High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Operating mechanism structure or arrangement
Reexamination Certificate
1999-09-07
2001-05-01
Donovan, Lincoln (Department: 2832)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Operating mechanism structure or arrangement
C335S172000, C218S157000
Reexamination Certificate
active
06225588
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a trip device of a circuit breaker to break such a high current as short-circuit current as quickly as possible.
2. Description of the Background Art
There is a circuit breaker which is enclosed in a casing formed of an insulating molding. The circuit breaker is composed of switching contacts, an operating mechanism which opens/closes the switching contacts, a trip device which automatically releases a trip latch mechanism, when overcurrent flows, for working the operating mechanism to open the switching contacts, and an arc-extinguishing device for irresistibly extinguishing arc which is generated when the switching contacts are opened so as to break the current.
Generally, in an electric circuit, if the circuit breaker breaks an enormous abnormal current which occurs due to a short-circuit accident in the electric circuit as immediately as possible to limit the current flowing through the circuit to a small magnitude, the damage to the electric circuit can be made minimum and accordingly the damage to the circuit breaker itself can be reduced. Therefore, the circuit breaker which can more speedily break the short-circuit current can accordingly break a high short-circuit current immediately, so that the rated breaking capacity thereof can be increased.
The electromagnet is applied to a trip device of a conventional circuit breaker which operates upon occurrence of a short-circuit current. The electromagnet operates when the current flowing through a main circuit conductor of the circuit breaker exceeds a predetermined threshold so as to release the trip latch mechanism included in the operating mechanism and thus open the switching contacts.
Such an electromagnet is slow in operation due to inertia of a movable core, and thus it is impossible to break more speedily the short-circuit current when the current exceeds a threshold. In particular, when an enormous abnormal current flows to cause the switching contacts to repel each other due to the electromagnetic force and consequently the switching contacts are opened, the contacts could be brought into contact again unless the trip latch mechanism is immediately released. In such a case, the circuit breaker itself could suffer a great damage.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a trip device of a circuit breaker which can speedily operate in a reliable manner.
According to an aspect of the present invention, a trip device of a circuit breaker operates the circuit breaker that includes switching contacts, an operating mechanism which opens and closes the switching contacts, a trip latch mechanism which works the operating mechanism when released to open the switching contacts, and a housing which encloses at least the switching contacts. The trip device includes a pressure detection space having a wall portion with a repeatedly usable thin plate, an operating rod which protrudes from the pressure detection space when the pressure in the pressure detection space increases, and a return spring which returns the operating rod. The pressure detection space is arranged in the vicinity of the switching contacts, and the operating rod is arranged to release the trip latch mechanism when it protrudes.
In such a structure, when a great abnormal current flows to cause electromagnetic repulsion force and accordingly the switching contacts are opened, arc gas of high temperature and pressure is instantaneously generated and thus the wall portion having the thin plate of the pressure detection space is pressurized. The thin plate then yields to the pressure so that the internal pressure increases to cause the operating rod to protrude and accordingly release the trip latch mechanism. Consequently, the operating mechanism works immediately to complete the tripping operation. During this operation, the arc gas just directly pressurizes the thin plate which surrounds the pressure detection space, and any piece of metallic material that is melted in the vicinity of the switching contacts due to high temperature does not interrupts the movement according to the operating mechanism. In addition, the arc gas itself does not work the trip latch mechanism in order to release it, therefore, the trip latch mechanism and its surroundings are not exposed to the arc gas. After the abnormal current is broken, the arc gas disappears so that the internal pressure of the housing of the switching contacts becomes the atmospheric pressure to return the thin plate to its original shape. As a result, the internal pressure of the pressure detection space returns to its original state, the operating rod is also returned by the return spring, and accordingly, a waiting state to prepare for the next breaking operation starts.
According to another aspect of the invention, the pressure detection space of the trip device of the circuit breaker in the above one aspect of the invention is placed in a cavity which is formed within a wall of the housing, and a through hole is formed at a wall which separates the cavity containing the pressure detection space from the housing enclosing the switching contacts. Any special material or space for arranging the pressure detection space is thus unnecessary and the structure is simplified.
According to still another aspect of the invention, the pressure detection space of the trip device of the circuit breaker in the above one aspect of the invention is composed of a cavity which is formed within a wall of the housing, a through hole which is made at a wall which separates the cavity from the housing, and a thin plate formed to close the through hole.
The wall of the housing itself can be utilized as the pressure detection space, and thus a simplified structure is realized.
According to the another and still another aspects of the invention concerning the trip device of the circuit breaker, the circuit breaker is of a multipole type which has switching contacts in each pole, and a pressure detection space common to different poles adjacent to each other is placed at a wall of the housing which separates the adjacent poles. The structure is thus simplified since the trip device need not be provided at each pole.
In the trip device of the circuit breaker according to any aspect of the invention, a small opening is provided to the pressure detection space so as to allow the outside air to flow. Accordingly, the pressure detection space can easily be returned after pressurization.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3631369 (1971-12-01), Menocal
patent: 3787648 (1974-01-01), Kawasaki
patent: 4375022 (1983-02-01), Daussin et al.
patent: 4521756 (1985-06-01), Forsell
patent: 4943691 (1990-07-01), Mertz et al.
patent: 3-101023 (1991-04-01), None
Donovan Lincoln
McDermott & Will & Emery
Terasaki Denki Sangyo Kabushiki Kaisha
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