Electrical Engineering in Japan最新文献

There is concern that a reduction in power system inertia could lead to a reduction in frequency stability. In order to maintain frequency stability, it is important to estimate the area inertia. In this paper, we propose a method for estimating the area inertia using ambient measurement data of tie-line power flow and frequency measured by PMUs, etc. In the proposed method, the area inertia is estimated from the ambient measurement data based on spectrum analysis. Also, it is verified the effectiveness of the method by simulations using the IEEJ WEST 30-machine system model.

This paper proposes a local/remote control authority switching method in IEC 61850-based telecontrol systems. The proposed method enables control authority switching at arbitrary levels such as substations, substation sections, and individual transmission lines (individual bays). The testing results obtained from a prototype telecontrol system demonstrate the practicality of the control authority switching implemented based on the proposed method.

Stator windings of hydro generators are exposed to combined thermal, voltage, environmental, and mechanical stresses, which deteriorate the insulation performance. On the other hand, various stator faults occur in the stator. The stator faults are accompanied by partial discharges, which may lead to dielectric breakdown depending on the type of faults. This paper presents a case study of detecting stator faults by on-line partial-discharge diagnostics. The type of stator faults is identified based on reproducible experiments. Furthermore, the advantages of online partial-discharge diagnostics compared with offline diagnostic methods in detecting stator windings are discussed.

In this study, we discuss tele-operation of mobile robot to gather information in closed space after disaster. Information gathering by mobile robot need to communicate with operator. In this communication, Robot Wireless Sensor Networks (RWSN) has been proposed to expand tele-operation range by repeaters that relays wireless LAN. However, RWSN has risk such as communication disconnection due to repeater failure or radio frequency interference. When communication is lost, operator cannot tele-operation mobile robot. Therefore, we have proposed tele-operation using LoRaWAN as sub communication infrastructure. We discuss “proportional control tele-operation” as a method of operation when using sub communication infrastructure. In this method, operator's gamepad input is transmitted via LoRaWAN to enable constant operation. However, when the communication quality degrades cause back and forth vibration of mobile robot. This vibration leads to degrade operability of the mobile robot tele-operation system. Therefore, in this paper, we propose a system that suppress operability degradation by vibration of mobile robot.

A continuous voltage compensator (CVC) has been recently developed to improve the power quality of distribution lines. A CVC comprises series and shunt static power converters with transformers, and its circuit topology is based on a unified power flow controller (UPFC). Features of the CVC include fast active power control and precise imbalanced voltage compensation using a series converter, which are not accomplished by the conventional step voltage regulator (SVR) and thyristor voltage regulator (TVR) based on tap-change control. Further, the CVC contributes to stabilizing distribution lines by supplying reactive power and negative sequence current from the shunt converter. The details of the control strategies of series and shunt converters are proposed, and the validity of the proposed strategies is verified by fabricating a 200 V, 20 kVA scale-down CVC prototype. A 6.6 kV, 3,300 kVA full-scale CVC has been developed for comparing the voltage controllability with the conventional TVR, and the effectiveness of the CVC was demonstrated in the field test.

Considering optimization of the laying route for submarine power cables off the coast of Japan, there are many deepwater areas over depth of 1000 m. In Japan, submarine power cables have been installed at a depth of about 300 m as maximum; however, there is no track record beyond that level. The laying depth is deeper, the laying tension is larger. Therefore, as a result of discussion on the cable structure and material suitable for the laying in deep water, the aluminum conductor with keystone structure was applied for reducing the cable weight since the laying tension is proportional to the product of depth and weight. In this study, the prototype submarine cables of DC 500 kV class (transmission capability of 1 GW) equipped with the double steel wire armor were manufactured, then mechanical and electrical properties were evaluated in accordance with CIGRE TB 496 and TB 623. As a result, the cables of our design, on which the tensile bending test had been carried out in advance, passed the high-voltage 30 days load cycle test followed by the lightning impulse test without any defect.

Considering optimization of the laying route for submarine power cables off the coast of Japan, there are many deepwater areas over depth of 1000 m. In Japan, submarine power cables have been installed at a depth of about 300 m as maximum; however, there is no track record beyond that level. The laying depth is deeper, the laying tension is larger. Therefore, as a result of discussion on the cable structure and material suitable for the laying in deep water, the aluminum conductor with keystone structure was applied for reducing the cable weight since the laying tension is proportional to the product of depth and weight. In this study, the prototype submarine cables of DC 500 kV class (transmission capability of 1 GW) equipped with the double steel wire armor were manufactured, then mechanical and electrical properties were evaluated in accordance with CIGRE TB 496 and TB 623. As a result, the cables of our design, on which the tensile bending test had been carried out in advance, passed the high-voltage 30 days load cycle test followed by the lightning impulse test without any defect.

This paper presents an algorithm for the re-adhesion control of electric rolling stocks. Generally, an engineer manually adjusts parameters used in any re-adhesion control algorithm before a commercial operation. However, it depends heavily on the experience of the engineer. Therefore, developing an automatic adjustment system for re-adhesion control is imperative. To this end, we apply the particle swarm optimization (PSO) algorithm to re-adhesion control. In our approach, a cost function based on the averaged tangential force of an electric bogie is optimized by the PSO algorithm, and the parameters for re-adhesion control are automatically adjusted. In addition, experiments using a scale model railway vehicle are carried out to validate the proposed method.

This paper presents an algorithm for the re-adhesion control of electric rolling stocks. Generally, an engineer manually adjusts parameters used in any re-adhesion control algorithm before a commercial operation. However, it depends heavily on the experience of the engineer. Therefore, developing an automatic adjustment system for re-adhesion control is imperative. To this end, we apply the particle swarm optimization (PSO) algorithm to re-adhesion control. In our approach, a cost function based on the averaged tangential force of an electric bogie is optimized by the PSO algorithm, and the parameters for re-adhesion control are automatically adjusted. In addition, experiments using a scale model railway vehicle are carried out to validate the proposed method.

We have investigated the mechanism of coercivity evolution in magnets through multi-scale microstructural characterization. On the basis of these findings, our goal is to enhance the coercivity of heavy rare-earth-lean magnets by optimizing their microstructure. We have developed several new processes and demonstrated improved magnet properties. This review article describes (1) coercivity enhancement by the eutectic alloy diffusion process, (2) the development of light rare earth magnets, and (3) the development of high electrical resistance magnets. Recently, there has been an increasing demand for highly efficient magnet development that not only improves properties but also meets multiple requirements. Accordingly, (4) data-driven methods are being employed in ongoing magnet development.