Bulk superconductors can trap high magnetic fields exceeding that of conventional permanent magnets as a manifestation of a macroscopic quantum effect. In recent years, a new record trapped magnetic field has been achieved, and the applicability to various devices has been vigorously studied. In this review, the trends in the research and development of superconducting bulk materials, including flux pinning control and mechanical reinforcement for REBCO, magnetization techniques, new materials (MgB₂ and IBSC), and modeling and simulation, are summarized.

(RE)BCO, rare-earth based high temperature superconductors fabricated in the form of large, single grain bulk samples can trap comparatively large magnetic fields in relatively small sample volumes, unlike conventional permanent magnetic materials. Fabrication of (RE)BCO single grains has been achieved largely following the development of processing techniques based on melt growth (MG). In the present study, the recently developed alternative fabrication technique of infiltration and growth (IG) is discussed and its significance highlighted in the context of obtaining (RE)BCO bulk superconductors with dense microstructures. The necessity of employing a buffer layer in the IG methodology is elucidated. The path followed in solving the complex problem of controlling the amount of RE₂BaCuO₅ (RE-211) present in the microstructure of the end product to achieve enhanced and optimized flux pinning is described. A brief overview of the recently developed 2-step, buffer-assisted top-seeded infiltration and growth (BA-TSIG) fabrication technique, which enables successful fabrication of (RE)BCO bulks, is presented. Finally, two novel experiments based on the TSIG technique—fabrication of a bar-shaped YBCO sample (with size: 72mm × 24mm × 15mm) and multi-seeding of YBCO (with two NdBCO seeds in 0°-0° configuration, with aligned a-b planes)—are described and further potential options for the fabrication of complex-shaped (RE)BCO bulk components for specific practical applications are outlined.

This paper proposed a magnetic levitation type seismic isolation device composed of radial arrangements of High Temperature Superconducting (HTS) bulks and Permanent Magnets (PM). We first analyzed and compared the levitation force of an axial arrangement and radial arrangement of the HTS bulk and PM rail for the seismic isolation device, respectively. Due to Halbach arrangement of the PM rail, the radial type HTS seismic isolation device can provide a comparable levitation force to the conventional axial type device. We also investigated the dependence of the levitation force on the shape of the HTS bulk and PM rail to clarify the design guidelines of the radial type device. The analysis results showed that a thinner HTS bulk generated a larger levitation force per unit volume of the HTS bulk. The analysis also clarified the proper bulk width by considering the magnetic flux density distribution of the Halbach PM rail. We also found that increasing the volume of the PM rail does not greatly improve the levitation force of the radial type device. These results suggest that the levitation force of the radial type HTS seismic isolation device can be most effectively increased by arranging several thin HTS bulks in the longitudinal direction of the PM rails.

Uniform magnetic field using superconducting bulk magnets has been developed and new research and practical targets associated with commercial market have appeared. The analysis and measurement of a uniform field with the bulk HTS are introduced and reviewed.

We introduce a design of supply management system for a grid-connected Micro-Grid (MG) which we term the Multi-Scale Supply Operation. The concept of MG has been developed as an effective method for utilizing distributed generation units including renewable energy resources. Multi-Scale Supply Operation aims to enhance the economic efficiency of a grid-connected MG and to contribute to the long-term supply-demand balancing of the commercial grid. The operation system consists of the three layers for optimization and control: long-scale supply planning, medium-scale supply planning, and short-scale control. In particular, we introduce the medium-scale supply planning to manage the imbalance (i.e. the difference between planned and actual amounts of electric energy from the commercial grid) and thus to enhance the economic efficiency. We also introduce a formulation of the long-scale supply planning to consider a physical constraint in the short-scale control. Performance of the proposed design is evaluated with numerical simulations of MG using a set of practical parameters and measured time-series data.

In Japan, a large amount of photovoltaics has been introduced because of Feed-in Tariff for renewable energy resources. As the results, it is necessary to suppress the output of photovoltaics to maintain supply and demand balance. In the future, however, it is expected to make more effective use of renewable energy by demand-side management. This paper proposes a method to realize power trading among consumers who buy surplus electricity from photovoltaics by smart contracts on the blockchain. According to the conventional method in Japan, the transmission and distribution company, which is responsible for supply reliability, forecasts the surplus of solar power the next day, directs PV producers to suppress output. Conversely, this paper proposes that the PV producers search for customers who can carry out storing electricity and the demand shift in the local power exchange using the blockchain, in response to the output suppression command from the transmission and distribution company.

Installed capacity of photovoltaic (PV) systems has been increasing rapidly due to the enforcement of the feed-in tariff scheme in Japan. However, reverse power flows from PV systems cause voltage-rises in distribution networks. As for the voltage stabilization with reactive power compensation, SVC (Static Var Compensator) has been installed until now. On the other hand, reactive power compensation using demand side equipment is proposed as a promising alternative with its cost-effectiveness. This paper proposes a cost-effectiveness analysis method of reactive power compensators considering PV output curtailment and reveals the conditions that demand side equipment has a cost advantage. First, we defined an annual cost as the sum of annual equipment cost of reactive power compensators and opportunity cost associated with PV curtailment, then calculated an optimum curtailment ratio, which minimizes the annual cost. Through the analysis, we obtained following findings: (1) the higher the avoided cost is, the lower the optimum curtailment ratio is; (2) the higher the annual equipment cost of demand side equipment is, the higher the optimum curtailment ratio is; (3) the higher the PV penetration rate is, the higher the optimum curtailment ratio is. This is because as for the cost impact arising from increasing PV, the annual equipment cost is greater than the opportunity cost associated with PV output curtailment.

We investigated the mechanism by which a lightning strike generates overvoltage at a building's distribution board. We analyzed the overvoltage using VSTL electromagnetic analysis software and constructed a simplified mathematical model for calculating the overvoltage. The results confirmed that the overvoltage generated at the distribution board is not affected by the arrangement of the ground wires. The overvoltage is instead dominated by the potential difference between the ground electrodes, which is determined by the potential distribution in the surrounding ground. The overvoltage was calculated by the potential interferometry at steady state of the ground potential distribution. The calculated results of the overvoltages differed within ±10% from the analyzed results.

The effects of the generator shape and operating conditions on the power generating characteristics and the pre-ionization power in a seed-free pre-ionized inert gas plasma disk shaped MHD generator are examined by two-dimensional numerical simulation. The reduction of the area ratio of the generator outlet to the throat leads the high ratio of the isentropic efficiency to the enthalpy extraction ratio, and a high magnetic flux density and low inlet total pressure provide high enthalpy extraction ratio and the isentropic efficiency, as well as in the seeded plasma MHD generator. Then, the externally applied power for the pre-ionization of inert gas at the generator inlet is found to be reduced owing to the power generation with high electrical efficiency and low electrical conductivity.

When the bypass circuit of the PV module is open and the performance of solar cell drops by partial shadow, abnormality and so on, a part of solar cells generates heat and becomes a hotspot. In the worst case, since this malfunction is likely to lead to the fire, early detection is important. The technology proposed in this paper is intentionally to increase the temperature of the faulty part of PV module by applying an AC voltage with a power source. The temperature change is observed with an IR camera, and the fault point is identified by the frequency analysis to avoid the disturbance such as surrounding building and so on. In this paper, we describe the principle of detection technology and the effect of irradiance.

Recent growth of renewable energy (RE) generations with natural variability, would make the demand and supply regulation in a whole power system more difficult, and therefore, alternatives for demand and supply regulation resources would be required. The authors focus on co-generation system (CGS) owned by the consumers as one of regulation resources and have proposed a novel optimal operation strategy of CGSs to provide the demand and supply regulation. This paper discusses the optimal installation design including two configurations of CGS based on the economic viewpoints considering the energy supply cost and the financial incentive associated with the contribution for demand and supply regulation. The discussions are based on numerical case studies with the actual electrical and thermal demand profiles and equipment cost of CGS.

A numerical design method to determine basic specifications of high-performance frozen inert gas plasma (FIP) MHD generators is proposed. To validate the proposed method, time-dependent, two-dimensional (r-z) MHD numerical analyses are performed for several FIP MHD generators with different thermal inputs (30, 100, 300, or 1000MW) designed by the proposed method. The numerical results indicate that the designed FIP MHD generators with the thermal input of 100MW or more are able to be operated with the performance approximately same as the designed one. For the designed MHD generator with the thermal input of 30MW, however, the performance shown by the MHD numerical analysis is considerably lower than the designed one. For such a case, the performance can be improved by operating the MHD generator under an applied magnetic flux density larger and an inlet ionization degree lower than those designed values.