Hideo Fujinami

Charge Simulation Method with Complex Fictitious Charges for Calculating Capacitive-Resistive Fields

This paper describes a numerical method for calculating electric fields very accurately in configurations including voluime resistance or surface resistance. The principle of the method is to incorporate the field effect of the true charge caused by conductivity in that of complex fictitious charges by the charge simulation method (CSM). CSM with complex charges for computing multi-phase AC fields is also described with a calculated example. Results are given for comparison with analytical expressions and for a disc-type gas insulation spacer having either volume resistance or surface resistance.

Mechanism and effect of DC charge accumulation on SF/sub 6/ gas insulated spacers

Mechanism and effect of DC charge accumulation on the surface of a solid insulating support (spacer) have been studied in compressed SF/sub 6/ gas using various cylindrical model spacers. The distribution of surface charged is closely related to the normal component (gas side) E/sub n/ of electric field on the spacer surface. The ,maximum charge density can be estimated from the condition of E/sub n/=0. When voltage is applied in a polarity opposite to prestressed DC, surface charge increases the maximum field strength in the arrangement, resulting in the reduction of the insulating ability. It is possible to estimate the lowest flashover voltage due to surface charges only from numerical fields calculations. An anticharging spacer shaped along electric lines of force is proposed and studied. >

Requirements for power line magnetic field mitigation using a passive loop conductor

Magnetic field mitigation for overhead power lines using a passive loop conductor was studied. The aim of this study is to clarify the requirements for effective mitigation not in a specific region such as at the edge of the ROW (right of way) but everywhere around the conductors. For this purpose, the concept of current dipole moment was introduced and applied to the problem. First to determine the validity of the derived formula which estimates the induced current to the passive loop, a miniature transmission line model experiment was performed. Then, the mitigation effectiveness of the actual dimensions of several kinds of overhead transmission line arrangements were estimated by the calculation. The application of a current dipole moment, was sufficient for explaining the differences in the mitigation effectiveness depending on the conductor arrangement and for clarifying the requirements for effective mitigation.

Equivalent dipole moment method to characterize magnetic fields generated by electric appliances: extension to intermediate frequencies of up to 100 kHz

A previously proposed simple method to characterize magnetic fields near electric appliances was extended to intermediate frequencies of up to 100 kHz. The method consists of identification of the magnetic dipole moment that is equivalent to a magnetic field source of an electric appliance and simple estimation of the magnetic field distribution around the appliance. In addition, frequency characteristics of the magnetic field were taken into account by considering the harmonic components in the magnetic-field waveform for both power frequency and intermediate frequency ranges. For the application of the method, a wide-frequency range (from power frequency to 100 kHz) magnetic-field measuring instrument was developed and applied to appliances that generate intermediate frequency magnetic fields, i.e., an induction heating cooker, a TV set, and a metal detector. The results revealed that the method is adequate to quantify the magnetic field near the electric appliances at frequencies of up to 100 kHz.

Measurement of Accumulated Charge on Dielectric Surfaces with an Electrostatic Probe

ABSTRACT This paper discusses the measurement method of the accumulated charge (density σ) on the surface of solid dielectrics (specimens) such as DCGIS spacers. The relation between σ and the probe response has been discussed for various arrangements with uniform or nonuniform charge distributions. The charge in the surrounding area has a very large effect on the probe response especially for thick specimens. True surface charge distribution can be obtained by the multi-point measurement method with the aid of a numerical field calculation. The effectiveness of the method has been demonstrated experimentally for a model specimen.

Low stray ELF magnetic field exposure system for in vitro study.

An exposure facility for wide application to cell exposure to an ELF (extremely low frequency) magnetic field was developed. It is suitable for conducting experiments under a high-intensity, variable-frequency magnetic field, on the biological effects of the ELF magnetic field in an in vitro study. The exposure system consists of Merritts 4-square coil as a basic component to generate the required magnetic field intensity of 10 mT at 50 Hz with spatial field uniformity less than +/-3% in a 400 mm cube. Concentric compensation coils are adopted to eliminate the effects of stray fields on sham (control) samples in the vicinity of the exposure system. The uniformity of the magnetic field in the exposure coil, the increase in the power supply capacity due to the existence of compensation coils, and the stray field estimation were investigated carefully. After fabricating the system, performance tests were carried out and all the characteristics were found to be satisfactory. In addition, the ideal configuration for a concentric coil system was proposed.

Effect of Conduction on Field Behavior Near Singular Points in Composite Medium Arrangements

The electric field configuration has been analyzed numerically by the charge simulation method near a contact point where two media having surface or volume conductivity meet an electrode. Surface conduction with uniform surface resistivity moderates the field singularity, resulting in a uniform field throughout both media for very low resistivity. On the other hand, volume conduction magnifies the field singularity if only one medium has conductivity. For these capacitive-resistive fields, it appears impossible to derive a simple analytical expression of field strength such as can be derived for purely capacitive cases.

Breakdown characteristics of gases mixed with tetrachloroethylene mist under nearly uniform fields

A description is given of the breakdown characteristics of N/sub 2/ or SF/sub 6/ gas mixed with tetrachloroethylene mist under nearly uniform fields. The effect of the mist on the flashover voltage of the gas was experimentally studied for various gas pressures and applied voltage waveforms. A significant increase in the flashover voltage was produced by introducing the mist into the gas in the case of an applied impulse voltage. However, the voltage increased slightly only at low gas pressures when DC and AC voltages were applied. The effect of an electric field on the behavior of the mist is also discussed. Possible mechanisms by which the presence of the mist may contribute to the increase of the flashover voltage are discussed, and the increase is attributed principally to the scarcity of initial electrons in the gas mixed with the mist. >

Investigation of ELF magnetically induced current inside the human body: Development of estimation tools and effect of organ conductivity

Regarding the possible biological effects caused by exposure to ELF (extremely low frequency) magnetic fields, magnetically induced current inside the human boldy has been a focus of research. To clarify the induced current characteristics inside the human body, we develop estimation tools. One was a numerical calculation code and the other was a human model. The numerical calculation code was based on a surface charge method. The human model was composed of several organs and other parts of the human body, whose shapes were spheroids or cylinders. Organs taken into account were the brain, heart, lungs, liver, and intestines. The validity of the calculation code was shown by comparing it with an analytical solution using a homogeneous spheroid model. The discrepancy was within 6.5%. Applicability of the code to the human body was shown. In addition, by applying the calculation code to the human model, effects of organ conductivity differences vis-a-vis the induced current distribution were estimated. It was found that the organ conductivity value very much affected the induced current distribution inside the human body.

Development of detection method with a magnetic field sensor for incomplete contact in gas insulated switches and bus connecting parts

This paper describes a detecting method of incomplete contact in gas insulated switches and bus connecting parts. The principle of the method is to measure the change in magnetic field caused by the current distribution at an abnormal contact point. Fundamental studies with small-size bus models have shown that incomplete contact can be reliably detected with an opto-magnetic sensor in the case of aluminum enclosures. A feasibility study was also conducted for a full-scaled 300 kV GIS structure with more realistic incomplete contact conditions. >