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In this article, a novel concept of an inductive, saturated-core fault-current limiter (FCL) design is presented, capable of limiting three-phase faults. The design is based on high-remanence permanent magnets for biasing high-saturation electrical steel cores, thus minimizing the device volume, dimensions, and cost and allowing a relatively easy assembly process due to the magnetic symmetry of the model. By implementing a three-phase design in a single device, we harness the full potential of each magnet, substantially reducing the required material for achieving negligible losses during nominal operation while increasing current limiting during faults. A laboratory-scale, low-voltage prototype has been built and tested to prove the feasibility of the new concept, suggesting that upscaling to higher voltage devices is plausible. Extensive simulations, using finite-element analysis, have yielded insight into several measured phenomena, including a unique phase-coupling effect experienced during three-phase fault measurements.

We explore the effects of various receiver coil dimensions and configurations on power transfer efficiency and cost of operation, using advanced simulation tools. We demonstrate that the spatial distribution of the magnetic field leads to a non-monotonic dependence of the coupling coefficient on coil size. Thus, an optimal coil size, where the coupling coefficient peaks, should be regarded a crucial design parameter which affects the entire system performances. The incorporation of our findings into a multi-objective optimization algorithm is also discussed.

AC losses for a wide range of ac amplitudes and frequencies have been studied in magnesium diboride (MgB2 ) superconducting wire with 36 filaments and Monel sheath at different temperatures and dc current levels. The results show a strong nonlinear frequency dependence below 1 kHz, which crosses over to a more moderate linear behavior at frequencies up to 18 kHz. Surprisingly, the introduction of dc current causes a significant reduction in the ac losses. Finite element simulations yield ac losses consistent with that observed experimentally. The simulations show that the magnetic Monel sheath is a dominant source for ac losses in zero dc current and that nonzero dc current saturates the magnetization, thus reducing the ac losses.

Development of high-power superconducting applications requires the accurate estimation of AC losses in the superconductor. In applications such as superconducting magnetic energy storage, the charge/discharge/persistent switching frequency of the coil, resulting from pulse width modulation control algorithms, is usually in the kilohertz regime. Therefore, a thorough investigation of the losses in the kilohertz regime of AC currents superimposed on large DC currents is essential in order to ensure the device stable operation at a predefined temperature. We describe here a unique experimental setup designed and built for characterizing AC losses in superconducting wires and coils under such special conditions. To minimize the eddy currents induced in the apparatus, a cryostat vacuum vessel was made of Delrin, an insulating synthetic polymer. The measurement setup allows driving DC currents up to 150 A and superimposed AC currents with amplitudes up to 10 Arms and frequencies up to 18 kHz. The system utilizes conduction cooling to reach a wide range of temperatures between 6 and 100 K and allows measurements of 10 cm long superconducting wires and coils with a diameter of 40 cm. The loss is measured by the electrical method, i.e., by direct voltage and current waveform measurement, achieving a resolution better than 100 nW. The system described here will assist in developing superconducting wires and coils for high-power applications.

Designs of saturated-cores fault current limiters (FCLs) usually implement conducting or superconducting DC coils serving to saturate the magnetic cores during nominal grid performance. The use of coils adds significantly to the operational cost of the system, consuming energy, and requiring maintenance. A derivative of the saturated-cores FCL is a design implementing permanent magnets as an alternative to the DC coils, eliminating practically all maintenance due to its entirely passive components. There are, however, various challenges such as the need to reach deep saturation with the currently available permanent magnets as well as the complications involved in the assembly process due to very powerful magnetic forces between the magnets and the cores. This paper presents several concepts, achieved by extensive magnetic simulations and verified experimentally, that help in maximizing the core saturation of the PMFCL (Permanent Magnet FCL), including optimization of the permanent magnet to core surface ratios and asymmetrical placement of the permanent magnets, both creating an increase in the cores&rsquo, magnetic flux at crucial points. In addition, we point to the importance of splitting the AC coils to leave the center core point exposed to best utilize their variable inductance parameters. This paper also describes the stages of design and assembly of a laboratory-scale single phase prototype model with the proposed PMFCL design recommendations, as well as an analysis of real-time results obtained while connecting this prototype to a 220 &nbsp, V grid during nominal and fault states.

With two recent successful installations in a U.K. live grid, the saturated core fault current limiter (SCFCL) has become one of the leading candidates for commercial fault current limiting devices. In this work, we review the concept developed at Bar-Ilan University, which was later adapted by GridON, for a novel compact SCFCL. This SCFCL utilizes a superposition of a closed dc magnetic circuit and an open ac magnetic circuit to overcome the intrinsic problem of transformer coupling found in traditional SCFCL designs. It also allows the use of a single magnetic core for a full ac current cycle limiting. In addition, the relatively short path for the dc magnetic circuit supports copper coils as an alternative to superconducting bias coils, allowing easier market penetration. The performances of the SFCL devices installed in live grids are described.

Current leads in cryogenic systems are a major heat source which eventually affects the entire system. It has been shown in recent years that Peltier elements are useful in reducing incoming heat into the cold system. In this article we present a new tapered cone-like configuration of the Peltier Current Leads which increases the power saving. This configuration is compared to the standard cylindrical configuration utilizing advanced ANSYS simulations. The simulations show an additional power saving of 4% when using the tapered lead configuration.

Effect of the winding density in the AC coils on the performance of a saturated cores fault current limiter (SCFCL) has been studied, exploiting Finite Element Analysis. For a given design, a fixed number of turns was concentrated at the center of the AC coils limb, resulting in high windings density. The coil length was then increased gradually along the limb, decreasing the winding density and therefore decreasing the coil impedance. However, we found that the ratio between the fault to nominal state impedances increases with decreasing winding density. The results are discussed and explained as originating from the change in the flux linkage of windings in the coil for various core states. In the nominal-state of the SCFCL, the core is saturated and the coupling between the windings is lower, given the lower winding density. However, when the core is desaturated during a fault, the magnetic interaction of the windings with the core strengthens, the coupling between the windings increases and contributes to higher fault-state impedance. Thus, reducing the winding density may serve in increasing the impedance ratio of the device and improving the performance of SCFCLs. The results suggest that the windings density in SCFCLs should be used as a significant design parameter.

Optimizing the efficiency of primary and secondary coil configurations for Dynamic Wireless Power Transfer (DWPT) in Electric Vehicles (EVs) requires means for accurate calculation of the mutual inductance in an array of coils. Based on finite element simulation method, we present a quick and accurate method for calculating the energy transfer capabilities of a given DWPT array. By consecutively switching on and off every coil and driving them with a constant current ramp rate, mutual inductances and a coupling coefficient matrix of the whole configuration is easily calculated. This method allows for relatively easy optimization and up-scaling of DWPT systems to multiple arrays of primary and secondary coils as well as implementing various coil designs and configurations. The data acquired using this method may also be used during real-time applications providing indications of vehicle relative alignment.

The saturated cores Fault Current Limiter (FCL) is one of the leading candidates for providing a commercial robust solution to the fault current problem. Basically, the saturated cores FCL offers low impedance during normal grid operation due to its saturated cores state and high impedance in fault events due to cores desaturation. We developed a method to obtain the nonlinear inductance curve L(I) of the saturated cores FCL from which we show that the dynamic inductance component, dL/dt, contributes significantly to the FCL limiting capabilities. Specifically, we show that in some parts of the AC cycle, the dynamic inductance term dominates over the static inductance in contributing to the voltage drop across the device. We conclude that the design of saturated cores FCL should consider the dynamic inductance and calculate its contribution to the FCL voltage to benefit from better device performances.

Self-assembly provides an information-economical route to the fabrication of objects at virtually all scales. However, there is no known algorithm to program self-assembly in macro-scale, solid, complex 3D objects. Here such an algorithm is described, which is inspired by the molecular assembly of DNA and based on bricks designed by tetrahedral meshing of arbitrary objects. Assembly rules are encoded by topographic cues imprinted on brick faces while attraction between bricks is provided by embedded magnets. The bricks can then be mixed in a container and agitated, leading to properly assembled objects at high yields and zero errors. The system and its assembly dynamics were characterized by video and audio analysis, enabling the precise time- and space-resolved characterization of its performance and accuracy. Improved designs inspired by our system could lead to successful implementation of self-assembly at the macro-scale, allowing rapid, on-demand fabrication of objects without the need for assembly lines.

A saturated core fault current limiter (SCFCL) is a non-linear core-reactor where the core is saturated by an external superconducting DC bias source to achieve a low core permeability at nominal AC currents. Fault current levels in the AC coils de-saturate the core and transform it to a higher permeability state, hence limiting the fault current. In this work we describe the transition between saturated and de-saturated states in three SCFCL configurations. The ‘effective core length’, Leff, of the SCFCL, defined as the length of the de-saturated AC core limb, is introduced for exploring this transition as a function of the current, I, in the AC coil. Practically, Leff allows one to see the SCFCL as an inductor with a variable core length, allowing calculations of the impedance of the SCFCL over the whole range of operating currents. The Leff(I) curve is further used to calculate the dynamics of the demagnetization factor in a SCFCL. We show that the strong change in the magnetic induction of a SCFCL at high current is the result of both increasing the effective core length and decreasing the demagnetization factor. The method and results presented here serve as an important tool for comparing between various SCFCL concepts not only by comparing their impedance values at the extreme fault and nominal current conditions but also by providing an insight into the full de-saturation process.

The process of driving the magnetic core of saturated-cores fault-current-limiters (SCFCL) out of saturation has been studied numerically using finite elements calculations. The de-saturated core section was found to grow dynamically starting from the central region below the AC coils and gradually expanding towards the coil edges with increasing AC current amplitude. During the transition, the core volume underneath the coils is non-homogeneously magnetized and the system is highly non-linear. An effective core volume that contributes to the SFCL impedance during fault can be defined for different current amplitudes. Two “open core” SCFCL models have been studied and compared for their dynamic de-saturation process. The results demonstrate the importance of the dynamic effective volume size to the current limiting process and suggest that prior art approximations based on full core desaturation are not sufficient for a detailed SFCL design.