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The majority of transmission-line faults are temporary short circuits. The short circuit arc is usually self-extinguishing after opening the transmission-line circuit breakers. High-speed reclosure of transmission-line circuit breakers can improve system stability. As the voltage level increases, arc deionization time increases as well, endangering system stability. Application of automatic single-phase reclosing makes it possible to increase system stability even for extremely high voltage transmission lines. Automatic single-phase reclosing is used to clear single-phase-to-ground faults, which are about 80% of the transient faults. In order to have successful fast reclosing, different methods are used to extinguish the arc. One of the common methods is to use a single-phase reactor in the neutral of shunt reactor, when transmission line is compensated with shunt reactors. As of now, the effect and parameters of this neutral reactor are usually determined based on the steady-state analysis without exact system and arc modeling. In this research work, the investigation of a neutral reactor application is performed for transposed and untransposed transmission lines using transient simulation with appropriate models. Then, guidelines for selecting the appropriate amount for the neutral reactor are proposed. Index Terms--Arc modeling, neutral rector, secondary arc extinction, single-phase reclosing.

This paper describes the fundamental insulation characteristics of environmentally friendly gases; dry air, N2 and [N.sub.2] [O.sub.2] mixed gas. Conventional gas insulated switchgear (GIS) generally uses [SF.sub.6] as against over 72.5 kV class. We have proposed GIS with a vacuum circuit breaker against from 72.5 kV class to 170 kV class as [SF.sub.6]-free GIS. Because the insulation gas of this type of [SF.sub.6]-free GIS has the hardly unnecessary current interception performance, the optimal insulation gas can be selected based on fundamental insulation performance. From the standpoints of insulation performance and economical efficiency, we selected compressed dry air as the optimal insulation gas for this type of [SF.sub.6]-free GIS. However, the dielectric strength of dry air is approximately one-third that of [SF.sub.6] gas. Therefore, to achieve roughly the same size as conventional GIS, some strategies must be employed to enhance insulation performance. This paper investigates the influence of gas pressure and a gas/solid hybrid insulation structure. The insulation performance of the gas/solid hybrid insulation structure using an insulation coating was found to be better than that of a barrier. Moreover, the dielectric strength of particles adhering to a spacer under the compressed dry air was about 1.5 times higher than that under [N.sub.2]. Thus, the high insulation reliability of the gas/solid hybrid structure was high against particles was confirmed. In view of these investigative findings, this type of [SF.sub.6]-free 72.5 kV GIS which was designed and manufactured, was confirmed to comply with the IEC standard. Index Terms--Air insulation, disconnecting switches, electric breakdown, gas insulated switchgear, vacuum circuit breakers.

Air-magnetic circuit breakers are widely used for short-circuit protection in dc electric railways or industrial plants. The well-known drawbacks of these breakers are mainly a slow breaking action, a short lifetime, and high maintenance costs due to the destructive effects of the arc. The use of power semiconductors in a full-static circuit breaker configuration allows the elimination of these disadvantages but is limited by excessive conduction losses. The paper will present the study of a so-called hybrid breaker, drawing its name from the combination of a high-speed mechanical switch and a bi-directional integrated gate-controlled thyristor assembly connected in parallel. The paper also includes experimental results from a prototype real scale. Index Terms--Arcless interruption, fault current limiter, hybrid high-speed circuit breaker, integrated gate-controlled thyristor (IGCT), mechanical switch, metal-oxide varistor.

Considering fault current limiters for serial protection, many structures exist, from regulation to other complex systems such as circuit breakers, mechanical switches, or more conventional fuses. Up to now, only a few semiconductor current limiter structures have been described in the literature. Although current-regulative diode components already exist, their voltage and current capabilities ([V.sub.BR] = 100 V, [I.sub.max] = 10 mA), do not allow their use in power systems. This paper presents both simulation study and experimental results of a bidirectional current limiter structure based on a vertical SiC VJFET. The device was designed for serial protection in order to limit [I.sup.2]t value. Finite-element simulations were performed with ISE-TCAD software to design the device and evaluate its static electrical characteristics. Then, dynamic simulations were performed to underline current reduction ability and power losses adjustment by gate resistance value optimization. Finally, electrical characterization for a unidirectional and a bidirectional device were done up to 400 V. The measured specific on resistance [R.sub.ON] is in the range of 176 m[ohm] * [cm.sup.2]. Limiting capabilities have also been measured for a bidirectional device made of two unidirectional devices connected head to mil. The highest breakdown voltage value in 'current limiting state' was measured to be ~810 V, corresponding to a high power density of 140 kW/[cm.sup.2]. Index Terms--Command integration, current limiter, high voltage, JFET, serial protection device.

A study was conducted to present user guidelines for system application on the correct selection and application of molded-case circuit breakers within the established system of product standards and safety codes. A system evaluation approach was utilized for the evaluation and testing of distribution equipment. Interrupting ratings were then expressed as rms symmetrical values. In addition, the importance of wires in characterizing the performance of circuit breakers was examined.

This paper addresses the application of instantaneous-trip molded-case circuit breakers (MCCB's) in combination motor starters. These circuit breakers have been widely used in many industries for motor circuit protection. If they are not properly applied, situations of false tripping on motor starting and contact welding of contactors under low-level faults may occur. Energy efficiency motors compound the issue of false tripping on motor starting. This paper discusses the components of combination starters, reviews testing requirements, and provides examples of coordination with analysis of application issues and solution options. Index Terms - Combination motor starter, instantaneous-trip molded-case circuit breaker, low-voltage protection.

Low-voltage, direct current equipment in utility control systems, uninterruptible power systems (UPS), telecommunication systems, and elsewhere has received increasing attention in recent years. Power conditioning needs are one reason. Closer attention by regulatory agencies is another. This paper is intended to help fill a gap in available material on ratings and application characteristics of low-voltage circuit breakers in dc systems. Some of this material is prepared for use by the IEEE Battery Protection Working Group in developing a Guide for Protection of Stationary Battery Systems under project P1375.

This report presents the results of an extensive survey of utility practices for the protection of distribution lines at the substation. Results of similar surveys were published in 1983 (Ref. 1) and in 1988 (Ref. 2). In this survey, the first eight sections were comparable to the earlier surveys. In addition, these sections were expanded to collect more data on the reasons behind a practice and on the methods used. A ninth section was added to address the impact of Dispersed Sources of Generation (DSG) on distribution protection. The responses to this survey have been compared to the previous survey in an attempt to detect any trends in the protection of distribution circuits. Key Words - Distribution Protection, Protective Relaying, Reclosers, Reclosing, Phase Protection, Ground Protection, High Impedance Ground Fault.

A digital algorithm for the protection of parallel transmission lines has been implemented on a 16-bit single board computer. It has been tested on a physical model consisting of two synchronous machines connected through a double circuit line. The algorithm is based on comparing magnitudes of currents of two parallel lines. Details of the experimental set-up and the results of on-line tests for various operating conditions are presented. A procedure to adjust the relay settings adaptively is also incorporated. The results illustrate the successful operation of the algorithm in detecting faults on parallel lines. Key words: Digital protection, parallel lines, real-time implementation

Magnetic cores have been used in transformers for over a century. In this paper, the authors present a fundamental concept of using 'coreless' printed-circuit-board (PCB) transformers. With the aid of a high-frequency equivalent circuit, the use and basic characteristics of coreless PCB transformers are described. Optimal operating conditions for minimum input power requirement and maximum efficiency operations are identified. Coreless PCB transformers have the advantages of low costs, very high power density, no limitation due to magnetic cores, no magnetic loss and ease of manufacturing. They have the potential to be developed in microcircuits. A printed planar PCB transformer with a diameter of about 1.0 cm and power capability of 19W has been successfully tested. The power density of the PCB transformer demonstrated in this paper is 24 W/[cm.sup.2]. The maximum efficiency can be greater than 90%. The analysis has been confirmed with experiments. Coreless printed transformers have great potential in applications in which stringent height and space requirements have to be met. Index Terms--Coreless printed circuit board transformer, high frequency magnetics, microcircuits, passive components, power conversion.