K. Itaka

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.

Dielectric Characteristics of Compressed Gas Insulated Cables

This paper describes the dielectric characteristics of compressed gas insulated cables, particularly the dielectric performances of sulphur hexafluoride (SF6) gas and also of the insulating spacers.

Heat Transfer Characteristics of Gas-Insulated Transmission Lines

This paper reports on an investigation of the heat transfer characteristics of GILs under constant temperatures and under changing temperatures influenced by solar radiation and wind. It was verified that values calculated by our heat transfer formulas coincided well with measured values both for current-induced temperature rise of the conductor and enclosure and for temperature changes caused by solar radiation and wind. In addition, the influence of installation angle on conductor and enclosure temperature rises was investigated, and it was confirmed that the highest local temperature rises of a conductor and an enclosure above ambient temperature generally do not exceed the temperature rises of horizontal installation, although heat spots existed in tests.

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 550KV Gas Spacer Cable Part II The Voltage Characteristics and the Construction

5OOKV, 6,000A~12,000A gas spacer cables (GSPC) of single-core type and three-core type using pole and disc spacers have been developed.

Development and Installation of 275KV SF6 Gas-Insulated Transmission Line

In order to install a commercial 275kV gas-insulated transmission line (called GIL by the authors) on a route with many bends and inclines, a temperature rise test and long-term field test were performed to confirm the current capacity and thermo- mechanical and dielectric characteristics. Fault location and leakage gas removal tests were carried out to evaluate maintenance methods. Based on satisfactory results in all these tests, two circuits of 275kV GILs were installed to connect a gas-insulated substation of the Kansai Electric Power Co., Inc. to an overhead line.