Suenobu Hamano

Application Problems of SF6/N2 Mixtures to Gas Insulated Bus

Gas insulated bus (GIB) using SF6 gas has widely been applied in the world, because it has the advantages in reliability and in minimizing installation space. However SF6 is identified as a potent greenhouse gas and thus the efforts in preventing the release of SF6 in the environment, the study on recycling SF6and the research for alternative gas are now being performed1. in designing a GIB using alternative gas, there are many application problems such as a selection of alternative gas and its rated pressure to maintain the required dielectric and heat transfer performance. the problems on recycling SF6 are also essential in applying alternative gas using SF6 such as SF6/N2 mixtures.

Usefulness of Permanent Power Fuse in Control Centers with Molded Case Circuit Breakers

The increase in electric power consumption in industry has led to the development of modern distribution systems such as control centers having high kVA ratings and high prospective fault current. In such a situation, the improvement of the system usefulness such as reliability and cost effectiveness is the essential requirement. An index is presented to evaluate the system usefulness using the cost effectiveness for fault protection in a system of given bank kVA. The index is estimated on four different system structures of control centers, including one which utilizes Permanent Power Fuses (PPF). It is presented that the PPF combined with molded case circuit breaker in main circuit effectively improves the cost effectiveness in control centers with high fault current. Operating principles of the PPF and the control center utilizing the PPF are briefly outlined.

Dynamic Behavior of Gas-Blasted Arcs in SF 6 -N 2 Mixture

The arc quenching phenomenon in an SF6-N2 mixture was analyzed by using the simulation program developed by the authors. The gas flow from the cylinder to the arc was investigated as a function of SF6-N2 mixing ratio in relation to the configuration of the arc chamber. The pressure rise in the cylinder was measured to confirm the result of the simulation by varying the SF6-N2 mixing ratio. The result of the simulation suggests that the desirable configuration of arc chamber should be changed depending upon the mixing ratio of SF6-N2 mixture.

Mixing Process of Arced Gas With Cold Gas in the Cylinder of Gas Circuit Breaker

Mixing process of high temperature and low temperature gases in the cylinder during arc back was observed for a model GCB with and without puffer action by shadow method. The volume and the temperature of the mixing region were estimated based on the results of the observation . The rate of volume increase of the mixed gas is expressed as a function of the arc power. The temperature of the mixed gas was found to decrease within ten milli-seconds after the arc initiation to around 300 K and 500 K in the cases with and without puffer action, respectively.

Optical Observation of Self-Gas-Flow in GCB

The generation of self gas flow in a model SF6 gas circuit breaker without puffer action is observed by high speed photography, shadow photography using a Q-switch ruby laser and time-and space-resolved spectrography. The model breaker is specially designed for observation of gas flow in all the spaces from the cylinder to the exhaust space. The results of the observations are Icompared with a free burning arc and show that the self gas flow to the arc in the breaker reduces the diameter of the arc, and raises the temperature of the arc core. This model breaker interrupts the current of 3 kArms with a transient recovery voltage of 2 kV/?sec, though the pressure rise of the cylinder is less than 0.3 x l05 Pa.