Intrinsic Safety of Capacitive-Resistive Circuit

Electric-arc ignition test of methane gas has been carried out for some capacitive-resistive circuit models. The results of the minmum ignition voltages (Vm) for circuits with paticular parameters and with the discharged energy values, has been evaluated. The main results obtained are as follows; (1) Capacitive-resistive circuit connected with a power-supply is more liable to ignite methane than that without a power-supply in certain conditions. (2) Discharging resister R 2 and bleeder R 3 act to raise up the Vm, or enlarge the safety V-C zone. (3) The spark duration is found to be 50μ sec by means of both high-speed cameras and observation of sparking current. (4) The discharging energies for different capacitor values are found in consideration of the capacitordischarging character in the model with sparking duration of 50μsec. (5) An easier method is proposed for calculating Vm. (6) The theoretically obtainned values of Vm coincide with measured ones.