Patent Publication Number: US-4926018-A

Title: Moving mains arc movement loop

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a main contact blade assembly for a switching device, and more particularly, to a contact blade assembly for a circuit breaker wherein the configuration of the contact blade affects the arc produced between the contacts of a circuit breaker. 
     When the current carrying contacts of a circuit interrupting device are separated while a current is flowing through the contacts, an arc can be formed between the contacts. Depending on the intensity and duration of the arc, the contact material and materials surrounding the arc experience varying degrees of deterioration. For example, the contact surfaces can be eroded such that the resistance of the contact interface increases causing increased heating and further deterioration of the contacts. In dealing with this problem, it is desirable to either extinguish the arc in the shortest period of time possible and/or move the arc from between the contacts to a location where the damage done by the arc does not severely affect the operation of the circuit interrupting device. 
     Accordingly, it is important to provide means for extinguishing and/or moving an arc to a location where damage done by the arc is not critical. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a means for moving an arc from between the primary contacts of a circuit interrupting device to either the secondary contacts and/or means for disbursing the arc, such as an arc horn. 
     Accordingly, there is provided a movable contact blade comprising a contact means, and means for providing a magnetic field adjacent to the contact means, wherein the magnetic field is adapted to force an electric arc away from the contact means. 
     An advantage of the present invention is that the means for moving the arc is an integral part of the contact carrying member. Another advantage of the present invention is that the means for moving the arc is in close proximity to the primary contacts. 
     Various other objects and advantages of the present invention will become apparent from the following description, with reference to the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the current carrying contact blade assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, FIG. 1 illustrates a current path for a circuit breaker such as a molded case circuit breaker. For opening and closing the primary contacts 10, 12 there is provided a pivoting connection 14 and a movable contact blade 24 which provides a current path between the terminal 15 and the terminal 16. To interrupt the current carried by the circuit breaker, the contact 10 on the contact blade 24, and the fixed contact 12 are pulled apart. Under certain conditions, separating the contacts 10, 12 causes an arc to form between these contacts 10, 12. 
     As discussed above, it is important to move the arc from the primary contacts 10, 12 to an arc dispersing means such as a pair of secondary contacts 18, 20 and/or an arc horn 22. Moving the arc can be facilitated by producing a magnetic field which acts on the arc. An effective way to produce a magnetic field which will apply a force to the arc is to provide an electric current near the arc wherein the path of the current is substantially parallel to the axis of the arc, but the flow of current is in the direction opposite to the flow of current in the arc. In this situation, the force of the magnetic field produced by the current will force the arc away from the current path. 
     In the preferred embodiment of the contact blade 24, the blade 24 is configured such that a generally U-shaped current loop 26 is present in the blade 24 near the primary contacts 10, 12. As illustrated in the FIG. 1, the configuration of the blade 24 includes a notch 27 at the bottom of the blade 24 located adjacent to the contact 10 and a depressed region 30 at the top of the blade 24. The size of the depressed region 30 can be varied in size depending on the strength requirements of the blade 24 and the extent to which the legs 28, 29 of the U-shape current loop 26 are required to be parallel. For example, the depressed region 30 could be made so that the top contour of the blade 24 follows the dashed line 32 or the dashed line 33. 
     Referring to FIG. 1, when the depressed region 30 follows the dashed line 32, the main component of the load current in the right-most leg 28 of the current loop 26 substantially follows a line 34 parallel to the axis of the arc 36. When the depressed region 30 follows the contour of the solid line defining the top of the blade 24, the load current in the right-most leg 28 has a smaller component along the line 34. With either configuration, the load current is utilized by a means provided for producing a magnetic field which forces an arc from between the primary contacts 10, 12 toward the secondary contacts 18, 20 on the arc horn 22. 
     While one embodiment of a current carrying contact blade and several modifications thereof have been shown and described in detail herein, various other changes and modifications may be made without departing from the scope of the present invention. For example, the contact configuration can be varied depending on mechanical and/or electrical considerations.