Takushi Hara

Computation of Three-Dimensional Electric Field Problems by a Surface Charge Method and its Application to Optimum Insulator Design

This paper describes an improved surface charge method for computation of three-dimensional electric field distribution and its application to optimum insulator design. In this method, each curved surface on which the charge is distributed is divided into many curved surface elements instead of planar elements. After computing numerically the charge distribution, the distributions of both potential and electric field are obtained. Because the use of many curved surface elements provides a good approximation of the insulator contour, the correction of insulator contour to achieve optimum insulator design can be performed smoothly.

Heat Transfer Characteristics of Gas Spacer Cables

Heat transfer characteristics of the Gas Spacer Cable (GSPC) was investigated using a model cable. This paper presents the formulae which can be used to calculate the heat transfer of both a 3-core type GSPC and a 1-core type. This paper also describes the effect of gas pressure and gas mixture on the heat transfer characteristics.

Improved Structure Avoiding Local Field Intensification on Spacers in SF 6 Gas

Problems concerning local electric field intensification on a cone-type spacer which is fitted between flanges in SF6-gas-insulated apparatuses were investigated. Conventional structures, in which flat surfaces of the spacer come in contact with rounded corners of the flange, sometimes cause flashovers at considerably low voltages because of local field intensification. In the improved structure proposed by the authors, surface shape of the spacer and contact position are slightly changed in order to avoid local field intensification. Field calculations and experiments verified that the improved structure is effective for actual use.Problems concerning local electric field intensification on a cone-type spacer which is fitted between flanges in SF6-gas-insulated apparatuses were investigated. Conventional structures, in which flat surfaces of the spacer come in contact with rounded corners of the flange, sometimes cause flashovers at considerably low voltages because of local field intensification. In the improved structure proposed by the authors, surface shape of the spacer and contact position are slightly changed in order to avoid local field intensification. Field calculations and experiments verified that the improved structure is effective for actual use.

Development Of Compact 500 kv 8000 A Gas Insulated Transmission Line Study On Insulation Design

This paper describes the results of a study on insulation design performed in the development of a compact 500 kv 8000 A gas insulated transmission line (GIL). By adopting new design criteria (SF6 gas pressure: 0.6 MPa, allowable conductor temperature: 105 °C, insulator working stress: 5 kVeff/mm) instead of using conventional criteria (0.35 MPa, 90°C, 3 kVeff/mm respectively) we were able to produce a great reduction in GIL size. The behavior of conducting particles under high pressure conditions and the effectiveness of several particle control methods were studied and insulators equipped with a rib were developed for the compact GIL. A test line of 120 m length was constructed and is now undergoing the long-term field test.

Development of Fault Section Detecting System for Gas Insulated Transmission Lines

A fault section detecting system using optical magnetic field sensors developed for gas insulated transmission lines (GIL) is reported. A bismuth silicon oxide (Bi12SiO20, or BSO) single crystal was adopted for the optical nagnetic field sensor. A method of mounting the sensors to GIL which enables the sensors to detect the conductor current from outside the enclosure was developed. With the developed fault detector, faults occurring inside a section of GIL between sensors are detected by discriminating the phases of conductor currents detected by the sensors. The system was confirmed to have sufficient performance for application to commercial GILS.

Influence of local field-concentration on surface flashover characteristics of spacers in SF 6 gas

Influences of local field-concentration on surface flashover characteristics of spacers in SF6-gas-insulated coaxial electrode systems were investigated. Flashover tests and field calculations were performed for disc-type and post-type spacers with local field-concentration near the outer electrode The results for disc-type spacers show that the influence of local field-concentration on flashover becomes remarkable at the high pressure range. Results of tests and calculations of post-type spacers confirmed that under certain conditions local field-concentrations caused by field singularity near the gas-epoxy-electrode interface reduced flashover voltages, but also that the flashover characteristics of such spacers were able to be improved by some slight changes of conditions near the interface.

Effects of Internal Conductor to Enclosure Arcs on SF 6 Gas Insulated Transmission Lines

The effects of internal conductor to enclosure arcs on SF6 gas insulated transmission lines (GIL) were tested using 154 kV and 275 kV cables. Tests were conducted on the 154 kV cable with arc currents of 1 KA RMS and 2 KA RMS for durations of 1 ~ 4 seconds, and on the 275 kV cable with an arc current of 50 KA RMS for durations of 0.1 ~ 0.4 seconds. Various characteristics of these cables were measured, such as the velocity of arc travel, melting trends of the enclosure wall, the decomposition of SF6 gas, the pressure and temperature curves, damage to cable components, and the residual performance capability of damaged components. The data, from these measurements, the findings of these tests, contribute to the improved design and maintenance of GIL systems.

Development of Compact 500 kV 8000 a Gas Insulated Transmission Line-Dust Control during Field Jointing and Method for Detecting Conductive Particles

This paper describes the results of studies made on dust control during field jointing and a method for detecting conductive particles after installation in the development of a compact 500 kV 8000 A gas insulated transmission line (GIL). The study on dust control during field jointing proved that field jointing of the compact GIL can be done like conventional GIL in an easily fabricated vinyl shelter without a clean air flow. Harmful conductive particles can be detected with an Acoustic Emission (AE) sensor. This sensor is effective in improving the reliability of the compact GIL when used with a suitable ac voltage during field test. A 120 m long test line of compact 500 kV 8000 A GIL was constructed and, in a long-term field test, proved to have properties sufficient for practical use.

New Finite Element Field Calculation Technique in Which Continuity of Electric Flux is Satisfied

A new finite element technique to calculate electric field strength accurately has been developed. In this technique, new expressions for potential distribution in an element are derived in order to include electric flux densities as unknowns in basic equations. Trial calculations of coaxial cylinder models were performed by traditional methods and by new methods to examine the accuracy of field strength. The results show that the accuracy of field strength calculated by the new technique is much higher. By the calculation of a spacer which is used in SF6-gas-insulated equipment, the new technique was confirmed to be effective for practical use.