Hidehiro Nagamura

A new model of fault current limiter using YBCO thin film

Resistive fault current limiters which consist of a YBCO film and a normal conducting film were constructed. The YBCO film was connected by indium wires to the normal conducting film in parallel at intervals of about 10 mm to increase the allowed voltage across the fault current limiter during the current-limiting operation. Current limiting experiments show that an allowed voltage across the fault current limiter during current-limiting operation of over 13 V/cm was achieved. Moreover, by combining in parallel 2 sets of 3 serially connected fault current limiters fabricated using 100 mm/spl times/10 mm YBCO film, a rated power of over 20 kVA is obtained.

Performance verification of a practical fault current limiter using YBCO thin film

Aiming at a practical use of superconducting fault current limiter, a newly designed device which consists of YBCO thin films and normal conducting films has been developed. The configuration allows increase of the resistance of the YBCO film without excess heating and partial overvoltage. To verify the current limiting performance and the reliability of the device, an analogue simulator test with a condition equivalent to a typical distribution system has been conducted. The developed device can limit a fault current to a target level within a half cycle and the increasing speed of the resistance is fast enough to mitigate the current overshoot after the fault. The series and parallel connection of the unit devices are feasible to attain large capacity. These test results prove that the proposed device has sufficient performance for applying to an actual power system.

400V Class Resistive Fault Current Limiter using YBCO Thin Films

A resistive fault current limiter with 410 Vrms x 56 Arms was realized by connecting six current limiting elements in series. An element was composed of a YBCO thin film on LaAlO3 single crystal and a metal film on AIN. The YBCO thin film was connected electrically to the metal film in parallel. The voltage drops of each pair of limiting elements occurred within 0.3ms deviation after the fault occurred. Current limiting properties of an element using a YBCO thin film deposited on AI2O3 single crystal were also investigated. In this case, the maximum voltage per unit length of 4.3V/mm was obtained; a value five times as high as that of an element using LaAlO3.