06-04-2013, 04:52 PM
Surge current protection using superconductor.
Surge current protection.ppt (Size: 336 KB / Downloads: 81)
Fault Current
The short ckt current can exceed by a factor of 100 of the nominal current.
Produce mechanical and thermal stress proportional to square of the current.
Fault current limiter is used to limit this current, it must possess:
Zero impedance(at normal operation
High Impedance(at faults)
Provide detection and recovery of the fault instaneously(16ms)
Superconductor fault current limiter
Superconductor used because of their sharp transition from zero resistance at normal currents to finite resistance at higher current densities(above critical temp)
Type of Superconductor:Low Temperature(c<=23k),High Temp(c<=70)
C=critical temp
Types of Superconductor
Low Temp:Low AC losses. very high current carrying capacity, hotspots formation..
High Temp:poor heat conductor, no hot spots.Examples:BSCCO,YBCO compounds.
SFCL types includes Resistive SFCL,Inductive SFCL.
Resistive SFCL
Superconductor connected in series with the line to be protected.
To keep it superconducting, it is usually immersed in a coolant that is chilled by a refrigerator.
In case of a fault the inrush of current and magnetic field take the super conductor into the transition region, thereby the increasing resistance limits the fault current.
The behavior of resistic fault current limiter is largely determined by the length of the superconductor and the type of material used for it.