Since the trial manufacture of a 66-kV, 3-MVA unit in 1973, Fuji Electric has positively tackled the development to meet recent needs for safety and prevention of disasters. Now its actual supply record is 149 units (1,408 MVA), mainly in the 66/77-kV class, all in good operation. The latest supply is a 110-kV, 40-MVA unit to the underground substation of the Chugoku Electric Power Co. New technical achievements are (1) improved cooling in the winding with a zigzag flow (2) efficient cooling with high-head radiators (3) rationalized production using sheet windings for the class of 15 MVA or less (4) remarkable progress in gas flow analysis and three-dimensional electric field analysis.

Recently, with the increase in dependence on electric energy in social life, substation equipment has been still more required to improve in the reliability of power supply and harmony with the environment. To meet these social requirements, Fuji Electric has tackled the development of SF₆ gas-immersed transformers from the early stage, aiming at nonflammable, low-noise, compact transformers, principal equipment in substations, and has supplied 149 units (1,408 MVA in bank capacity), contributing to the realization of substations in harmony with the environment. This paper gives main examples of Fuji SF₆ gas-immersed transformers.

This paper describes the development of medium capacity SF₆ gas-immersed transformers with aluminum foil windings. Wide thin aluminum foils and sheets are used for the primary and secondary windings respectively. The characteristics of foil windings undergo theoretical analysis and verification, for example, direct measurements of current distribution and temperature rise in the windings and tests with insulation models. Finally, the full-scale model of a 3-phase, 66/6.6-kV, 5-MVA transformer was build and put to general type tests and special tests, including short-circuit tests to verify reliability.

Having solved the problem of the automatic winding of wide sheets which was thought difficult formerly, Fuji Electric has developed fully self-cooled SF₆ gas-immersed transformers with sheet windings which have superior total economical efficiency. This paper outlines investigations into basic characteristics of cooling and insulation and the result of verification with a model carried out during the development.

SF₆ gas-immersed transformers are used as substation equipment for public utilities that require harmony with the environment and prevention of disasters and for densely populated area such as cities and towns; therefore, high reliability is demands. In the production, control items in the processes from receipt of order to shipment are defined and reliable quality assurances are given. This paper outlines quality control for the production of SF₆ gas-immersed transformers and the contents of reliability verification tests carried out before marketing the new SF₆ gas-immersed transformers using sheet windings.

The new type SF₆ gas-immersed transformer (ALFOSΣ series) with sheet windings of aluminum foils has advantages such as no need for expert skill required in the manufacture of disk windings, reduction in the kind and number of parts, and reduction in the lead time for production. The prototype, put to a short-circuit test to verify the mechanical strength of transformers with sheet winding construction against electromagnetic force in a short-circuit condition, proves that it has short-circuit strength specified in JEC-2200-1995. This paper outlines the test results.

The sheet winding machine has been developed utilizing the latest mechatronics and cleaning technology. This machine is characterized by the capability for winding a wide aluminum foil and insulating films at high speed under a fixed tension. For the countermeasures of foreign materials, a special cleaner and electrostatic eliminators are installed in the machine as well as airflow in the winding room is controlled to improve the environment.

With a new design concept, Fuji Electric has developed a load tap-changer for SF₆ gas-immersed transformers that require a voltage regulating function. Its features are (1) the simplified tap-changing mechanism due to the use of a 2-resistance, 4-vacum-tube system (2) easy replacement of the vacuum tube by the cassette construction (3) avoiding metal power from abrasion using roller contact to the tap-selector as well as roller bearings to the selector driving mechanism (4) the electronically controlled motor-operating mechanism changed from mechanically controlled one, resulting in a reduction by half in the number of mechanism parts, advanced function, and high reliability.

Recent social requirements for nonflammability and safety of substation equipment have become strong and pushed the application of SF₆ gas-immersed transformers meeting these requirements. In the field of the 6-kV class where formerly the mainstream was oil-immersed transformers and molded ones, there are growing needs for SF₆ gas-immersed transformers and they are desired on the market. Under the circumstances, Fuji Electric has developed a series of small capacity SF₆ gas-immersed transformers in the 6-kV class. This paper gives an outline of the series.

The sputtering in low gas pressure is characterized in that selectivity to particles incident on the substrate is given by placing the substrate above the central axis of the target and also setting the distance between the target and the substrate nearly equal to the mean free path. With this, YBCO (YBa2Cu3OX) which is superior in surface flatness and crystallization is obtained at a growth rate of 13 nm/min. In addition, the YBCO film formed by this method shows that activated oxygen discharged from the target contributes to the film oxidation and YBCO grows in a orthorhombic system.

With the progress in research and development for electronic components and devices using high polymers, there is a growing demand for the development of methods for evaluating the properties of these materials. This paper describes the methods for evaluating the properties of the materials, citing amorphous silicon solar cells with film substrates as an example. The results obtained from this investigation have been reflected on the conditions of manufacturing processes and the design of lamination.