High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Housing structure
Reexamination Certificate
2000-01-03
2001-07-03
Gellner, Michael L. (Department: 2832)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Housing structure
C335S017000
Reexamination Certificate
active
06255615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains in general to switches that employ contacts maintained in hermetically sealed housings that contain a medium having a higher dielectric strength than air and more particularly to such switches that employ a single drive rod to move the contacts relative to each other.
2. Background of the Invention
Circuit breakers provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. Typically, circuit breakers include a spring powered operating mechanism which opens electrical contacts to interrupt the current through the conductors on an electrical system in response to abnormal conditions. In particular, vacuum circuit interrupter apparatus has been known which includes separable main contacts disposed within an insulating housing. Generally, one of the contacts is fixed relative to both the housing and to an external electrical conductor which is interconnected with the circuit to be controlled by the circuit interrupter. The other contact is moveable. In the case of a vacuum circuit interrupter, the moveable contact assembly usually comprises a stem of circular cross section having the contact at one end enclosed within the vacuum chamber and a driving mechanism at the other end which is external to the vacuum chamber. An operating rod assembly is provided which carries a rotatable contact bell crank which is slidable on the operating rod and rotates about a pivot pin upon motion of the operating rod. This plate is connected to the stem or drive rod of the moveable contact. Motion of the plate causes motion of the moveable contact into or out of engagement with the fixed contact.
The operating rod assembly is operably connected to a latchable operating mechanism which is responsive to current. When an abnormal condition is reached, the latchable operating mechanism becomes unlatched which causes the operating rod to move to the open position. The motion of the operating rod, in turn, causes the contact or crank to rotate and, as discussed above, this controls motion of the moveable contact. The operation of this type of vacuum interrupter is more fully described in U.S. Pat. No. 5,095,293, issued Mar. 10, 1992 to the assignee of the present invention.
Vacuum interrupters or reclosers are typically used, for instance, to reliably interrupt medium to high voltage AC currents of several thousands of amperes or more. Reclosers are interrupters that are designed to automatically reclose after a given delay and for a given number of times in an attempt to automatically re-establish the circuit. However, from the standpoint of this invention, the principles discussed herein apply equally well to both.
Typically, in accordance with the prior art practices, one vacuum interrupter is provided for each phase of a multiphase circuit and the interrupters for the several phases are actuated simultaneously by a common latchable operating mechanism. This does not permit point-on-wave switching among the multiple phases and can give rise to arcing and uneven contact wear. Co-pending patent application, Ser. No. 09/476,243 (Attorney Docket No. 97-PDC-524), filed concurrently herewith and assigned to the assignee of this invention, addresses this problem by supplying independent means for actuating the vacuum interrupters respectively associated with each phase of the circuit.
In general, the prior art had actuated the circuit interrupters to the open condition before servicing. While that action opens the circuit it does not drain the circuit of residual charge that can, under certain circumstances, create a safety issue. The aforecited co-pending application recognizes the desirability of providing a mechanism for grounding the circuit before maintenance takes place. Accordingly, an optimum design for achieving that objective is desired.
SUMMARY OF THE INVENTION
These and other needs are satisfied by the present invention which comprises a circuit switch design that in the broader sense includes two contacts; one stationary and one moveable. The stationary contact has an annular opening through which a drive rod, which is attached to a moveable contact, extends. The drive rod reciprocates the moveable contact between at least two positions; one in contact with the annular stationary contact and the other in the open position where the moveable contact is spaced from the annular stationary contact. Typically, the contacts are sealed in a vacuum vessel and the drive rod is mounted to slidably and sealably extend through the vacuum vessel where it is connected to an actuation mechanism. The seal typically employed to maintain an effective barrier while enabling drive rod motion is a bellows seal.
In the preferred embodiment a fixed stationary contact is provided on the side opposite the moveable contact in juxtaposition to the annular stationary contact. In this configuration, the drive rod reciprocates the moveable contact between three positions. The first position situates the moveable contact in electrical communication with the fixed stationary contact; the second position places the moveable contact between the fixed and annular stationary contacts establishing an open circuit condition; and the third position is where the moveable contact is moved into electrical communication with the stationary contact having the annular opening.
A further enhancement includes placing a raised annular contacting surface on the side of the moveable contact opposing the stationary contact having the annular opening. Preferably the inside diameter of the raised surface on the moveable contact is larger than the diameter of the annular opening in the stationary contact. Another enhancement places insulation on the corners of the annular opening of the first stationary contact. In addition, the drive rod of the moveable contact can be insulated, e.g., covered with a ceramic. Desirably, the size of the annular opening in the stationary contact is large enough to prevent arcing with or without the assistance of the foregoing insulation.
In this preferred embodiment either one of the stationary contacts is connected to ground and the other stationary contact is connected to line. The moveable contact is connected to the load. In this way, a load can be conveniently connected to its electrical power source, disconnected or grounded to facilitate maintenance.
REFERENCES:
patent: 4743876 (1988-05-01), Milianowicz et al.
patent: 5095293 (1992-03-01), Patel et al.
Gellner Michael L.
Nguyen Nhung
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