Superconducting electric machine
Superconducting electric machines are electromechanical systems that rely on the use of one or more superconducting elements. Since superconductors have no DC resistance, they typically have greater efficiency. The most important parameter that is of utmost interest in superconducting machine is the generation of a very high magnetic field that is not possible in a conventional machine. This leads to a substantial decrease in the motor volume; which means a great increase in the power density. However, since superconductors only have zero resistance under a certain superconducting transition temperature, Tc that is hundreds of degrees lower than room temperature, cryogenics are required.
Now there is more interest in superconducting AC synchronous electric machines (alternators and synchronous motors). The direct current electromagnet field winding on the rotor (rotating member) use superconductors but the alternating current multiphase winding set on the stator (stationary members), which have no practical support by superconductors, uses conventional, normal conduction copper conductors. Often the stator conductors are cooled to reduce, but not eliminate, their resistive losses.
DC homopolar machines are among the oldest electric machines. Michael Faraday made one in 1831.Superconducting DC homopolar machines use superconductors in their stationary field windings and normal conductors in their rotating pickup winding. In 2005 the General Atomics company received a contract for the creation of a large low speed superconducting homopolar motor for ship propulsion. Superconducting homopolar generators have been considered as pulsed power sources for laser weapon systems. However, homopolar machines have not been practical for most applications.
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