Patent Application
20110100958
The present disclosure relates to circuit breakers, and, more particularly, to a debris collection groove formed in an exhaust vent of a circuit breaker for collecting debris produced during a circuit interruption.
Vents relieve pressure in circuit breakers generated by debris and ionized gases produced during a circuit interruption and can be situated near grounded metal that is part of the circuit-breaker enclosure or near a line-side bus, which is at a different voltage than the exiting gas. Debris generated during the circuit interruption can include metal particles that can be made molten by hot ionized gases. When the debris exits the circuit breaker, it can reduce the dielectric strength of the vent path and the through-air and over-surface dielectric spacings to grounded metal or bussing just outside the vent and promote a ground strike or cross-phase. Conventional ways of reducing debris exiting the circuit breaker include covering the vent opening with a screen or a perforated plate. But these obstructions increase the internal pressure generated during the circuit interruption, which can be undesirable.
The present invention avoids significantly increasing the internal pressure inside the circuit breaker while trapping some of the debris that is produced during a circuit interruption. Whereas the conventional thing to do was to add at the exit of the vent channel a screen or a perforated plate, which would catch some of the debris, the present invention proposes to turn that conventional wisdom on its head by doing precisely the opposite—i.e., removing any obstruction at the exit of the vent channel and instead forming a groove or slot near the exit of the vent channel to trap some of the debris in the groove or grooves as the debris is being expelled from the circuit breaker. In vent channels having a serpentine shape with multiple bends, the groove is best formed near the last bend at the opening of the vent channel. Higher-density debris tends to collect toward the outer part of the bend, so placing one or more grooves there will increase the ability of the groove to trap more debris.
The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
A vent channel 104 is formed in the housing 102 and includes a front pressure area 120 and a back pressure area 122. The front pressure area 120 of the vent channel 104 is positioned proximate the movable contact 110 when it is disengaged from the stationary contact 112. A gas pressure exerted upon the front pressure area 120 is greater than a gas pressure exerted upon the back pressure area 122, which is distal (farther away) from the front pressure area 120 relative to the source of the debris produced when the movable contact 110 separates from the stationary contact 112.
The vent channel 104 has two bends corresponding to a first curved section 114 and a second curved section 116. The back pressure area 122 terminates at an uncovered opening 118 through the housing 102. The vent channel 104 includes a debris collection groove or slot 106 formed in the housing 102 in the back pressure area 122 such that at least some of the debris is collected in the debris collection groove 106 instead of exiting the circuit breaker 100 through the uncovered opening 118. As the debris travels from the front pressure area 120 to the back pressure area 122 and is finally expelled out of the opening 118, it first encounters the first curved section 114 and changes its direction of travel by more than 45 degrees. As it follows the curve around the first curved section 114, it continues toward the back pressure area 122 until it encounters the second curved section 116, which changes the debris' direction of travel again by more than 45 degrees. In
The debris collection groove 106 operates like a screen or perforated plate that has been conventionally installed at the opening 118, but without affecting the internal pressure in the vent channel 104 during interruption of the circuit breaker 100. Because the opening 118 can remain uncovered and free of a screen or perforated plate, incorporating a groove 106 at the opening 118 does not significantly increase the internal pressure as any obstruction placed at the opening 118 would. The effective cross-section of the vent channel 104 is not reduced, and the flow rate of the exiting gases is not reduced because the opening 118 is uncovered and free of any obstruction, such as a screen or perforated plate. By reducing the amount of debris that is expelled from the circuit breaker 100, the potential for a ground strike or cross phase is reduced.
As can be seen from
It is advantageous to position the grooves near the last bend of the vent channel, because the higher-density debris tends to travel to the outside of the bend. A groove positioned near the end of that bend would tend to trap the higher-density debris as it rounds the last corner before exiting the circuit breaker.
Although the grooves shown in the figures are formed as mere indentations or cuts into the housing, more elaborate or differently shaped grooves are contemplated. For example, a groove whose opening transitions into a reservoir, like a flask, can trap more debris in the reservoir area. The groove need not extend across the entire surface of an inner wall of the vent channel. Multiple grooves or slots can be formed along the inner wall of the vent channel in a linear configuration or according to a pattern. An object is that before the debris has a chance to exit the vent channel, the debris has somewhere else to go within the vent channel, but the cross section of the vent channel is not compromised and no obstruction is placed near the exit of the vent channel that would undesirably increase the internal pressure within the circuit breaker. The grooves according to the present invention actually allow the cross section of the vent channel to be increased without causing an undesirable build-up of debris on the grounded metal or bussing external to the circuit breaker.
While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
