Magnetic Trip Adjustment Based on Spring Load Variation

A co-pending patent application, Ser. No. 60,692, filed July 25, 1980, entitled "Apparatus For Variably Adjusting A Magnetic Level With A Translating Spring Force", by Mabel Esteves assigned to the common assignee of this application, and filed concurrently herewith, concerns related subject matter.

This invention relates to varying of magnetic tripping current in a circuit breaker by varying the spring load on the armatures, and, in particular, by varying such spring load simultaneously by means of rotation of a common crossbar. Accordingly, it is a general object of this invention to provide new and improved devices of such character.

This invention utilizes the mechanical variation of springs to adjust the mechanical tripping current level of a multi-pole circuit breaker, it being noted that virtually all magnetic trip devices include a spring loading system.

This invention recognizes that a force on a spring, especially a torsional spring, can be largely varied while maintaining the compactness of its physical appearance.

Generally, in the past, the magnetic trip level of circuit breakers were not variable or adjustable. Thus, since circuit breakers were produced to "standard" conditions, separate selected circuit breakers were required for selected magnetic levels.

Specifically, it is believed that at least one manufacturer offers for sale circuit breakers having adjustable magnetic trip levels by virtue of adjustable gaps. Some such device uses a comparatively large variable gap of 600 to 800 mils.

An object of this invention is to provide for new and improved combinations utilizing a spring, especially a torsional spring, for applying a variable force for restraining an armature from attraction by a magnet.

Another object of this invention is to provide for new and improved circuit breakers in which the magnetic trip level can be adjusted and varied.

Still another object of this invention is to provide for new and improved multi-pole circuit breakers in which the magnetic trip level currents for all poles can be simultaneously varied and adjusted.

Yet another object of this invention is to provide for new and improved circuit breakers, having adjustable magnetic trip levels, with smaller gaps--in the order of 100 mils--than corresponding circuit breakers of the prior art.

In accordance with one embodiment of this invention, a combination includes an armature adapted to be attracted by a magnet, a spring which restrains the armature from attraction by the magnet, and means for varying a force on the spring. In accordance with another embodiment, three armatures are each adapted to be attracted to respective ones of three magnets. Three springs are each adapted to restrain a respective one of the armatures from attraction by its respective magnet. The forces on the three springs are simultaneously varied. In accordance with yet another embodiment, a magnet is in close proximity to an electrical conductor so that when excessive current flows therein, a magnetic field is generated in the magnet. A spring restrains an armature from attraction by the magnet when the magnetic field is generated therein. A force on the spring is varied so as to vary a magnetic level. The combination can include a circuit breaker mechanism which is adapted to be activated by particular movement of a trip bar. Movement of the armature toward the magnet causes particular movement of the trip bar, thereby activating the circuit breaker mechanism.

In accordance with yet another embodiment of the invention, a three pole circuit breaker includes, in combination, three electrical conductors, three magnets, three armatures, and three springs. Each spring is adapted to restrain a respective one of the armatures from attraction by its respective magnet when a magnetic field is generated therein due to excessive current flowing through a respective conductor in close proximity to the respective magnet. The forces on the three springs are simultaneously varied so as to vary a magnetic level of the circuit breaker. In accordance with certain features of the invention, a circuit breaker combination is adapted to be actuated by a particular movement of any one of three trip bars. Each trip bar is so associated with a respective one of the armatures that movement of the respective armature toward the respective magnet causes particular movement of the associated trip bar, thereby actuating the circuit breaker mechanism. In accordance with other features of the invention, the three pole circuit breaker further includes a housing. The means for simultaneously varying forces on the springs includes a common rotatable crossbar coupled to the three springs. A cam is affixed to a button within the housing, the button being rotatable from without the housing. Link means, responsive to movement of the cam, causes rotatable movement of the crossbar.

In accordance with various embodiments of the invention, the springs referred to, in the combinations just described, are torsional springs.

Other objects, advantages, and features of the invention will become more apparent from the following description, when read in conjunction with the accompanying drawing, in which:

FIG. 1 is a schematic perspective, partly broken away, illustrating one embodiment of the invention, including a rotating link; and

FIG. 2 is a partial sectional view illustrating how the link in FIG. 1 can be rotated.

Referring to the drawings, there is depicted various principal elements of my invention in a schematic manner. A three pole circuit breaker 11 includes a casing or housing 12 having individual electrical conductors 13a, 13b, 13c therewithin. The three electrical conductors 13a, 13b, 13c are generally associated with three phases of an electrical system, but they can be otherwise independent of each other. Each electrical conductor has its respective magnet 14 associated therewith. (Though the magnet can be termed a "pole piece", for convenience and consistent usage, the term "magnet" will be used throughout the specification.)

A respective armature 16a, 16b, 16c is associated with each magnet 14a, 14b, 14c, each being pivotable about a respective pivot 17a, 17b, 17c. A stop 18 is associated with each armature 17 to limit the maximum amount of gap between the armature and magnet.

An adjustment button 19, having a knurled surface 21, is mounted within the cover 22 of the housing 12. The button, thus, is rotatable within the housing, but is rotatable from without the housing.

Rotation of the button 19 causes appropriate rotation of a cam 23 which rotates within an elongated slot 24 of a rotating link 26 which is affixed to a rotatable crossbar 27.

The crossbar 27 is secured to the case or housing 12 of the circuit breaker by means of axial supports center mounted to prevent non-axial loadings. The crossbar 27, as stated, is coupled to the link 26 which is coupled to the rotating button at the cover 22 of the circuit breaker.

A torsional spring 28a, 28b, 28c is affixed to the crossbar 27 and is coupled to its respective armature 16a, 16b, 16c.

The rotation of the button 19 creates a lateral type motion on the link 26 that provides the necessary rotation to the crossbar 26. This process is transferred into loading of the torsional spring 28, thus varying the current levels required by the magnet 14 to pull the spring loaded armature 16.

With regard to each pole of the circuit breaker, a circuit breaker mechanism 29a, 29b, 29c is adapted to be actuated by a particular movement of a trip bar 31a, 31b, 31c. The trip arm 31a is so associated with the armature 16a that movement of the armature 16a toward the magnet 14a causes particular movement of the trip bar 31a, thereby actuating the circuit breaker mechanism 29a.

Use of the torsional springs 28 is highly advantageous since space requirements for such springs are minimal.

Through common adjustment of the button 19, the forces on the three torsional springs 28a, 28b, 28c are simultaneously varied. Thus, the magnetic level for the circuit breaker can be conveniently varied.