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Superconducting Magnetic Energy Storage (SMES) is proposed for electric utility load leveling. Attractive costs, high diurnal energy efficiency (> 92%), and rapid response are advantages relative to other energy storage technologies. Recent industry-led efforts have produced a conceptual design for a 5000 MWh/1000 MW energy storage plant which is technically feasible at commercially attractive estimated costs. The SMES plant design includes a protection system which prevents damage to the magnetic coil if events require a rapid discharge of stored energy. This paper describes the design and operation of the coil protection system, which is primarily passive and uses the thermal capacity of the coil itself to absorb the stored electromagnetic energy.

The paper presents a novel configuration of an axial hybrid magnetic bearing (AHMB) for the suspension of steel flywheels applied in power-intensive energy storage systems. The combination of a permanent magnet (PM) with excited coil enables one to reduce the power consumption, to limit the system volume, and to apply an effective control in the presence of several types of disturbances. The electromagnetic design of the AHMB parts is carried out by parametric finite element analyses with the purpose to optimize the force performances as well as the winding inductance affecting the electrical supply rating and control capability. Such investigation considers both the temperature dependence of the PM properties and the magnetic saturation effects. The electrical parameters and the force characteristics are then implemented in a control scheme, reproducing the electromechanical behavior of the AHMB-flywheel system. The parameter tuning of the controllers is executed by a Matlab/Simulink code, examining the instantaneous profiles of both the air-gap length and the winding ampere-turns. The results of different dynamic tests are presented, evidencing the smooth air-gap changes and the optimized coil utilization, which are desirable features for a safe and efficient flywheel energy storage.

Abstract Electromagnetic energy harvesters have been studied intensively in the past decade as non-stop power solutions for low-power wireless electronic devices. We here exploit a new way, i.e., forming an abrupt change of magnetic flux density, to improve harvester performance. A new transducer is proposed, which is primarily composed of a set of magnet array, a pair of springs and a coil array. Four cases are investigated: cubic magnets in Halbach and alternative configurations; triangle magnets in Halbach and alternative configurations. We examined the magnetic flux density distribution via the finite element method (FEM) and ensured the nonexistence of phase difference in two contiguous coils. We fabricated a prototype and conducted comprehensive tests, of frequency sweep with and without external resistances, of matching impedance and of obtaining maximum RMS power output. The FEM analysis indicates that the harvester in the cubic alternative case has the largest changing rate of the magnetic flux density (MFD) in terms of the magnitude and the distance range of the change. Experiments verify the FEM simulation and the prototype with the cubic alternative magnet array shows the highest voltage response of 20 V and a maximum RMS power output of 35.5 mW under a harmonic excitation of 9.8 m/s2, which is much higher than those in the other cases. In term of the volume and mass power density, the alternative arrangement of cubic magnets displays the most desirable outputs at 0.4955 mW/cm3 and 0.28 mW/g, respectively, which are three and two times as high as those of the second best case - the triangle Halbach case. This detailed study reveals the considerable benefits brought by the magnet arrays of alternating polarity and configuration, and paves a new way to improve the performance of electromagnetic energy harvesters.

With the global trend of carbon reduction, high-speed maglevs are going to use a large percentage of the electricity generated from renewable energy. However, the fluctuating characteristics of renewable energy can cause voltage disturbance in the traction power system, but high-speed maglevs have high requirements for power quality. This paper presents a novel scheme of a high-speed maglev power system using superconducting magnetic energy storage (SMES) and distributed renewable energy. It aims to solve the voltage sag caused by renewable energy and achieve smooth power interaction between the traction power system and maglevs. The working principle of the SMES power compensation system for topology and the control strategy were analyzed. A maglev train traction power supply model was established, and the results show that SMES effectively alleviated voltage sag, responded rapidly to the power demand during maglev acceleration and braking, and maintained voltage stability. In our case study of a 10 MW high-speed maglev traction power system, the SMES system could output/absorb power to compensate for sudden changes within 10 ms, stabilizing the DC bus voltage with fluctuations of less than 0.8%. Overall, the novel SMES power compensation system is expected to become a promising solution for high-speed maglevs to overcome the power quality issues from renewable energy.

In this paper, the three dimensional finite element method previously presented by these authors is applied here, for the first time, to laminated iron core devices with considerable magnetic saturation. This includes a practical form of anisotropy effects associated with magnetic nonlinearities in laminated cores. The calculation of the stored magnetic energy in the field is based on three distinct B-H magnetization characteristics in the x, y and z directions depending on the orientation of the iron core laminations. Agreement between calculated and measured flux densities and magnetizing inductance of a coil and a single phase shell type transformer confirm the validity of the method and its applicability to saturated iron cores.

Cooling process of big superconducting magnets from temperature of surrounding to the critical temperature is a verycomplicated process from economical as well as from technical view. In case when cryostat containing experimental device overcoolitself from normal temperature directly with liquid helium the consumption would be considerably higher than in case that we use liquidnitrogen for first overcool. Thus whole process of overcooling would be considerably nonprofitable. The article describes experiencewith overflowing of superconducting magnets installed in laboratory at the Technical University in Kosice, where the research projectfor the electric energy in the magnetic field storage takes place.

Abstract Electromagnetic reactors are used to carry out practical tasks of automatic control of power lines operation modes, distribution grids and energy supply systems of the industrial enterprises. The reactors’ characteristics significantly depend on the harmonic’s manifestation magnetic field saturation, which is different in the magnetization modes of reactors: forced, free and symmetrical. For the purpose of their analysis, a generalized mathematical model of the cross-sectional magnetic circuits of static ferromagnetic devices with rotating magnetic field has been developed on the base of nonlinear magnetic circuits theories. It was found that the best mode is symmetric magnetization, characterized by the following advantages: an increased range of reactive power control, enhanced stabilizing effect on the controlled current, reduced losses in steel, increased speed and the absence of “shaking” vibrations of the reactor magnetic core. It is shown that the free magnetization mode is close in its merits to the symmetric magnetization mode.

A procedure is proposed for analysis of maximum mismatch angle between the half couplings of a magnetic clutch and highly coersive permanent magnets (formed from alloys of rare-earth elements ‐ samariumcobalt and neodium-iron-boron) during the start-up of an asynchronous motor is proposed for the design of hermetically sealed machines (pumps, compressors, mixers, etc.). In hermetically sealed machines with a magnetic clutch (pumps, vacuum cleaners, compressors, mixers), the driving and driven parts are coupled elastically one with the other, and are displaced relative to one another by an angle that varies during movement (the mismatch angle of the poles of the magnetic clutch). Prior to start-up of the driving asynchronous electric motor, the magnets of a cylindrical magnetic clutch are situated coaxially, and the half couplings opposite one another. The forces of interaction between the magnets are directed toward the center of the axis of rotation of the clutch along lines connecting the centers of the poles of the magnets. The torque of the clutch is equal to zero in this position. During start-up, the driving half couple, which is mounted on the shaft of a driving electric motor, is turned through a certain angle, while the driven half clutch, which is mounted on the shaft of the effective member of the machine, remains in place, since the connection between the half couplings is not rigid. Moreover, the centers of the poles of the magnets are also displaced relative to one another by this same angle, and the directions of the interaction forces of the magnets are changed ‐ tangential components of the interaction forces are manifested. A torque develops in the clutch under the action of all tangential magnetic forces. When the torque of the clutch is greater than the torques created by the resistance forces (friction, load, and inertia), the driven half coupling is withdrawn beyond the driving half coupling, and an additional load develops on the driving electric motor, which lowers its dynamic torque. The acceleration of the driving half coupling is reduced, and the driven half coupling approaches the driving half coupling. As a result, the load, mismatch angle, and torque of the clutch (acting on the driving half clutch) are reduced, and the driving motor is again accelerated, leading to an oscillatory process. The maximum torque transferred by the clutch should exceed the in-service torsional moments due to the resistance forces in order to avoid breaking of the magnetic bond between the half couplings (rotations of the half couplings with different frequencies, resulting in a marked reduction in the torque being transferred). It should be pointed out that after the pause associated with restoration of the broken magnetic bond, the torque of the clutch is fully restored ‐ i.e., the clutch can be used as a protective link. After acceleration from rest, the torque transferred by the clutch is reduced (consequently, the mismatch angle is also reduced) due to disappearance of acceleration of the rotating masses, and the effective operating regime of the clutch and machine is established.