H. Nishikawa

Development of Zinc Oxide Ceramic Energy Absorbers for DC Thyristor Circuit Breakers

The performance and the overall bulk of low-voltage DC thyristor power circuit breakers explained in this article tend to be determined by the media in which circuit interruption is performed. The zinc oxide ceramic energy absorber is an extinguishing medium with capabilities beyond the counterparts used in the conventional high-speed circuit breakers. The withstand-voltage, the interrupting time and the surge energy to be extinguished during interrupting are considered, together with parameter values specified in JEC Standard. Each energy absorber for the prototype DC 1500V-3000A thyristor circuit breaker consists of twenty four 115 mmo 15 mm thick zinc oxide ceramic elements and is capable of absorbing 400 kJ. The performance of these assembled devices in an energy absorber and incorporated with a thyristor circuit breaker as well as in the discrete form have been verified.

Harmonic Current Interruption Phenomena In ARC Furnace Filter Circuits

The current interruption phenomenon in arc filter circuit containing harmonic current was experimented in the field and analyzed by TNA (Transient Network Analyzer) and numerical analysis to calculate the recovery voltage. The recovery voltage when the filter circuit contains harmonic current becomes greater than that obtained in the IEC-specified test using a small leading current.

Response Analysis of Metal-Enclosed Switchgear Shaken by Ground Oscillation

A seismic performance is one of the important performance of the metal-enclosed switchgear. To evaluate that, experimental modal analysis was applied to three types of the metal-enclosed switchgear to determin the dynamic characteristics such as natural frequencies, damping ratios and mode shapes. With the resultant modal data, response analysis of the metal-enclosed switchgear was done under sine wave shaking from the ground and confirm a good agreement between analytical result and the experimental data using a shaking table. In addition, the response to the ground oscillation with seismic waves (Taft waves) was analysed to clarify the response of the metal-enclosed switchgear to the earthquake.

Thyristor Valve Gapless Arrester Element Lifetime Performance and Thermal Stability

For the purpose of developing thyristor valve gapless arrester, a ZnO element was developed and examination was conducted on such characteristics of gapless arrester as life characteristic, thermal runaway characteristic and surge withstand capability, these being essential to rational design of thyristor valve gapless arrester. Especially for evaluating the life characteristic and thermal runaway, a small-scale 3- phase bridge thyristor converter was manufactured to provide the same stress as in the actual system. Based on the result of experiment using the 3-phase bridge thyristor converter, a d.c. 125kV thyristor valve gapless arrester capable of lowering the protective level was developed. The gapless arrester is currently undergoing field testing in the actual system.