). (Some chemistry!) While BSCCO can operate at liquid-nitrogen temperature, the magnetic field levels to which it can operate and the amount of current that it can carry in a superconducting manner at liquid-nitrogen temperature is limited. This is particularly so as compared to second-generation HTS materials, typically involving YBa2Cu3O7–x (yttrium-barium-copper oxide, YBCO for short) or REBa2Cu3O7–x (rare-earth-barium-copper oxide, REBCO for short). At the moment, both of these HTS materials are still relatively expensive as compared, for example, to the NbTi alloy superconductor currently used (in liquid helium) for MRI.
A compromise between low- and high-temperature operation is offered by an intermediate temperature (Tc = 39K) MgB2 superconductor that has been developed in recent years. One review also cites particular applications for which this superconductor is suited.2
POWER APPLICATIONS, OF A SCALE TO LIGHT CITIES
Efforts to develop superconducting components for commercial electric power have been pursued worldwide for over fifty years. But to my knowledge none of these devices have as yet been accepted for widespread commercial use. Some development work still continues, but it is much diminished compared to what was being pursued even fifteen years ago.
The key to success will be to make superconducting devices low enough in cost and sufficiently reliable that they pay for themselves on the long term. Just one day of unscheduled “down time” can cut drastically into the dollars that would be saved through the improved efficiency and the operational advantages of these more complex superconducting devices. Competitive cost and reliability will be essential. Even if short-term tests are completely successful and show superconducting devices to be economically and functionally very attractive, it may take many years to demonstrate the reliability demanded for acceptance by an appropriately conservative power industry.
To give you some sense of the effort, I describe below some typical projects, several of which I either led or worked on at various stages in my career: as a materials scientist, physicist engineer, or project manager.
Fusion Reactors
The absolute need for superconductors in magnetic confinement types of fusion reactors is described in Chapter 20.
Superconducting Generators
Although eventually superconducting generators were constructed to power levels of 70 MVA (for our purposes 70 megawatts, or 70 million watts), I cite here an earlier development in which I participated, as both designer of the superconductor and foreman and designer of the instrumentation that was used for the test.
Figure 24.1 shows the 5 MVA superconducting generator that we built and successfully tested at Westinghouse in the early 1970s.3 At the time, many of us thought that superconductors would revolutionize the power industry. The 5 MVA was the most powerful superconducting generator built until that time. (The generator is located behind the engineers standing to the center and left. I am the bearded fellow who is standing to the far right.) I show this figure to give you some sense of the compactness of a machine that is capable of providing the power to light five thousand homes.4
Fig. 24.1. A 5 MVA (for our purposes, 5 megawatt) superconducting generator after successful test in 1972, with some of the Westinghouse design and test team alongside. Left to right, in the front row, are Jim Parker, Don Litz, Adolphus Patterson, Cliff Jones, and Tom Fagan; standing, are John Mole, Henry Haller, and author Mike Walker. (Image reprinted with permission from R. D. Blaugher et al., “Superconductivity at Westinghouse,” Superconductivity News Forum 6, no. 20 [2012]: 12.)
Project Organization and Partial Department of Energy Support
As the development of large-scale power components advanced sufficiently, demonstration projects were started (and some have been completed) to place superconducting power components into actual use in commercial operating situations. In the United States, these demonstrations have often been accomplished in team efforts involving a superconductor manufacturer, a device manufacturer, universities with specific relevant expertise, and an electric-power company that would put the hardware into use, along with engineers and scientists from one of the Department of Energy's major laboratories. DOE partially supported and monitored many of these projects, and the projects normally underwent an annual peer review.
To give you some sense of the scale and purpose of these projects, I mention two of them, those familiar to me mainly from my involvement as engineer and project manager at IGC's SuperPower division, near Albany, New York.
Transmission-Line Cables
This cable was constructed, installed, demonstrated, and then retired. (I had only a preliminary involvement in the project's getting started, just before I retired in 2002.) It was a nearly quarter-mile-long HTS underground transmission-line cable, installed and operated for many years in a standard utility right-of-way connecting two National Grid substations in Albany, New York. One impetus for superconducting cable development is the present 7 percent to 10 percent loss of electrical power caused by the electrical resistance of conventional copper transmission-line cables. A further advantage is that each superconducting cable can carry three to five times the power of a conventional cable in the same underground duct space, so that the substitution of HTS cables into present cable tunnels may provide increased power without the need for increased excavation and rights of way. (This is a really big deal in the fight for crowded underground space below some major cities!)
Our project's flexible, vacuum-jacketed superconducting cable was installed and operated initially in 2005 using a first-generation BSCCO HTS superconductor. In 2007, thirty meters of the cable was replaced with a higher-Tc YBCO second-generation HTS superconductor, also demonstrating the ability to make joints and successfully operate with these joints. Both sections use liquid nitrogen as a coolant. The line carries 800 amperes in each of its three phases, each at 34,500 volts for a power delivery of 48 MVA (that would be 48 megawatts if it were all resistive power, enough to light 48,000 average homes).
Partners with SuperPower on this project were Sumitomo Electric Industries, Linde, and National Grid. Funding was supplied in part from the New York State Energy Research and Development Authority (NYSERDA) and the US Department of Energy.
(I note a recent such development: A fault-current-limiting superconducting cable has been bringing power into City Center in Essen, Germany, on the grid since March 2014. It delivers up to 40 MVA (for our purposes, think of 40 megawatts) at 20,000 volts over a distance of one kilometer [0.6 miles].5)
Fault-Current-Limiting Transformer
Another project, one that I started and led through most of its first (transformer only) phases, has morphed and advanced considerably into a program to build a combined HTS superconducting-fault-current-limiting (SFCL) transformer. This superconducting transformer promises to be smaller, lighter, quieter, and more efficient than conventional transformers. It should be able to operate during faults6 at above-rated currents without danger to transformer life. With liquid nitrogen as an electrical insulator and coolant, rather than conventional transformer oil, the HTS transformer will not be a potential fire hazard. (After all, nitrogen does not burn, and it already comprises 80 percent of the air, so the release of nitrogen into the atmosphere is also not a problem.) And with the added fault-limiting capability, this transformer would provide downstream protection for substation circuit breakers and greater upstream grid flexibility, all without any negative impact on overall grid performance.
The objective of this project was to design, develop, manufacture, and install on a live utility host site a medium-power smart-grid-compatible superconducting fault-current-limiting transformer. This transformer would step down7 an incoming 69,000 volts to an outgoing 12,470 volts while delivering 28 MVA of power (that would be 28 megawatts if it were all resistive power). The SFCL transformer will use second-generation HTS superconductors cooled and insulated in liquid nitrogen. The project was slated for completion in 2015. It was funded in part by the US Department of Energy. Partners with SuperPower on this project were Waukesha Electric Systems (formerly Waukesha Transformer), Southern California Edison (SCE), Oak Ridge National Laboratory, and the University of Houston (TcSUH). (Rochester Gas and Electric and RPI, Rensselaer Polytechnic Institute, were partners through the earlier phases before SCE and TcSUH came on board.) Waukesha experienced a change in management and chose to withdraw from the project, so it has continued only as more of a proof of concept than a transformer demonstration.
Here in the United States, approximately 140,000 medium-power transformers are approaching forty years of service, that is, they are nearing the end of their useful life. They will soon need to be replaced, and the development of this new and improved superconducting transformer technology, if it is successful, would be timely for an updating of this component throughout the entire US power grid.
These are only a few of the projects being pursued by just a few companies developing materials or applications for superconductors. By now you have a sense of the difficulty in achieving success in the power sector. Though important contributions are being made, we need to soberly evaluate the status and possible overall impact of these developments, and we must recognize that acceptance by a necessarily conservative power industry does not usually come quickly. But much is being done in superconnectivity overall. To give you an idea of work being done by industry, governments, and universities worldwide, note that the Applied Superconductivity Conference, which is held every two years, is just one of several major conferences at which new or ongoing work on superconducting materials or devices is reported. Typically well over five hundred presentations are made to report works in progress at each ASC conference.8
Remember, we have considered in Part Five only some of the many modern inventions under development or in operation that either have been spurred by or are properly understood through our quantum view of the world around us. What we have learned and produced in the last seventy years, aided by our understanding of quantum mechanics, is truly amazing. What we do in the next twenty years will boggle the mind!