Inductive Superconducting Fault Current Limiter Research Articles

Experiment Studies of a DC Inductive Superconducting Fault Current Limiter With Energy Dissipation Capability

Experiment Studies of a DC Inductive Superconducting Fault Current Limiter With Energy Dissipation Capability

Comparison of Initial Current Limiting Performance of Two Inductive Superconducting Fault Current Limiters With Different Electrical Coupling Between Cores and Coils

It is possible to improve the performance of the superconducting fault current limiters and to apply power system as a method for reducing the volume and weight of the superconducting fault current limiters using iron core and coil. This study thus manufactured a superconducting current limiting element using a coated conductor with high specific resistance, and applied it to two models with an iron core and coil (a model consisting of three separated iron cores and coils and a model integrating three coils through one iron core) for the comparison and analysis of the current limiting characteristics. Of the two aforementioned models, the separate-iron-core/coil model with additive polarity wiring offered a higher current limiting rate, but under each wiring condition (subtractive polarity and additive polarity wirings), the two models' current limiting rates were found not to be very different. The superconducting current limiting element's thermal strain was determined to be smaller in the integrated model than in the separate-iron-core/coil model, but the integrated model created quench resistance of the superconducting current limiting element at the sound phase (S phase), suggesting that the result increased the critical current of the superconducting current limiting element. Further studies should be done, however, through the structural change of the integrated model.

Current limiting characteristics of a resistance-inductance type superconducting fault current limiter

The superconducting fault current limiter (SFCL) can effectively and quickly limit the fault current, which is appropriate for the voltage source converter high voltage direct current (VSC-HVDC) transmission system to reduce the fault current. A new resistance-inductance type SFCL using the structure of the inductive superconducting coils is presented. The current limiting and inter-turn insulation characteristics of resistance-inductance type SFCL are studied. A simulation model is developed for the comparison of inductive and non-inductive type superconducting coils. The simulation results show that the inductive superconducting coils can significantly reduce the fault current rise rate by more than 42% over the non-inductive superconducting coils. The voltage distribution of the inter-turn channels is calculated by the presented method.Utilizing the voltage distribution, the electric field distribution can be obtained, which is important for the insulation design. Some inductive type pancake superconducting coils were fabricated, and the DC impulse current tests were carried out. The testing results and simulated results have a good agreement, which shows that the inductive type SFCL can effectively limit the fault current.

Electromechanical Analysis of Core- and Shell-Type Inductive Superconducting Fault Current Limiters Under General Fault Conditions

In transmission and distribution grids, electrical currents in rated conditions can reach hundreds of amps. Under fault conditions, these currents can reach ten times or more their rated value. In power devices, particularly in superconducting fault current limiters (SFCLs), this current rise leads to the development of electromechanical forces that can damage the superconducting tape, so should be properly analyzed, for the sake of equipment integrity. Additionally, when asymmetric faults occur in the grid, the desired circumstance is that a fault in one phase does not affect the other ones, to minimize damages and disturbances in the grid and protection devices. In this article, core- and a shell-type inductive SFCLs are tested under several fault conditions. The main objectives are to measure and analyze the electromechanical forces developed in each superconducting winding, to evaluate their integrity after faults, and to compare the performance of both types of limiters under the same fault conditions. Electromechanical forces measurements in the three phases are made simultaneously, using a device based on strain gauges, calibrated to operate at 77 K. This article contributes to evaluating the robustness and best geometry of this inductive limiter of transformer type.

Optimization of Inductive Superconducting Fault Current Limiter for Distribution Networks

Superconducting fault current limiter (SFCL) has been recommended as an idea current limiting method. And Inductive SFCL is one of the potential candidates of SFCL, with its advantages of fast responding, no quench and quick recovery characteristics. Recently years, several ISFCLs have been installed in demonstration projects all around the world. This paper focuses on the optimal configuration of ISFCL designed for distribution networks. Considering the current limiting performance and total cost of ISFCL, the optimal model of ISFCL parameters is established to choose suitable parameters for target system. Results of this paper are used to guide the design and fabrication of ISFCL prototypes.

Performance Evaluation Approach of Superconducting Fault Current Limiter in MMC-HVDC Transmission System

For a voltage-source-converter (VSC) based high voltage direct current (HVDC) system using modular multilevel converter (MMC) topology, it is vital to address the emergency DC fault current problem, and superconducting fault current limiter (SFCL) is a very serviceable and competitive solution. This paper proposes a performance evaluation approach for applying SFCL in MMC-HVDC transmission system. Firstly, according to different action stages of SFCL and DC circuit breaker (DCCB), the fault development process of the MMC-HVDC is elaborated. The fault current peak, dissipated energy of DCCB and fault clearance time are probed, and the critical limiting impedance is theoretically deduced. Then, three aspects of electrical stress, thermal stress and fault handling speed are specially considered, and a performance evaluation system with multiple indicators is built to assess SFCL functions. Using MATLAB, the performance assessment of a resistive SFCL and an inductive SFCL in a 320 kV/1.6 kA MMC-HVDC system is done. From comparative analyses, it is concluded that the resistive SFCL overall outperforms the inductive SFCL, and while the critical current-limiting resistance and inductance are gained. The suitability and feasibility of the proposed performance evaluation approach are validated.

Further study of a novel inductive SFCL for multiterminal HVDC systems

Multiterminal high voltage direct current (HVDC) systems are developing rapidly lately. However, the high rising rate of fault current and the lack of interrupting capacity of the available DC circuit breakers hinder the further development of multiterminal HVDC systems. Being aimed at the challenge, this paper proposes a novel inductive DC superconducting fault current limiter (SFCL) to cooperate with available DC circuit breakers to cope with the short-circuit fault current in a multiterminal HVDC system effectively. In the normal power transmission of a multiterminal HVDC system, the SFCL presents low impedance and enables a smooth reclosing operation after an interruption. It is able to make a maximum use of the permeability of the iron core to offer a large inductance to curb the rising rate of the fault current in the early few milliseconds as a fault takes place. In addition, it can have an adjustable current limiting threshold to match the different requirements of different grid protection schemes. In this paper, first the working principle of the proposed SFCL is introduced. Then the experimental results on a concept-proofing prototype are reported and analyzed. The experimental results have verified the principle and functional ability of the proposed SFCL.

Current-limiting characteristics of a modified flux-coupling type superconducting fault current limiter and its effects on the transient stability of a multi-machine power system

A modified flux-coupling type superconducting fault current limiter (SFCL) is proposed here for suppressing fault currents. The modified SFCL consists of a coupling transformer, an yttrium barium copper oxide (YBCO) pancake coil, and a controlled switch. By flexibly adjusting the controlled switch's contact states based on the system operational conditions, the coupling transformer's primary inductance as well as the YBCO coil's normal-state resistance are incorporated into the main system for current limitation. Because the modified SFCL has the advantages of resistive and inductive SFCLs, it may improve the power system's transient behavior. Hence, the SFCL's effect on the transient stability of a multi-machine power system was also theoretically investigated. Further, simulations were conducted for accessing the SFCL's performance characteristics under different fault conditions. The results show that using the proposed SFCL can effectively restrain the increased fault current and improve the bus voltage sag; meanwhile, the imitated multi-machine system's power-angle oscillation can be obviously reduced.

Study on Sustainable Current-Limiting Capability of a Saturation-Based dc I-SFCL Prototype

If the inductive superconducting fault current limiter (I-SFCL) cannot maintain its current-limiting capacity before the dc fault is isolated, it will lead to a secondary fault in the dc system, and cause an impact on the system primary equipment. Therefore, the study of sustainable current-limiting capability is an important aspect in the dc SFCL researches. In this paper, the sustainable current-limiting capability of a saturation-based dc I-SFCL prototype was discussed in details. Through the dc current-limiting performance experiments, it is found that the sustainable current-limiting capability of this type of SFCL has a negative correlation with its reverse saturation degree, which can be affected by the design parameters. The influence factors of reverse saturation were first analyzed through the mathematical model of this prototype. Afterward, combined with the experiments, the sustainable current-limiting capability of the proposed dc I-SFCL is fully explored by changing the coil current and the number of turns, which offers a reference for parameter design of I-SFCL in the future engineering application.

Modeling of the DC Inductive Superconducting Fault Current Limiter

DC fault current limiter is an important device for the dc system, because the action speed of the existing selective protection cannot match the dc fault developing speed. Due to its excellent capacity on limiting dc fault rising speed, the analyses of dc inductive type superconducting fault current limiter (I-SFCL) are attracting more attention. In this paper, a modeling method for dc I-SFCL is proposed to describe its nonlinear characteristic of inductance. Firstly, the structure and working principle of the dc I-SFCL is briefly introduced, and the magnetic equivalent circuit is established according to the magnetic field distribution. Then, the relationship between dc transient current and the current-limiting inductance of dc I-SFCL is discussed. By analyzing the equivalent magnetic circuit, a mathematical I-SFCL model is proposed in Matlab based on the actual geometric and electrical parameters. Finally, under the same dc test platform, the magnetic flux density, the voltage and the current of dc I-SFCL in Matlab model are compared with that in finite element method (FEM) model. Simulation results verifies the validity and the correctness of the model.

Comparison of resistive and inductive superconductor fault current limiters in AC and DC micro-grids

Superconducting Fault Current Limiters (SFCL) have been used in power systems for many years, however the best possible positioning of different SFCL still needs a lot of work. Resistive and Inductive are two types of SFCL used in power system. Function of both these current limiters is to control the fluctuations and abnormalities in the system by introducing a high impedance in it, through transforming itself from normal stage to superconducting stage. In this research, placement of resistive SFCL and inductive SFCL in AC and DC microgrids (MG) are analyses at two different positions; at the point of integration of conventional source and distributed generator (DG) and at the point where DG is added to the system. The AC and DC microgrids contains industrial and residential loads, while they use respective main wind power generation source and photo voltaic power source along with conventional power, supplied from main grid. The behavior of both types of SFCL in their grid models is analyzed through MatLab Simulations, in order to compare their effectiveness and determine best possible position to place them.

Numerical Study on Transient State of Inductive Fault Current Limiter Based on Field-Circuit Coupling Method.

As the capacity of the power grid continues to expand, high-level fault currents might be caused during a contingency, and the problem of short-circuit current over-limitation is imminent. The high-temperature superconducting (HTS) fault current limiter (FCL) is an effective method to solve this problem. In this paper, a transient numerical model for the process of limiting current in the inductive FCL is proposed. The model is based on the coupling of multiphysics finite element simulation and a circuit model. The voltage source is used as input, which can simulate the macroscopic characteristics in the process of limiting current, such as the voltage and current waveforms, and can also simulate microscopic characteristics, such as temperature, magnetic field, and electrodynamic force distribution. The short-circuit experimental data of an air core inductive superconducting fault current limiter (SFCL) prototype was compared with the simulation results to verify the reliability of the simulation.

Enhancing Fault Ride-Through Capability of DFIG-Based Wind Turbines Using Inductive SFCL With Coordinated Control

Doubly fed induction generators (DFIGs) have difficulties to ride through serious faults just relying on modified controls due to limited power ratings in rotor-side converters. This paper presents a new protection strategy for DFIGs by combining an inductive superconducting fault current limiter (SFCL) with coordinated control. The SFCL topology, system modeling, and transient control are presented. Under normal conditions, the inductive SFCL can act as a filter benefiting the steady-state operation. When faults occur, the simulation results show that the peak values of the stator current, rotor current, dc voltage, and electromagnetic torque oscillation can be effectively suppressed. With transient voltage control, the required positive sequence reactive current can be generated to supply dynamic reactive support. Moreover, proper switching off of the SFCL and coordinated control can smooth the transient recovery process after a fault.

Experiment study on an inductive superconducting fault current limiter using no-insulation coils

No-insulation (NI) coil made of 2 G high temperature superconducting (HTS) tapes has been widely used in DC magnet due to its excellent performance of engineering current density, thermal stability and mechanical strength. However, there are few AC power device using NI coil at present. In this paper, the NI coil is firstly applied into inductive superconducting fault current limiter (iSFCL). A two-winding structure air-core iSFCL prototype was fabricated, composed of a primary copper winding and a secondary no-insulation winding using 2 G HTS coated conductors. Firstly, in order to testify the feasibility to use NI coil as the secondary winding, the impedance variation of the prototype at different currents and different cycles was tested. The result shows that the impedance increases rapidly with the current rises. Then the iSFCL prototype was tested in a 40 V rms/ 3.3 kA peak short circuit experiment platform, both of the fault current limiting and recovery property of the iSFCL are discussed.

Feasibility Study of Closed-Loop No-Insulation Coil to Shield Alternating Magnetic Field

No-insulation (NI) coil made of 2G high-temperature superconductor tape is widely used in a dc magnet due to its excellent performance of engineering current density, thermal stability, and mechanical strength. While the charging/discharging delay of the NI coil has become the biggest obstacle to applying it into an ac power device. In this paper, as a preliminary study, we test the capability of the NI coil to shield alternating magnetic field (AMF). When shielding AMF, the NI coil works in inductive mode such that each turn in the NI coil is induced at the same time and there might no longer exist any delay caused by turn-to-turn current path. To verify this hypothesis, three closed-loop coils, two NI coils, and an insulated (INS) coil are fabricated. The result of the contrast experiments shows that the NI coil could shield all the alternating magnetic flux through it, independent of turn-to-turn resistance and frequency of the background AMF. This capability is promising for the NI coil to be applied in the inductive superconducting fault current limiter (iSFCL) as the secondary winding, which can shield all the magnetic flux generated by the primary winding to keep the impedance of the iSFCL at a very low level during normal the operation of the power system.

SmartCoil - Concept of a Full-Scale Demonstrator of a Shielded Core Type Superconducting Fault Current Limiter

Within a German government funded project with the partners Siemens and KIT, we present the concept and first results for a full-scale inductive superconducting fault current limiter. It is based on the well-known shielded core concept but does not need the deployment of an iron core. Aim of the project is the construction and test of one phase with a nominal current I = 600 A and a voltage of U = 10 kV, i.e., a protected power of P = 10 MVA for the three-phase system. The shielding is provided by a stack of superconducting rings, i.e., YBCO-tapes soldered to closed rings, with a radius of R = 0.7 m. To obtain a sufficient coupling between the reactor (primary coil, warm) and the shielding stack, the minimization of the gap between both is crucial. The paper presents numerical work with respect to the overall geometry and the physical properties (limitation behavior, ac-losses) of the device. Also a suitable superconducting material had to be qualified. Finally, a test equipment for single components (rings) was built up and successful tests of first superconducting full size components are reported.

Design and Application of the SFCL in the Modular Multilevel Converter Based DC System

There is an urgent need for the fault current limiter to guarantee the stability of the dc system. For this reason, the improved inductive superconducting fault current limiter (SFCL) is designed and its working principle is addressed. By analyzing the transient characteristics of the dc fault in modular multilevel converter based dc system, the current-limiting effects of the proposed SFCL are studied in detail. According to the current-limiting requirements and the coordination among the converter, the fault current limiter and the dc circuit breaker, the desired impedance of the SFCL is discussed in this paper. Finally, the effectiveness and correctness of the analyses have been verified by the simulation results based on the PSCAD/EMTDC simulation

MgB2-based superconductors for fault current limiters

A promising solution of the fault current problem in power systems is the application of fast-operating nonlinear superconducting fault current limiters (SFCLs) with the capability of rapidly increasing their impedance, and thus limiting high fault currents. We report the results of experiments with models of inductive (transformer type) SFCLs based on the ring-shaped bulk MgB2 prepared under high quasihydrostatic pressure (2 GPa) and by hot pressing technique (30 MPa). It was shown that the SFCLs meet the main requirements to fault current limiters: they possess low impedance in the nominal regime of the protected circuit and can fast increase their impedance limiting both the transient and the steady-state fault currents. The study of quenching currents of MgB2 rings (SFCL activation current) and AC losses in the rings shows that the quenching current density and critical current density determined from AC losses can be 10-20 times less than the critical current determined from the magnetization experiments.

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

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.

Analysis of Electromagnetic Forces in Superconducting Fault-Current Limiters Under Short-Circuit Condition

Electrodynamic forces developed under short-circuit events must be well characterized in power-grid applications, as they can compromise the integrity of network systems, particularly power transformers, but also inductive superconducting fault current limiters (SFCLs). These strains can destroy windings causing failure of the devices and affecting power-grid operation. In this paper, the analysis of electrodynamic forces developed in an inductive SFCL of transformer type under such extreme conditions is carried out based on finite-elements method (FEMs). The secondary of the envisaged devices is built by high-temperature superconducting (HTS) coated conductors and distinct configurations (radially and axially distributed windings) are analyzed in order to determine the most adequate for electromagnetic forces minimization. FEM results for developed radial and axial forces are evaluated and compared, as well as current distribution and normal magnetic induction in each winding.