Attila Györe

Application possibilities with continuous YBCO loops made of HTS wire

In our previous experiments we have produced YBCO rings machined from bulks for superconducting applications. In this work we examine the arrangement of the continuous superconducting loop made of HTS wire for advanced applications. A Korean group of researchers led by Hee-Gyoun Lee produced 100% BSCCO loops from tape for the first time in 2006 [1]. In our solutions we use parallel and serial turns from perfect YBCO loops made from HTS wire. Production of multi-serial turns is not the same as the wind and flip [1] method. In our case the twisting of the YBCO wire along its longitudinal axis can be avoided. We check the quality of the perfect YBCO loops with the transformation of the DC magnetic field [2]. In the case of the AC application we describe a new arrangement of the self-limiting transformer with using these loops. This self-limiting transformer can be a voltage or current restricting system. The paper presents the results of our experiments and opens new advanced applications of perfect YBCO loops made of HTS wire focusing on the efficiency and importance of the Korean team in creating the perfect closed loop.

Investigation of High Temperature Superconducting Self-Limiting Transformer With YBCO Cylinder

The high temperature superconducting (HTS) self-limiting transformer (SLT) is a combination of a transformer and a fault current limiter in one unit. SLT is supposed to supply an HTS cable. This device may have two or more copper and/or superconducting windings and one or more YBCO cylinder(s) placed on a separate limb to operate when short circuit currents occur. We designed and built a small-size self-limiting transformer with copper primary and secondary windings and one YBCO cylinder. Experimental investigations of the quench process under a selected design scenario of current limitation are made. Analytical and numerical calculations are performed to simulate the self limiting quench performance of YBCO cylinders and the operation of the device. The simulations incorporate the HTS cable model. The results are used to inform the realization of the self-limiting transformer pre-prototype. Results of the quench model solution are evaluated in relation to the experimental results. The acceptable agreement between the experiments and theoretical modeling helps to construct the basis for the design of a 50 kVA to 100 kVA self limiting transformer device.

Improvement of functionality and reliability by inductive HTS fault current limiter units

The inductive type high temperature superconducting fault current limiter (HTS FCL) is one of the prospective and developing applications of HTS materials. A transformer type FCL build up of YBCO rings using a magnetic core with an adjustable air gap has been built and studied. For the practical applications of HTS FCLs in industrial environments we have investigated various connections of individual FCL units, viz. series, parallel and matrix (combination of series and parallel) arrangements of FCL groups to increase the fault power capacity as well as the reliability of HTS FCLs. A modeling method and a respective simulation have been developed, which include the hysteresis and heating of the HTS and the nonlinear characteristics of the magnetic core. Simulation results were verified by tests. We propose an important application viz. a self-limiting transformer using HTS YBCO rings, which is a combination of a transformer and a fault current limiter in one unit. The theory and the build-up of such a transformer is described, test results with respect to the operation of the self-limiting transformer are presented.

Experimental Analysis of Different Type HTS Rings in Fault Current Limiter

The inductive type high temperature superconducting fault current limiter (HTS FCL) is one of the forthcoming and progressing applications of HTS, which can make electric power networks more powerful and integrated. In our case a transformer type FCL built up of different types of YBCO and Bi2212 hollow cylinders using a magnetic core with an adjustable air gap was investigated and analyzed with respect to their activation and recovery behaviors. A PC controlled measurement system with electromagnetic relay was developed to record the sudden short-circuit fault processes. For theoretical analysis a new model of the superconductor and 3D FEM program code, to calculate the magnetic field distribution in the HTS and the FCL (which is inserted into the power network) are being developed. This experimental analysis shows the effect of properties of the HTS parts on the operation of the FCL. Having performed the tests, the relevant results allow one to fit the HTS rings to the adequate applications.

Multiphysical Finite Element Modeling of Inductive Type Fault Current Limiters and Self Limiting Transformers

A coupled finite element model of inductive type fault current limiter was developed for transient calculations. The model includes two dimensional finite elements for magnetic field directly coupled with network elements and sequentially coupled three dimensional finite elements for thermal calculations. A computer simulation was developed for implementing the model. Both iron and HTS nonlinearity are handled. The HTS model takes the E-J characteristic into account that depends on flux density and its orientation as well as on the temperature. With 3D thermal calculation the model also handles material inhomogeneity along the perimeter. The simulation results were compared with measurements performed on experimental model of a self limiting transformer.

Upgrading electric power quality by superconducting flywheels

Abstract An experimental flywheel based on high temperature superconductors was constructed. The aim of the study is to investigate the possible use of this technology to improve electric power quality against voltage disturbances. Some preliminary results on the flywheel performance are reported.

Fault current limiter with novel arrangement of perfect YBCO loops made of HTS wire

In this work we examine a novel arrangement of a perfect closed superconducting loop made of HTS wire in a fault current limiter. This paper presents the results of our experiments with this device, which may open a new path for advanced applications by using continuous, perfectly closed superconducting YBCO loops. During the experiments we compared the fault current limitation in two arrangements. At the same time we also test the operation and application possibilities of the continuous YBCO loop developed by our own technology.

System Investigation of High Temperature Superconducting Self-limiting Transformer

A high temperature superconducting (HTS) self-limiting transformer (SLT) is a combination of a transformer and a fault current limiter in one unit. We designed and built a small-size self-limiting transformer. This device has two or more copper windings and one or more HTS ring(s) placed on a separate limb to operate when short circuit currents occur. We have investigated several constructions on the experimental device, viz. iron core with two or more limbs. The self-limiting transformer was connected to various loads: resistive, capacitive and inductive. The effects of various loads were studied, which helps fit the parameters of HTS SLT to the electric power network. A calculation about a real power network in order to realize the requirement for the SLT is presented.

Experimental Determination of Optimal Construction of Current Limiting Transformers Using HTS Tapes and Rings

The current limiting or self-limiting transformer (CLT, SLT) is a multifunctional device which combines the functions of a usual power transformer with the functions of a current limiter. Various constructions of the CLT and fault current limiters (FCL) were investigated in order to realize the optimized constructional outline. Small scale devices were investigated with one or more YBCO rings and BSCCO tape(s). The rings were placed on one or two limbs of the devices. The HTS ring was replaced with HTS tape in order to realize a new FCL construction. The main goal is to decrease the leakage field and to increase the mainfield reactance. The magnetizing current is to be reduced. The upscalability i.e. increase of the power rating is investigated as well. The CLT was investigated experimentally for both sudden short circuit and steady state (transformer) operation modes in cases of several selected configurations. The activation currents of the devices were determined in cases of sudden short circuit and transformer operation modes. The results are used to find the optimum constructional outline realization of the current limiting transformer.

Series and parallel connections of inductive high-temperature superconducting fault current limiters

High-temperature superconducting (HTS) fault current limiters (FCLs) can make electric power networks more reliable. For an inductive type FCL we have developed and applied a special design to significantly reduce the impedance in normal operation mode, and to properly adjust the impedance in limitation mode. The FCL can be designed with predictable parameters, and can withstand thousands of activation and recovery cycles. For practical application of HTS FCLs in industrial environments we have investigated the possibilities to increase power rating and reliability. For the purposes mentioned we have examined various FCL topologies: series, parallel and matrix arrangements. In this paper we present the results of experimental studies of the mentioned and practically useful FCL topologies. Tests were performed for series and parallel connections of FCLs to investigate the fault processes in the individual units and the resultant effects of the whole FCL group.