Patent Publication Number: US-9406474-B2

Title: Circuit breaker heaters and translational magnetic systems

Description:
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. 1B ; 
         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  100   a , a second portion  100   b  and a third portion  100   c  disposed between first portion  100   a  and second portion  100   b . First portion  100   a  may be connected to one or more electrical conductors (not shown), and second portion  100   b  may be connected to one or more load conductors (not shown). Bi-metal element  300  has a first end  310  coupled to third portion  100   c  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  100   b  and third portion  100   c.    
     Referring now to  FIGS. 2A-2C , example heater  100  is described in more detail. As shown in  FIG. 2B , first portion  100   a  has a first surface  100   a   1  disposed in a first plane P 1 , and second portion  100   b  has a second surface  100   b   1  disposed in a second plane P 2  that is substantially parallel to first plane P 1 . First surface  100   a   1  is separated by a first predetermined distance D1 from second surface  100   b   1 . 
     Third portion  100   c  is disposed between first portion  100   a  and second portion  100   b , and has a third surface  100   c   1  disposed in a third plane P 3  that is substantially perpendicular to first plane P 1 . In this regard, heater  100  has a ramp-shape. Third surface  100   c   1  has a first predetermined length L1 and extends between upper end  100   e  and lower end  100   f  of third portion  100   c . Third surface  100   c   1  is separated by a second predetermined distance D2 from a left end  100   g  of second surface  100   b   1  (and second portion  100   b ). 
     Heater  100  includes a curved portion  100   d  coupled between second portion  100   b  and third portion  100   c . In particular, curved portion  100   d  extends between left end  100   g  of second portion  100   b  (at a plane parallel to second plane P 2 ) and upper end  100   e  of third portion  100   c  (at a plane parallel to third plane P 3 ). 
     First predetermined distance D1 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  100   a  and second portion  100   b . First predetermined distance D1 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 L1 may be constrained by the minimum required contact area between third portion  100   c  and bi-metal element  300 , and the dimensions of bi-metal element  300 . For example, if the minimum required contact area is A1, and bi-metal element has a width of W1, first predetermined length must be at least A1/W1. First predetermined length L1 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 T1 substantially along its entire length. Thickness T1 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. 1B , 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  100   a ′, a second portion  100   b ′ and a third portion  100   c ′ disposed between first portion  100   a ′ and second portion  100   b ′. In addition, heater  100 ′ includes a fourth portion  100   d ′ coupled between second portion  100   b ′ and third portion  100   c ′ at a top surface of second portion  100   b ′. Bi-metal element  300  is coupled to third portion  100   c ′ and fourth portion  100   d ′. Translational magnetic system  200  is coupled to heater  100 ′ between second portion  100   b ′ and third portion  100   c′.    
     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  100   c ′ has a smaller surface area for contacting bi-metal element  300 . Fourth portion  100   d ′ provides additional surface area for contacting bi-metal element  300 . Fourth portion  100   d ′ may be fabricated from the same or different material as heater  100 ′, and may be bonded to second portion  100   b ′ 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.