Patent Application
20050046539
This invention relates generally to circuit breakers, and, more particularly, this invention relates to a rotor assembly with electrical isolation.
A current limiting circuit breaker is generally a high current circuit interrupting device capable of substantially limiting the duration and the intensity of current destined to flow in a circuit experiencing short circuit fault. To limit the duration and the intensity of short circuit currents, a circuit breaker must, within the shortest possible time, separate its contacts. This separation of the contacts is achieved by rapidly accelerating movable contact arms through an open gap. Upon the intense overcurrent conditions that result in the separation of the contacts, however, arcing often occurs between various parts in the circuit breaker. Arcing between the contacts is usually extinguished by passing the arc through an arc dissipating means. However, arcing may occur between other components of the circuit breaker as well.
Rotary contact arrangements are typically rotatably arranged on a support shaft between the fixed contact arms of the circuit breaker and function to interrupt the flow of current in the event that a short circuit occurs. A rotary contact arrangement employs a rotor and a pair of rotor springs to maintain contact between the movable contact arms and the fixed contact arms, thus maintaining a good electrical connection between the contacts. The compression forces provided by the rotor springs must be overcome when the contacts become separated and the circuit “blows open” due to the occurrence of opposing electrodynamic repulsion fields between the movable contact arm and the fixed contact arm.
Commonly, multiple contacts, each disposed within a cassette, are arranged within a circuit breaker system for protection of individual phases of current. The operating mechanism is positioned over one of the cassettes and generally connected to all of the cassettes in the system. Because of the close position between each of the cassettes, and between each cassette and the operating mechanism, the spacing between poles of opposite polarity could lead to dielectric failure.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by an electrically isolated rotor assembly for a circuit breaker. The electrically isolated rotor assembly includes a rotor having a first side and an opposing second side, a first isolation cap disposed on the first side, a second isolation cap disposed on the second side, and means for preventing dislocation of the first and second isolation caps from the rotor during rotation of the rotor.
In other embodiments, a cassette assembly for a circuit breaker includes a first cassette half piece having an interior surface, a first aperture formed on the interior surface, a second cassette half piece having an interior surface facing the interior surface of the first cassette half piece, and an electrically isolated rotor assembly trapped between the first and second cassette half pieces. The electrically isolated rotor assembly includes a rotor having a first side and an opposing second side, a first isolation cap disposed on the first side, the first isolation cap having a first centrally located knob facing the first cassette half piece, and a first bushing surrounding the first knob, wherein the first bushing is sized for securement within the first aperture within the first cassette half piece and wherein the rotor is rotatable within the cassette assembly about a pivot created by the first bushing, first knob, and first aperture.
In other embodiments, an isolation cap and bushing for a rotor assembly, includes an isolation cap having an exterior surface, an interior surface for facing the rotor assembly, an outer periphery having a lip for extending towards the rotor assembly, a centrally located knob on the exterior surface, and a bushing having a circular member concentrically surrounding the knob.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
Referring to
Referring to
Referring to
Electrical transport through rotary contact assembly 40 of circuit breaker cassette assembly 38 occurs from line-side contact strap 22 to an associated first fixed contact 54, through first and second movable contacts 56, 58 secured to the ends of a movable contact arm, shown generally at 62, and to an associated second fixed contact 60 on load-side contact strap 44. Movable contact arm 62 is pivotally arranged between two halves of a rotor 64 and moves in conjunction with rotor 64 upon manual articulation of rotor 64. Rotor 64 is rotatably positioned on a rotor pivot axle, the ends of which are supported by inner parallel walls of electrically-insulative cassette half-pieces 42.
The circular rotor 64 includes a contact spring slot 148 formed on each side thereof. A first contact spring 138 extends between a pair of spring pins 140, 142 within contact spring slot 148 and a second contact spring (not shown) extends between pins 140, 142 in a similar manner on the opposite side of rotor 64. An aperture 146 extends through rotor 64. Aperture 146 allows for a link connection by means of an extended rotor pin or drive pin 34 with the circuit breaker operating mechanism to allow a manual intervention for opening and closing the circuit breaker contacts.
The arc chute assemblies 50, 52 are positioned in the first electrically insulative cassette half piece 42 adjacent the respective pairs of first fixed and first moveable contacts 54, 56, and second fixed and second moveable contacts 60, 58. The first and second movable contacts 56, 58 and moveable contact arm 62 move through a passageway provided by the arc chute assemblies 50, 52 in order to engage and disengage from the respective first and second fixed contacts 54, 60. Each arc chute assembly 50, 52 is adapted to interrupt and extinguish the arc which forms when the circuit breaker 10 is tripped and the first and second moveable contacts 56, 58 are suddenly separated from the first and second fixed contacts 54, 60.
Referring back to
Turning now to
Turning now to
Each side 206, 208 of the rotor assembly 202 also preferably includes an outer periphery 210 including intermittent indentations 212 and protrusions 214. That is, in the generally circular rotor assembly 202, a radius of the rotor assembly 202 measured at the location of an indentation 212 will be less than a radius of the rotor assembly 202 measured at the location of a protrusion 214. Furthermore, as shown in
The rotor assembly 202 may further include an inner periphery 216 where the indentations 212 are not included and thus the radius of the rotor assembly 202 is the same as that of the outer periphery 210 at the location of a protrusion 214. A stopping surface 218 is thus created between the outer periphery 210 at the location of an indentation 212 and the inner periphery 216.
The rotor assembly 202 is flanked by a pair of isolation caps 230, 232 which each include a bushing 234, 236, respectively, to form the electrically isolated rotor assembly 200. The first and second isolation caps 230, 232, and first and second bushings 234, 236 may be identical for reducing manufacturing expenses. The first isolation cap 230 is sized for secure placement upon the first side 206 of the rotor assembly 202. Likewise, the second isolation cap 232 is sized for secure placement upon the second side 208 of the rotor assembly 202. That is, when the caps 230, 232 are placed upon first and second sides 206, 208, the caps 230, 232 lie flush with the rotor assembly 202. Each isolation cap 230, 232 preferably includes an outer periphery 252 with an outer radius that may be substantially equal to the outer radius of the rotor assembly at the location of a protrusion 214 on the outer periphery 212 or at the inner periphery 216 of the rotor assembly 202. Each isolation cap 230, 232 further includes an inner periphery 252 which is interrupted by gaps 254. The inner periphery 252 may have an inner radius substantially the same, or slightly greater than, an outer radius of the outer periphery 210 of the rotor assembly 202 at the location of an indentation 212 such that the isolation cap fits securely over the rotor assembly 202 by having the inner periphery 252 of the isolation caps 230, 232 overlap the outer periphery 210 of the rotor assembly 202. The isolation caps 230, 232 further include an edge periphery 256 which abuts against the stopping surface 218 of the rotor assembly 202 when the isolation caps 230, 232 are securely installed. The inner periphery 252 further includes isolation cap abutting surfaces 258 which push against the rotor assembly abutting surfaces 220 when the rotor assembly 202 rotates. Likewise, the rotor assembly abutting surfaces 220 abut against the isolation cap abutting surfaces 258 when the rotor assembly 202 rotates. This feature prevents the isolation caps 230, 232 from slipping relative to the rotor assembly 202 during swift and sudden rotations of the rotor assembly 202.
The isolation caps 230, 232 further each include an inner surface 260 which faces the first side 206, and the second side 208, respectively of the rotor assembly 202, and an outer surface 262 which faces an interior of the cassette half pieces 42 and 242. The inner surfaces 260 of the isolation caps 230, 232 cover the springs 138. Additionally, the inner periphery 252 of the isolation caps 230, 232 covers the opposite end portions of the springs 138 where they are secured via the pins 140, 142. The isolation caps 230, 232 are preferably made from thermoset plastic with superior arc track resistance to serve as a contamination seal to the live parts of the rotor assembly 202, and to provide electrical dielectric integrity between poles of opposite polarity to greater than 2500 Volts after short circuit. Although the use of thermoset plastic is described, it should be understood that the use of other materials with suitable insulative properties would also be within the scope of this system 200. Because of the design of the isolation caps 230, 232, dimensional stability is provided to the rotor assembly 202 and the contact arm assembly in all phases of operation.
The inner surface 260 also includes at least one inwardly protruding pipe 264 that is sized for receipt within the aperture or apertures 146. A complimentary externally protruding pipe 266 extends from the outer surface 262. The externally protruding pipe 266 may be received within the slotted apertures 270 formed within each cassette half piece 42, 242. A longitudinal axis is aligned with the apertures 146, and pipes 264, 266 such that the rotor pin or drive pin 34 passes freely therethrough and the longitudinal axis of the drive pin 34 is aligned with the longitudinal axis passing through the aperture 146 and pipes 264, 266. The pipes 264 and 266 extending from the isolation caps 230, 232 help protect the drive pin 34 as it moves through the slotted apertures 270 during rotation of the rotor assembly 202. Also, the pipes 264, 266 offer support to the drive pin 234 and also act as a “poke-yoke” feature. The pipes 264, 266 prevent the rotor system from getting assembled upside down.
On the outer surface 262 of each isolation cap 230, 232 there is preferably provided a centrally located, exteriorly protruding knob 272. A longitudinal axis passing through the knob 272 defines a pivot axis for the rotor assembly 202. Surrounding an outer periphery of each knob 272, there is preferably provided a bushing 234, 236. Each bushing is sized to fit within each aperture 204 provided on the interior of each cassette half piece 42, 242, as shown in
While a specific embodiment of a circuit breaker is shown, it should be understood that this system may be retrofitted in other molded case circuit breakers based on the construction of the rotor system.
The electrically isolated rotor assembly 200 thus provides electrical isolation between the live parts in the rotor assembly 202 and live parts of adjacent poles of opposite polarity. Also, the electrically isolated rotor assembly 200 provides a bearing pivot that results in minimal wear during mechanical operation. Also, the electrically isolated rotor assembly 200 provides a seal to prevent arcing contamination from the rotor springs 138 that could lead to dielectric failure between poles of opposite polarity.
While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.
