Kazuyuki Tsurunaga

Development of a new 6.6 kV/ 1500 A class superconducting fault current limiter for electric power systems

A superconducting current limiter comprising a noninductively wound AC superconducting coil (trigger coil) connected in parallel with a limiting coil was developed. A model electric power system for the application of this type of superconducting current limiter was created, 400 V/100 A class model superconducting current limiters were fabricated, and various current limiting tests were performed with respect to short-circuit currents and phases varied over a wide range. The results demonstrate that the proposed current limiter possesses performance characteristics fully adequate for application to the model system. A 6.6 kV/1500 A class superconducting trigger coil was developed, with a scale permitting, in principle, validation tests of applicability to actual power systems. This coil was demonstrated to be capable of limiting short-circuit currents by a factor of 1/30, and was subjected to detailed evaluation of current-limiting characteristics. >

6.6 kV/1.5 kA-class superconducting fault current limiter development

The authors have developed and tested a 6.6-kV/1.5-kA-class fault current limiter wound with a 42-strand AC superconducting wire having ultrafine NbTi filaments in a high-resistivity matrix. In experiments, voltages up to 7.2 kV were applied to the limiter with phase angles of 0, 45, and 90 degrees . The limiter was able to limit the fault current to 1.8 kA from the 55-kA short-circuit current that would flow in a circuit without a limiter. >

Superconducting fault current limiter development

The authors have developed and tested a 400-V 100-A-class fault current limiter wound with AC superconducting wire with ultrafine NbTi filaments. The limiter consists of noninductively wound superconducting trigger coils and a superconducting limiting coil which acts as a reactor. Excessive fault currents initiate quenching in the trigger coils and these currents, which have flown in trigger coils in nonfault conditions, are commutated from the trigger coils to the limiting coil. In an experiment, a fault current level was successfully limited to 120 A with a limiter whose terminal voltage at the limiting condition was 420 V.

Development of Superconducting AC Fault Current Limiter

The authors have developed a new superconducting fault current limiter whose impedance during normal operation is very small. During fault conditions, the limiter behaves as a superconducting reactor. The limiter consist of a superconducting limiting coil and a superconducting trigger coil. The former coil has a larger critical curent than the latter coil. These coils are wound non-inductively on coaxial cylindrical formers and are parallel connected to each other. They are wound with AC superconductor having ultra-fine NbTi filaments. The limiter has a very little impedance because both coils are in superconducting state during normal operation. On the other hand, in the case of fault conditions, the trigger coil quenches at a critical current. After the’ trigger coil quenching, the limiter becomes a superconducting reactor because current in the coil decreases very rapidly with rapidly developing resistive normal zone. The fault current is, therefore, limited by the superconducting limiting coil to a certain value determined by the coil inductance. In experiments, the authors have succeed in limiting a fault current level to 200A, with a limiter whose terminal voltage under limiting conditions was 54V.

The current status of superconducting fault current limiter development

Abstract Demand for electric power in Japan has been steadily increasing in recent years.To meet this demand, power networks have been more robustly connected with a view to improving their reliability. However, this has been accompanied by a trend toward a greater incidence of fault currents in these power networks. If a fault current limiter is used to connect these systems, electric power utilities will be able to accommodate electric power through the superconducting limiter from a system with excess capacity to another system in which the available power is insufficient, while the limiter protects systems from the influence of faults in a system. The authors have developed a 6.6 kV/2.0 kA class superconducting fault current limiter used for power distribution substations, as the preliminary stage of development of current for trunk power systems. In order to reduce impedance under normal operating conditions and quickly switch to high impedance in a fault condition, the limiter consists of a pair of double-layer non-inductive superconducting windings connected in series. Each winding is wound with a 36-stranded AC superconducting wire having ultra-fine NbTi filaments in a high-resistivity matrix. The device successfully limited a 6.9 kA short-circuit current to 3.4 kA and transmitted continuous power at 2.0 kArms.

Development of 6.6kV/1.5kA-class superconducting fault current limiter

The authors have developed and tested a 6.6kV/l.5kA-class superconducting fault current limiter, wound with an AC superconducting wire having ultra-fine NbTi filaments in Cu-10%Ni matrix. In experiments, voltages up to 6.6kV were applied to the limiter. The limiter was able to successfully limit the fault current to 1.8kA from the 55kA short-circuit current that would flow in a circuit without a limiter. Interestingly, the limiting current peak value depends on the applied voltage. This transient phenomenon was analysed based on a model including flux flow resistance contribution. Experimental results were explained with the model.

TEST ON SUPERCONDUCTING AC FAULT CURRENT LIMITER

The authors have developed a new super conducting fault current limiter whose impedance during normal operation is very small. During fault conditions, the limiter behaves as a superconducting reactor. The limiter consists of a superconducting limiting coil and a superconducting trigger coil. The former coil has a larger critical current than the latter coil. These coils are wound non-inductively on coaxial cylindrical formers and are connected in parallel to each other. They are wound with AC superconductor having ultra-fine NbTi filaments. The limiter has a very little impedance, because both coils are wound non-inductively and in superconducting state during normal operation. On the other hand, in the case of fault conditions, the trigger coil quenches at a critical current. After the trigger coil quenching, the limiter becomes a super conducting reactor, because non-inductiveness is broken by trigger coil current. The fault current is, therefore, limited by the super conducting limiting coil to a certain value determined by the coil inductance. In experiments, the authors have succeeded in limiting a fault current level to 200A, with a limiter whose terminal voltage under limiting conditions was 54V.