Published in “Global Power Engineering and Technology, Business Briefing” Jan. 2000, pp 105-109

Prospects for Superconducting Electric Power Technology for the 21st Century

R. D. Blaugher*

The last few years, leading up to the turn of the century, have seen a number of impressive demonstrations for superconducting electric power apparatus, using both high-temperature (HTS) and low-temperature superconductors (LTS). These successes have resulted in high expectations for the commercialization of this technology in the 21st century. In the United States, the Superconducting Electric Power Systems Program, sponsored by the U.S. Department of Energy (DOE), has supported the construction and test of a “15-kV class” HTS fault-current limiter (FCL), an ~1000-hp HTS synchronous motor, a 50-m HTS transmission cable, a prototype HTS generator coil for an advanced rotor design, and a 1-MVA transformer prototype. In Europe, a prototype 630-kVA HTS transformer was tested and installed for sustained evaluation at a Swiss electric utility and additional programming is under way for development of transformers, FCLs, and transmission lines. Japan also showed outstanding progress with the demonstration of 50- m HTS transmission cables and a prototype HTS transformer. Japan also successfully tested three different LTS rotor configurations for their “70-MW class” synchronous generator: a LTS-FCL, suitable for utility application, was tested at 69 kV and a 10kWh flywheel using HTS superconducting bearings was also tested. These collective demonstrations, which achieved or exceeded design specifications, were highly successful and raised expectations for applying superconductivity to the electric power sector. Are these expectations justified and what are the factors that will facilitate the realization of widespread integration of SC electric power components? In the following, I will discuss some of the economic benefits, market forecasts, and performance features for using superconductivity within electric power systems. In addition, some critical problems are identified that must be satisfactorily solved to permit eventual commercialization within the electric power sector.

The elements for success

The primary feature for the superconductivity effort within the United States is its focus on using HTS in the various power related applications. The key argument advanced for HTS usage versus LTS is the relaxation of the cryogenics with liquid nitrogen as the primary cryogen, thus eliminating the need for liquid helium which should improve the reliability for the entire system. HTS would also offer the added advantage of reduced refrigerator cost and reduced power requirements for the refrigeration. The present achievements in HTS electric power components were only possible due to the availability of long lengths of HTS wire and tape fabricated from the oxide superconductors, Bi-2223 and Bi-2212. Outstanding progress has been made over the last two years with respect to improved performance for the BSCCO conductor. Nevertheless, the current and field performance at 77 K, for the Bi-based wire, is considered marginal for operation at liquid nitrogen temperature for some of the applications which is critical to facilitate commercialization. Also, the present cost for the HTS conductor although steadily decreasing is still expensive and presents a major concern for eventual widespread commercialization. The future commercialization of HTS electric power components is thus dependent on better conductors with improved transport performance in magnetic fields of 1-3 T at 77K and cost reduced to below $10/kAm. The HTS cable application, as discussed later, is unique in its performance advantage and thus has more margin with respect to the cost of conductor. It thus follows that the key requirement for the superconducting technology is the demonstration of significant performance advantages and improved life-cycle costs over conventional apparatus. The performance advantage is critical and viewed with greater importance than efficiency improvements since most of the power apparatus is already highly efficient. Another key element for success is proven reliability for the entire superconducting system, i.e. the superconducting technology must exhibit reliability features comparable or better than conventional apparatus.

The worldwide market for new electrical power equipment is currently anticipating an upturn, resulting from a number of factors. In the United States, the equipment is aging, typically more than 25 years old, and seriously in need of replacement. Also many of the utilities within the U.S. are looking at “independent” forecasts for increased capacity requiring more generators, transmission lines, and transformers. The Energy Information Administration (EIA) forecasts that the World Electricity Consumption will nearly double from the present 14 trillion kWh to ~23 trillion kWh in 2020. The deregulation climate within the U.S. should eventually make the superconducting technology highly attractive with its prospect for improved efficiency, performance, and lower life-cycle costs, which should allow individual utilities to be more cost-effective. In addition, the superconducting technology would offer significant environmental advantages with oil-free transformers and transmission lines and less pollution due to reduced fuel requirements.

The widespread use of superconductivity within the global electric power systems is long past due, but as we approach the turn of the century, even with the successes we have had with both LTS and HTS demonstrations, we again find ourselves asking the same questions we asked in the 1980s: Will superconductivity truly find a home in the electric power systems? And will this open, much like Magnetic Resonance Imaging, a whole new commercial opportunity for superconductivity with predicted worldwide “energy” related sales by 2020 exceeding $40 billion (as forecast by the International Superconductivity Industry Summit and reproduced in figure 1). A recent book published by Knight Kiplinger, World Boom Ahead identified the superconductivity technology as one of the important energy-related business opportunities for the next century.

The problems facing commercialization of SC power apparatus as we enter the next millennium are different from the problems the technology faced in the early 1980s. During this period, worldwide demand was quite weak with very few new orders for power equipment. This business climate led directly to the termination, by the mid-1980s, of most of the major SC power research throughout the world. Only the Japanese Super-GM program survived, with a continued effort to develop a SC generator competitive with conventional equipment for market introduction near the turn of the century. The Japanese program, although quite successful, is currently not considering a follow-on effort to develop a commercial “200-MVA class” SC generator primarily due to their own forecast of higher costs for the SC generator, i.e., the projected cost for a SC 200-MVA generator would be sufficiently high to prevent serious competition with conventional generators. This situation is ominous and all of the other superconductivity efforts under way need to take notice. The only major development effort related to SC power applications within Japan that will continue into the next century is an energy storage program to develop a 1 MWh flywheel system using superconducting bearings.

The situation in the U.S. is quite different with the DOE Program sponsoring the development of transformers with ratings of 5/10 MVA for 2001, a pre-commercial prototype for a 5000-hp motor for 2002, and two separate SC transmission programs incorporating different design approaches. One of these programs will install, in 2001, a 24-kV, 100-MVA, three phase transmission line, that will provide power to the City of Detroit, Michigan, from the Detroit Edison Frisbie substation. It is expected that successful testing of this SC transmission system will be followed by similar underground installations in other large U.S. cities. The use of SC transmission to replace aging oil filled transmission cables in existing transmission ducts within the cites is a clear case for the “performance” advantage of superconductivity. The SC transmission lines typically offer 2-5 times the capacity of a conventional line having identical cross section. The Detroit Edison project will replace nine (800 A) conventional lines with three (2400 A) superconducting cables. Because there is no easy alternative for expanding capacity for intra city utilization, the SC transmission cable is a solution that once proven and demonstrated in a utility environment will command a premium price. This observation is certainly consistent with the financial support that has gone into the research and development of SC cables by companies such as Pirelli Cavi, Southwire, Sumitomo, Siemens, and Furakawa.

Major electric utilities and utility research organizations, such as the Electric Power Research Institute and its counterpart in Japan, have also supported SC cable development for many years. The improved efficiency for large SC motors with near 2% anticipated should also be a major opportunity for superconducting technology. The highly efficient SC motors with 50% reduced losses and half the volume of conventional motors should be attractive to the large motor users as long as the total installed cost is competitive with existing motor technology.

Benefits for Superconductivity

The overall impact and economic benefits for SC integration within the electric power systems can be evaluated by a simple sector analysis. The methodology for providing electric power throughout the world can be presented as a flow diagram that progresses from the conversion or fuel side into electrical generation, then into the transmission and distribution (T&D) sector, and finally to the retail user or demand side. The fuel step currently operates typically with a 30% conversion efficiency, which is the lowest efficiency component of the entire cycle. The U.S. system currently uses ~32 quads (Q) on the fuel side and delivers ~10 Q of electric energy to the demand side. Note that 0.1 quad of electrical energy (1015 Btu) is equivalent to ~$2 billion in "retail electric sales" at $0.07/kWh.

Demand side

Within the United States, electric motors account for ~64% of the demand-side electrical consumption, which is currently at 6.4 Q, with nearly 50% consumed by large motors (>1000 hp). Assuming major introduction of large SC motors over the next 10-20 years that have an efficiency improvement of ~2% including the refrigeration losses, the total reduced electrical cost to the industrial customers would represent a savings of around 0.1 Q or ~$2 billion/year. A 0.1 quad savings on the demand side would also lead to reduced fuel costs, which would translate into markedly reduced emissions for the electric power producer. The projected world market for large motors, >1000 hp, should increase in 10 years from the current $1.4 B/yr to around $2.5 B/yr, which presents a major opportunity for superconducting motors. A conventional 5000-hp motor, combined with an adjustable speed drive (ASD), is currently priced between $400,000 to $600,000. A highly efficient SC motor also with ASD and complete cryogenic support, that was competitively priced, would thus offer a substantial market by 2010 of nearly $300 million/year assuming a modest market penetration of ~10%. Superconducting motors with increased efficiency and operational flexibility would provide significant payback over the first few years, and combined with their reduced size, should be extremely attractive to the large motor users.

Transmission and Distribution

Within the T&D sector, the potential for markedly reducing the typical 7%-10% T&D losses using superconducting technology is highly attractive. It is expected that the majority of the savings projected to occur would be due to the replacement of large power transformers with a minimum efficiency improvement of 0.1%. If we consider the transmission network for the United States, which is typical of most systems throughout the world, it is reasonable to project that SC underground transmission technology would only compete with overhead transmission lines in limited applications.

The current transmission system within the United States, rated at 69 kV and above, including all underground cable, contains ~440,000 miles. The underground component of this system, rated at 69 to 345 kV, is about 3000 miles, or roughly 0.7%. Some 80% of this underground transmission are pipe-type cables, at voltages below 161 kV, which are potential candidates for retrofit using the so-called “warm-dielectric” superconducting cable design that is under development (primarily by Pirelli) in the U.S. and Italy. It is estimated that nearly 20% of this underground transmission is more than 30 years old and will need replacement in the not too distant future. By 2010, because of increased electric power demand, it is projected that ~170,000 miles of additional T&D lines will be needed. This projection assumes that U.S. consumer demand for electricity will double from the present to 2030.

Because a conventional overhead line cost ~$100,000/mile, a total market near $20 billion could be forecast for new transmission systems. It is reasonable that the SC underground cable market offering 2-5 times increased capacity for equivalent cable geometry would be attractive even with a premium price of ~$2M/mi for replacement or upgrade of existing underground systems. (Note that the current cost for conventional underground cable is around $750,000/mile hence a SC underground cable with capacity equivalent to an overhead line would be attractive, even with the higher price). Assuming major capture of the retrofit market, the potential market for SC transmission within the United States could be around $50 million/yr, with some possible use in new underground transmission installations beyond just the retrofit market. It is presently unclear how the deregulation process in the U.S. will influence the market with demand for new transmission cable. Although it is expected that new transmission corridors over long distances will still utilize the lower cost overhead, right-of-way problems and hopefully reduced cost for SC transmission 5-10 years out may promote consideration for high capacity superconducting lines.

Discussions with various utilities about possibly expanding the transmission system to facilitate “power wheeling” as a result of deregulation indicate that this will not occur in the near term. During this time frame, utilities may be driven instead to improve their local systems with SC transmission because it would offer the ability to reinforce the network at higher capacity. Retrofit, rationing, and expansion of overloaded corriders would also be attractive in some cases. Deregulation may eventually offer an opportunity for major restructuring of the existing electric transmission network with the introduction of new, improved, high-capacity superconducting links between the existing “power pools” or grid-connected generation regions within the United States. There does not appear to be a near-term opportunity for SC transmission for improved "long-distance" transmission links. It is conceivable, however, that long SC DC links may at some point become attractive if the cost for DC conversion is lowered and the economics for wheeling power between the operating regions become truly cost-effective.