Patent Application
20130334174
The present disclosure relates generally to electrical distribution equipment and, more particularly, to a high interrupting rating circuit breaker.
Circuit breakers are designed to have an interrupting rating capacity (also called a service breaking capacity or ICS) that specifies a maximum theoretical current that the circuit breaker is rated to handle in a repeatable and safe manner that does not cause damage to the physical or operational integrity of the circuit breaker. For example, a circuit breaker can have a service breaking capacity (or interrupting rating) of 20 kA at a maximum voltage of 690V. But this rating capacity is not adequate for installations with high current availability, such as marine, buildings, or information technology installations, which can have a current availability up to 100 kA at a maximum voltage of 690V. For these installations, a single 20 kA circuit breaker cannot be used without violating applicable standards. However, in some installations, for example in marine installations, space constraints limit the maximum physical dimensions of a circuit breaker that can be installed. If the current rating is increased from 20 kA to 100 kA, the circuit breaker would still need to meet or exceed stringent standards, such as promulgated by IEC (International Electrotechnical Commission) and UL (Underwriters Laboratories), concerning mechanical strength, dielectric withstand, and temperature rise performance requirements. The conventional way to support a higher interrupting rating is to increase the size of the circuit breaker components to handle the higher current levels, which in turn increases the overall size of the circuit breaker. But increasing the overall size of the circuit breaker is undesirable in space-constrained installations. What is needed is an improved circuit breaker design that allows the circuit breaker to perform interruption at a higher interrupting rating while complying with all relevant standards without increasing the physical dimensions or weight of an otherwise lower-rated circuit breaker.
An improved circuit breaker is disclosed that performs interruption at higher interrupting ratings while fully complying with standards, such as the IEC and UL standards. In some implementations, the circuit breaker uses a modular construction with a double-break design, such as described in U.S. Pat. No. 4,910,485, which is capable of developing arc voltage quickly to achieve current limitation and fast interruption. Extending the default interruption capability from 690V/20 kA to 690V/100 kA without changing the overall physical dimensions of the circuit breaker size raises structural and dielectric challenges that are overcome by aspects of the present disclosure. Some of the solutions to improve the structural strength of the circuit breaker to achieve the higher interruption rating include any one or more of the following: (1) the use of an adhesive bond between the interrupters and the circuit breaker housing; (2) forming part of the interrupter housing using compression molded thermoset sheet molding compound (SMC); or (3) using high-strength bolts and nuts with a controlled bolt preload during the assembly process. These structural improvements reduce the separation between the interrupter sides during a short-circuit fault and limit the propagation of short circuit byproducts (e.g., molten particles) that contribute to the degradation of the dielectric performance of the circuit breaker following a short circuit event.
When the interrupter housing is made of two pieces (for example, case halves) joined together to form the housing, the adhesive is applied to a bottom surface of the housing across both pieces near the exhaust outlet of the interrupter. Gas and pollution produced during an interruption following an electrical fault, such as a short-circuit, exit through the exhaust outlet. Normally, the gas and pollution should exit the exhaust outlet and be routed through exhaust ports in the base of the circuit breaker and finally exhausted out of and away from the circuit breaker through the exhaust ports. However, the pressure during the microseconds that a fault lasts is very sudden and intense, allowing some of the gas and pollution to escape into a gap between the bottom of the interrupter housing and the interior surface of the base of the circuit breaker. When this happens, the pressure forces produced by these wayward gasses and pollution cause the interrupter housing to lift away from the base of the circuit breaker and cause the case halves of the interrupter housing to be forced apart from one another. The adhesive opposes the tendency of the interrupter housing to lift away from the housing and to separate along its lengthwise seams at least along the bottom part where the adhesive is applied. But moreover, applying an adhesive at strategic locations on the bottom of the interrupter housing across both pieces of the interrupter housing further allows the adhesive, once cured, to act as a barrier to gas and pollution that would otherwise find their way underneath the interrupter housing. Thus, all or nearly all of the gas and pollution released during an electrical fault will find its way through the exhaust outlet and be safely exhausted out of the exhaust ports.
The foregoing and additional aspects of the present disclosure will be apparent to those of ordinary skill in the art in view of the detailed description of various aspects, which are made with reference to the drawings, a brief description of which is provided next.
The foregoing and other advantages of the present disclosure will become apparent upon reading the following detailed description and upon reference to the drawings.
Although the subject matter will be described in connection with certain aspects, it will be understood that the subject matter described herein is not limited to those particular aspects. On the contrary, the inventive subject matter is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope as defined by the appended claims.
Referring to
As shown in
The handle 108 is operated to manually reset the circuit breaker 100. The handle 108 is also adapted to serve as a visual indication of one of several positions of the circuit breaker 100. When the circuit breaker 100 is in the ON position, current flows unrestricted through the circuit breaker 100 between the line terminals 106A and the load terminals 106B, and to the electrical load(s) or circuit that the circuit breaker is designed to protect. Another position of the circuit breaker 100 is a TRIPPED position in which the flow of current through the circuit breaker 100, and consequently through the protected loads or circuits, is interrupted.
Electrical current enters the circuit breaker 100 through the line terminal 106A and exits the circuit breaker 100 through the load terminal 106B. A conventional switching mechanism (not shown) within the circuit breaker 100 is activated when the current through the circuit breaker 100 exceeds the rated current by a predetermined threshold over a specified period of time. The switching mechanism causes the handle 108 to move from the ON position to the TRIPPED position, thereby interrupting the flow of current through the circuit breaker 100.
As stated, during the actuation of the circuit breaker 100 from the ON position to the TRIPPED position, interruption gases become present within the circuit breaker 100. The gases attempt to exit the circuit breaker 100 from within, and considering that the pressure from the interruption gases is substantial, the base 102, the mechanism cover 110 and the trim cover 116 must be sufficiently supported and mounted to one another to prevent the gases from damaging them as well as the circuit breaker. Additionally, the base 102, the mechanism cover 110 and the trim cover 116 must be sufficiently supported and mounted to one another to prevent the gases from escaping from within the circuit breaker 100.
Optional cover clips 202 can be further secured between the interrupters 204a,c and the mechanism cover 110, to the circuit breaker 100 during an interruption event, strained by high pressure interruption gases and pollution. The cover clips 202 couple to the respective outer interrupters 204a,c. Each of the cover clips 202 is bent to form an L-shape where a first portion 206 is fastened to the interrupter assembly 200 by a fastener 208 and a second portion 210 that is bent at an orthogonal angle relative to the first portion 206 includes an aperture 212 for receiving a screw 99 that secures the cover clip 202 to the mechanism cover 110 as shown in
After the mechanism cover 110 is coupled to the base 102, the trim cover 114 is placed on top of the mechanism cover 110 to further assemble the circuit breaker 100. The cover clips 202 provide added support and mechanical stability to allow the circuit breaker 100 to withstand forces from interruption gases within the circuit breaker 100. It should also be noted that although only two cover clips 202 are shown and described, more than two or only one cover clips can be incorporated in the circuit breaker 100.
In
The interrupter assembly 200 includes a spacer 442 (seen in
The bolts 310a-f are high-strength bolts and one, some, or all of the bolts 310 can be hollow to allow gas to escape through the bolts between adjacent interrupters 202a,b,c. Each of the high-strength bolts has a property class strength rating of at least 10.9 as rated by the International Organization for Standardization (ISO). The bolt threads can be patch-locked with a fused nylon patch, for example, to create an irreversible fastening between the bolts 310 and the nuts 312. As opposed to rivets, the bolts 310 allow for much greater preload control in which the assembler can control the torque in a way that is repeatable and quantifiable. This allows the interrupter housing 300 to be designed akin to a pressure vessel, in which the torque is carefully controlled to achieve the proper clamping force between the two pieces 302, 304 while also preventing them from separating during an electrical fault due to pressure buildup inside the housing 300. Controlled bolt preload avoids under- or over-tightening of the two pieces 302, 304 together to form the housing 300, and further use less space compared to self-tapping screws or rivets. Because the heads and nuts can be recessed into the molded housing or at least sit flush relative to a major surface of the molded housing 300, there is no weight or space penalty associated with using bolts and nuts.
Optionally, some or all of the nuts 312 can be received in corresponding detented channels. For convenience, two detented channels 314a,b are described because they can be best seen in
As can be seen in
The adhesive 420, 422, 424 has characteristics to anchor the two pieces 302, 304 to the interior surface 402 of the base 102, to prevent the interrupter 202a,b,c from being lifted away from the base 102 responsive to an electrical fault, and to prevent the two pieces 302, 304 from separating away from one another responsive to the electrical fault. These characteristics can include a maximum service temperature sufficient to retain a compliance and strength of the adhesive 420, 422, 424 during and following a short-circuit interruption of the circuit breaker 100 in the presence of electrical current at a maximum interrupting rating (such as 100 kA) of the circuit breaker 100. The maximum service temperature can be at least 90 degrees Celsius or at least 100 degrees Celsius. The characteristics can include a single component and a moisture-curing sealant that forms permanent elastic bonds. A single-component adhesive requires no mixing. When the base 102 and the housing 300 of the interrupter 202a,b,c are composed of dissimilar materials, another adhesive characteristic can be that it has a capability to bond dissimilar materials together. For example, if the base 102 is composed of a polycarbonate material or of a nylon material, another characteristic is a substrate adhesion sufficient to bond with the polycarbonate or nylon material of the base 102. Polycarbonate material in particular is difficult to bond to, so the adhesive 420, 422, 424 has a substrate adhesion characteristic sufficient to bond with polycarbonate.
Other characteristics include non-dripping (flow without running), moisture-cured, a relatively fast cure rate (e.g., 24-48 hours), high temperature resistance (e.g., at temperatures exceeding 90 or 100 degrees Celsius), permanently elastic with good dampening and compliance such that the adhesive does not harden and become brittle once cured, high bond strength while remaining flexible after full cure. Other characteristics can include a minimal amount of volatile organic compounds (VOC) for compliance with environmental regulations or standards. The adhesive should not chemically damage the interrupter housing 300 or the base 102 after applied. By way of example only, a suitable adhesive sharing all of these characteristics is a calcium carbonate-based sealant such as the 3M760 sealant available from the 3M Company. This adhesive is a one-component, moisture-cured adhesive, bonds dissimilar materials, is permanently elastic, has high tensile strength, and a high modulus. The tack-free time is 10-30 minutes, the rate of cure is than 3.5 mm per 24 hours, the Shore A hardness is 55, the tensile strength is 4.5 MPa, its service temperature is between −40 to 100 degrees Celsius, has a thick paste consistency, and a VOC content of 29.1 g/l. It should be emphasized that this adhesive is merely exemplary and other suitable adhesives can be used instead.
The adhesive 420, 422, 424 allows the entire structure comprised of the interrupter assembly 200, the two pieces of each interrupter 202, and the base 102 to collaborate together to resist the forces during an interruption event that want to force these pieces and parts apart from one another and to damage them. The adhesive 420, 422, 424 also has good flow characteristics that allow it to flow to fill the space proximate the exhaust ports 410 between the bottom surfaces 411, 412, 414 of the interrupter 204a,b,c and the interior surface 402. The adhesive 420, 422, 424 plays an important structural role in its selected characteristics and strategic placement inside the circuit breaker 100 near the exhaust ports and across both halves of the interrupter housings. The interrupting rating of the circuit breaker 100 can be at least 2-5 times higher than an interrupting rating of a non-improved circuit breaker that lacks the adhesive 420, 422, 424 disclosed herein. For example, the interrupting rating of the circuit breaker 100 is at least 100 kA at a maximum voltage (e.g., 690V), whereas the interrupting rating of the non-improved circuit breaker is 20 kA at the same maximum voltage without the adhesive 420, 422, 424, bolts 310 and nuts 312, and SMC-formed interrupter housing 300, yet both improved and non-improved circuit breakers have respective bases with the same overall physical dimensions (e.g., length and width or footprint dimensions of the base 102). In this example, the interrupting rating has increased fivefold without incurring any size or non-negligent weight penalty.
To assemble the improved circuit breaker having a service breaking capacity (interrupting rating) higher than a service breaking capacity of a non-improved circuit breaker without increasing a length or width dimension of a base of a housing of the non-improved circuit breaker, a housing or base 102 for the circuit breaker is provided. The two pieces 302, 304 are abutted along respective lengthwise surfaces to form the interrupter housing 300. The interrupter housing 300 has a first end 460, 462, 464 (
The two pieces 302, 304 can be formed of a compression molded thermoset sheet molding compound (SMC). The two pieces 302, 304 can be abutted along respective lengthwise surfaces thereof such that a first plurality of apertures 306 in a first of the two pieces 302 align with a second plurality of apertures 308 in a second of the two pieces 304 to form a set of apertures 306, 308 extending through a width W of the interrupter housing 300 formed by the two pieces 302, 304. Bolts 310 are fastened to a corresponding number of nuts 312 through the set of apertures 306, 308 in the interrupter housing 300 to secure the two pieces 302, 304 together.
While particular aspects and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the present disclosure as defined in the appended claims.
