Hiroshi Arita

Solid-state current limiter for power distribution system

To prevent voltage decrease of distribution systems, the principle and fundamental characteristics of a solid-state current limiter using GTO thyristors were investigated. Basic components of the apparatus were a fast solid-state switch and a current limiting impedance of low resistance in parallel with the switch. Experimental results of the test current limiter showed the fault current was limited successfully, regardless of DC component size. The time from detection of fault occurrence to interruption of the fault current by the solid-state switch was 40 mu s. This time was very short in comparison with that before the fault current reached a large value. Thermal rise of the solid-state switch for conduction was solved by a self-cooling apparatus using a noncombustible cooling liquid. The results indicated that the solid-state current limiter was a valuable protecting device for high fault current distribution systems. >

Principle and characteristics of a fault current limiter with series compensation

A power system fault current limiter with series compensation, which is composed of a compensation capacitor and a limiting reactor in series, is proposed. A solid-state switch connected in parallel with the capacitor controls either the ordinal series compensation or fault current limitation. A feasibility study of the current limiter by simulation analysis is presented and the effectiveness of the current limiter is evaluated from the viewpoints of transient stability improvement and device capacity. The current limiter is a useful protection device for large, high power transmission systems.

Thyristor controlled ground fault current limiting system for ungrounded power distribution systems

A thyristor controlled ground fault current limiting system (TGCL) was proposed to prevent one-line ground fault current rises due to increased capacitance to ground. Basic components of the TGCL are a main ground fault current limiter, which rapidly adjusts a compensating reactor level for the capacitance to ground, and the TGCLs controller. Control is ensured by an in-phase control method for zero-phase sequence voltage and current. The method determines the direction of ground faults and the compensating reactor level. The fast control which can be realized shows the TGCL is a valuable protecting system for high ground fault current distribution systems.

Switching characteristics of the triggered vacuum gap for a high-repetition-rate pulse-power source

Switching characteristics of sealed-off triggered vacuum gaps (TVGs) were examined from the viewpoint of a high repetition rate at high current discharge. With a triggered energy of 11 J, it was possible to fire the main gap in both the anode and cathode modes of operation. In repetitive discharge experiments, the TVG-tube was put in the center of the cylindrical conductor and the switching tube inductance was about 27 nH. The TVG-tube was confirmed to have capabilities for 1000 shots with a pulse current of 120 kA and a high repetition rate of 5 Hz. These experimental results indicated that the TVG-tube is a potential repetitive closing switch for the plasma X-ray source. >

Interruption ability of a self extinguishing type gas circuit breaker

Interruption ability of a self-extinguishing-type gas circuit breaker has been investigated while varying several structural factors. With a thermal puffer cylinder (0.7 l volume), excellent interruption ability (9.5 to 31.5 kA at 84 kV) was obtained for the condition of a breaker-terminal fault (BTF). In the condition of a short-line fault (SLF), however, its interruptible arcing time width at the same current levels was only 0.2 to 0.3 cycles, where 0.5 cycles was proposed. The critical current, which is the minimum current which the breaker can interrupt, was several kiloamperes. >

Fault current limiting system for 500‐kV power systems

Recently, expansion in the scale of power systems and development of localized power sources are leading to an increase in fault current of 500-kV systems. In the future, it is quite likely that the fault current at the interconnection of such power systems may exceed the rated short-time current of existing electric power facilities. As one of the solutions of this problem, a thyristor-controlled series-resonant-type fault current limiter (FCL) is proposed to restrain the fault current. This paper deals with the FCL system configuration, the placement method of the FCL in power systems, the outline of the FCLs specification, and the operation method of the protective relay in the multimachine system. Finally, the effectiveness of the FCL is evaluated from the viewpoints of limiting the fault current by simulation analysis. The FCL is shown to be a useful protection device for large, high-capacity power systems.

Soft X-ray emissions by high-current vacuum discharges

Soft X-ray emissions by Z-pinch discharge between vacuum spark electrodes are examined. Mainly aluminum and molybdenum were utilized to generate soft X-rays, and emissions resulted for pulse currents of about 150 kA. These emissions increased as the discharge current increased. A large X-ray intensity was obtained when a spherical anode and a conical cathode were used. A stable spot plasma was produced for an electrode separation distance of 2 mm. For molybdenum, the X-ray emission of the 0.52-nm line and continuous X-rays of 0.65-1.2 nm were observed. The X-ray continuum was assumed to be a recombination continuum. For aluminum alloy containing magnesium, the 0.62-, 0.66-, 0.72-, 0.78-, and 0.92-nm lines were observed. The experimental results indicate that vacuum spark is a potential exposure source for X-ray lithography. >

Technology for adaptive error recovery in wireless communication environments

Environmentally adaptive error recovery (EAER) technology for wireless communication was developed to reduce the number of communication errors and the time needed for recovery in industrial wireless networks. EAER adapts the communication frequency to the radio environment by changing the radio frequency to a better one when communication errors occur by pre-measuring the radio environment at each slave. The pre-measurement is done by having slaves measure the radio environment using test signals sent by the master. EAER was able to continue the communication within three super frames when a noise signal was applied to a communication channel.