Analysis of Nozzle Ablation Characteristics of Gas Circuit Breaker

Thermal puffer type gas circuit breakers have become a mainstream of high voltage circuit breaker, because they are compact in size and interrupt high current with low driving energy. In this type, ablation gas of nozzle material flows back to a puffer chamber during nozzle clogging, and it increases gas temperature and pressure in the puffer chamber. Namely, ablation gas plays an important role for puffer pressure build-up. However, the nozzle ablation characteristics are not yet well known. In this paper, we developed calculation program of nozzle ablation and using this program, we analyzed the amount of nozzle ablation and throat diameter after current interruption. The results found that the amount of nozzle ablation increases in proportion to the 2.2 power of interrupting current, and this calculation results agree fairly well with experimental results. It was also found that the dc component included in interrupting current greatly influences the amount of nozzle ablation. However, the phase of major current loop does not influence the amount of nozzle ablation.