Yukio Kurosawa

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. >

Vacuum Circuit Breaker Electrode Generating Multi-Pole Axial Magnetic Field and its Interruption Ability

Because the phase of the eddy currents in an electrode lags that of the main interruption current, a rather strong axial magnetic field remains at current zero in the space between a pair of electrodes when an interruption current is large. The authors analyzed the magnetic field on a circular conductor which was centered in a coil to stimulate an axial magnetic field type electrode. Because the authors found it difficult to eliminate the residual magnetic field from an electrode, they developed a new type electrode structure which does not generate a residual magnetic field at the center of an axis. An experimental vacuum interrupter equipped with this kind of electrode performed very well at testing voltages from 7.2 kV to 72 kV. Hitachi has applied this new type electrode in the development of a 7.2 kV 63 kA vacuum circuit breaker.

Voltage distribution characteristics of series connected SF/sub 6/ gas and vacuum interrupters immediately after a large AC current interruption

Transient voltage distribution characteristics of a hybrid interrupter module have been examined using an experimental model of a hybrid breaker. Tests were conducted to study the voltage distribution between the SF/sub 6/ gas and the vacuum interrupters immediately after a long current interruption. It is found that the voltage distribution is determined by the resistive impedances of respective interrupters during the post arc current flow and by the capacitive impedances of the interrupters contact gaps after the post arc current diminishes. >

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. >

A diagnostic technique to detect abnormal conditions of contacts measuring vibrations in metal enclosures of gas insulated switchgear

Better reliability in gas insulated switchgear is the goal of a diagnostic technique for abnormal conditions at large current conducting contacts. The detection of peculiar vibrations from artificially simulated abnormal contacts during current conducting and their measurement in metal enclosures, and distortion of the voltage waveform across the abnormal contacts and their analysis are shown. Fig. 1 shows the contacts used in this experiments. The peculiar vibration in metal enclosure is shown in Fig. 2(a) and its FFT analized results is shown in Fig. 2(b). According to the dependence between vibrations and contact voltage shown in Fig. 3, the vibration peak values at 600 Hz which is even integer times current frequency are increase as the contact voltage increases. As the results, there is a possibility to detect abnormal conditions of contacts by the measurement of metal enclosure vibrations.

Post arc current of vacuum interrupter after large current interruption

Postarc current characteristics of a vacuum interrupter have been examined under a condition of high-current interruption. A measurement technique was developed in which a shunt for measuring postarc current was set in a synthetic test circuit voltage source. Postarc current was measured after a 20-57 kA current interruption. The magnitude was greatly influenced by the rate of current decline. Residual resistance between electrodes was calculated from the measured values of recovery voltage and postarc current. The recovery of residual resistance was very rapid immediately after current zero and become slow later. >

Low Surge Vacuum Circuit Breakers

Low surge vacuum circuit breakers were developed which used a new electrode material cobalt-silver-selenium alloy. Their chopping current level was below 1.0 A and their high frequency current interruption ability was about 24 Aus. These levels were much lower than those of conventional electrode materials and did not change after load current interruption lifetime and short circuit current interruption tests. From switching tests with motors and no-load transformers, safe operation of these vacuum circuit breakers, without any surge absorber, was confirmed ; the surge level caused by current chopping and the multiple reignition surge level caused by high frequency current interruption were far below the apparatus insulation levels. Furthermore, the new material showed good interruption ability.

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. >

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. >

Investigation of an SF/sub 6/ ultra high voltage circuit breaker using an opening resistor and auxiliary interrupter

Stresses of an interrupter during current interruption with a resistor in a UHV power system were calculated with a simple method. Interrupting abilities of some interrupters were compared by interrupting tests. A small puffer type interrupter showed the most suitable characteristics for the resistor interrupter. To realize a time interval of 28 ms from the opening of the main interrupter to the opening of the resistor interrupter, a delayed operating mechanism was constructed with independently movable parts. The operating characteristics of the mechanism were measured, and the required delay time was achieved. >