Electricity: circuit makers and breakers – Electric switch details – Cases and bases
Reexamination Certificate
1999-10-29
2001-06-05
Friedhofer, Michael (Department: 2832)
Electricity: circuit makers and breakers
Electric switch details
Cases and bases
C200S050210
Reexamination Certificate
active
06242702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to circuit breaker units and more particularly to circuit breaker units for large capacity circuit breakers, such as draw-out type circuit breakers.
2. Description of the Related Art
Circuit breaker units comprise, in part, circuit breaker backmolds which are commonly used as mounting surfaces for turnable joint mounts, current transformers and metering transformers.
The turnable joint mounts connect with the field serviceable connections to which the circuit breaker protects against short circuit and overload situations. The backmold is the main interface between the circuit breaker and the field serviceable connections. Therefore, the circuit breaker backmold must be reliable, safe and cost effective.
On large capacity circuit breakers, such as a draw-out type circuit breaker, extreme forces are placed along the horizontal axis of the backmold when engaging and disengaging (also known as “racking”) the circuit breaker and when connections are made between the turnable joint mounts and field service connections, which can weigh in excess of 200 lbs. Force is also exerted on the backmold when the circuit breaker, often rated up to 6,000 amps, is tripped. Alone or in combination, these forces can cause deflection or bowing in a conventional backmold, which is made from thermoset materials, such as Bakelite®, a phenolic resin, that are heated in compression or injection molds.
Electrical clearance parameters and the dimensions of the circuit breaker enclosure limit the ability to add a bracing element to the backmold in order to provide greater strength and resist deflection and bowing. Therefore, in order to produce a backmold with sufficient strength, the compression or injection molds used to produce the conventional backmold must be of a suitable depth. Typical Bakelite® backmolds have a thickness of 4-5 inches and therefore, it is not feasible to add a brace to the backmold because of the limited space within the circuit breaker unit.
Other disadvantages with the use of conventional backmolds include the difficulty experienced when making modifications to the backmold. Conventional backmolds produced by compression or injection molding processes require changes in the mold when modifications are to be made to the backmold. Changes in the design of the mold are extremely costly because of the complexity of the mold. In contrast, less complex molds are used in manufacturing pultrudled backmolds and a majority of the features on the pultruded backmold can be post-machined. Therefore, when changes need to be made to a pultruded backmold, changes are made in the machining process and not necessarily the mold itself.
SUMMARY OF THE INVENTION
The present invention comprises a circuit breaker unit having a backmold that can withstand horizontal axial forces, which can cause deflection or bowing of the backmold. The circuit breaker unit of the present invention comprises an enclosure, a cradle for mounting and dismounting the circuit breaker from the field serviceable connections and a pultruded backmold attached to the cradle for providing support to the turnable joint mounts, which engaged both circuit breaker clusters and the field serviceable connections. The pultruded backmold is molded with at least one horizontal rib adjacent a top end, a bottom end or in an area between the top and bottom ends. The horizontal rib provides additional strength to the pultruded backmold.
The pultruded backmold of the present invention comprises a composite material, preferably a plurality of fiberglass fiber encased in a polyester resin which is pulled through a heated die. By utilizing a pultrusion process, the fibers in the composite material are oriented in such a manner as to provide a high strength backmold. Additionally, the pultruded backmold has a thickness of only 1½-1¾ inches compared to the 4-5 inch thick conventional backmold. The molds used in producing the pultruded backmold do not need to be as deep or complex as the compression or injection molds used to produce a conventional backmold. Therefore, single piece pultruded backmolds can be manufactured with less support and structural geometry, which reduces the likelihood of failure due to hidden flaws and manufacturing costs.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may better be understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
REFERENCES:
patent: 3663773 (1972-05-01), Powell
patent: 3806768 (1974-04-01), Gryctko et al.
patent: 4205207 (1980-05-01), Clausing
patent: 4447858 (1984-05-01), Farag et al.
patent: 5424910 (1995-06-01), Lees
Cirves Gregory A.
Mittelstadt Chad Raymond
Spiegel Jacob Birk
Friedhofer Michael
Golden Larry I.
Irfan Kareem M.
Square D Company
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