Carlos Y. Shigue

Fault Current Limiter Using YBCO Coated Conductor—The Limiting Factor and Its Recovery Time

A fault current limiter (FCL) based on an arrangement of parallel connected high temperature superconducting tapes constituting a limiter element was designed and tested in 220 V line for a fault current peak between 1 kA to 2 kA. The limiter employed second generation (2G) HTS tapes of YBCO coated conductor reinforced with stainless steel. Four tapes were electrically connected in parallel with 0.4 m effective length per element wherein 16 elements connected in series constitutes a single-phase unit. The FCL performance was evaluated through over-current and current fault tests. Its recovery characteristics were used to design the shunt protection. The designed limiting ratio is 4 for 16 elements and the experimental result for one element showed a 20% limiting ratio. For the fault current test one element can withstand five cycles of fault without degradation. It was observed recovery times below 0.5 s under nominal load using a shunt resistance of 173 mOmega.

Evaluation of Electrical Properties of Lap Joints for BSCCO and YBCO Tapes

The joint process between tapes of coated conductors is a critical issue for the most of the applications of high temperature superconductors (HTS). Using different fabrication techniques joints of YBCO coated superconductors were prepared and characterized through electrical measurements. For soldering material low melting point eutectic alloys, such as In-Sn (m.p. 116degC) and Sn-Pb (m.p. 189degC) were selected to prepare lap joints with effective length between 1 to 20 cm. The splice resistance and the critical current of the joints were evaluated by I-V curve measurements with the maximum current strength above the critical current, in order to evaluate the degree of degradation for each joint method. Pressed lap joints prepared with tapes without external reinforcement presented low resistance lap joint nevertheless some critical current degradation occurs when strong pressing is applied. When mechanical pressure is applied during the soldering process we can reduce the thickness of the solder alloy and a residual resistance arises from contributions of high resistivity matrix and external reinforcement. The lap joints for reinforced tape were prepared using two methods: the first, using ldquoas-suppliedrdquo tape and the other after reinforcement-removal; in the latter case, the tapes were resoldered using Sn-Pb alloy. The results using several joint geometries, distinct surface preparation processes and different soldering materials are presented and analysed. The solder alloy with lower melting point and the longer joint length presented the smallest joint resistance.

Procedure for measuring electrical resistivity of anisotropic materials: A revision of the Montgomery method

A procedure for determining the electrical resistivity of anisotropic materials is presented. It offers several improvements to the well-known Montgomery method. One improvement, in particular, is the ability to obtain the electrical resistivity for all three axes of an orthorhombic crystal analytically, rather than using the iterative approach suggested by Montgomery for the third axis. All necessary equations are derived and their application in determining the tensor components of the electrical resistivity is explained in detail. Measurements on isotropic specimens were executed in order to test the foundations of the method. Measurements on anisotropic samples are compared with measurements obtained by using the standard four-probe method, revealing good agreement.

Test of a Modular Fault Current Limiter for 220 V Line Using YBCO Coated Conductor Tapes With Shunt Protection

A modular superconducting fault current limiter (SFCL) consisting of 16 elements was constructed and tested in a 220 V line for a fault current between 1 kA to 7.4 kA. The elements are made up of second generation (2G) YBCO-coated conductor tapes with stainless steel reinforcement. For each element four tapes were electrically connected in parallel with effective length of 0.4 m per element, totaling 16 elements connected in series. The evaluation of SFCL performance was carried out under DC and AC tests. The DC test was performed through pulsed current tests and its recovery characteristics under load current were analysed by changing the shunt resistor value. The AC test performed using a 3 MVA/220 V/60 Hz transformer has shown the current limiting ratio achieved a factor higher than 10 during fault of up to five cycles without conductor degradation. The measurement of the voltage for each element during the AC test showed that in this modular SFCL the quench is homogeneous and the transition occurs similarly in all the elements.

Test Results of a Superconducting Fault Current Limiter Using YBCO Coated Conductor

A single-phase superconducting fault current limiter (SFCL) using a 0.9 m length of YBCO coated conductor (CC) tape was tested in 220 V-60 Hz line for fault current up to 1 kA, operating in 77 K. In this work are presented the I-V experimental curves measured under DC and AC currents for the electrical characterization of the CC tape in order to design a low voltage current limiter. The experimental setup is described and the test results are presented for a unit conducting a steady nominal AC current of 50 A and also during the fault time (1 to 5 cycles.) The performance of the CC-based SFCL providing the limiting resistance developed in the whole tape length after few milliseconds of the beginning of the fault was analyzed.

Test Results of a Superconducting FCL Using Bifilar Coil of BSCCO-2212

A single-phase superconducting Fault Current Limiter using a bifilar coil of BSCCO-2212 tube was tested in 220 V-60 Hz line during fault current between 1 kA to 4 kA, operating in 77 K. In this work are presented the critical current dependence as a function of an external magnetic field applied and the results can be used to predict the current limiter performance. The experimental setup is described and the test results are presented for the unit conducting a steady nominal AC current of 200 A, and also during the fault time (1 to 6 cycles). The performance of the bifilar coil to provide the limiting impedance associated with the dynamic resistance developed during the beginning of the fault was analyzed and compared with other types of superconducting current limiters

Single layer cylindrical and helicoidal coil with voids between successive turns electromagnetic field calculation to be used in superconductor current limiter simulator for design purpose

A very accurate mathematical method, named helicoidal method, to calculate the flux density vector B produced by the current circulating in the resistive single-phase superconductor electrical current limiter (RSCL) coils, at any point of the its whole space, using the Biot-Savarts Law is presented in this paper. It is very important to remember that these coils are single layer concentric cylindrical coils with voids (free space) between its neighbor turns which turns present helicoidal form. The calculation of the vector B, at any point of the space of the coils, is used in the dynamic simulation of the RSCL for design and operation purposes, but it is also used to calculate the self-inductance of each electrical current limiter coil and the mutual inductance between each pair of coils, which are necessary to determine the equivalent impedance of the RSCL. To verify the proposed method accuracy the self-inductance of three different coils, made with copper wire, are calculated, measured and the results are compared.

Annealing effects on the electrical and superconducting properties of a Cu-15vol%Nb composite conductor

In this paper, annealing effects on the electrical and superconducting properties of a multifilamentary Cu-Nb composite were investigated. During annealing, noticeable changes in the microstructure take place, in special those related to recovery and recrystallization of copper and niobium followed by spheroidization and further coarsening of the Nb-filaments. Results show that spheroidization becomes significant only above 800/spl deg/C and, even after annealing at severe conditions, e.g., 1050/spl deg/C for 32 h, the continuity of the niobium-conducting path is partially preserved. The influence of these microstructural changes on the superconducting and normal properties of the multifilamentary Cu-15vol%Nb composite conductor is discussed.

Single-phase resistive superconductor electrical current limiter

This paper presents the analysis, design, construction and AC test results of low voltage single-phase resistive superconductor electrical current limiters. Two different types of resistive superconductor current limiter are presented: the first one is built with three concentric, cylindrical and helicoidal coils connected in parallel and the second one is built with two superposed cylindrical helicoidal coils connected in series and in opposite magnetic polarities. Both are built using the GEC Alstom CuNi matrix superconductor type C wire for AC applications, wound on G-10 tubes and the final assembly is mechanically arranged and immersed in a cryostat filled with liquid helium at 4 K. The superconductor material in this wire is the NbTi alloy.

Fault Current Limiter Using Transformer and Modular Device of YBCO Coated Conductor

In this work, we report on the evaluation of a superconducting fault current limiter (SFCL). It is consisted of a modular superconducting device combined with a short-circuited transformer with a primary copper winding connected in series to the power line and the secondary side short-circuited by the superconducting device. The basic idea is adding a magnetic component to contribute to the current limitation by the impedance reflected to the line after transition of the superconducting device. The evaluation tests were performed with a prospective current up to 2 kA, with the short-circuited transformer of 2.5 kVA, 220 V/660 V connected to a test facility of 100 kVA power capacity. The resistive SFCL using a modular superconducting device was tested without degradation for a prospective fault current of 1.8 kA, achieving the limiting factor 2.78; the voltage achieved 282 V corresponding to an electric field of 11 V/m. The test performed with the combined SFCL ( superconducting device + transformer) using series and toroidal transformers showed current limiting factor of 3.1 and 2 times, respectively. The test results of the combined SFCL with short-circuited transformer showed undesirable influence of the transformer impedance, resulting in reduction of the fault current level.