Kunio Hirasawa

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. >

Floating Vector Processor for Power System Simulation

This paper analyzes microprogram functions of the sparse matrix solution to obtain faster power system simulations such as the power flow calculation and transient stability analysis. The hardware structure and extended instructions of a floating vector processor (FVP) which realize simulation speed up are presented. Experimental results of a sparse matrix calculation and a power flow calculation lead to the following results: (1) the sparse matrix calculation, by the FVP is completed about 1.6 times faster than by a conventional array processor; (2) the processing speed of the FVP is ten to fifteen times faster than that of the general purpose supermini- computer Hitachi V90/50 Control Computer on the conditions that the programming style of the programs executed by the FVP is microprogramming fit to the FVP architecture, and the programs executed by the V90/50 are programmed in Fortran with simple optimization; and (3) the speed of the total power flow calculation by the V90/50 with FVP is 2.6 times faster than that by the V90/50 alone.

Analytical prediction of transient breakdown characteristics of SF/sub 6/ gas circuit breakers

A study was conducted to estimate transient breakdown voltages (V/sub BD/s) between contacts of a puffer-type SF/sub 6/ gas circuit breaker. When contacts are opening, compressed gas is blasted between them by an insulating nozzle. The gas pressure fluctuates greatly in the contact region. The authors suggest that this pressure fluctuation causes transient V/sub BD/s. It is demonstrated that very accurate transient V/sub BD/ characteristics can be calculated by combining the gas flow and electric field analyses and breakdown probability. The numerically calculated transient V/sub BD/ characteristics agree fairly well with the transient recovery voltages during the capacitive current interruption. >

Experimental Approach to One-Cycle Puffer Type SF6 Gas Circuit Breaker

An experimental model of one-cycle circuit breaker based on the puffer principle has been developed. This experimental model was designed for 242/245kV 4OkA rating for one break per pole, to meet the ANSI and IEC Standard specifications. Through laboratory tests, it demonstrated minimum and maximum interrupting times of 0.5 and 1.3 cycles for both the 90o short line fault (SLF) and 100o breaker terminal fault (BTF) conditions, including symmetrical and asymmetrical current wave shapes. The experimental one-cycle breaker is furnished with a new type of puffer interrupter which is designed to work under high SF6 gas pressure and has a suction chamber as well as the conventional compression chamber, and provided with a newly developed oil hydraulic operating mechanism with a pilot valve driven by a force motor.

High-frequency reignition current and its influence on electrical durability of circuit breakers associated with shunt-Reactor current switching

Very-high-frequency and high-peak reignition currents were measured in shunt reactor banks rated at 33 kV 40 MVA during breaking operations of a gas circuit breaker (CB). To measure those kinds of high-frequency transients in reactor circuits in service, a noninvasive method of measuring was proposed using Rogowski coils and capacitive coupled antennas. Some combinations of metals in an electrical collector used in CBs tend to get severely eroded by the high-frequency reignition currents. The paper also proposes a test circuit that can yield high-frequency reignition currents to evaluate the electrical durability of CBs.

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. >

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. >

Simulations on Interruption of Circuit Breaker in HVDC System with Two Parallel Transmission Lines

This paper describes the Erectro Magnetic Transients Program (EMTP) simulation results for a study on specifications and duty of an HVDC circuit breaker in an HVDC system. The HVDC breaker employs an inverse current injection method and a capacitor precharged from the line voltage. The HVDC system is mono-polar, but has two parallel transmission lines and is the simplest multi-terminal system. The simulations demonstrated that the HVDC breaker can interrupt successufully under various breaking conditions.

Research on a New Type Magnetic Puffer Gas Circuit Breaker

The magnetic repulsive force which arises between a secondary short circuit ring and a primary coil through which short circuit current flows was used for a new magnetic puffer gas circuit breaker. A floating piston type magnetic puffer circuit breaker showed much success in experiments and the examples of theoretically calculated results together with a fixed piston type magnetic puffer circuit breaker are shown by the authors for the first time. It is proved that the interrupting performance of SF6 gas circuit breakers is much improved with the addition of a simple magnetic drive mechanism as shown in the following.