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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]

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]

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]

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]