A new interruption method for low-voltage, high-capacity, air-break contactors through suppression of hot blowoff gases

The purposes of this study are to suppress the blowoff of hot gases from an arc chamber and to shorten the arcing time in the interruption of overcurrents. The blowoff of hot gases is suppressed by the cooling action of a porous metal plate attached in front of the gas exhaust holes of an arc chamber. From heat analysis, it is estimated that exhaust gas temperature is reduced to less than 10% of the temperature of hot gases in the arc chamber using the porous metal plate. The arcing time is shortened by a unique commutation electrode and arc runner. For interruptions of a 6 kA current in a 480 V circuit, the maximum arcing time of the new method is shortened by about 40% compared with that of a conventional method. From observation using a high-speed framing camera, it is concluded that the shortening of arcing time is due to an effective arc-drive by the commutation electrode and arc runner. The new method has been applied to contactors of 600 A and 800 A frames having the maximum rated operational voltage of 660 V.