Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H73/00—Protective overload circuit-breaking switches in which excess current opens the contacts by automatic release of mechanical energy stored by previous operation of a hand reset mechanism
  • H01H73/02—Details
  • H01H73/04—Contacts
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/12—Contacts characterised by the manner in which co-operating contacts engage
  • H01H1/14—Contacts characterised by the manner in which co-operating contacts engage by abutting
  • H01H1/22—Contacts characterised by the manner in which co-operating contacts engage by abutting with rigid pivoted member carrying the moving contact

Definitions

• Circuit breakers often have a moving contact mounted on a fixed pivotable blade that is controlled by an operating mechanism.
• a pair of links are directly connected to the movable blade to open and close the circuit breaker contacts as shown in Figure 1.
• 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 f orce 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. It is an object of this invention to provide a circuit breaker with a movable blade pivot assembly having a low friction coefficient.
• 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
• 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.
• the operation of the operating mechanism is described in more complete detail in patent application
• the contact springs 44 are the only components that creates contact force.
• 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 ledge 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.
• 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.
• the load terminal ledge 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 ledge 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 ledge 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.

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Applications Claiming Priority (2)

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ID=25447246

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Citations (4)

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• 1987
  • 1987-10-23 CA CA000550113A patent/CA1310046C/en not_active Expired - Lifetime
  • 1987-10-23 EP EP19870907568 patent/EP0296183B1/de not_active Expired - Lifetime
  • 1987-10-23 DE DE19873784065 patent/DE3784065T2/de not_active Expired - Fee Related
  • 1987-10-23 WO PCT/US1987/002830 patent/WO1988003324A1/en active IP Right Grant

Patent Citations (4)

Non-Patent Citations (1)

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