Masashi Ohchi

Novel scheme for drawing electric lines of force using scalar potential

The electric lines of force are trajectories comprising the tangents of the lines of forces that act on the electric charge in the electric field. In the complicated system of the multi-dielectric and multi-conductor media, the lines of force are not necessarily continuous on the interface of the dielectric media. In the engineering application, the visualization of the electric fields is quite essential. It has been strongly believed that the electric lines of force can relatively easily be plotted using numerical analysis. However it is practically difficult to draw the electric lines of force proportional to the intensity of electric field using a scalar potential with the 2-D finite element method. The paper proposes the novel scheme of drawing the electric lines of force based on the electric displacement using the scalar potential and illustrates the distribution of electric field of the capacitor with a long distance as an example.

Finite element analysis of insulator built-in type of voltage-current sensor with compensation winding

The real-time observation of a power factor will be indispensable for the maintenance and the stable voltage regulation in three-phase power distribution systems. To carry out the observation, the authors have devised and proposed an insulator built-in type of voltage-current sensor. According to their previous investigations on the sensor, it was found theoretically that a serious phase shift in the measured waveforms of the voltage and the current might occur owing to the electromagnetic interference of each phase. In the paper, they propose the compensation winding for the current sensor in the horizontal and vertical power distribution systems.

Numerical electric field analysis of simulated human brain

The authors have investigated a nondestructive measurement method of various permittivity in a human brain. To establish the method, they have used a measurement method of a long distance small parallel-electrode air capacitor with additional electrodes, in which an electric potential equals to one of the respective main measurement electrodes. Such an air capacitor will be utilized to measure the permittivity which depends on the temperature in a brain. In this paper, the electric lines of force of a simulated human brain have been visualized using Finite Element Method (FEM) and the predicted capacitance based on the method has been estimated.

Resin molded type of voltage-current sensor for real-time measurement of power factor in power distribution systems

The authors have proposed the voltage-current sensor embedded in a ceramic insulator for the real time observation of the power factor in three-phase power distribution systems and carried out the finite element analysis of it to investigate its characteristics and verify its feasibility. However, the sensor will have problems with production costs and manufacturing process. In the paper, the authors propose a new resin molded type of voltage-current sensor with a compensation winding for the current sensor part and discuss its electromagnetic behavior and the constitution of four kinds of electrodes theoretically.

Development of autonomously mobile robot with control system connected by TCP/IP network

The purpose of this paper is to detail the development of a mobile robot and control support system. The robot has five infrared (IR) ray sensors and three ultrasonic sensors to enable it to follow a guide person with an IR ray transmitter. The robot follows the IR rays emitted by the transmitter and moves towards its destination. The control system has been developed by using network technology (client/server model) based on the TCP/IP protocol; the CPU of the robot system has a low-enough speed for this. The advanced control strategy for the mobile robot is carried out with a high-speed host server computer connected through the TCP/IP network. In this paper, the autonomous mobile robot system and the control support system aided by the TCP/IP network are described.

Calculating leakage reactance of 9-winding transformer using time-dependent 3D FEM analysis

Calculating leakage reactance of transformers is a very important factor in designing transformers. It is difficult to calculate the leakage reactance in multiple-winding transformers, because their structures are more complicated. The finite element method (FEM) is useful to obtain the leakage reactance in such a complex case. Using a 3D FEM analysis, leakage reactances have been calculated and compared to experimental results. But, there were differences between the results of FEM analysis and the experimental results. In this paper, the leakage reactance is calculated by using a coupled-field analysis, which combined electromagnetic field analysis and electric circuit analysis, for simulation of short-circuit test in multiple-winding transformer. The results of this analysis showed that current values of parallelly connected primary windings are very different by the physical geometry of the secondary winding. The leakage reactances calculated by using the coupled-field analysis are qualitatively the same as experimental results.

Development of a web-based remote experiment system for electrical machinery learners

Experiments have critical roles in engineering education. However, it is not easy to conduct experiments because of their high costs of equipment and unavailability. Remote experiment systems have coped with this issue. Using remote experiment systems, users can conduct experiments regardless of their locations or times. Remote experiment systems have been developed worldwide, but most of the systems are developed for personal computers, and therefore cannot be used with smartphones or tablets. This study aims to develop a remote experiment system which can be used with smartphones or tablets. The proposed system provides remote control of a DC motor by PWM control and remote measurement of a single phase alternator. The user interface of the system is designed without Web plug-ins so that users can use the systems with their smartphones or tablets as well as their personal computers.

Feasible method of calculating leakage reactance of 9-winding transformer for high-voltage inverter system

Calculating leakage reactance of transformers is a very important factor in designing transformers. In the traditional two-winding transformer, the calculation methods of leakage reactance have been presented using the inductance deduced by the geometry mean length between two windings. However, it is difficult to calculate the leakage reactance in multi-winding transformers, because its structure is more complex. Finite element method (FEM) is useful to obtain the characterization of the electromagnetic behavior of the magnetic components. FEM is an accurate method but its computational cost is very high. In this paper, the leakage reactance of 9-winding transformer was calculated by using an ordinary three dimensional FEM (3D FEM) and hybrid FEM which is a quasi-three dimensional analysis method. The comparison results show that the hybrid FEM is able to calculate the leakage reactance with a low computational cost.

Simulation of resin molded type sensor in pole switch for power delibery systems

The current sensor of the voltage-current sensor system proposed by us is two air-core sensing coils connected in series to each other with an opposite polarity. By doing so, it can measure the harmonics and power factor while removing the influence from power lines of other phases. When the sensors are surrounded by an iron case, EMF may be influenced. However, it has been confirmed that a large change is not observed with regard to measurement of harmonics, and the proposed sensors can be used without problem. Therefore it was found out that the proposed sensor is able to perform power measurements in a state of being incorporated in the pole switch.

Development of power measurement system in Simulated Micro Grid system for education

In recent years, “Smart Grid” obtains much attention. In the our laboratory, “Simulated Micro Grid System” for supporting learning of power engineering has been designed and implemented. The system helps young engineers to understand the principles of the Smart Grid technology. In this study, we have developed a power measurement system for our Simulated Micro Grid System. AD conversion is essential in the power measurement system to control components in the Simulated Micro Grid System and deliver measured data on the Web. In this paper, we have proposed two methods, AD conversion using ART-Linux and AD conversion using SH-3 microcomputer. The method by ART-Linux is used when real-time control is required. Moreover, the method by SH-3 microcomputer is used when there are many measurement targets.