Control systems forming networks and handing increasingly sophisticated information require high reliability of systems as a whole. Overall reliability has to be pursued not only in control equipment but also in integrated systems including objects of control, operation by men, environment (temperature, noise, and power failure) and so on.
The paper describes the basic technology for realizing high-reliability systems such as fault detection methods, continuous operation with a fault masked, fail-safe systems against damage, and fault locating and recovery, as well as preventing faults.

Reliability is strongly demanded by man-machine interfaces in the recent large-scale, sophisticated, high-performance process control systems. This article describes various considerations for making man-machine interfaces suit human characteristics and ability and for minimizing human error in the following classification: (1) Human engineering from the viewpoint of mechanisms, (2) Information input systems to men, (3) Operation reliability, (4) Measures against alarms, (5) Reliability of components.

Control microcomputers have made rapid progress being backed up by technical innovation represented by the development of microprocessors. They are playing an important role as the core of diversified control system applications, and fault tolerant and reliable computing technology for them is strongly demanded. The point of the technology is fault tolerance mainly consisting of fault detection, error recovery, and diagnosis and restoration of faults. This paper introduces an outline of the technology and its application to FASMIC G500 as well.

Digital controller applications have been diversified widely because of its high performance and a fault of the controller itself have an inestimable economical or social influence; then its reliability is essential in systems. The reliability of controllers depends on "prevention of faults" and "minimized influence when a fault occurs"; now particularly important is technology to put the latter in practice. The methods thereof are fault detection systems and fault-tolerant systems such as multiplexed redundancy and degenerate operation; however, multiplexed redundancy will be a royal road to high reliability because hardware is becoming smaller in size and lower in cost.

The promotion of automation in industries has accelerated making various equipment and devices intelligent and forming networks with communication functions.
The article introduces the concept of high-reliability technology in "control network systems"on a floor level or on a field level and the technology in Fuji Electric's standard control systems: local area network system "DPCS-F" and field area network system "F-Net."

Remote supervisory control systems are used by many widearea industries such as electric power, waterworks, traffic, and the like. A fault exerts an influence to a very wide extent and generally it takes much time to restore a fault of controlled equipment located in a distant place; then it is a keen problem to secure required reliability. The paper describes considerations for the system reliability: (1) Completion of RAS functions, (2) Storage of RAS information, (3) Duplexed systems, and also the actual developments in SAS series: (1) Quick fault locating, (2) Shortening of failure duration, (3) Quick investigation into the cause of a fault.

Application types and production of digital relays have rapidly increased and there will be a big market for them. Digital relays are used not only in the field of electric power, such as power generation, transformation, and distribution, but also in electric railways and iron and steel industries. They are applied to instrumentation and control as well as to protection.
This article introduces the status of recent digital relaying systems.

Since transmission lines are distributed over a wide area, fault locators are necessary for quick measurement of an accurate distance to a fault position to remove the fault as soon as possible.
Conventional fault locators utilize a surge receiving system or a pulse radar system. Fuji Electric, however, has recently applied an advanced digital protective relaying system and developed impedance type fault locators to practical use, which is outlined in this paper.

In substations, digital systems were applied first to protective relaying systems; then they are being introduced to supervisory and control systems aiming at intelligence.
This article describes an outline of Fuji Electric's pioneering development and commercialization of digital automatic restoration equipment based on its microprocessor technology.

This paper introduces the simulation technique of protection relays citing a differential relay system generally used for the protection of generators or transformers.
This simulation was carried out by installing an analytical system in a workstation which can varify relay response behavior including the transient characteristics of a CT (current transformer) and the dynamic characteristics of a filter in relays when a fault current including a transient direct current at power system failure flows into the CT.

Electronics-applied distribution automation systems have recently introduced for a stable power supply and efficient system operation. The remote terminal units that control automatic section switches are installed on the poles of distribution systems, and used in very severe conditions such as direct lightning impulses, radio wave noise, and environmental impacts; moreover, extremely high reliability is demanded for high-reliability power supply. This paper introduces our environmental protection technique to meet the requirements.