Transformers have been improved not only in higher voltage and larger capacity, but also in nonflammability and a high degree of safety by the introduction of gas insulation. Gas insulated switchgear has allowed for a more compact design incorporating 3-phase common encapsulation and complex construction. Protection, control, and supervisory systems have been digitalized making good use of microelectronics. Next-generation substations will be made intelligent, self-regulative, entirely gas-insulated, and more compact aiming at suppling higher quality power, economically and in harmony with the environment. This paper outlines the concept of development and our attitude.

In the field of transformers, technical developments have been achieved to meet requirements for high voltage and large capacity, environmental harmony with oilless, nonflammable construction, small size and light weight. This paper introduces the technologies of cores, windings, insulation, and low noise in oil-immersed transformers, those of high-head radiators and electronic control systems for the driving mechanism of on-load tap changers in gas-insulated transformers, and those of uni-molded windings type developed to reduce size and weight in cast-resin transformers.

More compactness and higher reliability are demanded by gas insulated switchgear (GIS) that has come into wide use rapidly.
This paper describes an outline of technologies for compact design and solid-state control circuits from among recent Fuji Electric's GIS technologies. To realize compact design, we adopted compound construction and phase segregation. As for solid-state control circuits, we put them to various performance verification tests and confirmed sufficient performance for practical use.

Fuji Electric has developed an optical current measuring system using the Faraday effect in magnetooptics and an optical voltage measuring system using the Pockels effect in electro-optics to be used in gas-insulated switchgear (GIS)
The ratio error has proved to be within ±1.0% under rated current and voltage, and the temperature stability, within ±1.0%. The actual measurement of short-currents proved that the short-circuit current characteristics of the current measuring system would be accurate enough in practical use.

This paper describes a recent tendency in insulation coordination in power networks, a new zinc oxide element developed by Fuji Electric, and the principle, structure, and features of a newly developed transmission-line arrester. The features of the arrester is as follows:
(1) superior insulation coordination,
(2) large surge current performance,
(3) compact and light,
(4) excellent pressure-relief performance, and
(5) superior weatherproof characteristics.

There is increasing needs for medium voltage switchgear particularly to be more labor-saving in maintenance and be downsized under recent social conditions. Downsizing with air-solid insulation instead of air is one of measures taken to meet the needs, but conventional technology had its limit. On the basis of gas insulation technology over 72kV, Fuji Electric has developed a 24-kV gas-insulated cubicle that was improved in maintenance, affection by the environment downsizing, and safety by sealing a vacuum circuit breaker, a 3-point disconnecting switch, an earthing switch, and low-pressure SF₆ in an aluminum cast container.

Demand for the stable supply of quality power has been increasing with the progress of high information society. The improvement of the equipment is indispensable to reliable power supply. A large number of circuit breakers are installed and playing on important part in power supply in generating plants and substations, and 7.2-kV vacuum circuit breakers amount to a considerable portion of the breakers. Fuji Electric has developed a solenoid-operated vacuum circuit breaker to improve the reliability and maintainability of 7.2-kV breakers, which is outlined in this paper.

It is about ten years since digital protective relays came into use. Microprocessors and other electronics technologies have made rapid progress during this period, and protective relays using these technologies have been developed steadily. Digital control apparatus in substation have also improved remarkably into digital coordinated systems of combined protection and control.
This paper gives an outline of the system and hardware configurations of microcomputer based protective relay and control systems.

The gas-insulated power apparatus is reliable equipment that is not affected directly by a change in external environment; however, visual inspection is impossible inside the unit, so monitoring equipment is used to detect an abnormality in-service early and to carry out a quick repair if a failure such as a dielectric breakdown occurs.
This paper outlines the monitor items, sensors and transducers, detection principles, and electrical performance of the preventive maintenance equipment and fault locator for gas-insulated power apparatus and introduces examples of practical uses.

The expert system has the following functions to prevent transformer failure: (1) carries out automatic analysis of dissolved gas in oil, (2) detects abnormality early with sensor information such as partial discharge, oil temperature, winding temperature, and LTC torque, (3) carries out general diagnosis based on expert knowledge using these data, and outputs the result of diagnosis, cause of abnormality, location, and remedy, (4) predicts time to inspect the LTC contacts and to replace the filter of the hot-line oil purifier. The above is on-line, and off-line diagnosis can be made by the keyboard entry of gas-in-oil data.

The progress of digital control technology and power electronics technology has brought technical innovation into traction substations that supply power to electric railroads, that is, typical high-speed mass transport means in and around large urban areas.
This paper describes the features, purpose, supply record, and tendency mainly of distributed microelectronics switchboard systems that characterize the new substations. It also has a proposal including noticeable points at the investigation of a predictive maintenance system that is expected to be put to practical use in the near future.

Extra-high-voltage substations have rapidly come to demand higher reliability in recent years as industrial plants made progress in the function, sophistication, and capacity. This paper outlines considerations in planning industrial substations under the situation and introduces cubicle type gas-insulated switchgear (C-GIS) widely used for 66/77kV receiving systems. Also it introduces centralized monitoring and control systems that realize laborsaving supervision and enhanced functions with rapidly advanced data processing equipment.

To meet the requirements of intelligent facilities and globalized societies, recent buildings have more and more demanded increase in supply capacity, high-quality power, and 24-hour year-round uninterruptible power supply. In view of the prevention of disasters, resistance to flame or nonflammablity is required. Under these circumstances, many substations of the 24 to 84kV class for buildings adopt a dual power supply system and SF₆ gas-insulated equipment. In the substation of a certain building at work, renewal including the increase of capacity was carried out within permissible power cutoff hours.