Patent Application
20090256659
The disclosed embodiments relate to contacts that conduct current, and in particular, contacts that experience repulsion forces when mating as a result of the amount of current conducted by the contacts.
Circuit breakers are generally used to protect equipment from overcurrent situations caused, for example, by short circuits or ground faults. When an overcurrent condition occurs, electrical contacts within the circuit breaker are designed to open, interrupting current flow through the circuit breaker to the equipment. Circuit breakers may be designed for high quiescent currents and high withstand currents. To maintain a high withstand current rating, the contacts must be locked closed at the current withstand rating and be able to withstand the large electrodynamic repulsion forces generated by the current flow.
Circuit breakers have a variety of designs including blow open and non-blow open contact arms, overcentering and non-overcentering contact arms, single contact pair arrangements with the contact pair at one end of a contact arm and a pivot at the other end, double contact pair arrangements, also referred to as rotary breakers, with a contact pair at each end of a contact arm and a contact arm pivot intermediate the two ends, single housing constructions with the circuit breaker components housed within a single case and cover, and cassette type constructions, also referred to as cassette breakers, with the current carrying components of each phase housed within a phase cassette and each phase cassette in turn housed within a case and cover that may also include an operating mechanism. Multipole circuit breakers are generally available in two, three, and four pole arrangements, with the two and three pole arrangements being used in two and three phase circuits, respectively. Four pole arrangements are typically employed on three phase circuits having switching neutrals, where the fourth pole operates to open and close the neutral circuit in a coordinated arrangement with the opening and closing of the primary circuit phases.
When current carrying contacts of a circuit breaker are closing on a fault, the current through the contacts is very high resulting in significant electromagnetic repulsion forces between the contacts. These electromagnetic repulsion forces impede breaker closing.
The fixed and movable contact assemblies 105, 110 are generally constructed to withstand closing on a fault. When closing on a fault, as the first and second arcing contacts 120, 130 contact each other, the currents flowing through the first and second arcing contacts 120, 130 are close to each other and cause an electromagnetic repulsion force represented by vector 140 due to a constriction effect. The electromagnetic repulsion force acts opposite the applied closing force and applies a torque in a direction opposite the closing rotation of the movable contact assembly 110. The electromagnetic repulsion forces are directly proportional to the magnitude of the current and indirectly proportional to the distance between the contacts when the current flow follows a path of a loop between the contacts.
Thus, the repulsion force 140 is essentially perpendicular to a moment arm 145 representing a distance from the rotation point 115 to the center of the force vector 140. In this embodiment, the moment arm has a significant magnitude resulting in a significant additional closing force required to close the fixed and movable contact assemblies 105, 110.
It would be advantageous to provide a circuit breaker with reduced or redirected repulsion forces.
The following are non limiting exemplary embodiments.
In one embodiment, an apparatus includes a plurality of contacts for interrupting current flow when an overcurrent condition occurs, each contact including a mating face displaced at an angle with respect to a pivot point of at least one of the contacts, where the displacement of the mating faces is configured to minimize a repulsion force moment arm from the pivot point of at least one of the contacts.
In another embodiment, a method includes displacing mating faces of a plurality of contacts at an angle with respect to a pivot point of at least one of the contacts, and configuring the displacement to minimize a moment arm from the pivot point of at least one of the contacts to reduce electromagnet repulsion forces between the contacts when an overcurrent condition occurs.
The foregoing aspects and other features of the presently disclosed embodiments are explained in the following description, taken in connection with the accompanying drawings, wherein:
The disclosed embodiments may include a plurality of contacts with characteristics that operate to minimize electromagnetic repulsion forces between the contacts.
Circuit breaker 200 may include a fixed contact assembly 205 and a movable contact assembly 210 that pivots about a rotation point 215. The movable contact assembly 210 may generally include one or more first arcing contacts 220 and one or more first main contacts 225. The fixed contact assembly 205 may include one or more second arcing contacts 230 and one or more second main contacts 235. The fixed and movable contact assemblies 205, 210 may be constructed to withstand closing on fault. Upon closing, the first and second arcing contacts 220, 230 may be configured to contact each other before the first and second main contacts 225, 235.
While the disclosed embodiments are described in terms of arcing contacts and main contacts in a circuit breaker, it should be understood that the disclosed embodiments may be utilized with any contacts that are subject to repulsion forces during closing.
In this embodiment, the first arcing contact 220 may have a first mating face 305 and the second arcing contact 230 may have a second mating face 310. The first and second mating faces 305, 310 may be disposed at an angle that reduces or minimizes a moment arm 315 from rotation point 215. Due to the angular orientation of the first and second mating faces 305, 310 the currents flowing through the first and second arcing contacts 220, 230 may generally travel further away from each other, or may travel an extended distance through the first and second arcing contacts 220, 230. The electromagnetic repulsion forces may be reduced by introducing a larger loop into the current path as the forces are indirectly proportional to the distance between the contacts when the current flow is in a loop formation.
This may operate to reduce or minimize an electromagnetic repulsion force 320 resulting from the current flowing through the first and second arcing contacts 220, 230.
The angular orientation of the first and second mating faces 305, 310 may also operate to change the direction of the electromagnetic repulsion force 320 applied to the first and second arcing contacts 220, 230. As shown in
It should be understood that the foregoing description is only illustrative of the present embodiments. Various alternatives and modifications can be devised by those skilled in the art without departing from the embodiments disclosed herein. Accordingly, the embodiments are intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.
