Circuit breaker with particle trap

Details Circuit breaker with particle trap Circuit breaker with particle trap

2000-01-13

2001-10-23

Scott, J. R. (Department: 2832)

High-voltage switches with arc preventing or extinguishing devic

Arc preventing or extinguishing devices

Housing structure

C174S016200, C218S043000, C218S068000, C200S293000

Reexamination Certificate

active

06307172

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to the art of high-voltage circuit breakers and particularly to circuit breakers with gas-insulated tanks enclosing separable contacts.
Gas-insulated circuit breakers are known. Such circuit breakers generally include separable contact elements contained within a sealed tank filled with an inert insulating gas for reducing arcing. Specifically, the gas is typically sulfurhexaflouride (SF
6
) due to its good insulative and arc interruption properties.
Despite careful manufacturing practices, an assembled circuit breaker tank can contain undesirable foreign particles, such as dust, metal shavings from machined parts, etc. Although unlikely, it is also possible that hardware, e.g., nuts, washers, screws, etc., could work loose during operation. It is undesirable for such particles, particularly metallic conductive or semiconductive particles, to freely reside within the tank. Such particles, if permitted to remain free, can interfere with the operation of the circuit breaker, causing undue arcing, flashing or promoting breakdown between metallic components. The presence of particles greatly reduces the breakdown voltage of the circuit breaker. Sensitivity to particles increases with the voltage across the circuit breaker due to the increased electric field stress levels. Circuit breakers are now constructed capable of handling very high voltages, for example 362 kV and higher.
In a conventional tank, the operation of the contacts can cause such particles to move about. For example, it is known that the operation of opening and closing the contacts causes shocks and vibrations capable of moving loose particles within the tank. Also, in a “puffer” type circuit breaker, the operation of opening the contacts results in flows of SF
6
gas capable of blowing loose particles around the tank.
Traps for foreign particles are known in the art of high-voltage gas insulated transmission lines, but it has been previously believed for several reasons that a particle trap in a tank section of a high voltage circuit breaker would be ineffective. A primary reason is that circuit breakers are not field tested with a “conditioning” AC voltage as are gas insulated lines. The use of particle traps in transmission lines requires that an AC test voltage be gradually raised from low levels to a level higher than the operating voltage. This moves particles into receptacles provided in the gas chamber designed to trap the particles before the particles can cause a breakdown. Furthermore, the severe mechanical shock that occurs in a circuit breaker and the blasts of SF
6
gas in “puffer” contacts could force undesirable movement of particles.
Efforts have been made to include a particle filter or trap in gas insulated systems which include circuit breakers, however these systems utilize means remote from the circuit breaker tank, such as within the aforementioned gas insulated transmission lines, to attempt to capture particles present in gas flows through the system. U.S. Pat. No. 4,219,366 discloses a gas-insulated system including circuit breakers wherein gas insulated transmission lines connected to the circuit breakers include a sticky coating. U.S. Pat. No. 3,943,315 discloses a particle filter located in a circuit of SF
6
flow pipes supplying SF
6
gas to a circuit breaker tank from an external SF
6
gas source and compressor.
It is desirable to immobilize foreign particles within a tank of a high-voltage circuit breaker in order to assure effective circuit breaker operation and to minimize potential damage.
SUMMARY OF THE INVENTION
The present invention provides a circuit breaker including a contact mechanism movable between an open and closed position, a driving mechanism operable to drive the contact mechanism between the open and closed positions, and a tank having at least one wall defining an interior chamber enclosing the contact mechanism, the interior chamber being filled with a gas, such as SF
6
. The wall defines a trap in a bottom of the tank for collecting foreign particles.
In an embodiment, the trap is shaped as an elongated, recessed channel located on the bottom of the tank. In an embodiment wherein the circuit breaker tank is generally cylindrical in shape, the channel is axially directed relative to a longitudinal axis of the tank. The channel preferably extends substantially along a length of the cavity within the tank which encloses the contact mechanism. The channel can have various shapes, including, but not limited to, a flat bottom shape, U-shape, or V-shape.
According to an embodiment, a portion of the wall of the tank adjacent to the channel forms a lip that slopes downwardly toward the channel along one or both sides of the channel.
In an embodiment, adhesive material is disposed in the channel for immobilizing particles that enter the trap.
An advantage of the present invention is to provide a trap for a high-voltage circuit breaker which traps foreign particles within a tank of the circuit breaker without relying only on electric field induced movement of the particles into trap. The invention uses the mechanical shock, vibration and gas flow from the operation of the breaker during initial testing to move any loose particles to the particle trap. The particles are immobilized during operation due to the low electrical field in the bottom of the particle trap.
Another advantage of the present invention is to provide a particle trap in a high-voltage circuit breaker which is easy to clean.
A further advantage of the present invention is to provide a particle trap in a high-voltage circuit breaker which is simple and inexpensive to manufacture.
Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the preferred embodiments, the Figures and the claims.


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A.H. Cookson, “Recent Research in the United States on the Effect of Particle Contamination Reducing the Breakdown Voltage in Compressed Gas-Insulated Systems”, International Conference on Large High Voltage Electric Systems, Aug. 25-Sep. 2, 1976.
A.H. Cookson, “Effect of Conducting Particles on AC Corona and Breakdown in Compressed SF6”, Westinghouse Research Laboraties.
Philip C. Bolin, “Update on Field Experience with Compressed Gas-Insulated Transmission Systems”, reprinted from vol. 41, Proceedings of the American Power Conference, 1979.

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