About Superconductivity

A 21st century power technology primer

What is Superconductivity?

When cooled below a critical temperature, superconductive materials lose all resistance to the flow of direct electrical current and, therefore, are 100% efficient when carrying DC power. Superconductors conduct alternating current (AC) with only a slight dissipation of energy.

Advantages of Superconductor Wire

Compared with standard copper wire, superconductor wire offers two main advantages in all applications:

• Superconductor wire conducts electricity with little or no resistance and associated energy loss.
• Superconductor wire can carry 150 times the current that a conventional wire of similar dimensions can carry

The 3 essential conditions for superconductivity

As illustrated in Figure 1 at right, three conditions must be satisfied simultaneously in order for a material to exhibit superconducting behavior:

1. The material must be cooled below a certain temperature, known as its superconducting transition or critical temperature (Tc).
2. The current passing through a given cross-section of the material must be below a characteristic level known as the critical current density (Jc).
3. The magnetic field to which the material is exposed must be below a characteristic value known as the critical magnetic field (Hc).

Figure 1. Three essential conditions for superconductivity

From LTS to HTS: The evolution of superconductivity

While superconductive materials were discovered in 1911, their practical and commercial viability remained very limited for many decades. This was because no known material exhibited superconductivity at a critical temperature higher than 23 Kelvin, or –418° Fahrenheit. (To put those numbers into perspective, 0°K, or absolute zero, equals –459°F.) The superconducting materials of this period are now known as low temperature superconductors (LTS). The costs of such cooling for LTS systems is exorbitant, which has rendered them impractical for widespread commercial applications beyond magnetic resonance imaging (MRI) systems.

A significant breakthrough occurred in 1986 at an IBM laboratory in Zurich, Switzerland when Dr. K. Alex Muller and Dr. J. George Bednorz identified a ceramic oxide compound which they demonstrated to be superconductive at 36°K (-395°F). A series of related ceramic oxide compounds that have higher critical temperatures, including those used today by American Superconductor, were subsequently discovered. These materials are known as high temperature superconductors (HTS). Drs. Muller and Bednorz shared the 1987 Nobel Prize for Physics, one of four Nobel Prizes that have been awarded to date for work on superconductivity. 

     >>Superconductivity Glossary

     >>Applications of Superconductivity
 

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