| 摘要 |
PROBLEM TO BE SOLVED: To provide a circuit breaker having high current limiting and breaking performance in a range from a small current to a great current without the need for increasing the withstand pressure strength of a case beyond necessity while suppressing temperature rise along with the flow of a load current in a normal state and suppressing excessive rise of pressure in a breaking chamber during breaking a great current. SOLUTION: The breaking chamber 1e partitioned with a partition wall 1d is defined in the case and a current breaking part stored therein is isolated from an opening/closing mechanism part and an overcurrent tripping device, and then a gas exhaust port 1f is opened to the back of an arc-extinguishing device. A vent hole 1g is formed in the breaking chamber 1e at its end on the opposite side to the gas exhaust port 1f in communication with the external of the case. In the vent hole 1g, a valve mechanism 11 is provided which has a ventilating valve 12 and a pressure release valve 13 combined, the former being operated to be opened at a pressure level or lower where pressure in the breaking chamber rises during breaking a small current, and to be closed at a pressure level not lower than that, and the latter being operated to be closed at a pressure level during breaking a small or medium current and to be opened at a higher pressure level during breaking a great current, to releases excessive pressure to the external of the case. COPYRIGHT: (C)2009,JPO&INPIT
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