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Valve reactors (VR) with multiple magnetic cores are important electrical components in ultra-high voltage direct current systems. The impact current and high-order harmonics during their operation can lead to additional losses and temperature rise in the valve reactors, posing a threat to insulation aging, and even causing serious incidents such as combustion and explosions. Therefore, it is necessary to accurately quantify and analyze the loss characteristics of valve reactors under different magnetic materials. This article first theoretically analyzes the electromagnetic and temperature characteristics during the actual operation of VR; then, it analyzes and calculates the magnetic field distribution and electromagnetic losses of a single magnetic core. Finally, it establishes a three-dimensional equivalent model of VR and conducts transient electromagnetic-thermal coupled finite element simulation to reveal the magnitude and spatial distribution of VR temperature changes. [ABSTRACT FROM AUTHOR]

Saturated core fault current limiters are effective means to limit short-circuit currents in high voltage power systems. To solve its problems of a low rate of utilization and large loss, this study proposes a multifunctional saturated-core fault current limiter (MFFCL) with a hybrid excitation system. The MFFCL can limit the short-circuit current and control power flow to reduce losses. The composition and topological structure of the MFFCL are provided, an equivalent electromagnetic circuit model of the MFFCL is then established, and its working mechanisms of limiting current and regulating power flow are analyzed. Following this, a finite-element simulation model of the MFFCL is built to investigate its electromagnetic characteristics and verify its performance in terms of limiting current. The power flow regulation function of the MFFCL was verified through the field-circuit coupling method. Finally, a laboratory-scale prototype of the MFFCL and a test platform was designed to test it. The results of the experiments verified the correctness and feasibility of the proposed structure. It can adequately control power flow in its normal state, and can limit the short-circuit current to 60% of the original in case of a fault. [ABSTRACT FROM AUTHOR]

Orthogonal controllable reactors (OCRs) have the advantages of low distortion and linear inductance regulation. However, traditional OCRs suffer from two vital problems, namely, their small inductance regulation range and large space occupation. To solve these issues, a new compact OCR is proposed in this study. First, the magnetic circuit of the reactor is established through theoretical analysis. Second, the simulation model is established and the inductance regulation characteristics of the reactor are obtained. Third, the key parameters are optimized for better performance based on Pareto optimality and a genetic algorithm. Finally, based on the optimized parameters, a new prototype of the OCR is developed and experimental work is carried out to verify the analysis. The results show that, compared with the traditional model, with the same material consumption, the space occupation of the new topology is reduced by 53.7% and the inductance regulation range is increased by 69%. Experimental results also show that increasing the area of the orthogonal region can significantly increase the inductance regulation range of the reactor. Based on the OCR, the filter with a variable resonance frequency can be formed, which is of significant application value in situations where the harmonic frequency is constantly changing. [ABSTRACT FROM AUTHOR]

The traditional saturated core type fault current limiters (TFCLs) cause large energy absorption and high overvoltage in direct current circuit breakers (DCCBs). Energy absorbing FCLs (AFCLs) cause coils to bear the fault current for a long period and the fault energy absorption is slow. In order to solve the problems of TFCLs and AFCLs, a novel fast energy storage dc FCL (EFCL) topology is proposed in this article. The EFCL not only reduces the overvoltage and energy absorption of DCCBs but also quickly stores energy. First, the working principle and topology of the EFCL are proposed. The design requirements of the main electrical and core size parameters are then analyzed. Then, the key electrical parameters are optimized by electromagnetic circuit simulations. The economy is analyzed. Finally, the whole process simulation and FCL comparison simulation are carried out. The feasibility of the EFCL is verified by the comparison of simulation with experiment. [ABSTRACT FROM AUTHOR]

In order to limit the extremely fast rising trend of fault current in a high voltage direct current system, a permanent magnet (PM) biased dc saturated core fault current limiter (DCSFCL) was proposed previously. However, the demagnetization problem of the PM and compromised fault limiting inductance value caused by the inserted PMs are two major issues that need to be solved. In this article, a hybrid-material based fault current limiter (HMFCL) is proposed. First, by means of reconstructing the iron core topology and substituting different soft magnetic materials with their hybrid benefits, the proposed novel HMFCL can present instant change in fault limiting inductance value without threating the safety of the PMs. Then, the Jiles–Atherton hysteresis modeling technique is applied on the HMFCL and its electromagnetic feature is analyzed. The parameters of HMFCL are optimized using genetic algorithm as well. Finally, the effectiveness of the proposed HMFCL is proved by various device and system level simulations as well as a prototype experiment. Results reveal that the proposed HMFCL can limit the fault current by over 80% compared with traditional smoothing reactor. [ABSTRACT FROM AUTHOR]

A DC system saturated core fault current limiter (DCSFCL) was proposed to limit the fast rising trend of fault current in HVDC system. However, traditional method to calculate and design the DCSFCL tend to neglect leakage flux around the permanent magnet (PM), leading to large calculation error and inappropriate design procedure. The novel contribution of this paper is that it proposed a modularization method to analyze the permeance of both PM and adjacent air. Hence, the leakage flux effect is considered properly and a more accurate permeance matrix can be derived in a pure mathematical way. In this case, DCSFCL can be calculated much faster than the FEA simulation program with a promising accuracy regarding fault limiting performance. More importantly, design flow of the DCSFCL and related PM biased devices was given as well. Calculation result shows that inductance value calculated by the proposed method has less than 1% error compared with fine meshed FEA simulation result and about 20% increase in accuracy compared with traditional method that neglects PM leakage flux effect. Prototype of the DCSFCL was also built and experimental tests were carried out to verify the correctness of the proposed method. [ABSTRACT FROM AUTHOR]

When the fault current in high voltage direct current (HVDC) systems rises to a higher level, the DC circuit breakers will have either insufficient capacity or will require larger sizes with increased costs. Fault current limiters (FCLs) can reduce the turn-off stress and the stringent requirements on breakers, thereby also lowering their cost. The use of saturated core FCLs, which have fast response times and low power loss, is a promising approach for this issue. However, the parameter design principles for this kind of FCL has so far not been discussed in the literature. The design is often based on reactors that does not consider the transient performance. In this study, an optimized design method for permanent magnets saturated core FCLs in HVDC transmission systems, is proposed. The constraint conditions, parameter optimization and modification steps are discussed, and an optimized FCL design is obtained with the lowest cost and expected current-limiting function. Both simulations and experiments are conducted, and the results demonstrate the validation of the proposed method. Finally, a cost evaluation among main types of inductive FCLs is carried out and suggestions for scaling up saturated core FCLs to HVDC applications are given. [ABSTRACT FROM AUTHOR]

To reduce the iron loss and noise of a three-phase reactor composed of grain-oriented (GO) steel plates, two types of core structures are proposed in this article. In the first type, the ordinary brick core model is improved to a hybrid one composed of GO and nonoriented steel plates, and in the second type, the T-joint part of the ordinary oblique-joint core model is improved to a straight joint. To show the effectiveness of the improved models, the iron loss and displacement distributions in the four core structures are evaluated using the 2-D magnetic field and mechanical analyses. In these analyses, the magnetic characteristics of the anisotropic cores are considered in detail. Namely, in the magnetic field analysis, the ${B}$ – ${H}$ curves in the arbitrary directions are considered. In the iron loss calculation, the rotational iron loss is calculated using the iron loss curves in the arbitrary directions. Moreover, the methods of calculating the displacements due to electromagnetism and magnetostriction considering the anisotropic ${B}$ – ${H}$ curves and magnetostriction in the arbitrary directions are proposed. It is shown that the iron losses and displacements of the two proposed core structures can be reduced compared with the ordinary ones. Moreover, the second proposed model is the most attractive one because both the iron loss and displacement are smaller than the other models. [ABSTRACT FROM AUTHOR]

A fault current limiter is an effective mean of limiting fault currents. The simultaneous use of three single-phase current limiters requires significant amounts of ferromagnetic material and space. This article proposes a three-phase saturated-core fault current limiter (T-SCFCL) that employs a common yoke and a permanent magnet to mitigate the restrictions of material and space. T-SCFCL delivers good performance for single-phase, two-phase, and three-phase faults. In this configuration, flux flowing through the permanent magnets is generated by a three-phase unbalanced current, thereby reducing the loss in eddy current and improving stability while significantly reducing the volume of the core. An algorithm is provided for use in the design of the FCL structure. A simulation was conducted based on the finite element method and a prototype manufactured and tested to verify effectiveness. The results prove that the proposed method is efficient. [ABSTRACT FROM AUTHOR]

Large fault direct current with fast rising speed has always been a significant threat to high voltage direct current systems. Fault current limiters (FCLs) are one of the most promising solutions. However, the biased permanent magnets (PM)s in traditional FCLs have large magnetic reluctance that causes FCLs to have small inductance changing ratios when a fault occurs. In this study, a novel three-limb topology of a saturated iron core-type fault current limiter (TSFCL) is proposed and a central PM bias limb is inserted to force flux flow through this limb. Therefore, the inductance changing ratio is greatly enhanced and the steep rising trend of fault current will be restrained effectively. The operating principles and characteristics of the TSFCL are analyzed to verify the deductions. Moreover, different lengths and cross-sectional areas of the inserted PM are tested and optimization study is carried out. The results show that the clipping inductance has a 55% increase compared with a traditional two-limb model. Moreover, compared with the existing smoothing reactor and traditional two-limb model, proposed topology can decrease the fault current by 45% and 16% within 5 ms, respectively. Finally, a typical HVDC system was built and the effectiveness of proposed TSFCL was verified. [ABSTRACT FROM AUTHOR]

Soft magnetic composites (SMCs) are composed of ferromagnetic particles surrounded by electrical insulation. To establish a homogenization technique for the magnetic field analysis of an electrical machine with an SMC core, we have already proposed a method to evaluate the effective permeability and iron loss of the SMC core using a cell model of one particle taking into account the nonlinear magnetic characteristics and eddy currents. However, the measured eddy current loss cannot be represented by using the proposed method. In this article, a 3-D eddy current analysis method modeling the anomalous eddy current loss due to the movement of domain walls in the cell model is developed based on the Pry and Bean magnetic domain model. The effect of the non-uniformity of the domain structure on the anomalous eddy current loss is investigated. It is shown that the measured eddy current loss can be almost represented by adding the anomalous eddy current loss to the classical one. [ABSTRACT FROM AUTHOR]

A novel multi-function saturated-core fault current limiter (MFCL) with two operating modes is proposed in this paper. MFCL can achieve fault current limitation and power flow management by switching operating mode: current-limiting mode and power-flow-controlling mode, which realizes technology convergence. The MFCL consists of an iron core with rotatable magnetic valve, ac coils, dc coils, and a fault-limiting reactor. The operating principle of the MFCL and the design of the rotatable magnetic valve are analyzed in this paper. The finite-element analysis (FEA) model based on Maxwell is used to analyze the MFCL. Simulation results depict that the MFCL can limit fault current effectively and provide variable impedance for power flow controlling. [ABSTRACT FROM AUTHOR]

Local force distribution is required to evaluate the deformation and vibration of a core in an electrical machine using the mechanical analysis. In the local force calculation, the Minkowski and Chu models with linear and nonlinear energy expressions are often used for the Maxwell stress tensor in linear or nonlinear condition, respectively. In the nonlinear magnetic field analysis, the volume forces, which move a magnetic body, obtained by using the above two models coincide with each other, whereas their local forces, which deform the magnetic body, are different. In this paper, a new expression of Maxwell stress tensor derived from Fleming’s left-hand rule is proposed. Then, the local forces of a simple magnetic body obtained by using various expressions of Maxwell stress tensor are compared with that obtained from the equivalent magnetizing current method. The surface force obtained from the proposed Maxwell stress tensor coincides with the equivalent magnetizing current method, and it is much different from those obtained by using the Minkowski and Chu models in this simple analytical model. Finally, the local force distribution in a 2-D finite element model is also demonstrated to show the necessity of the proposed model. [ABSTRACT FROM AUTHOR]

A novel direct current system fault current limiter (DCSFCL) based on the principle of nonlinear magnetization was proposed to limit fast rising fault current of the dc system. Different materials were also tested to find the iron core material. However, the existing material is not able to obtain both two necessary indexes, namely, a large saturation point and fast demagnetization speed. Hence, the performance is not satisfactory using a single material. In order to obtain the best performance for the DCSFCL, mixed materials were applied to combine the advantages of different soft magnetic materials. Furthermore, magnetic valves were also added to the original DCSFCL topology, which is an effective method to optimize the clipping performance and reduce the usage of materials. The 2-D models were built and finite-element analyses were carried out to verify these assumptions. Compared with a traditional smoothing reactor, the proposed new model not only limits the fault current by 55.4%, but also reduces the usage of both magnetic material and permanent magnets by over 20%. [ABSTRACT FROM AUTHOR]

The saturated-core fault current limiter (SFCL) is an effective device for limiting fault current. This paper proposes and analyzes a novel bridge-type SFCL (BSFCL) that uses a permanent magnet (PM) to reduce dc bias while improving the stability of the PM. The bridge structure in the BSFCL consists of four coils and a fault-limiting reactor which is used to limit fault current. The ac and the dc share coils to help reduce energy loss. The iron core uses air-gap branches to offer paths for ac flux, which reduces eddy current in the PMs and enhances their stability. The operating principle and characteristics of the BSFCL were analyzed using the electromagnetic coupling method. To investigate the effects of parameters on the performance of the BSFCL, various finite-element analysis simulations were performed by Maxwell. Experimental results of a 220 V prototype verify the effectiveness of the BSFCL. [ABSTRACT FROM AUTHOR]

The permanent-magnet-biasing saturated core fault current limiter (PMFCL) is one of the most promising devices to limit the fault current. To improve the biasing ability of permanent-magnets (PMs) and reduce the cost of PMFCL, this paper proposes a novel compact permanent-magnet-biased fault current limiter (CPMFCL). The three-limb structure can reduce the size and cost; the optimal small-section structure can improve the biasing ability of PMs and reduce the usage amount of PMs. First, the principle, equivalent magnetic circuit, and small-section optimized structure are introduced. To validate the principle and performance of CPMFCL, various finite element analysis simulation and optimization study are performed in Maxwell-3D. A 220 V/10 A CPMFCL prototype is designed and tested. The simulation and experimental results demonstrate that, compared with traditional PMFCLs, the CPMFCL has the advantages of smaller size, better biasing capacity of PMs, lower possibility of demagnetization, and excellent fault clipping performance. [ABSTRACT FROM AUTHOR]

The application of fault current limiter is an effective method to limit fault current. The saturated-core fault current limiter (SFCL) is one of the promising devices. However, its commercialization is limited by the high demands for the ferromagnetic material and the dc source generating magneto motive force. This paper proposes a novel three-phase compact SFCL (CSFCL) in which a common core and a permanent magnet are used to solve the mentioned challenges. The common core can significantly reduce the amount of required ferromagnetic material. The basic operating principle of CSFCL is introduced based on the analysis of the CSFCL’s magnetic circuit and equivalent electrical circuit. Finite-element analysis (FEA) simulations were performed by ANSOFT to validate the effectiveness of the CSFCL’s fault clipping performance. [ABSTRACT FROM AUTHOR]

The saturated core fault current limiter (SFCL) is one of the most effective methods for limiting fault current. A permanent magnet (PM)-biased SFCL (PFCL) can reduce dc bias current and additional energy consumption. However, the thermal stability of NdFeB PMs in PFCL poses a major challenge. This paper proposes a novel hybrid-type SFCL (HSFCL) topology that can reduce this risk. In the HSFCL, a hybrid PM/dc coil is designed to saturate the core, and a fault-limiting reactor is used to guarantee fault-clipping performance. The new structure provides air-gap branches for the time-varying magnetic field produced by alternating current, which reduces the eddy current in the PMs and enhances their stability. Electromagnetic coupling is used to analyze the operating principles and characteristics of HSFCL. Finite-element analysis simulations were performed using Maxwell and compared with verification experiments, proving that HSFCL is efficient in fault clipping and PM reliability enhancement. [ABSTRACT FROM AUTHOR]

Eddy-current loss of NdFeB permanent magnets (PMs) is widely analyzed in PM motors. This paper proposes a coupled 2-D transient finite-element analysis (FEA) of the saturated core fault current limiter (SCFCL) and 3-D analytical model of PMs to evaluate eddy-current loss in SCFCL. The comparison between the result from coupled method and that from 3-D FEA verifies the applicability of the coupled method in analyzing eddy current loss of PMs in SCFCL. The 3-D analytical model of PM is applied to analyze the effect of segmentation on the reduction of PM’s eddy-current loss. And the results show that segmentation along width has a better performance, which is also verified by 3-D FEA. [ABSTRACT FROM AUTHOR]

A saturated core fault current limiter (SCFCL) is a promising device for limiting the fault currents effectively, and improving the safety and reliability of power systems. Due to the core structure and the coupling effect between the ac and dc windings, traditional SCFCLs suffer the drawbacks of insufficient clipping performance and large size. Moreover, theoretical analysis of fault clipping performance has received little attention. Therefore, this paper proposes a novel bridge-type SCFCL (BSFCL). Compared with the traditional type, the BSFCL effectively reduces size and cost by using a bridge-type structure. In addition, the proposed additional limiting inductor improves the fault clipping performance of SCFCL. This paper first presents the principle and characteristics of BSFCL. Then, a theoretical analysis of clipping performance and parameter design method of BSFCL are presented in detail. Finally, the principle and performance of BSFCL are validated through electromagnetic simulation and experiments. The simulation and experimental results demonstrate the effectiveness of the theoretical analysis and the structure. The influence of different BSFCL parameters on fault clipping performance is also discussed. [ABSTRACT FROM PUBLISHER]

The fault current limiter (FCL) is one of the most useful measures for limiting fault currents in power systems. This paper introduces a new structure for a parallel-type permanent magnet (PM)-biased saturation-based FCL (PPFCL). The PPFCL consists of two magnetic devices connected in parallel and in magnetic counter opposite to each other. The operating principle and the core inductances in different states were analyzed using an electromagnetic equivalent circuit. In addition, a 220 V/10 A experimental prototype was designed and tested in a simple system and compared with Maxwell-3-D simulation and analytical methods. Finally, a 10 kV case-study model was created and compared with a series-type FCL, which verified the effectiveness of the limiter in high-voltage, large-capacity application. Experimental and simulation results have demonstrated that the PPFCL exhibits fast response and low impedance during normal operations, as well as high bias capability and low possibility of demagnetization of the PM during fault conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel compact high-voltage (HV) test system based on a magnetically controlled resonant transformer (MCRT) is proposed. This system is used to perform a power-frequency HV on-site voltage withstanding test. First, the basic principle of the MCRT is introduced. Next, a Fourier analysis based on the equivalent magnetic and electrical circuits of the MCRT is described. This analysis provides a design reference for the basic MCRT parameters. In addition, a finite-element model was constructed to verify the MCRT design. Finally, an MCRT prototype was designed to verify the effectiveness of the test system. Compared with the traditional HV test systems, the proposed test system in this paper has the advantages of compact structure, stable secondary voltage, and wide reactance adjustment range. [ABSTRACT FROM AUTHOR]

To reduce the requirement of dc-coil-generated magnetomotive force, this paper analyzes the method of using permanent magnets (PMs) to saturate the core. In this paper, a novel bridge-type hybrid saturated-core fault current limiter (BHFCL) is proposed to investigate the influence of PM. For the BHFCL, a bridge structure is designed to guarantee the fault clipping performance, with a fault limiting reactor. In addition, the compact structure of magnetic device and the shared coil of alternating current and dc could reduce cost and losses. To compare the influence of PMs on the performance of BHFCL and to validate the effectiveness of the proposed BHFCL, various FEA simulation models in a simple system are carried out by ANSOFT. The simulation results demonstrate that the BHFCL could achieve considerable energy consumption reduction with little effect on the normal condition voltage drop as well as the fault clipping ability. The BHFCL is efficient in fault clipping, and the performance is shown to depend mainly on the value of the reactor included in the bridge. [ABSTRACT FROM AUTHOR]

Magnetic-valve controllable reactor (MCR) has been widely applied in many kinds of industries, such as power systems and ferrous metallurgy. As electrical equipment, MCR can adjust its reactance smoothly and continuously, which has advantages like low dissipation and maintenance costs, high reliability. In this paper, a precise 2-D field-circuit coupling model of MCR is established by the finite element analysis software-ANSYS, and then the analysis of the harmonic characteristics of this model is presented in detail. Compared with the conventional numeric method, the proposed method could obtain more practical and accurate results and also has the ability to analyze electromagnetic field. Meanwhile, an experimental platform of a 2200 VA/380 V MCR is built. This paper provides detailed harmonic characteristics analysis of simulation and experiment. The simulation and experimental results verify that the proposed method is more accurate than using conventional ways. [ABSTRACT FROM PUBLISHER]

Magnetically controlled reactors (MCRs) are usually used as three-phase shunt reactors. They have low harmonic distortion independent of the third harmonic current because most three-phase MCRs are delta connected. However, as arc suppression coils, MCRs are operated in the single-phase mode, and the harmonics can be much higher than those of three-phase MCRs. In this paper, the structure and the mathematical model of a two-stage saturable MCR (TSMCR) are proposed. There are two stages with different lengths and areas in the iron cores. The stages saturate at different times when the TSMCR outputs reactive current. The current harmonics of the first saturated stage can be compensated for when the second stage begins to saturate, to reduce the total harmonics of the output current. The mathematical model that reveals the distribution characteristics of the current harmonics for the TSMCR is also presented. A study of the mathematical model indicates that there are two key factors that affect the total current harmonics of the TSMCR. One is the parameter k, which represents the area ratio of the second stage to the first stage. The other one is the parameter m, which represents the ratio of the length of the first stage to the total length of the magnetic valve in the iron core. The simulations and experiments show that the maximum current harmonics of the novel MCR can be limited to 3.61% of the rated output current when k and m are chosen according to the theoretical mathematical model. [ABSTRACT FROM PUBLISHER]