ROTARY CONTACT ASSEMBI. Y FOR HIGH AMPERE-RATED CIRCUIT BREAKERS Background of the Invention US patent 4,616,198 entitled"Contact Arrangement for a Current Limiting Circuit Breaker"describes the early use of a first and second pair of circuit breaker contacts arranged in series to substantially reduce the amount of current let through upon the occurrence of an overcurrent condition.
When the contact pairs are arranged upon one movable contact arm such as described within US patent 4,910,485 entitled"Multiple Circuit Breaker with Double Break Rotary Contact", some means must be provided to insure that the opposing contact pairs exhibit the same contact pressure to reduce contact wear and erosion.
One arrangement for providing uniform contact wear is described within US Patent 4,649,247 entitled"Contact Assembly for Low-voltage Circuit Breakers with a Two-Arm Contact Lever". This arrangement includes an elongate slot formed perpendicular to the contact travel to provide uniform contact closure force on both pairs of contacts.
US patent 5,030,804 entitled"Contact Arrangement for Electrical Switching Devices"describes providing a pair of cylindrical plates on either side of the contact arms and forming elongated slots within each of the cylindrical plates.
Other examples of circuit breakers employing rotary
contacts are found in US patent 5,281,776 entitled"Multipole Circuit Breaker with Single Pole Units; US patent 5,310,971 entitled"Molded Case Circuit Breaker with Contact Bridge Slowed Down at the End of Repulsion Travel"; and US patent 5,357,066 entitled"Operating Mechanism for a Four-Pole Circuit Breaker".
State of the art circuit breakers employing a rotary contact arrangement employ a rotor assembly and pair of powerful expansion springs to maintain contact between the rotor assembly and the rotary contact arm as well as to maintain good electrical connection between the contacts, per se. The added compression forces provided by the powerful expansion springs must be overcome when the contacts become separated by the contact "blow open"forces of magnetic repulsion that occur upon extreme overcurrent conditions within the protected circuit before the circuit breaker operating mechanism has time to respond.
One purpose of the invention is to describe a rotary contact arrangement having expansion springs arranged between the rotary assembly and the rotary contact arm that maintain good electrical connection between the contacts during quiescent operating current conditions while enhancing contact separation upon occurrence of extreme overcurrent conditions.
Summary of the Invention A circuit breaker rotary contact assembly employs a common pivot between the rotor assembly and the rotary contact arm. A pair of off-center expansion springs directly engages the rotor at one end and engages the rotary contact arm via a linkage arrangement at an opposite
end thereof. Both the rotary contact arm and the rotor assembly are slotted at the points of contact with the extension springs for tolerance compensation between the rotary contact assembly components as well as to reduce contact wear and contact erosion.
Brief Description of the Drawings Figure 1 is a top perspective view of a circuit breaker employing a rotary contact assembly according to the invention; Figure 2 is a top perspective view of the complete contact assembly contained within the circuit breaker of Figure 1; Figure 3 is a an enlarged top perspective view of the rotor in isometric projection with the contact arm assembly of Figure 2; Figure 4 is an enlarged front plan view of the rotary contact arm assembly according to the invention with the contacts in the CLOSED position; Figure 5 is an enlarged front plan view of the rotary contact arm assembly according to the invention with the contacts in the OPEN position; and Figure 6 is an alternate embodiment of the rotary contact arm assembly according to the invention.
Description of the Preferred Embodiment
A multi-pole circuit breaker 10 is shown in Figure 1 consisting of a case 14 and cover 15 with an operating handle 16 projecting from the cover through an aperture 17. The operating handle interacts with the circuit breaker operating mechanism 18 to control the ON and OFF positions of the central rotary contact arm 30, and central rotary contact arm assembly 32 within the circuit breaker operating mechanism. The contact arm assembly 32 being formed within the central pole 11. A first rotary contact arm 22 and first rotary contact arm assembly 20 within a first pole 12, on one side of the operating mechanism 18 within the central pole 11, and a second rotary contact arm 24 and second rotary contact arm assembly 21 within a second pole 13 on the opposite side of the central pole, move in unison to provide complete multi- pole circuit interruption. An elongated pin 38 interconnects the operating mechanism 18 with the center, first and second rotary contact arm assemblies 32,20,21. As described within the aforementioned US Patent 4,649,247 a rotor 19 interconnects each of the rotary contact arms 22,24,30 with the corresponding pairs affixed contacts 27,27'and, movable contacts 28,28'.
The rotor 19 in the circuit breaker assembly 9 is depicted Figure 2 intermediate the line strap 23 and load strap 31 and the associated arc chutes 33,34. The first rotary contact arm assembly 20 and second rotary contact arm assembly 21 of Figure 1 are not shown herein but are mirror images of the central rotary contact arm assembly 32 and operate in a similar manner. The arc chutes 33,34 are similar to that described within US Patent 4,375,021 entitled"Rapid Electric Arc Extinguishing Assembly in Circuit Breaking Devices Such as Electric Circuit Breakers". The central rotary contact arm 30 moves in unison with the rotor 19 that, in
turn, connects with the circuit breaker operating mechanism 18 of Figure I by means of the elongated pin 38 to move the movable contacts 28,28'between the CLOSED position depicted in solid lines in Figure 4 and the OPEN position. The clevis 35 consisting of the extending sidearms 36,37 attach the rotor 19 with the circuit breaker operating mechanism 18 and the operating handle 16 of Figure 1 to allow both automatic as well as manual intervention for opening and closing the circuit breaker contacts 27,27'and 28, 28'. The rotor 19 is positioned between the line and load straps 23,31 along with one of the contact pairs 28'to hold the contacts in close abutment to promote electrical transfer between the fixed and moveable contacts during quiescent circuit current conditions. The operating pivot pin 29 of the central rotary contact arm 30 extends through the rotor 25 and responds to the rotation movement of the rotor to effect the contact closing and opening function in the manner described within the Italian Patent Application (751T 100) entitled"Rotary Contact Assembly for High Ampere-Rated Circuit Breakers".
In accordance with the teachings of the invention, a hinged attachment between the slotted rotor surfaces 19A, 19B arranged on opposite sides of the slotted movable contact arm 30 within the rotor assembly 39 as now shown in Figure 3 provides for automatic tolerance compensation between the slotted rotors and the slotted movable contact arms within all three poles 11-13 of the circuit breaker 10 of Figure 1. The slotted contact arm 30 includes a slotted pivot aperture 46 for receiving the pivot pin 29 and a pair of top and bottom links 48,49 attached to the slotted movable contact arm by means of pins 52,53 and apertures 54,55 arranged within the V-shaped slots 50,5 1. The slotted rotor 19 defines a pair of outer surfaces 19A, 19B each include central apertures, one of which is shown at 60 for receiving the pivot pin
29, along with opposing shallow slots 44A, 44B and opposing deep slots 45A, 45B, as indicated. A first expansion spring 40 is attached to the slotted rotors by means of first pins 42A, 42B. The slotted contact arm 30 is inserted within the slot 63 formed within the slotted rotor intermediate the rotor outer surfaces 19A, 19B.
The first pin 42A extends through the shallow slot 44A and the second pin 42B extends through the deep slot 45B. The first pin 42A extends under the surface 61 defined under the movable contact 30A and then through one end of an opposing expansion spring 58 on the rotor outer surface 19B. The second pin 42B extends through the deep slot 45B, through the aperture 56 in the top link 48, and then through the other end of the expansion spring 58 on the rotor outer surface 19B. A second expansion spring 41 is attached to the slotted rotor by means of second pins 43A, 43B.
The second pin 43A extends through the deep slot 45A, through the aperture 57 in the bottom link 49, and then through one end of an opposing expansion spring 59 on the rotor outer surface 19B.
The second pin 43B extends through the shallow slot 44B, over the surface 62 defined on the movable contact arm 30B and then through the other end of the expansion spring 59 on the rotor outer surface 19B.
The slotted rotor assembly 39 is depicted in Figure 4 with the movable contacts 28,28'on the opposite ends of the contact arms 30A, 30B in the CLOSED condition relative to the fixed contacts 27,27' (shown in Figure 1). The top and bottom links 48,49 are arranged on the top and bottom parts of the slotted contact arm 30 within the V-shaped slots 50,51 and within the associated slots 45A, 45B on the slotted rotor 19 as viewed from the rotor surface 19A. The expansion spring 41 is shown arranged
between the pins 43A, 43B and the expansion spring 40 between the pin 42B in the top link 48 and the pin 42A is omitted to show the positional relationship between the line offeree Fi, directed through the pins 42B, 52 in the top link 48. This arrangement provides optimum contact pressure between the movable and fixed contacts 28,27, 28', 27'hile allowing for contact wear compensation and tolerance adjustment between the components within the rotor assemblies 39 within the individual poles within the circuit breaker of Figure 1.
Upon occurrence of a large overcurrent condition within the circuit breaker assembly of Figure 2 containing the slotted rotor assembly 39 of Figure 5, the magnetic repulsion forces generated between the movable and fixed contacts 28, 27,27' (shown in Figure 1) within the circuit breaker assembly drive the movable contact arms 30A, 30B and the associated movable contacts 28,28'in the counterclockwise direction about the pivot pin 29 to the OPEN position shown in Figure 5. The rotation of the upper link 48 moves the link pin 52 to the position indicated in Figure 5 such that the line of force exerted by the expansion springs 40,41 (Figure 3) is now directed through the pins 42B, 52 in the top link 48 as indicated at F2, locking the slotted contact arm 30 in the OPEN position to prevent re-closure of associated the movable and fixed contacts 28,27,28', 27'until the circuit breaker operating mechanism 18 shown in Figure 1 has responded to separate the movable and fixed contacts 28,27,28', 27'within each of the circuit breaker poles 11-13. Upon movement of the circuit breaker operating handle 16 to reset the circuit breaker operating mechanism, the slotted contact arm 30 rotates in the clockwise direction about the pivot 29 to return the contact arms
30A, 30B to the CLOSED position shown in Figure 4. It has been determined that the automatic expansion and contraction of the springs 40,41,58,59, the top and bottom links 48,49 and the provision of the slots 44A, 44B, 45A, 45B of Figure 3 results in the best tolerance adjustment between the rotor assembly 39 than has ever heretofore been attainable in so-called rotary contact arrangements with self locking contact arm capabilities within circuit breakers.
US patent 4,616,198 entitled"Contact Arrangement for a Current Limiting Circuit Breaker"describes a circuit interruption arrangement having a single pair of fixed and movable contacts that become separated by rotation of a single contact arm to which the movable contact is attached at one end.
In further accordance with the teachings of the invention, a semi-rotor assembly 64 is depicted in Figure 6 to include a semi-rotor 65 having a circular forward surface as indicated at 65A and a planar rear surface as indicated at 65B.
The movable contact 69 is positioned at one end of the contact arm and the pivot pin 70 attaches the contact arm to the semi-rotor 65 at the opposite end thereof. A contact braid 72 is fixedly attached to the movable contact arm as indicated at 73 at one end, and to the load strap 74 at the opposite end as indicated at 80. In a similar manner as described with respect to Figures 3-5, a link 75 connects with the contact arm 68 at one end by means of the pin 77 and is positioned within the slot 65C within the semi-rotor 65 and is retained therein by means of the extended pin 79. A similar expansion spring 81 extends between the pin 79 at one end of the expansion spring as indicated at 78 and the extended pin 82 within the slot 67 at the opposite end of the expansion spring as
indicated at 83. An opposing expansion spring (not shown) extends between the pin 79 and the extended spring pin 82 on the other side of the semi-rotor assembly 64. The link 75 is arranged such that the force line F3 exhibited by the expansion spring between the semi-rotor and the contact arm is directed along the link pins 77,79 resulting in the maximum contact pressure exhibited between the movable and fixed contacts 69,71 when the contacts are in the CLOSED position indicated in solid lines. Upon occurrence of a large overcurrent condition within the circuit breaker assembly of Figure 2 containing the semi-rotor assembly 64 of Figure 6, the magnetic repulsion forces generated between the movable and fixed contacts 69,71 within the circuit breaker assembly drive the movable contact arm 68 and the associated movable contact 69 in the counterclockwise direction about the pivot pin 70 to the OPEN position indicated in dashed lines. The force line F4 exhibited by the expansion spring between the semi- rotor and the contact arm is now directed along the link pins 77,79 in such a manner that the movable contact arm 68 is locked in the OPEN position to prevent re-closure of associated the movable and fixed contacts 69,71 until the circuit breaker operating mechanism 18 shown in Figure 1 has responded to separate the movable and fixed contacts 28,27 within each of the circuit breaker poles 11-13. Upon movement of the circuit breaker operating handle 16 to reset the circuit breaker operating mechanism, the movable contact arm 68 rotates in the clockwise indicate direction about the pivot 70 to return the contact 69 to the CLOSED position in the manner described earlier.
The provision of a link connection between a rotor assembly and a movable contact arm has been shown herein to
improve performance of a circuit breaker during contact separation as well as contact closure. The arrangement of at least one expansion spring between the link and the associated rotor provides optimum contact force by compensating for component tolerance and contact erosion and wear while still maintaining a reliable means for locking the contact arm 30 open in the event of an over current condition.
What is claimed is:
