Circuit breaker with adjustable magnetic trip unit

An adjustable magnetic trip unit for a circuit breaker (1) is equipped with a magnet yoke (16), an armature element (18) that works therewith to actuate a trip shaft (14), and an adjusting bar (23) that can be tilted about the axis (15) of the trip shaft (14) for adjusting the distance (L) between the magnet yoke (16) and the armature element (18). This magnetic trip unit can be used in a circuit breaker (1) having a plurality of breaker cassettes (30) arranged adjacent to one another wherein the adjusting bar (23) extends parallel to the axis (15) of the tripping shaft (14) and on which are arranged a plurality of adjusting arms (24) corresponding to the number of breaker cassettes (30).

BACKGROUND OF THE INVENTION
 The invention relates to circuit breakers with a magnetic trip unit, and,
 more particularly, to circuit breakers with an adjustable magnetic trip
 unit.
 Circuit breakers typically provide protection against the very high
 currents produced by short circuits. This type of protection is provided
 in many circuit breakers by a magnetic trip unit, which trips the circuit
 breaker's operating mechanism to open the circuit breaker's main
 current-carrying contacts upon a short circuit condition.
 Modern magnetic trip units include a magnet yoke (anvil) disposed about a
 current carrying strap, an armature (lever) pivotally disposed near the
 anvil, and a spring arranged to bias the armature away from the magnet
 yoke. Upon the occurrence of a short circuit condition, very high currents
 pass through the strap. The increased current causes an increase in the
 magnetic field about the magnet yoke. The magnetic field acts to rapidly
 draw the armature towards the magnet yoke, against the bias of the spring.
 As the armature moves towards the yoke, the end of the armature contacts a
 trip lever, which is mechanically linked to the circuit breaker operating
 mechanism. Movement of the trip lever trips the operating mechanism,
 causing the main current-carrying contacts to open and stop the flow of
 electrical current to a protected circuit.
 It is necessary for such magnetic trip units to be reliable. In addition,
 it is desired that magnetic trip units be adjustable, so that the breaker
 can be adjusted to trip at different levels of overcurrent. It is also
 desired that the magnetic trip units be compact.
 BRIEF SUMMARY OF THE INVENTION
 In an exemplary embodiment of the invention, a circuit breaker with
 adjustable magnetic trip unit includes a magnet yoke disposed proximate to
 an electrically conductive strap, and an armature pivotally disposed
 proximate to the magnet yoke. A trip shaft is configured to interact with
 a latching mechanism of the circuit breaker. The trip shaft has a cam
 extending therefrom, with the cam being arranged proximate to the
 armature. An adjusting bar is arranged to pivot around the trip shaft. The
 adjusting bar includes an adjusting arm extending therefrom. The adjusting
 arm contacts the armature for adjusting the distance between the magnet
 yoke and the armature.

DETAILED DESCRIPTION OF THE INVENTION
 A circuit breaker 1 equipped with the adjustable magnetic trip unit of the
 present invention is shown in FIG. 1. The circuit breaker 1 has a rotary
 contact arm 2, which is mounted on the axis 3 of a rotor 4 such that it
 can rotate. The rotor 4 itself is mounted in a terminal housing or
 cassette (not shown) and has two diametrically opposed satellite axes 5
 and 6, which are also rotated about the axis 3 when the rotor 4 rotates.
 The axis 5 is the point of engagement for a linkage 7, which is connected
 to a latch 8. The latch 8 is mounted, such that it can pivot, on an axis
 10 positioned on the circuit breaker housing 9. In the event of an
 overcurrent or short circuit condition, the latch 8 is released by a
 latching mechanism 11, moving the contact arm 2 to the open position shown
 in FIG. 1.
 The latching mechanism 11 can be actuated by a trip lever 13 that pivots
 about an axis of rotation 12. The other end of the trip lever 13 contacts
 a trip shaft 14, which is mounted on an axis 15 supported by the circuit
 breaker housing 9. Disposed on the trip shaft 14 is a cam 14a, which can
 be pivoted clockwise in opposition to the force of a torsional spring 14b
 wound about the axis 15.
 Mounted to the circuit breaker housing 9 in the bottom region of the
 circuit breaker is a magnet yoke 16, which encircles a current carrying
 strap 17 electrically connected to one of the contacts of the circuit
 breaker 1. Arranged facing the magnet yoke is an armature element 18 in
 the form of a metallic lever, which is hinge-mounted by means of hinge pin
 sections 19 (see FIG. 3) to hinge knuckles (not shown) formed on the
 circuit breaker housing 9. The armature 18 is also connected to strap 17
 by a spring 20, which biases the armature 18 in the clockwise direction,
 away from the magnet yoke 16. In its upper region, armature 18 is equipped
 with a clip 21 rigidly mounted thereon, which can be brought into contact
 with the cam 14a by pivoting of the armature in a counter-clockwise
 direction. Movement of cam 14a by the armature 18 causes the trip shaft 14
 to rotate about axis 15 and thereby actuate the latching mechanism 11 by
 means of the trip lever 13. Once actuated, latching mechanism 11 releases
 latch 8 to initiate the tripping process in circuit breaker 1. While the
 clip 21 is described herein as being mounted to armature 18, the clip 21
 can also be formed as one piece with the armature 18, preferably of metal.
 Referring now to FIG. 2 and FIG. 3, an adjusting bar 23 extends parallel to
 the axis 15 and is mounted on the axis 15, by means of support arms 22.
 The adjusting bar 23 has an adjusting arm 24 which is threadably engaged
 to an adjusting screw 25 for calibrating the trip unit. Adjusting bar 23
 also includes a lever arm 26 which extends to a side of the adjusting bar
 23 diametrically opposite adjusting arm 24. The end of the lever arm 26 is
 in contact with a cam pin 27 of a rotary knob 28, which is mounted in a
 hole in the upper wall of the circuit breaker housing 9 (FIG. 1). The
 surface of the rotary knob 28 is equipped with a slot 29 to make it
 possible to adjust the rotary knob 28 with the aid of a suitable tool,
 such as a screwdriver.
 In the unactuated state of the magnet yoke 16, which is to say when the
 contact arm 2 (FIG. 1) is closed and an overcurrent is not present, the
 adjusting screw 25 is in constant contact with an angled surface of the
 clip 21. Contact between adjusting screw 25 and the angled surface of the
 clip 21 is ensured by a tensile force exerted by the spring 20 on the
 armature 18. The force of the angled surface of the clip 21 on adjusting
 screw 25 biases the adjusting bar 23 in a clockwise direction about axis
 15, thus forcing lever arm 26 away from yoke 16 and against pin 27. In
 this state, it is possible to change the tilt setting of the armature 18
 either by extending (or retracting) adjusting screw 25 downward from
 (upward to) adjusting arm 24, or by rotating the adjusting bar 23 about
 axis 15 by adjusting the rotary knob 28. Thus, the distance L shown in
 FIG. 2 between the flap 18 and the magnet yoke 16 is adjusted, thereby
 setting the current at which the trip unit responds.
 One advantage of the present invention is that an extremely reliable
 adjustment mechanism is guaranteed by the interaction of the adjusting bar
 23, which rotates around the axis 15 of the trip shaft 14, and the rotary
 knob 28 that interacts therewith via cam pin 27. Moreover, this mechanism
 is easy to produce and is compact in design. The tripping device of the
 present invention has only a few elements, which can be accommodated, in a
 space-saving manner, laterally in the switch.
 The circuit breaker with adjustable magnetic trip unit shown in FIGS. 1, 2,
 and 3 operates as follows. First, a person adjusting the circuit breaker I
 by turning rotary knob 28 sets the position of the adjusting bar 23 on the
 axis 15 and thus the distance between the armature 18 and the magnet yoke
 16, as shown in detail in FIG. 2. Because of the relatively greater length
 of the lever arm 26 as compared to the adjustable arm 24, the adjustment
 made by rotary knob 28 is fine. It must be noted here that a coarser
 adjustment of the distance L between the magnet yoke 16 and the flap 18
 can be accomplished by turning the adjusting screw 25 during installation
 of the trip unit in the circuit breaker housing 9.
 In the case of a short circuit, an overcurrent naturally occurs, which
 flows through the current carrying strap 17. This activates the magnet
 yoke 16 to the extent that when a specific current is exceeded, the
 magnetic force generated by the magnet yoke is sufficient to attract the
 armature 18 in opposition to the tensile force exerted by the spring 20.
 Armature 18 pivots towards yoke 16, and the cam 14a is pivoted clockwise
 in FIG. 1 (counter-clockwise in FIG. 2) by the clip 21 until the trip
 lever 13 is actuated. Actuation of the trip lever 13 then tilts the
 latching mechanism 11 such that it in turn can release the latch 8 for a
 pivoting motion, upward in FIG. 1, about the axis 10. This motion is
 caused by a spring, which is not shown in detail in FIG. 1. The motion of
 the linkage 7 that is coupled with the pivoting motion of the latch 8
 brings about a rotation of the rotor 4 by means of the axis 5, and thus
 finally a disconnection of the contact arm 2 from the current carrying
 straps.
 As shown in FIG. 3, the trip unit can be arranged for use in a circuit
 breaker 1 having a plurality of breaker cassettes 30, with each cassette
 10 having its own contact arm 2 and rotor 4 arrangements. While only one
 cassette 30 is shown, it will be understood that one cassette 30 is used
 for each phase in the electrical distribution circuit. Adjusting bar 23
 extends along the row of circuit breaker cassettes 30, parallel to the
 axis 15 of the trip shaft 14. Extending from adjusting bar 23 are several
 adjusting arms 24 corresponding to the number of circuit breaker cassettes
 30. Also formed on the adjusting bar 23 is one lever arm 26, which is
 sufficient to rotate the adjusting bar 23 about axis 15 and, thus, pivot
 the armatures 18. The tripping sensitivity in each circuit breaker
 cassette 30 can be adjusted separately by means of the screws 25 carried
 by each adjusting arm 24. As a result, individual calibration of each
 circuit breaker cassette 30 can be undertaken independently of the
 adjustment of rotary knob 28.
 It will be understood that a person skilled in the art may make
 modifications to the preferred embodiment shown herein within the scope
 and intent of the claims. While the present invention has been described
 as carried out in a specific embodiment thereof, it is not intended to be
 limited thereby but is intended to cover the invention broadly within the
 scope and spirit of the claims.