Improvement of Functionality and Reliability by Inductive HTS Fault Current Limiter Units

Abstract

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.Index Terms-Fault current limiter, high-temperature superconductors, inductive-type, superconducting devices. I. INCREASING POWER RATING AND RELIABILITY OF THE FAULT CURRENT LIMITERT HE inductive type high-temperature superconducting (HTS) fault current limiter (FCL) is one of the prospective and developing applications of HTS, which can make electric power networks more reliable [1]. In our case a transformer type FCL built up of YBCO rings [2] using a magnetic core with an adjustable air gap is being investigated. The basic design is one with a closed magnetic core. This design allows fast activation and recovery processes both within 5 ms. We 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 [3], [4].For practical applications of HTS FCLs in industrial environments we investigated the possibilities to increase power rating and reliability. For the mentioned purposes we investigated various FCL topologies. In our terms topology means the type of connections of individual units. Units can be arranged in series, parallel and combined (matrix) connections. 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 [5]. Fig. 1 shows the interrelations of the two parallel connected FCLs. Increasing the current, it achieves the activation value of FCL#1, its main field impedance appears and it limits the current of its own branch. The current decreases along this branch and, at the same moment, the current of FCL#2 increases. When the current exceeds the activation value of FCL#2, it is also activated. In this state the whole FCL group is in the limitation mode.When decreas...

Analysis of the effect of location and failure rates of fault current limiters on substations reliability

“…In other studies, the effects of using an FCL over network protection have been investigated while in Didier et al, the effects of FCL and its impedance type on increasing stability have been explained. In many articles, the effects of FCL on system reliability have been discussed . Although in the mentioned references, efforts have been made by the authors to evaluate the system reliability by using FCL, there are approximations and limitations that can reduce calculation accuracy.…”

“…These limitations are as follows: Adding any component to the system can change the system's reliability because of its failure rate. In a number of studies, it is assumed that the FCLs are completely reliable and their failure rate has been ignored in the calculations. The fault current reduction due to using FCL can reduce thermal and mechanical tensions on the network components . This may reduce the failure rate of the components .…”

“…The capacitive and inductive resonance limiters in Naderi et al 1 and Xiaoqing et al 4 and solid state FCLs in numerous studies [8][9][10][11][12][13] have been investigated. In a number of studies, [14][15][16] FCLs are studied on the basis of superconductor property. Moreover, in other studies, [17][18][19][20] hybrid FCLs have been introduced that combine different types of FCLs.…”

“…In many articles, the effects of FCL on system reliability have been discussed. [14][15][16][17][21][22][23][24][27][28][29][30][31][32][33][34] Although in the mentioned references, efforts have been made by the authors to evaluate the system reliability by using FCL, there are approximations and limitations that can reduce calculation accuracy. These limitations are as follows:…”

Parallel-Resonance-Type Fault Current Limiter

“…Therefore, an ideal FCL should have another important characteristic in addition to listed characteristics. It should play the load impedance role and be equal to load impedance during fault to better operation in such performances [7][8][9][10][11].…”