Abstract :
Thermal puffer-type gas circuit breaker (GCB) has a
high dielectric and current interruption capability. In order to design
a good thermal puffer GCB, it is important to know the blast
pressure for arc cooling. Although pressure calculation programs
have been developed and used for design work, the basic characteristics,
such as contribution of nozzle ablation gas to puffer pressure
rise, amount of back flow gas to puffer chamber, and pressure distribution
along gas passages during current interruption, are not
well known. In this paper, pressure rise, mass flow, and temperature
calculations were carried out using a new calculation model,
which takes mechanical compression by puffer piston, nozzle ablation
in the nozzle throat and arc energy into consideration.
By analysis of the calculation results, we found the pressure rise
mechanism is as follows. While fixed contact located in the divergent
part of nozzle, all of the ablation gas generated from the nozzle
wall cannot be exhausted from the nozzle and it leads to high-pressure
generation in the nozzle throat. This pressure causes transfer
of hot ablation gas back to the puffer chamber via gas passage.
The puffer pressure increases thermally due to temperature rise
by this mechanism. At a longer arcing time, as high puffer pressure
was already established in the puffer chamber, the nozzle ablation
gas cannot flow back to the puffer chamber. Besides as mass flow
through nozzle is limited by low gas density, the puffer pressure
rise is obtained by the mechanical compression of puffer piston.
