Applications

Several applications for superconducting wire have been identified and some have been fully developed into commercial products. The key applications identified to date include the following:

• Medical applications: MRI, NMR and related systems; particle beam accelerators
• Electric power applications: superconducting FCLs, superconducting cables, power utility transformers, motors and generators, and superconducting magnetic energy storage (SMES)
• Transportation applications: magnetic levitation (Maglev)
• Science applications: particle bending magnets, high energy physics (HEP), and magnetic confinement fusion energy

MgB₂ superconducting wire can be applied to these applications and yield considerable improvements in cost and overall performance.

MRI

Existing superconducting MRI systems use niobium titanium (NbTi), a metal superconductor, and require liquid helium bath cooling, which results in large, high-cost systems. The current MRI market growth is driven by three factors: 1) the requirement for having a more open structure, 2) the use of smaller and less complicated systems, and 3) the need to lower the cost of MRI diagnoses to the patient (and the insurance carrier). These factors can be satisfied by building and supplying smaller, less complicated (liquid helium free), lower cost superconducting MRI systems. This will require magnets that can operate at higher temperatures (higher than 4.2 K) and can be cooled conductively with a cryocooler cold-foot and small refrigerator instead of convectively in a large liquid helium container and an attached re-condensing refrigerator. MgB₂ superconducting wire will function in the 20 to 30 K temperature range and can be supplied at an overall wire cost similar to that of NbTi wire, which operates at 4 K (or lower). Along the same lines, MgB₂ can be supplied at one-tenth the cost of ceramic high-temperature superconductors (YBCO and BSCCO).

The combination of lower wire price, higher operating temperature, and lower cooling costs will enable MRI manufacturers to build systems that require no liquid helium to directly cool the magnet, offer more open access to meet market needs, and have lower initial system costs and lower operating costs.

Superconducting FCLs

Superconducting FCLs have been investigated and developed for at least the past 15 years. Their principal advantages are their negligible influence on an electrical network under normal operating conditions, a response time that is practically instantaneous, and automatic response to a high-current fault without the need for an external trigger. There are basically two types of superconducting FCLs, resistive and inductive. A resistive type is one that responds to a fault condition by transitioning from a superconducting state to a normal resistive state. An inductive type superconducting FCL remains continuously superconducting during a fault and uses switching transistors responding to the over-voltage that develops as a fault is held back by the superconducting coil’s inductance. A resistive type superconducting FCL is considered best for most power applications.

MgB₂ is known to have a very sharp transition from a superconducting to a normal state, which makes it ideal for the resistive type superconducting FCL. Also, the normal zone heat propagation of MgB₂ is rapid compared with alternative ceramic superconductors. This characteristic minimizes hot spots in the conductor and facilitates design with the variety of highly resistive sheath materials that can be used to match the required post-quench normal conducting state. MgB₂ wires have shown good limiting properties at 50 Hz in the temperature range of 20 to 30 K. With its potentially low cost and the ability to operate at moderate cryogenic temperatures, MgB₂ is very attractive as a cost effective superconducting FCL element.

The inductive type superconducting FCL involves the use of superconductor coils fabricated with considerably longer lengths of superconductor wire than required for a resistive type superconducting FCL. Coils made from MgB₂ superconductor may be suitable in the 20 to 30 K operating range for inductive superconducting FCLs where they apply to particular electrical distribution systems.

Specification for Hyper Tech's Initial Distribution FCL

Initial Commercial Size for Distribution FCL for utilities, and distributed power (wind, solar, fuel cells, and turbine-generators)	Specification range
Voltage	13.8 kV
Frequency	50 or 60 Hz
Continuous maximum operating current	1,000-2,000 amps
Fault current limit, amps	2 times maximum operating current
Hold time at fault current limit	6-60 cycles
Operating time to limit peak	¼ cycle
Reset Time (recovery time), seconds	Varies based on customer need

Transformers

Superconducting transformers will be smaller in size and weight and have lower losses compared with transformers fabricated using conventional copper wire. Transformers made with MgB₂ superconducting wire will cost less to manufacture compared with using other high-temperature superconductors. The operating costs for superconducting transformers in 30 MVA and larger sizes will also be less compared with conventional oil-cooled copper transformers.

Superconducting transformers have several advantages over conventional transformers. First, there is more than a 30% reduction of total energy loss and more than a 45% reduction in total weight. This translates into at least a 20% reduction in total cost of ownership. Second is the elimination of oil from the transformer, which is an environmental concern with today’s transformers. In addition to these attributes, the superconducting transformer may significantly benefit an entire electrical system by reducing the short circuit current and by having lower transformer impedance.

Motors and Generators

Superconducting motors and generators have several potential advantages. They can operate with a high power density, be lightweight, and occupy a relatively small volume. They are highly efficient and reliable as well. MgB₂ wire can offer advantages in several of the motor and generator systems currently being demonstrated. In one design, the superconducting homopolar motor, MgB₂ offers the potential for higher power densities and increased temperature margins compared with the alternative superconductors. Because of its intrinsic lighter weight, lighter weight field coils are possible. In the alternative superconducting rotor design, MgB₂ offers a lighter weight motor and a much lower cost conductor than the high temperature superconductors now under test.

SMESand MagLev Trains

Both superconducting magnetic energy storage (SMES) and magnetically levitated trains (MagLev) require large coils. The typical magnetic fields generated in them are in the 2 to 5 T range. A low-cost superconductor is important in both cases because of the large amount of wire necessary. MgB₂ superconductor has the potential to become the wire of choice because of its low cost and large temperature margin compared with alternative superconductors.

Magnetic Separation

Superconducting magnetic separators using NbTi operating at 4 K in liquid helium have been commercially available since the early 1980s. The primary application of superconducting magnetic separators is removing iron from kaolin clay. These systems typically operate in the 2 T range. Experimental systems have also been built for various wastewater treatment demonstration projects.

Higher field systems in the 2 to 5 T range have been suggested for certain magnetic separation systems. Because these systems are typically large diameter bore magnets (i.e., 1 to 2 meters), they require a large amount of superconducting wire. This necessitates a low cost superconducting wire in order to be cost effective. MgB₂ superconductor is a low cost wire with a wide operating temperature margin that can enable large conduction cooled magnets that operate in the 10 to 25 K range.

HEP Applications

A long-term goal in HEP applications is the production of an MgB₂ wire that will produce engineering current densities of at least 1.2 x 10⁵ A cm^-2 at 4 K in fields of 12 to 16 T. While MgB₂ has the potential for reaching this performance goal, further refinements in its production are necessary. Once achieved, MbB₂ will also be in the range to satisfy several other near-term accelerator-related requirements such as in multi-poles, and wigglers.