Estimation of Gas Discharge Rates in EHV Gas Circuit Breakers

The basic philosophy of a two-stage blast interrupter is the combination of self-blast and puffer interrupting principles. Conventionally, analytical techniques are used to calculate thermodynamic properties, prior to simulation, in different zones of the interrupter model. It is important to validate these results on gas circuit breaker for various test duties specified by IEC prior to its evaluation at short circuit laboratory. In view of above, numerical techniques have been developed to calculate the SF6gas pressure-rise in various interrupter volumes and gas flow rate across different passages of interrupter with respect to time instant. In order to validate the analytical model developed in the study, an experimental set-up has been established to measure transient pressure-rise generated during circuit breaker operation. Further, to understand the gas flow pattern during circuit breaker operation, authors developed a CFX model. By using this numerical model, the gas flow rate distribution across various passages and through the insulated nozzle has been computed. Finally, the effect of nozzle profile and gas flow passage areas on transient pressure levels as well as its distribution across inter-electrode gap has been discussed in detail as part of the study.