High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Housing structure
Reexamination Certificate
2000-01-03
2002-03-26
Gellner, Michael L. (Department: 2833)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Housing structure
Reexamination Certificate
active
06362445
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains in general to switchgear and other switching equipment which use hermetically sealed interrupters employing insulation having a higher electrical resistance than air and more particularly to compact switchgear that employ modular components to reduce the overall size of the system.
2. Background Information
Circuit breakers provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and abnormal 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 have been known which include 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 a vacuum chamber and a driving mechanism at the other end which is external to the vacuum chamber. An operating rod assembly comprising a push rod, which is fastened to the end of the stem opposite the moveable contact, and a driving mechanism provide the motive force to move the moveable contact into or out of engagement with the fixed contact.
The operating rod assembly is operatively connected to a latchable operating mechanism which is responsive to an abnormal current condition. 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 bell crank to rotate and, as discussed above, this controls motion of the moveable contact.
Compression springs are provided in connection with the operating rod assembly in order to be able to separate the moveable contact from the fixed contact and to assure the necessary force so that the contacts will not accidentally open under inappropriate conditions. In addition, when appropriate circumstances requiring interruption of the circuit do arise, an adequate force is needed to open the contacts with sufficient speed. If the contacts do not open quickly, there is a risk of the contacts welding together and failure to interrupt the current.
Vacuum interrupters or reclosures are typically used, for instance, to reliably interrupt medium voltage ac currents, and in the case of vacuum interrupters also high voltage ac currents of several thousands of amperes or more. Reclosures include interrupters that are designed to typically operate in a range of current measured in amperes, rather than kiloamperes, and automatically reclose after a given delay, and for a given number of times, in an attempt to automatically reestablish the circuit. However, from the standpoint of this invention the principles discussed herein apply equally well to both, as well as to other load break switches, circuit breakers and switch disconnects.
Typically, in accordance with prior art practices, one vacuum interrupter is provided for each phase of a multi-phase 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 voltage transient and uneven contact wear.
Medium size switchgear employing vacuum interrupters typically have a front low voltage portion just to the rear of the front panel which typically includes the breaker controls. The low voltage portion is electrically insulated, through the use of standoffs, from high voltage portions which include the vacuum interrupters. The standoffs permit sufficient spacing of the conducting components so that air within the housing can be an effective insulator to isolate the low voltage portions of the switchgear from the high voltage components. However, this spacing also contributes to the size of the units.
More recently attempts have been made to reduce the size of these units by hermetically sealing them and filling them with a gaseous insulator having a higher dielectric capacity than air, such as SF
6
However, this creates a number of environmental concerns.
Accordingly, an improved medium voltage switchgear design is desired that reduces the overall size and enhances the serviceability of the unit.
SUMMARY OF THE INVENTION
These and other needs are satisfied by the present invention which comprises a circuit switching system made up of a number of plug-in, integral, modular units with each module enclosed within solid electrical insulation that isolates the conducting members that interface between modules, from contact with lower voltage portions of the surroundings. In one embodiment, one of the modules comprises a vacuum switching device (hereafter referred to as the “isolator module”) having a plurality of stationary contacts and a moveable contact mechanism which is connectable to any one of the stationary contacts which are all enclosed in a vacuum vessel, also known as a vacuum bottle. At least two conducting circuit elements are respectively connected to one of the stationary contacts and the moveable contact mechanism with a second stationary contact grounded. The moveable contact within the vacuum vessel of the isolator module is connectable to a contact on a separate breaker module, which can also contain a vacuum circuit interrupter. Each external electrical connection on the isolator module which is connectable to either a line source, e.g., main bus bar, or an electrical connector on the separate breaker module, terminates in an insulated electrical connector that is designed to mate with a complementary insulated electrical connector on the line source, and the breaker module. The other external electrical connections on the switching system modules that interface with either other modules in the system or the circuit interface, also, similarly employ complementary insulated electrical connectors, electrically insulating the interface from the external environment and sealing those mating electrical connectors from contact with lower voltage portions of the surroundings, while maintaining a good electrical connection; with the possible exception of a ground connection. If only a single line source is used when the isolator module is designed to accommodate more than one, the exposed electrical connector is fitted with a fully insulated, complementary connector, in the form of a complementary non-electrically conducting plug, to isolate the unused electrical connector from lower voltage portions of the surrounding switching system or environment, e.g., air. The vacuum isolator module is operable to connect the breaker module alternatively to one or more sources or ground in the event servicing is required or, with both contacts in the open state the isolator module can isolate the breaker module in a floating condition.
The breaker module forms a second modular component of this invention that includes a conventional vacuum interrupter, designed to withstand the currents experienced by the breaker function, whose terminals are connected to insulated electrical connectors that protrude through the vacuum vessel. Desirably both breaker module insulated electrical connectors protruding through the vacuum bottle are of the same design so that either can be connected to either side of the circuit. The breaker module further includes an integral, or separate, in-line actuator which is dedicated to actuating the moveable contact on the breaker module and is preferably enclosed within an insulated housing that could encompass both the vacuum vessel and the in-line actuator. In a preferred embodiment the in-
Davies Norman
Hodkin George Alfred
Marchand Francois J.
Marshal Trevor Brian
Theisen Peter J.
Gellner Michael L.
Moran Martin J.
Nguyen Nhung
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