Decrement of Arc Conductance Affected by Gas Flow Late to Axial Center as Function of Nozzle Throat in Gas Circuit Breaker

Abstract

Recently, the stable supply of electric power has been in dispensable for power generation, transmission and distribution system of electric power. When the accident occurs in power system such as lightning surge, short-circuit fault or grand fault, the fault current brings about instantaneous voltage drop. The economy would be badly damaged by this phenomenon. Therefore, it is important to interrupt the arc as soon as possible. The GCB (Gas Circuit Breaker) has been researched for performance to interrupt the arc more quickly and clearly. However, the serious problem of thermal re-ignition occurs after interruption of the arc. This is caused by TRV (Transient Recovery Voltage). It is mainly considered that the factor of thermal re-ignition is the arc temperature. This is because the arc conductivity depends on arc temperature. Therefore, it can be estimated that the quick arc temperature decrement contributes to improvement of the arc braking performance. In this paper, the decrement of the arc conductance affected by the gas flow late to the axial center in the gas circuit breaker was elucidated. In this calculation, gas bluster shape was changed as a parameter in order to calculate the arc conductance and temperature distribution. As a result, the arc conductance decreased with increasing the gas flow rate to the axial center. This is because that the nozzle throat inlet is set upper middle part and outlet downstream is set between electrodes. Therefore, the gas flow late to the axial center plays an important role for decrement of the arc conductance.