1. Field of the Invention
The invention relates to electrical switching apparatus, such as, for example, circuit breakers and, more particularly, to circuit breakers employing a slot motor. The invention also relates to methods of installing slot motor assemblies in circuit interrupters.
2. Background Information
Circuit interrupters, such as circuit breakers, are employed in diverse capacities in power distribution systems. A circuit breaker may include, for example, a line conductor, a load conductor, a fixed contact and a movable contact, with the movable contact being movable into and out of electrically conductive engagement with the fixed contact. This switches the circuit breaker between an on or closed position and an off or open position, or between the on or closed position and a tripped or tripped off position. The fixed contact is electrically conductively engaged with one of the line and load conductors, and the movable contact is electrically conductively engaged with the other of the line and load conductors. The circuit breaker may also include an operating mechanism having a movable contact arm upon which the movable contact is disposed.
In order to enhance the speed of separation of the separable contacts, the contacts may be disposed within a slot motor, which increases interruption performance. Ring-shaped or loop-shaped slot motors typically have two assemblies, an upper assembly and a lower assembly. Both of the upper and lower assemblies include a corresponding insulative housing and a plurality of plates composed of magnetically permeable material (e.g., steel), which surrounds the separable contacts and the movable contact arm of the circuit breaker. The lower assembly is disposed below the fixed contact. When the power circuit is live, an electrical arc may be drawn between the separable contacts during separation. The electrical current interacts electromagnetically with the slot motor to induce a magnetic field in the magnetic material of the slot motor, which, in turns, interacts with the separating contacts and the movable contact arm to accelerate the contact opening process. Examples of slot motors are disclosed in U.S. Pat. Nos. 4,375,021; 4,546,336; 4,546,337; 4,549,153; 4,970,482; 5,694,098, and 6,281,459.
As shown in
The operating mechanism 10 controls the spring-biased movable contact arm 18 to pivot the movable contact 8 into and out of electrical contact with the corresponding stationary contact 9. A contact arm spring 28 biases the second end 20 of the movable contact arm 18, proximate the operating mechanism crossbar 22, in order to maintain the closed position (shown in phantom line drawing) of the pair of movable and stationary contacts 8,9.
A slot motor having a relatively narrow width channel is essential for effective current-limiting and arc quenching. However, assembly of a narrow width channel slot motor becomes a manufacturing challenge since the narrow width channel and the shape of the reverse loop conductor prevent assembly. For example, in one prior proposal, such as the circuit breaker 6 of
There is room for improvement in electrical switching apparatus, such as circuit breakers, employing a slot motor.
There is also room for improvement in methods of installing slot motor assemblies in circuit interrupters.
These needs and others are met by the embodiments of the invention, which provide, for example, a split core slot motor or a U-shaped slot motor assembly that do not require that the reverse loop conductor be deformed.
In accordance with one aspect of the invention, an electrical switching apparatus comprises: a housing; separable contacts; an operating mechanism structured to open and close the separable contacts; a power conductor comprising a first conductor and a second reverse loop conductor, the second reverse loop conductor carrying one of the separable contacts; and a split core slot motor comprising: a first slot motor portion having a number of coupling points, and a second slot motor portion having a number of corresponding coupling points, wherein the coupling points of the first slot motor portion engage the corresponding coupling points of the second slot motor portion to form the split core slot motor, wherein both of the first and second slot motor portions cooperate to form a base of the split core slot motor, and wherein the base of the split core slot motor is disposed between the first conductor and the second reverse loop conductor.
The number of coupling points may be one coupling point and the number of corresponding coupling points may be one corresponding coupling point; and the one coupling point and the one corresponding coupling point may be coupled between the first conductor and the second reverse loop conductor.
The number of coupling points may be two coupling points and the number of corresponding coupling points may be two corresponding coupling points; and the two coupling points and the two corresponding coupling points may be coupled between the first conductor and the second reverse loop conductor.
The coupling points of the first slot motor portion may engage the corresponding coupling points of the second slot motor portion to form the split core slot motor without deforming the reverse loop conductor.
Each of the first slot motor portion and the second slot motor portion may comprise an insulative cover made of an out-gassing material.
The power conductor may further comprise an intermediate conductor having an arcuate profile intermediate the first conductor and the second reverse loop conductor; and the insulative cover may be molded to form fit the arcuate profile of the intermediate conductor.
As another aspect of the invention, an electrical switching apparatus comprises: a housing; separable contacts; an arc chute proximate the separable contacts; an operating mechanism structured to open and close the separable contacts; a power conductor comprising a first conductor and a second reverse loop conductor, the second reverse loop conductor carrying one of the separable contacts; and a split core slot motor comprising: a first slot motor portion having a number of coupling points, and a second slot motor portion having a number of corresponding coupling points, wherein the coupling points of the first slot motor portion engage the corresponding coupling points of the second slot motor portion to form the split core slot motor, wherein both of the first and second slot motor portions cooperate to form a base of the split core slot motor, and wherein the base of the split core slot motor is disposed between the first conductor and the second reverse loop conductor.
The split core slot motor may have a generally U-shape.
As another aspect of the invention, a method of installing a slot motor assembly in a circuit interrupter comprises: employing a generally U-shaped slot motor assembly having two legs and a base; employing a circuit breaker power conductor including a first conductor and a second reverse loop conductor; passing one of the legs of the generally U-shaped slot motor assembly between the first conductor and the second reverse loop conductor; positioning the base of the generally U-shaped slot motor assembly proximate the second reverse loop conductor; and rotating the generally U-shaped slot motor assembly until the base is between the first conductor and the second reverse loop conductor.
The method may further comprise disposing the one of the legs of the generally U-shaped slot motor assembly generally planar with respect to the first conductor and the second reverse loop conductor before rotating the generally U-shaped slot motor assembly about 90° until the legs of the generally U-shaped slot motor assembly are generally normal with respect to the first conductor and the second reverse loop conductor.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly.
As employed herein, the terms “generally U-shaped” or “generally U-shape” shall mean that the shape of a corresponding structure has the general shape of the letter “U,” in which the bottom of such letter or structure is rounded, generally round, square, generally square, or partially round and partially square, or has the general shape of a base member with two leg (or arm) members extending upward from the ends of the base member.
The invention is described in association with a circuit breaker having a single pole, although the invention is applicable to a wide range of electrical switching apparatus having any suitable number of poles (e.g., two; three; or more).
Referring to
The example split core slot motor 115 of
The insulative cover portions 126,128 include a surface 133 (
Alternatively, the laminations 130 may be held in place by the internal side walls 134,136 (
The coupling point 118 is a post and the corresponding coupling point 122 is a recess. The coupling point post 118 engages the second slot motor portion 120 at the coupling point recess 122 thereof to form the split core slot motor 115.
The coupling point 118 of the first slot motor portion 116 engages the corresponding coupling point 122 of the second slot motor portion 120 to form the split core slot motor 115 without deforming the reverse loop conductor 114. In other words, the first slot motor portion 116 engages the corresponding second slot motor portion 120 without the need to move and, thus, deform (e.g., by otherwise bending it away from the first conductor 112) the reverse loop conductor 114.
The example split core slot motor 115′ of
Alternatively, the laminations 130′ may be held in place by the internal circuit breaker side walls 134′,136′ (
The power conductor 110′ includes intermediate conductor 138 having an arcuate profile 140 intermediate the first conductor 112′ and the second reverse loop conductor 114′. The shapes of the insulative cover portions 126′,128′ are preferably molded (as best shown in
The coupling points 118′ of the first slot motor portion 116′ engage the corresponding coupling points 122′ of the second slot motor portion 120′ to form the split core slot motor 115′ without deforming the reverse loop conductor 114′. In other words, the first slot motor portion 116′ engages the corresponding second slot motor portion 120′ without the need to move and, thus, deform (e.g., by otherwise bending it away from the first conductor 112′) the reverse loop conductor 114′.
For the slot motors 115,115′ of respective
The slot motor 115 of
The slot motor 115′ of
The slot motors 115,115′ and the respective arc chutes 144,144′ of
The open air space 146,146′ above the respective generally U-shaped slot motors 115,115′ prevents re-striking of the arc between the separable contacts 104,106. In contrast to a conventional slot motor, the much larger air space 146,146′ between the movable arm 148 (as best shown with the circuit breaker 100′ of
The insulative cover portions 126,126′,128,128′ of the slot motors 115,115′ of
The disclosed split core slot motors 115,115′ have a generally U-shape and snap together around the respective copper reverse loop conductors 114,114′. These arrangements do not require any deformation of such copper conductors 114,114′ during assembly. This structure provides improvements in the short circuit interruption performance of the circuit breakers 100,100′ because of the relatively narrow width channel of the slot motors 115,115′ for the movable arm 148, the open ended structure of the generally U-shape, and the gassing material of the insulative cover portions 126,126′,128,128′. This structure also improves economics by employing a two-piece slot motor that is assembled over the example closed-ended reverse loop conductors 114,114′. Also, the relatively low profile slot motors 115,115′, as contrasted with conventional full-doughnut slot motors, reduce the probability of dielectric breakdown during interruption, especially in relatively “lower” current interruption (e.g., about 10 kA).
Another non-limiting example of the insulative cover material is a suitable glass filled polyester. One example is Rosite® 3550D, which is marketed by Industrial Dielectrics, Inc. of Noblesville, Ind. This material preferably provides some suitable out-gassing responsive to an arcing event.
Preferably, as shown in
Referring to
The slot motor 160 is installed in a circuit interrupter (not shown), such as the circuit breaker 100 of
As shown in
The geometry of the U-shaped slot motor 160 allows it to be slid around the reverse loop conductor 172 rather than having to bend that conductor. This avoids adding stresses that might cause undesired contact height changes.
The disclosed slot motors 115,115′,160 use the general geometry of a conventional slot motor except that the shape thereof is not a complete loop or general doughnut, is relatively low in height, and has a relatively narrow width contact channel as contrasted with conventional circuit breaker slot motors. The relatively narrow width contact channel places the magnetic material closer to the movable contact arm, such as 148, thereby increasing the movable arm opening velocity and the arc velocity. This enhances the magnetic field and promotes faster initial opening of the movable arm, thereby increasing the arc voltage at a faster rate. This also places the gassing material (e.g., CMF) insulative cover portions 126,126′,128,128′,174 in close proximity to the stationary contact 106 and, thus, close to the arc. This greatly increases the pressure and cools the arc and the stationary contact, especially early in the arcing sequence. All of this improves the current limiting capability of the circuit breakers 100,100′ and does not permit the arc to reignite at current zero.
The relatively lower height of the slot motors 115,115′, 160 and the resulting open air spaces 146,146′ prevents dielectric breakdown of the contact gap, especially at current zero. In contrast, conventional doughnut slot motors can cause a re-ignition at current zero, especially in 10 kA short-circuit testing. The dielectric strength of the slot motor insulation is greatly reduced during arcing due to the high surface temperature and metal deposition on the surface of such insulation. Also, the movable arm 148 is in close proximity to the inner wall of the conventional slot motor. This relatively short air gap can easily breakdown due to the residual hot plasma and the reduced dielectric strength of the slot motor insulation.
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
Number | Name | Date | Kind |
---|---|---|---|
4375021 | Pardini et al. | Feb 1983 | A |
4546336 | Petrie et al. | Oct 1985 | A |
4546337 | Petrie et al. | Oct 1985 | A |
4549153 | Forsell et al. | Oct 1985 | A |
4970482 | Jacobs et al. | Nov 1990 | A |
5694098 | Mody et al. | Dec 1997 | A |
6281459 | Munsch et al. | Aug 2001 | B1 |