Low Voltage Vacuum Circuit Interrupter

The provision of a solid state switch across a pair of separable contacts to reduce arcing between the contacts, when separated, is disclosed within U.S. patent application Ser. No. 610,947 filed May 16, 1984 entitled "Solid State Current Limiting Interrupter" in the name of E. K. Howell and now abandoned. This application is incorporated herein for purposes of reference and should be reviewed for a good description of the circuit components used within the solid state switch.

The absence of an arc between the contacts, when separated, allows smaller contacts which in turn are more readily separated in the early stages of the current waveform to further reduce contact heating and deterioration. U.S. patent application Ser. No. 684,307 filed Dec. 20, 1984 entitled "High Speed Contact Driver For Circuit Interrupter Device now abandoned" and U.S. Pat. No. 4,620,122, entitled "Piezoelectric Contact Driver For Circuit Interrupters", both in the name of E. K. Howell, disclose contact drivers for rapid circuit interruption by means of a pair of fixed contacts and a bridging contact operated by a contact driver. Both the aforementioned U.S. patent application and U.S. Patent are also incorporated herein for purposes of reference. The use of the solid state switch in combination with the high speed contact driver to separate the contacts allows the solid state circuit components to be reduced in rating and hence more economically feasible. U.S. Pat. No. 4,607,148 entitled "Change Of State Contact Material For Electric Circuit Interrupters", also in the name of E. K. Howell, describes a contact structure that allows for a reduction in the contact holding force which is required to provide low contact resistance between the contacts. This results in the use of smaller contacts and contact holding springs. This Application is incorporated herein for purposes of reference and should be reviewed for a good understanding of the materials and arrangement used to promote these benefits.

By the synergistic combination of a solid state switch, high speed contact driver and change of state electrode materials, the size of the contacts and the means for separating the contacts can be reduced sufficiently to enable containment within an evacuated envelope. The use of the evacuated envelope now allows either the fixed contact pair or the bridging contact to be fabricated from copper metal rather than silver. The copper provides good electrical conduction between the contacts along with a substantial reduction in materials costs. The copper remains oxide-free under the vacuum contained within the sealed envelope as well as when reducing-type gases are employed instead of vacuum.

A low voltage vacuum interrupter consisting of a pair of fixed contacts and a bridging contact under the control of a high speed contact driver are arranged within an evacuated envelope. The fixed contacts comprise copper metal while the bridging contact comprises a change of state layered metal contact. A solid state switch connected across the fixed contact pair allows the contacts to be separated without the occurrence of any arc whatsoever.

FIG. 1 is a side sectional view of a single break low voltage vacuum interrupter according to the invention; and

FIG. 2 is an exploded top perspective view of the low voltage interrupter of FIG. 2 prior to assembly.

A low power single break vacuum interrupter 115 is shown in FIG. 1 and consists of a first copper bar 116 having an aperture 117 for electrical connection with an external circuit and a second larger aperture 118 which defines a space 118A, as indicated. Within this space is arranged an apertured and flexible diaphragm 119 containing an expansion diameter 120 and through which a contact rivet 121 is inserted and fixedly attached by means of a bead 130 of silver solder. An apertured stem 126 supports a pair of closely spaced wires 122, 123 for moving the diaphragm and the single contact 127 A single ceramic disc 124 is arranged between the first copper bar 116 and a second copper bar 128. The second copper bar contains an aperture 129 at one end for electrical connection with an external circuit. The single contact 127 mates with a surface of the second copper bar shown generally at 131 to provide an electrically conductive path from the second copper bar 128 through the single contact 127 and diaphragm 119 to the first copper bar 116. When a current pulse is applied to the closely spaced wires 122, 123 the force applied to the contact rivet 121 lifts the diaphragm and the single contact out of contact with the second copper bar 128 to interrupt the electrical connection between the first and second copper bars.

The low power single break vacuum interrupter of FIG. 1 is assembled in the manner depicted in FIG. 2 and described as follows. The second copper bar 128 is arranged with the aperture 129 oriented opposite from the aperture 117 through the first copper bar 116. The ceramic disc 124 is then arranged on the second copper bar such that the aperture 125 surrounds the contact mating surface generally described at 131 and forms a space generally shown at 125A in FIG. 1. The flexible diaphragm 119 is placed on the ceramic disc with the expansion diameter 120 within the disc aperture and with the contact rivet 121 and apertured stem 126 concentrically arranged within the aperture 118 provided through the first copper bar and with the closely spaced wires 122, 123 extending through the aperture. When the components are assembled as depicted in FIG. 1, they are placed within an evacuation chamber and are evacuated and sealed in the manner described earlier. The low power single contacts vacuum interrupter 115 is useful in circuits wherein the current transport through the flexible diaphragm 119 is insufficient to cause excess heating of the diaphragm.

It is thus seen that the use of a solid state switch across a pair of contacts contained within an evacuated chamber allows the contacts to rapidly separate to interrupt circuit current with little or no deterioration due to arcing or chemical activity. The vacuum also allows the circuit to interrupt upon the occurrence of a very small separation distance because of the excellent dielectric properties inherent in the vacuum environment.