AND TRANSLATIONAL MAGNETIC SYSTEMS

BACKGROUND

This invention relates generally to circuit breakers, and more particularly to circuit breaker heaters and translational magnetic systems.

Circuit breakers typically include one or more electrical contacts, and provide protection against persistent over-current conditions and short circuit conditions. In many circuit breakers, a thermal-magnetic trip unit includes a heater and magnetic system. Existing thermal-magnetic trip units typically include a first planar portion, and a second U-shaped portion disposed around an electromagnetic coil. A bi-metal element may be coupled to the first portion of the heater using a shunt to allow heat transfer from the heater to the bi-metal element, and to locate the bi-metal element in a desired position.

However, the shunt requires numerous additional components and thus increases the cost and complexity of the circuit breaker. SUMMARY

In a first aspect, a thermal-magnetic trip unit is provided for a circuit breaker. The thermal-magnetic trip unit includes a heater and a translational magnetic system coupled to the heater. The heater includes a first portion, a second portion, and a third disposed between the first portion and the second portion. The first portion has a first surface disposed in a first plane, and the second portion has a second surface disposed in a second plane that is substantially parallel to the first plane. The first surface is separated by a first

predetermined distance from the second surface. The third portion has a third surface disposed in a third plane that is substantially perpendicular to the first plane. The third surface has a first predetermined length and is separated by a second predetermined distance from the second surface.

In a second aspect, a circuit breaker is provided that includes a heater and a translational magnetic system coupled to the heater. The heater includes a first portion, a second portion, and a third disposed between the first portion and the second portion. The first portion has a first surface disposed in a first plane, and the second portion has a second surface disposed in a second plane that is substantially parallel to the first plane. The first surface is separated by a first

predetermined distance from the second surface. The third portion has a third surface disposed in a third plane that is substantially perpendicular to the first plane. The third surface has a first predetermined length and is separated by a second predetermined distance from the second surface. In a third aspect, a thermal-magnetic trip unit is provided for a circuit breaker. The thermal-magnetic trip unit includes a heater and a translational magnetic system coupled to the heater. The heater includes a first portion, a second portion, and a third disposed between the first portion and the second portion. The first portion has a first surface disposed in a first plane, and the second portion has a second surface disposed in a second plane that is substantially parallel to the first plane. The third portion includes a third surface

disposed in a third plane that is substantially

perpendicular to the first plane. The fourth portion is coupled to the second portion and the third portion at a top surface of the second portion. Numerous other aspects are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present invention can be more clearly understood from the following detailed description considered in conjunction with the following drawings, in which the same reference numerals denote the same elements throughout, and in which:

FIGS. 1A-1C are top, front and right-side views of an example thermal-magnetic trip unit in accordance with this invention;

FIGS. 2A-2C are top, front and right-side views of an example ramp-shaped heater for use in thermal-magnetic trip units in accordance with this invention;

FIGS. 3A-3C are top, front and right-side views of an example translational magnetic system for use in thermal-magnetic trip units in accordance with this invention ; FIG. 4A is a more detailed view of the example thermal-magnetic trip unit of FIG. IB;

FIG. 4B is a view of the example thermal-magnetic trip unit of FIG. 4A in an over-current operating

condition;

FIG. 4C is a view of the example thermal-magnetic trip unit of FIG. 4A in a short-circuit operating

condition; and

FIG. 5 is a view of an alternative example thermal- magnetic trip unit in accordance with this invention

DETAILED DESCRIPTION Existing thermal-magnetic trip units often include a current-carrying heater that has a first portion coupled to a bi-metal element, and a second portion coupled in series with a magnetic system. To open the electrical contacts within specified time limits in response to an over-current condition, the contact area between the bi ^¬ metal element and the heater must be sufficiently large. In some existing thermal-magnetic trip units, a bi-metal element is coupled to a planar heater via a shunt. The shunt increases the contact area between the bi-metal element and the heater, but requires numerous additional components and thus increases the cost and complexity of the circuit breaker.

Some existing thermal-magnetic trip units avoid the need for a shunt by using a ramp-shaped heater in which the bi-metal element is coupled to a vertically-oriented portion of the heater. However, such systems typically use a conventional magnetic system in which the second portion of the heater wraps around an electromagnet coil. Such conventional magnetic systems, however, are usually harder to calibrate at high amperage ratings. Also conventional magnetic systems are bulky and require longer heaters to wrap around an electromagnet coil. In view of the foregoing difficulties and desired assembly

attributes, improved thermal-magnetic trip units are provided that include a ramp-shaped heater and a

translational magnetic system.

Referring to FIGS. 1A-1C, an example thermal- magnetic trip unit 10 in accordance with this invention is described. Thermal-magnetic trip unit 10 includes a heater 100 coupled to a translational magnetic system 200 and a bi-metal element 300. Heater 100 includes a first portion 100a, a second portion 100b and a third

portion 100c disposed between first portion 100a and second portion 100b. First portion 100a may be connected to one or more electrical conductors (not shown) , and second portion 100b may be connected to one or more load conductors (not shown) . Bi-metal element 300 has a first end 310 coupled to third portion 100c of heater 100, and has a second end 320 having a contact surface 330.

Translational magnetic system 200 is coupled to heater 100 between second portion 100b and third portion 100c.

Referring now to FIGS. 2A-2C, example heater 100 is described in more detail. As shown in FIG. 2B, first portion 100a has a first surface lOOal disposed in a first plane PI, and second portion 100b has a second

surface lOObl disposed in a second plane P2 that is substantially parallel to first plane PI. First

surface lOOal is separated by a first predetermined distance Dl from second surface lOObl.

Third portion 100c is disposed between first portion 100a and second portion 100b, and has a third surface lOOcl disposed in a third plane P3 that is substantially perpendicular to first plane PI. In this regard, heater 100 has a ramp-shape. Third surface lOOcl has a first predetermined length LI and extends between upper end lOOe and lower end lOOf of third portion 100c. Third surface lOOcl is separated by a second predetermined distance D2 from a left end lOOg of second surface lOObl (and second portion 100b) .

Heater 100 includes a curved portion lOOd coupled between second portion 100b and third portion 100c. In particular, curved portion lOOd extends between left end lOOg of second portion 100b (at a plane parallel to second plane P2) and upper end lOOe of third portion 100c (at a plane parallel to third plane P3) .

First predetermined distance Dl and second predetermined distance D2 may be constrained as a result of physical space limitations within the circuit breaker, and/or locations of other components that are coupled to first portion 100a and second portion 100b. First

predetermined distance Dl may be between about 12 mm to about 15 mm, although other dimensions may be used.

Second predetermined distance D2 may be between

about 14 mm to about 17 mm, although other dimensions may be used.

First predetermined length LI may be constrained by the minimum required contact area between third

portion 100c and bi-metal element 300, and the dimensions of bi-metal element 300. For example, if the minimum required contact area is Al, and bi-metal element has a width of Wl, first predetermined length must be at

least Al/Wl. First predetermined length LI may be between about 15 mm to about 25 mm, although other dimensions may be used. As shown in FIG. 2B, heater 100 may have a uniform thickness Tl substantially along its entire length.

Thickness Tl may be between about 2 mm to about 5 mm, although other dimensions may be used. Persons of

ordinary skill in the art will understand that heater 100 alternatively may have a thickness that varies along its length. Heater 100 may be manufactured from copper, copper alloys, or other similar material. Heater 100 may be fabricated using a machine press or other similar method.

Referring now to FIGS. 3A-3B, example translational magnetic system 200 is described in more detail.

Translational magnetic system 200 includes armature 210, an armature locator 220, a yoke 230, an armature guide pin 240, a spring 250, and a calibration nut 260.

Armature 210 is coupled to armature locator 220, which includes a recess 222 and a cylindrical bore 224.

Armature guide pin 240 extends through cylindrical

bore 224 and a comparable cylindrical bore (not shown) in armature 210. In this regard, armature 210 and armature locator 220 may slide on armature guide pin 240.

Spring 250 is disposed on armature guide pin 240 between armature 210 and calibration nut 260. Calibration nut 260 can be used to adjust the length and force of spring 250.

Current conduction in heater 100 generates a magnetic field that attracts armature 210 to yoke 230.

However, spring 250 biases armature 210 away from

yoke 230. For relatively low currents within the rated operating range of the circuit breaker, the magnetic field strength generated by yoke 230 is insufficient to overcome the force provided by spring 250. In a short circuit condition, however, yoke 230 generates a magnetic field strength that overcomes the force of spring 250, causing armature 210 (and armature locator 220) to be pulled down towards yoke 230.

Referring now to FIGS. 4A-4C, the operation of thermal-magnetic trip unit 10 in three different operating modes is described. FIG. 4A depicts example thermal- magnetic trip unit 10 in an initial, non-trip condition. FIG. 4A is similar to FIG. IB, but also includes a

thermal-magnetic trip bar 400 that includes a thermal trip bar 410 that has a bi-metal interface 420, and a magnetic trip bar 430 that has an armature interface 440, with the thermal trip bar 410 and the magnetic trip bar 430 mounted on a common pivot point 450. Bi-metal interface 420 is disposed adjacent contact surface 330 of bi-metal

element 300, and armature interface 440 is disposed in recess 222 of armature locator 220.

Referring now to FIG. 4B, the operation of thermal- magnetic trip unit 10 in a first operating condition

(e.g., an over-current or thermal trip condition) is described. When an over-current condition occurs, the temperature of bi-metal element 300 increases, and second end 320 of bi-metal strip 300 begins to deflect from its initial position. If the temperature of bi-metal

element 300 increases sufficiently, due to the current draw exceeding a predefined level, contact surface 330 engages bi-metal interface 420 of thermal trip bar 410.

As a result, thermal trip bar 410 rotates clockwise about pivot point 450 from its initial position to a second, tripped position, which activates a trip mechanism (not shown) and opens electrical contacts (not shown) of the circuit breaker.

Referring now to FIG. 4C, the operation of thermal- magnetic trip unit 10 in a second operating condition (e.g., a short-circuit or magnetic trip condition) is described. As described above, when a short circuit condition occurs, yoke 230 generates a magnetic field that is sufficiently strong to overcome the force of

spring 250, and cause armature 210 to move downward from its initial position on armature pin 240. As a result, armature locator 220 engages armature interface 440, which causes magnetic trip bar 430 to rotate clockwise about pivot point 450. In addition, magnetic trip bar 430 engages thermal trip bar 110, which causes thermal trip bar 110 to rotate clockwise about pivot point 450 from its initial position to the second, tripped position, which activates the trip mechanism and opens electrical contacts of the circuit breaker.

Referring now to FIG. 5, an alternative example thermal-magnetic trip unit 10 ' in accordance with this invention is described. Thermal-magnetic trip unit 10 ' includes a heater 100 ' coupled to a translational magnetic system 200 and a bi-metal element 300. Heater 100' includes a first portion 100a ', a second portion 100b ' and a third portion 100c ' disposed between first portion 100a ' and second portion 100b'. In addition, heater 100' includes a fourth portion 100d' coupled between second portion 100b ' and third portion 100c ' at a top surface of second portion 100b'. Bi-metal element 300 is coupled to third portion 100c' and fourth portion 100d'.

Translational magnetic system 200 is coupled to

heater 100 ' between second portion 100b ' and third

portion 100c ' .

Compared with heater 100, alternative heater 100' has two substantially right-angle bends instead of a ramp shape, and requires fewer bends, but third portion 100c ' has a smaller surface area for contacting bi-metal

element 300. Fourth portion 100d' provides additional surface area for contacting bi-metal element 300. Fourth portion 100d' may be fabricated from the same or different material as heater 100 ', and may be bonded to second portion 100b ' using adhesives, fasteners, brazing, welding, or other similar method.

The foregoing merely illustrates the principles of this invention, and various modifications can be made by persons of ordinary skill in the art without departing from the scope and spirit of this invention.