S. Kozak

Bio: S. Kozak is an academic researcher from University of Cambridge. The author has contributed to research in topics: Fault current limiter & Superconducting magnetic energy storage. The author has an hindex of 15, co-authored 39 publications receiving 513 citations.

Comparison of Inductive and Resistive SFCL

Abstract: This article presents a comparison of inductive and resistive superconducting fault current limiter built with the same length of high temperature superconducting (HTS) tape. The resistive limiter is constructed as a noninductive bifilar winding. The inductive coreless limiter consists of primary winding and secondary shorted winding. Both limiters are connected parallel to the additional Cu primary winding, which helps to reduce the power dissipated in the HTS windings during and after a fault. It also ensures that in cases of an HTS tape failure, the protected circuit will not be disrupted. The limiters are very fast and the first peak is almost equally limited by both types of limiters.

Design and Tests of Coreless Inductive Superconducting Fault Current Limiter

Abstract: In this work, we report on the design and tests results of a coreless inductive SFCL with a 600 A rated current for MV distribution system. The fault current limiter comprises of 4 identical units immersed in liquid nitrogen bath. Each unit consists of 3 windings. The primary and secondary windings made of 2G HTS tape SF12050 are magnetically coupled with the primary Cu winding. The high magnetic coupling between superconducting primary and secondary windings gives a low voltage drop on the limiter at nominal current. The presented solution reduces the size and the weight of the device. Tests performed at high power test facility prove the limiting capability of the coreless inductive SFCL.

Design and testing of 230 V inductive type of Superconducting Fault Current Limiter with an open core

Abstract: A single-phase, 230 V Superconducting Fault Current Limiter using two Bi2223 HTS tubes with the total critical current 2.5 kA situated in vacuum insulated cryostat has been described in this paper. We designed and manufactured the inductive SFCL with an open core as core shielded type acquired the optimal design parameters by using Finite Element Method. We tested the limiter performances at liquid nitrogen temperature 77 K. We proved that the performances of properly designed limiter with open core could be comparable to the limiter with closed core.

Properties comparison of superconducting fault current limiters with closed and open core

Abstract: The high-T/sub c/ superconducting fault current limiter (SFCL) can be classified into resistive, inductive and hybrid types. The inductive type HTSFCL seems to show most prospect due to the simple design (construction) of the secondary superconducting winding in the form of ceramic type BSCCO and for the reduction of current leads. In an inductive type SFCL, ferromagnetic cores for magnetic flux are applied, however open cores are also taken into consideration in order to simplify the construction. The results of experimental and computational investigations of inductive SFCL parameters are presented in this paper.

Tests and Performance Analysis of Coreless Inductive HTS Fault Current Limiters

Abstract: Superconducting fault current limiters (SFCL) are designed to protect the electrical grid from faults that result from lightning strikes, downed power lines and other system interruptions. The rapid increase of impedance of the SFCL reduces the short current in the circuit. Several coreless constructions of inductive SFCLs have been tested. The space between the windings is the thick of the polyimide film kapton insulation to increase the coupling and reduces the leakage reactance. Both primary and secondary windings have been immersed in liquid nitrogen. The presented solutions reduce the size and the weight of the device. A few limiters based on HTS 1G and HTS 2G tapes has been described, tested and compared.

Case Studies In Superconducting Magnets Design And Operational Issues

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Fault Current Limiters in Power Systems: A Comprehensive Review

Abstract: Power systems are becoming more and more complex in nature due to the integration of several power electronic devices. Protection of such systems and augmentation of reliability as well as stability highly depend on limiting the fault currents. Several fault current limiters (FCLs) have been applied in power systems as they provide rapid and efficient fault current limitation. This paper presents a comprehensive literature review of the application of different types of FCLs in power systems. Applications of superconducting and non-superconducting FCLs are categorized as: (1) application in generation, transmission and distribution networks; (2) application in alternating current (AC)/direct current (DC) systems; (3) application in renewable energy resources integration; (4) application in distributed generation (DG); and (5) application for reliability, stability and fault ride through capability enhancement. Modeling, impact and control strategies of several FCLs in power systems are presented with practical implementation cases in different countries. Recommendations are provided to improve the performance of the FCLs in power systems with modification of its structures, optimal placement and proper control design. This review paper will be a good foundation for researchers working in power system stability issues and for industry to implement the ongoing research advancement in real systems.

Comparison of Inductive and Resistive SFCL to Robustness Improvement of a VSC-HVDC System With Wind Plants Against DC Fault

Abstract: For that wind plants are connected to an electric power grid through voltage source converter-based high-voltage direct-current (VSC-HVDC) transmission, the improvement of the VSC-HVDC system's robustness against a dc short-circuit fault is critical. This paper suggests the inductive and resistive superconducting fault current limiter (SFCL) to alleviate the fault current and enhance the system's transient behaviors. Each of the two SFCLs is installed in series with the dc transmission line, and once the fault is detected, the current-limiting inductance or resistance will be activated to affect the system characteristics. Herein, wind plants are based on doubly-fed induction generators, and related theoretical derivation and transient simulation analysis are done. From the results, both of the two SFCLs can limit the dc fault current, improve the dc-voltage sags and suppress the power fluctuations. By comparing the specific performance indexes including current-limiting ratio and restraining capability to voltage/power fluctuations, the resistive SFCL is more preferable than the inductive SFCL. At the end, the SFCL optimization technique considering current-limitation, voltage stability, and device cost are discussed, so as to further promote the SFCL's application in the VSC-HVDC system.

Application of a SFCL for Fault Ride-Through Capability Enhancement of DG in a Microgrid System and Relay Protection Coordination

Abstract: Concerning that a short-circuit fault happens inside a microgrid system, parts of distributed generation (DG) units may not meet the fault ride-through (FRT) requirements and will be enforced to disconnect. This paper suggests a modified flux-coupling-type superconducting fault current limiter (SFCL) to improve the DG's FRT capability, and investigates the relay protection coordination in the microgrid. The SFCL's structural principle is introduced, and according to the fault characteristic of the microgrid under its grid-connected and islanded statuses, the modified SFCL's application fields are conducted. Furthermore, the directional overcurrent protection and differential protection are proposed for the microgrid's two statuses, respectively. Based on the transient simulations in the MATLAB, the SFCL's positive effects on enhancing the DG's FRT capability can be confirmed, and also it will not affect the relay protection coordination. A comparison of the conventional distance relay protection and the proposed protection scheme is performed, and the latter has a better applicability than the former to match the SFCL. Finally, regarding the impacts of fault type and fault resistance on the FRT operation and the proposed protection, technical discussions are performed preliminarily, and the application value of the SFCL integrated with the proposed protection is clarified further.

Current–Time Characteristics of Resistive Superconducting Fault Current Limiters

Abstract: Superconducting fault current limiters (SFCLs) may play an important role in power-dense electrical systems. Therefore, it is important to understand the dynamic characteristics of SFCLs. This will allow the behavior of multiple SFCLs in a system to be fully understood during faults and other transient conditions, which will consequently permit the coordination of the SFCL devices to ensure that only the device(s) closest to the fault location will operate. It will also allow SFCL behavior and impact to be taken into account when coordinating network protection systems. This paper demonstrates that resistive SFCLs have an inverse current-time characteristic: They will quench (become resistive) in a time that inversely depends upon the initial fault current magnitude. The timescales are shown to be much shorter than those typical of inverse overcurrent protection. A generic equation has been derived, which allows the quench time to be estimated for a given prospective fault current magnitude and initial superconductor temperature and for various superconducting device and material properties. This information will be of value to system designers in understanding the impact of SFCLs on network protection systems during faults and in planning the relative positions of multiple SFCLs.