Patent Application
20090115556
1. Field of the Invention
The present invention relates generally to electromagnetic actuators and more specifically to actuators such as trip mechanisms found in circuit breakers, accessories of circuit breakers, relays, or actuators.
2. Discussion of the Related Art
Referring to
The magnetic torque on the armature 14 is adjusted by turning a screw 20 to set the magnetic air gap (g). The smaller the magnetic air gap (g) the higher the magnetic torque. However, as the armature 14 moves closer to the yoke 13, the force of the return spring 22, attached to the bell crank 24 for resetting the armature 14, also increases, thus counteracting the effect of the magnetic torque. The net result is a reduced sensitivity of the system to gap adjustment and a lower net torque on the armature 14. This may not be desirable in applications where the input current is low.
In one embodiment of the present invention a divided adjustable armature for the trip mechanism of a circuit breaker allows for two independent adjustments: first, of the magnetic air gap (g) between the yoke and the armature and second, of the clearance (c) between the trip bar and the back plate of the armature, thus allowing the mechanical spring force of the trip mechanism to be unchanged while adjusting the magnetic gap to set the trip current point. The performance of electromagnetic actuators can thus be enhanced by increasing their response to magnetic air gap adjustment. This allows a circuit breaker trip mechanism to use a reduced level of trip current or achieve a wide range of armature torque, or both. Thus, the present invention is especially useful for low trip current breakers.
In a typically known magnetic tripping system, such as discussed above, the reduction in armature to yoke gap (g) is accompanied by an increase in the force of the mechanical spring 22 applied to the armature 14, here through bell crank 24, thus reducing the net torque applied to the armature 14 and resulting in a flat response. The present invention can increase the sensitivity of electromagnetic actuators to electric current and eliminate the flat spot found in the curve of trip current versus magnetic air gap for known tripping systems.
Also in the known system, the clearance (c) between the armature 14 and the trip bar 16 changes, making the system response non-linear and calibration difficult. The present invention eliminates this interdependence by allowing adjustment of the magnetic air gap (g) without altering the clearance (c) or the tension of the armature return spring 22.
In one embodiment of the present invention a circuit breaker has a trip assembly with an armature electromagnetically attractable to a yoke, whereby the armature can be driven towards the yoke to release a trip bar. The trip assembly also has a return spring operably interacting with the armature for resetting the trip assembly. The armature of the trip assembly is divided, with a ferromagnetic front plate having a surface facing towards the yoke and a back plate adjustably settable in a fixed position relative to the front plate whereby the back plate can impinge on the trip bar to initiate the opening of a circuit. A first adjustment linkage is included for adjustably setting a magnetic air gap between the yoke and the front plate without material effect on the operating tension of the return spring. A second adjustment linkage for adjustably setting a relative position between the back plate and the trip bar is further included.
In some embodiments of the invention the front plate and the back plate of the divided armature are kept rigidly attached together by means of a first screw and an anti-backlash set screw. The back plate to trip bar clearance can be adjusted with a second screw independently of the magnetic air gap. Thereby adjustment of the magnetic air gap via the first screw does not affect the armature return spring tension and adjustment of the magnetic air gap does not affect the clearance between the back-plate and the trip bar. Thus the present invention can provide higher sensitivity of the net armature torque to magnetic air gap adjustment, higher response of trip current to magnetic air gap adjustment, a higher range of tripping current adjustment, a very low end tripping current and a very linear response of tripping current to the magnetic air gap adjustment.
In still other embodiments a circuit breaker according to the present invention may have a trip assembly with an armature electromagnetically attractable to a yoke, whereby the armature can be driven towards the yoke to release a trip bar, and with a return spring for resetting the trip assembly. The trip assembly can comprise a divided armature on a mounting plate included within the trip assembly, the divided sections being a ferromagnetic front plate having a surface facing towards the yoke and a back plate attached to the front plate opposite the surface facing toward the yoke, for impinging on a trip bar to initiate the opening of a circuit. A first adjustment screw can be included between the front plate and the back plate for adjustably setting a magnetic air gap between the yoke and the front plate; and a second adjustment screw can be included between the back plate and the mounting plate for adjustably setting a clearance between the back plate and the trip bar.
Thus, an adjustment of the first screw will not materially affect the operating tension of the return spring. In some embodiments this circuit breaker may include an antibacklash set screw between the two armature pieces for fixing the distance therebetween. In some embodiments this circuit breaker may be arranged whereby the front plate threadably receives the first adjustment screw which is contained within the back plate for setting the clearance between the back plate and the front plate. In some embodiments this circuit breaker may be arranged whereby the second adjustment screw is threaded through the mounting plate and impinges on the back plate for setting the clearance between back plate and a trip bar.
As seen in
Electric current flowing in a conductor (not shown) inside the yoke 39 creates a magnetic field that results in the ferromagnetic front plate 35 of the armature 31 being attracted towards the yoke 39. The armature 31 carries the back plate 41 that eventually hits the trip bar 43. Back plate 41 can be made of a nonmagnetic material. When the trip bar 43 has rotated sufficiently, the hammer 53 is released to strike a breaker delatching mechanism (not shown) as will be understood by those in the art. The return spring 49 returns the trip unit to its initial position through the bell crank 51 in contact with the back plate 41. By adjusting the magnetic air gap (g), the armature torque and therefore the tripping current setting can be controlled.
This adjustment is carried out by first loosening an antibacklash set screw 55 and then turning the first screw 45 in or out to vary the magnetic air gap (g). This change in magnetic air gap does not affect the trip bar clearance (c) or the tension of the return spring 49. Consequently, the change in the magnetic torque is not offset by a change in the spring force. The result is a better system response and greater range of tripping current settings. The set screw 55 is then retightened to eliminate any backlash between the front plate 35 and the back plate 41.
Prior to performing the magnetic air gap adjustment, the trip bar clearance (c) is set by adjusting the second screw 47 anchored in the mounting plate 33 and extending towards the back plate 41. An armature pivot 34 serves as a fixed base for the armature sub-assembly. The front plate 35, the back plate 41 and the bell crank 51 are all hinged on the mounting plate 33. The second screw 47 is threaded through the mounting plate 33. The trip assembly housing 57 is typically the structure to which all the other parts are anchored.
It will be appreciated that within the practice of the present invention many variations may occur, such as the set screw 55 can be replaced by another means to eliminate backlash between the front plate 35 and the backplate 41. Further alternatives may include spring elements which can be used to perform the function of the backplate 41 and the set screw 55 and also keep the divided plates of the armature pre-loaded as further discussed below. In some embodiments the front plate and the back plate of the armature may be formed from a single piece flexure, as further discussed below. It will also be appreciated that the same principle of a divided armature can be applied to a system where the armature return spring acts directly on the backplate with the bell crank removed as seen in
Referring to
Referring to
In
This divided armature system can be applied to any device that is based on an electromagnetic actuation principle. This includes, but is not limited to, tripping systems and accessories of circuit breakers, relays, actuators. Having thus described a divided armature for an electromechanical actuator; it will be appreciated that many variations thereon will occur to the artisan upon an understanding of the present invention, which is therefore to be limited only by the appended claims.
