Core Superconducting Fault Current Limiter Research Articles

A 3-D Finite-Element Method Approach for Analyzing Different Short Circuit Types in a Saturated Iron Core Fault Current Limiter

In several cases, substations have become incapable of supporting faults due to increase in short-circuit levels. Fault current limiters (FCLs) are a potential solution for this problem. Among several FCL topologies presented in the literature, the saturated iron core superconducting fault current limiter (SIC-SFCL) has shown promising results in real tests in substations. In this context, this article presents the impacts of different kinds of short circuit on the SIC-SFCL device. To reproduce various types of fault, the SIC-SFCL is modeled in a 3-D framework considering both ferromagnetic and superconducting nonlinearities. Moreover, the proposed 3-D finite-element method model can couple the SIC-SFCL to the electric power system, also representing the electrical grid and the protection systems. For this investigation, the dc-bias superconducting coil’s normalized current density and the iron cores’ magnetic flux density are examined in light of different kinds of short circuit. The simulations are compared with measurements in a bench prototype, showing a maximum error of 16.5%. Furthermore, different types of short circuit are investigated and compared, which is possible only using a 3-D model. The highest limitation occurs in the phase-to-phase short-circuit case. In the dc circuit of the SIC-SFCL, the highest transient period happens in the single-phase short circuit. Finally, the phase-to-phase fault presents the highest dc current during the transient.

A coupling method of the superconducting devices modeled by finite element method with the lumped parameters electrical circuit

Superconducting devices have been widely studied over these years. Their application can be found in cables for electric power transmission, energy storage systems, magnetic levitation, electric machines, and fault current limiters. The literature presents some formulations to model the superconductors’ behavior using the finite element method (FEM), such as the H, the AV, and the T formulations, among others. Many superconducting devices have been simulated and designed using some of these formulations. However, none method available offers a coupling between an electric power system, simulated using electrical lumped parameters, to the superconducting FEM model. In this context, this work introduces a methodology for coupling superconducting devices in FEM to lumped parameters composing the power system. Here, a case study with a Saturated Iron Core Superconducting Fault Current Limiter was presented to apply the proposed methodology. This research analyzes the influence of the self and external fields in the superconducting coil on its critical current density. Moreover, it investigates the DC-biased coil voltage drop and the superconducting resistance. Besides, the paper presents the simulations of short circuits for various DC currents applied to the superconducting coil. Short-circuit tests were performed for validating the simulation results, and it showed a maximum error of 15% for the compared points.

Multi-objective optimization for the superconducting bias coil of a saturated iron core fault current limiter using the T-A formulation

The short-circuit levels have increased considerably in transmission and distribution systems in the last years. Fault current limiter (FCL) devices are a potential solution to this problem. Among several FCL topologies, this group has good experience in the use of superconducting fault current limiters (SFCL) to reduce the electrical current during short-circuits. The literature also presents studies of the saturated iron core superconducting fault current limiter (SIC-SFCL) topology employing mathematical modeling and prototypes design. Some of them have shown promising results, including the construction of pilot prototypes in medium and high voltage substations. The SIC-SFCL simulation studies presented optimal topologies that reduce the amount of ferromagnetic material used in the core and represent well the behavior of this limiter. The finite element method and the finite element analysis are suitable to model the SIC-SFCL. However, a more detailed study focusing on the optimization of the DC bias superconducting coil of the SIC-SFCL has not been presented in the literature yet. In this context, this work proposes a multi-objective optimization method using the Nelder–Mead algorithm to find an optimal geometry for the superconducting coil. In this optimization, the objectives functions are: to maximize the critical current density in the high-temperature superconductor (HTS), minimize the voltage drop in the copper winding, minimize the current through the DC biased superconducting winding, and minimize the price of the HTS superconducting winding. Before implementing the multi-objective optimization algorithm, we have tested a non-superconducting saturated iron core prototype and used the results to validate the simulation models. After that, we have replaced the DC copper winding with an HTS coil in the simulations and initiate the optimization process. Results show that constructing the DC bias superconducting coil using the minimum possible fill factor might not be the best choice.

Modeling and Simulation of a Saturated Core Fault Current Limiter Integrated in a Typical Distribution System Based on PSCAD Environment

Due to load increasing and generation extensions of the electrical networks, the fault current levels may be largely changed. So, the short circuit capacity may easily exceed the installed equipment interrupting capacity such as circuit breakers. Nowadays there are different methods for restoring the fault current normal values. The traditional methods in power utilities consider one of three options: (1) Replace installed equipment with higher rated equipment or, (2) Install series reactors or, (3) Replace the existing transformers with high impedance transformers. In this paper a Saturated Core Superconducting Fault Current Limiter (SCSFCL) will be presented as an efficient method for solving this problem so that replacing existing circuit breaker infrastructure can be avoided or postponed. This paper simulated the SCSFCL based on the PSCAD environment. An 11 kV West Delta Egyptian Distribution System in TANTA region is modeled as a typical system with the proposed simulated model of SCSFCL. The model parameters are adapted by the authors to restore the fault current levels as their values before the integration of the Distributed Generation (DG) units. The obtained results ensure that the model is easily used in other distribution systems. The results show also that the model performances can meet utility’s needs in mitigating fault current at all types of fault and different fault positions

Impedance Control of a Saturated Core Superconducting Fault Current Limiter With an Improved Field Suppression

This paper presents the ac impedance control of a superconducting fault current limiter (SFCL), along with the minimization of undesirable voltage spike across dc biasing coil. The nonlinear state space model of the SFCL is established with SFCL current as state variable, ac impedance as output, and dc biasing current as input variables. From this dynamic model, it is observed that the impedance can be controlled between a minimum value, when both the cores are saturated due to high dc biasing current and a maximum value when both the cores are unsaturated due to field suppression (FS) or switching off the dc biasing source. At the same time, the undesirable but inevitable voltage across dc coil due to FS can be reduced by controlling the stiffness of the dc control current. A high-frequency modified bang–bang type controller is designed and simulated. The simulation shows that the controller not only tracks the reference impedance very well, but also reduces the induced voltage across dc coil. The controlled SFCL impedance not only reduces the prospective fault current, but is also useful for relay coordination especially for impedance relays.

Mathematical modeling and harmonic analysis of SISFCL

PurposeA saturated iron core superconducting fault current limiter (SISFCL) has an important role to play in the present-day power system, providing effective protection against electrical faults and thus ensuring an uninterrupted supply of electricity to the consumers. Previous mathematical models developed to describe the SISFCL use a simple flux density-magnetic field intensity curve representing the ferromagnetic core. As the magnetic state of the core affects the efficient working of the device, this paper aims to present a novel approach in the mathematical modeling of the device with the inclusion of hysteresis.Design/methodology/approachThe Jiles–Atherton’s hysteresis model is utilized to develop the mathematical model of the limiter. The model is numerically solved using MATLAB. To support the validity of model, finite element model (FEM) with similar specifications was simulated.FindingsResponse of the limiter based on the developed mathematical model is in close agreement with the FEM simulations. To illustrate the effect of the hysteresis, the responses are compared by using three different hysteresis characteristics. Harmonic analysis is performed and comparison is carried out utilizing fast Fourier transform and continuous wavelet transform. It is observed that the core with narrower hysteresis characteristic not only produces a better current suppression but also creates a higher voltage drop across the DC source. It also injects more harmonics in the system under fault condition.Originality/valueInclusion of hysteresis in the mathematical model presents a more realistic approach in the transient analysis of the device. The paper provides an essential insight into the effect of the core hysteresis characteristic on the device performance.

Optimized Design of Coils and Iron Cores for a Saturated Iron Core Superconducting Fault Current Limiter

Coils and iron cores are the key components of a saturated iron core superconducting fault current limiter (SI-SFCL). They determine the entire performance of SI-SFCLs under both operation modes of fault current limiting and normal power transmission. Besides, they have great impact on scale, weight, and manufacture cost, which are essential factors in developing functional and cost-effective SI-SFCLs. We have intensively investigated the correlation between the design parameters of coils and iron cores and their influence on SI-SFCL characteristics. Theoretical analysis and experimental measurements have been carried out and parameters of nonlinear calculation from theoretical analysis are derived from the results of experiments. A 500-V SI-SFCL was developed and a selection of experiments were designed and completed to prove that an optimized design exists under certain current limiting and voltage drop conditions. Details of methods and results will be presented and discussed in this paper.

Current limiting impedance comparison between different designs of iron cores of the flux‐lock‐type superconducting fault current limiter

Fault current limiters are playing an ever more important role in today's power systems and many of their different types have now reached maturity. Owing to the progress in superconducting technology, the superconducting fault current limiter (SFCL) has attracted increasing attentions. To investigate the efficacy of SFCL devices from a system point of view, the fault current limiting impedance is of great importance. This study proposed an improved structure of flux-lock type of SFCL and compares the current limiting impedance of different layouts. It focuses on the impacts of iron core shape on primary winding inductance. The analyses include simulations based on finite element method carried out in the simulation software ANAlysis SYStem (ANSYS). This study shows that an E-E-shaped core with an air gap is better than a closed core when being used for an SFCL. It is also found that for an iron core SFCL with fixed size, its rated fault current limiting impedance can be adjusted by changing the cross-sectional area of the iron core centre leg and the length of the air gap.

Performance analysis of saturated iron core superconducting fault current limiter using Jiles–Atherton hysteresis model

In this paper study of the Saturated Iron Core Superconducting Fault Current Limiter (SISFCL) has been carried out. Since in an SISFCL, the iron core plays a key role in distributing the magnetic flux, the hysteresis property of the core material has been introduced in a mathematical model to get a more accurate result. In this paper the Jiles–Atherton hysteresis model has been used for modeling the core. The equations are solved through numerical method and performances of SISFCL are analyzed for both normal and fault conditions. On further analysis it is observed that for suppression of higher value of fault current a high voltage develops across the DC source. Hence there is a chance of the DC source being damaged by the rise in voltage under fault condition. In order to protect the DC source, a shorted ring is introduced in the SISFCL circuit and its effects have been analyzed. It is noticed that the shorted ring has successfully reduced the voltage across the DC coil during fault condition while the performance of the limiter remains the same.

Electrical Insulation of HTS Coils in Saturated Iron Core Superconducting Fault Current Limiter

HTS coil is a key component for saturated iron core superconducting fault current limiter (SISFCL), which does not quench during all kinds of operation conditions of SISFCL. Voltages of the HTS coils have big differences among different operation conditions of SISFCL. During the normal operation, large dc current loaded on the HTS coils magnetize the iron core to saturated, and voltage on the HTS coils is very low. When a short-circuit fault occurs in the grid, dc current is cut off in milliseconds, resulting in high induced voltage on the HTS coils. After the fault is clear, a dc voltage is applied on the HTS coils for rapid magnetization of iron core. Design of electrical insulation for HTS coils is based on the above working conditions. In this paper, a dc breakdown test results of HTS tapes wrapped with Kapton as turn insulation, and the insulation structure, and the electrical test results of the HTS coils in 220 kV SISFCL are introduced in detail. Now, in-live operation of the 220 kV SISFCL also shows that the electric insulation of HTS coils is satisfied, reliable, and safe.

Modeling Analysis of Impedance Characteristics of Saturated Core Superconducting Fault Current Limiter

As one of the most applicable to high-voltage network superconducting fault current limiterSCFCL(saturated core superconducting fault current limiter) ,which use of core saturation properties can be achieved the current-limiting function without delay ,will be the most widely applied in the future,By analyzing the working principle of SCFCL,this paper use of PSCAD and finite element analysis software Ansoft to build the 500kV\/3150A grade SCFCL model and accurate calculation coil self-inductance and mutual inductance, the harmonic of each size and analyzed its Impedance characteristic on the different external parameters,The results show that SCFCL has a excellent performance for high voltage power network short-circuit current limitation, and provides important reference for design.

The Research of Relationship between SICSFCL and Distance Relay Protection of Power Grid

A Saturated Iron Core Superconducting Fault Current Limiter (SICSFCL) provides a powerful fault current limitation in high voltage and high capacity power grid. A 35kV/90MVA SICSFCL was installed in a 35 kV network for live-grid operation, in January 2008 at Puji substation, Kunming, China. With deep research on SICSFCL, the matching problem between SICSFCL and relay protection currently needs to be solved. This paper analyzes the influence that SICSFCL brings to the distance relay protection which is used widely in high voltage power grid, and considering the characteristics of microcomputer-based protection, this paper proposes a new algorithm to eliminate the influence.

Dc bias system of a 35 kV/90 MVA saturated iron core SFCL

Saturated iron core superconducting fault current limiter (SIC-SFCL) is a promising fault current limiting device for high or extra-high voltage power grids. It has low impedance in normal power transmission and turns high impedance when a short-circuit takes place. The dc bias system of a saturated iron core superconducting fault current limiter plays a key role in realizing these features. Our 35 kV/90 MVA SIC-SFCL has been running live-grid since January 2008 at Puji substation in Yunnan, China. In this paper, the working principle of the dc bias system will be introduced and results of artificially imposed short-circuit tests will be provided, which verifies the validity of this system.

Proposal of saturated DC reactor type superconducting fault current limiter (SFCL)

A new superconducting fault current limiter (SFCL) using DC biased saturated core have been proposed in this paper. All existing saturated core SFCL are AC type. The proposed SFCL is a DC reactor type where all the windings carry DC current. The B– H curve of a magnetic circuit shows that less inductance value can be achieved in saturated region and very high value in unsaturated region. The reactance window between the saturated and unsaturated region depends on magnetic material, core size and its biasing conditions. The proposed type of SFCL can be designed efficiently taking the full advantage of the reactance window in current limiting mode. The advantage of this type of SFCL over the existing DC reactor type is that, it shows very low value of inductance at normal operation and very high value during fault time. On the other hand, the existing DC reactor (bridge) type SFCL shows a fixed value of inductance both in normal and fault time. Some simulation results are presented here to show the performance of the proposed SFCL.

Design considerations for an inductive high T/sub c/ superconducting fault current limiter

The authors investigate the design feasibility of an inductive iron core superconducting fault current limiter. A simplified thermo-electromagnetic analysis of the operating behavior of the fault current limiter is presented. This design is based on a high temperature superconducting shield surrounding a magnetic circuit with a primary winding generating an AC magnetic field. During fault conditions the field penetrates the core resulting in a large impedance, and thus a limitation of the fault current. In the analysis of this design, for voltages and currents up to 25 kV root-mean-square (RMS) and 2000 A RMS, it is shown that recuperation times for superconductors operating at liquid nitrogen temperatures are acceptable. >