EP0296183B1

EP0296183B1 - Circuit breaker contact assembly

Info

Publication number: EP0296183B1
Application number: EP19870907568
Authority: EP
Inventors: John M. Winter
Original assignee: Square D Co
Current assignee: Schneider Electric USA Inc
Priority date: 1986-10-24
Filing date: 1987-10-23
Publication date: 1993-02-03
Anticipated expiration: 2007-10-23
Also published as: EP0296183A1; DE3784065D1; DE3784065T2; EP0296183A4; WO1988003324A1; CA1310046C

Abstract

A circuit breaker (10) having a movable upper blade (16) with a free floating pivot end (46). The operating mechanism (34) is solidly connected to the upper blade (16). The contact force is generated by a contact spring (44) which exerts an upward force on the lower blade (26). As the contacts (18, 22) separate, the force exerted on the upper blade (16) is virtually eliminated, reducing substantially the resistance at the pivot end (46) of the upper blade (16). The load terminal (12) and pivot end (46) of the upper blade (16) provide a current path parallel to that of the load side flexible connector (15).

Description

Circuit breakers often have a moving contact mounted on a fixed pivotable blade that is controlled by an operating mechanism. In some designs a pair of links are directly connected to the movable blade to open and close the circuit breaker contacts as shown in Figure 1.
As the current carried by the circuit breaker increases, constriction forces between the contacts may cause the contacts to blow apart. This problem is eliminated by increasing the contact force in any one of a number of ways. One method used in the prior art as shown in Figure 2, is to place a flat spring and/or coil spring between the movable blade and the blade carrier. The lower contact exerts an upward force A on the moving contacts at the right end of the movable blade. The flat spring positioned between the blade carrier and movable blade exerts a consistent downward force B near the middle of the movable blade. Since the operating mechanism is connected to the blade carrier and controls the position of the movable blade via the flat spring, the flat spring acts as the pivot point for the movable blade. After applying forces A and B to the movable blade, the resultant force C is exerted by the line terminal upwards on the pivot end of the movable blade. At all times, even as the movable blade opens, an upwards force will be exerted against the pivot point of the movable blade because of the springs trying to force apart the movable blade and the blade carrier. This upwards force wears down both the load terminal and the pivot end of the blade as shown by the phantom lines in Figure 3. The wearing of the terminal and the blade increases the resistance and the power loss of the circuit breaker. The power loss of a circuit breaker is particularly important when the circuit breaker is mounted in a panelboard or other enclosure having specific heat rise limitations.
US-A-2,600,233 discloses a circuit breaker having a movable contact bar 22 with a slot 20 that receives a pivot pin 16, and a projection 38 located below the slot 20 for engagement and bias by a leaf spring 34. The movable contact bar 22 further includes a contact 24 for engagement with a fixed contact 26.
GB-A-2,033,663, EP-A-0,145,990 and GB-A-2,166,906 disclose various circuit breakers having first and second movable contact arms wherein the movable contact arms are both associated with spring biasing means.
It is an object of this invention to provide a circuit breaker with a movable blade pivot assembly having a low friction coefficient.
It is a further object of this invention to provide a movable blade pivot assembly that has a parallel current path.
A circuit breaker comprising: a first contact mounted on a movable first blade, the first movable blade having a curved surface cooperating with a stationary flat load contact terminal surface to form a floating pivot adjacent one end; a second contact mounted on a second blade; an operating mechanism connected to the first movable blade, said operating mechanism moving said first movable blade between an open position and a closed position, wherein in said open position said first contact and said second contact are separated, wherein in said closed position said first contact and said second contact are engaged; characterized in that said second blade is movable and a resilient member acts on the second movable blade to move said second contact towards said first contact said resilient member providing the sole contact pressure when the circuit breaker is in the closed condition and resulting in said floating pivot experiencing substantially zero loading when said circuit breaker is in an open condition.
The foregoing and other objects, features and advantages of this invention will be apparent from the following more particular description of a preferred embodiment thereof, as illustrated in the accompanying drawings and in the claims.

Brief Description of the Drawings

Figure 1 is a side view of a portion of the contact assembly and mechanism of a circuit breaker.
Figure 2 is a side view of a portion of the contact assembly and operating mechanism of a prior art circuit breaker.
Figure 3 is a side view of a moving blade pivot assembly of Figure 2.
Figure 4 is a side view of a circuit breaker having a floating pivot blade in the closed position.
Figure 5 is a side view of a circuit breaker having a floating pivot blade in the manually opened position.
Figure 6 is a side view of a circuit breaker having a floating pivot blade in the tripped position.

Description of the Preferred Embodiment

Referring now to the drawings and in particular to Figures 4 and 5, the circuit breaker is indicated generally by the reference character 10. The current path through the circuit breaker is via the load terminal 12, load side flexible connector 14, upper blade 16, moving main contact 18 and moving arcing contact, lower main and arcing contacts 22 and 24, respectively, lower blade 26, line side flex connector 28 and line terminal 30. The contacts are open and closed by moving the upper blade 16 via the operating mechanism, indicated generally as 34.
In the circuit breaker closed position, as shown in Figure 4, the upper link 36 and lower link 38 form a nearly straight line to force the upper blade 16 and the upper blade carrier 40 down. The moving main contacts 18 and moving arcing contact then engage the lower main contacts 22 and lower arcing contact 24, depressing the contact springs 44 to provide the necessary contact force.
The contact spring 44 is the only component that creates contact force. In the circuit breaker closed position. the lower main and arcing contacts, 22 and 24, respectively, exert an upwards force on the right side of the upper blade 16 via the moving main and arcing contacts, as shown in Figure 4. The lower link 38 exerts a downwards force near the center of the upper blade 16 via the upper blade carrier 40. The upper blade carrier 40 is solidly connected to the upper blade 16.
The upper blade 16 is approximately rectangular in shape and has moving main contacts 18 and a moving arcing contact mounted at one end and a rounded pivot end 46 at the other end. The pivot end 46 rests on a surface 48 of the load terminal 12. The pivot end 46 of the upper blade 16 is free floating and does not rotate about a fixed point.
When the circuit breaker is in the closed position, as shown in Figure 4, the downwards force exerted by the lower link 38 and the upwards force exerted by the lower main and arcing contacts create a resultant downwards force exerted by the pivot end 46 on the surface 48. Since the lower link force is applied in approximately the middle of the upper blade 16, the upwards force at the contacts end of the upper blade 16 is approximately equal to the downwards force exerted by the pivot end 46.
When the circuit breaker is either manually opened or tripped, as shown in Figures 5 and 6, respectively, the operating mechanism 34 causes the upper link 36 and lower link 38 to collapse. The link pivot 50 moves to the left. as shown in Figures 5 and 6, causing the lower link 38 to move the upper blade carrier 40 and upper blade 16 in the upwards direction. The other components of the operating mechanism have different positions in the tripped position than in the manually opened position. It is sufficient for the purposes herein to recognize that in both positions the upper link 36 and lower link 38 collapse, causing the contacts to separate.
In the tripped or open position, the resultant force on the pivot end 46 is greatly reduced, essentially to zero, as soon as the contacts part. In these positions, the upper link 36 and lower link 38 hold the upper blade 16 open so that the only downwards force on the moving blade pivot end 46 is a portion of its own weight and any downward bias from the flex connectors 14. As soon as the moving contacts separates from the lower main contacts 22 and lower arcing contact 24, the contact spring 44 no longer exerts a force on the upper blade 16. There is no downwards force on the upper blade as that which resulted from the flat spring between the upper blade and the upper blade carrier in the prior art. For the greater portion of the opening cycle, there is little force on pivot end 46 of the upper blade 16, greatly reducing the wear on the pivot end.
The load terminal surface 48 and the pivot end 46 provide a current path parallel to that of the line side flexible connector 14. In the design as shown, roughly half of the current flows through each current path, thus reducing the power loss and heat rise. In the circuit breaker shown and described herein, the overall heat loss of the circuit breaker was reduced by approximately ten percent by the use of the two parallel paths.
The pivot end 46 and load terminal surface 48 provide a current path between the load terminal 12 and upper blade 16 via a pressure fit. The pressure connection between these two current carrying members must be as smooth as possible. Any wear on the pivot end 46 or on the load terminal surface 48 will cause that joint to deteriorate, resulting in a higher resistance in that current path. The part dimensions of the load terminal and upper blade are critical when a fixed pivot is used but not with the use of the floating pivot design.
The upper blade 16 is made of copper or another material having a low electrical resistance. Since these materials also often are relatively soft, the pivot end 46 of the upper blade 16 wears very poorly. Thus it is important to reduce the upwards force on the pivot as quickly and as much as possible. By eliminating the prior art spring positioned between the upper blade carrier 40 and the upper blade 16, the downwards force previously applied by the blade spring to the upper blade continuously is eliminated as soon as the contacts part. The wear on the pivot end 46 is reduced considerably. The watts lost through the circuit breaker will stay approximately constant during the life of the circuit breaker. The floating pivot design is a simple and inexpensive solution to a recurring problem.

Claims

A circuit breaker comprising: a first contact (18) mounted on a movable first blade (16), the first movable blade (16) having a curved surface cooperating with a stationary flat load contact terminal surface (48) to form a floating pivot (46) adjacent one end; a second contact (22) mounted on a second blade (26); an operating mechanism (34) connected to the first movable blade (16), said operating mechanism (34) moving said first movable blade (16) between an open position and a closed position, wherein in said open position said first contact (18) and said second contact (22) are separated, wherein in said closed position said first contact (18) and said second contact (22) are engaged; characterized in that said second blade (26) is movable and a resilient member (44) acts on the second movable blade (26) to move said second contact (22) towards said first contact (18) said resilient member (44) providing the sole contact pressure when the circuit breaker (10) is in the closed condition and resulting in said floating pivot (46) experiencing substantially zero loading when said circuit breaker (10) is in an open condition.
A circuit breaker as claimed in claim 1, characterized in that said operating mechanism (34) is pivotally connected to said first movable blade (16) to move said first movable blade (16) without any associated time delay.
A circuit breaker as claimed in claim 1, characterized in that said first movable blade (16) having a curved free floating portion adjacent one end, said second movable blade (26) being mounted about a fixed pivot.
A circuit breaker as claimed in claim 2 or 3, characterized in that said circuit breaker (10) includes a first terminal (12) and a first flexible connector (14), said first movable blade floating pivot (46) being positioned on said first terminal (12), said first flexible connector (14) being connected to said first terminal (12) and to said first movable blade (16).
A circuit breaker as claimed in claim 1, 2, 3 or 4, characterized in that said operating mechanism (34) is non-resiliently connected to said first movable blade (16).
A circuit breaker as claimed in claim 4, characterized in that said first terminal (12) has a flat portion (48) and said first movable blade floating pivot (46) is positioned on said flat portion (48).