Abstract:
A field-installable circuit breaker trip actuator unit includes a flux shifter unit that interfaces with the circuit breaker operating mechanism and is installable without dismantling the circuit breaker components. The flux shifter unit responds to an electronic trip unit to articulate the circuit breaker operating mechanism and separate the circuit breaker contacts upon occurrence of an overcurrent condition. A reset arrangement allows the trip actuator unit to be automatically reset upon completion of the contact separation process.

Description:
BACKGROUND OF THE INVENTION 
     High ampere-rated circuit breakers such as described within U.S. Pat. No. 3,073,936 entitled &#34;Electric Circuit Interrupter&#34; are currently employed within industrial manufacturing facilities to protect the electric equipment and buildings from damage due to overcurrent conditions within the electrical distribution system. Earlier manufactured circuit breakers employed thermal-magnetic trip units to determine overcurrent conditions and to articulate the circuit breaker operating mechanism to separate the circuit breaker contacts to interrupt the associated electric circuit. Later manufactured circuit breakers employed electronic trip units which contained so-called &#34;flux shift units&#34; to articulate the operating mechanism upon signal from the electronic trip unit. One example of an early electronic trip unit is found in U.S. Pat. No. 3,761,778 entitled &#34;Static Trip Control Unit for Electric Circuit Breaker&#34;. 
     Such robust circuit breakers remain in operation to this date without needing replacement or repair. However, state of the art digital electronic trip units of the type described within U.S. Pat. No. 4,672,501 entitled &#34;Circuit Interrupter and Controller Unit&#34; provide more reliable protection by closer control over the circuit interruption time and current parameters as well as providing communications and accessory options. It would be economically advantageous to incorporate state of the art digital electronic trip units within such existing circuit breakers without having to dismantle the circuit breaker operating components in the process. 
     One purpose of the invention, accordingly, is to provide a conversion unit that will incorporate digital electronic trip units within existing circuit breakers without having to dismantle the circuit breaker operating components. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an electronic trip unit conversion kit includes a flux shift unit and reset arrangement to articulate the circuit breaker operating mechanism upon the occurrence of an overcurrent condition to separate the circuit breaker contacts and to automatically reset the flux shift unit after the circuit breaker contacts have become separated. A connector link interacting between the circuit breaker operating mechanism cross bar and the conversion kit flux shift unit to provide the flux shift unit reset facility. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a circuit breaker with a part of the circuit breaker case removed to depict the circuit breaker contact arms, contacts and the circuit breaker trip unit conversion kit in accordance with the invention; 
     FIG. 2 is a top perspective view of the components of the trip actuator unit within the trip unit conversion kit of FIG. 1; and 
     FIG. 3 is an enlarged top perspective view of the trip unit conversion kit of FIG. 1 prior to insertion within the circuit breaker assembly of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an industrial-rated circuit breaker 10, such as described in aforementioned U.S. Pat. No. 3,073,936, with an operating handle 11 extending from the top with load straps 12 and line straps 13 arranged at opposite ends thereof. The movable contacts 15 at one end of the movable contact arm 14 and the fixed contacts 16 on the contact support 17 are shown in solid lines in the CLOSED condition and in phantom lines in the OPEN condition. The condition of the contacts are controlled by an operating mechanism (not shown) that is refrained from articulation by means of a trip latch 18 in the manner described within the aforementioned U.S. Pat. No. 3,073,936. 
     In accordance with the invention, a trip unit conversion kit 9, as shown in FIGS. 2 and 3 along with FIG. 1, includes a programmer or electronic trip unit 21 such as described in aforementioned U.S. Pat. No. 4,672,501 that connects with a trip actuator unit 20 by means of a wire conductor 22 and connectors 22A at one end. The trip unit conversion kit 9 is attached to the interior of the circuit breaker 10 by securing the conversion kit mounting bracket 29 to the circuit breaker accessory bracket 32 by means of screws 31. The trip actuator unit 20 is similar to that described in U.S. patent application Ser. No. 08/551,640 filed Nov. 11, 1995 entitled &#34;Electronic Trip Unit Conversion Kit for High Ampere-Rated Circuit Breakers&#34;. Upon receipt of a trip signal from the trip unit, the trip actuator unit 20 releases the flux shift plunger 19 which strikes a trip latch adjusting screw 23. The adjusting screw 23 is threaded into a trip latch extension 24 which is secured to the circuit breaker trip latch 18 by means of a screw 25. The flux shift plunger 19 rotates the trip latch 18 to the position shown in phantom allowing the operating mechanism (not shown) to separate the contacts 15, 16 as further described in the aforementioned U.S. Pat. No. 3,073,936. The connector link 26 is attached to the reset arm 27 within the trip actuator unit 20 at one end and to the circuit breaker crossbar 30 at the other end to return the flux shift plunger 19 within the flux shift unit 43 from the actuated position depicted in solid lines to the reset position shown in phantom. The reset spring 28 which is anchored at one end through a hole 33 in the conversion kit mounting bracket 29 and at the other end to flux shift reset bracket 47, biases the connector link 26, and reset arm 27 immediately upon extension of the connector link to the position shown in phantom and returns the flux shift plunger 19 to its home position when the circuit breaker contacts 15,16 are returned to their closed position. This is brought about by interaction between the connector link 26 with the circuit breaker crossbar 30 at one end and by connection between the connector link 26 with the reset arm 27 at the opposite end, such that the rotation of the cross bar to close the circuit breaker contacts moves the connector link 26 and the reset arm 27 back to the position depicted in solid lines as described in the aforementioned U.S. patent application Ser. No. 08/551,640. As further described therein, the flux shift reset bracket 47 that controls the position of the flux shift plunger 19, is attached to the reset arm 27 by means of bolts 41 and nuts 42. 
     As shown in FIGS. 2 and 3, the mounting bracket 29 is shaped from a single metal plate and defines a front wall 44 extending in the horizontal plane as viewed in FIG. 2 with a side wall 45 extending in the vertical plane at right angles to the front wall and with a bottom shelf 46 formed at one end. The electronic trip unit 21 is secured to the front wall of the conversion kit mounting bracket 29 with screws 34 and the trip actuator unit 20 is attached to the front wall via rubber grommets 35, washers 38, screws 36 and threaded apertures 37. The rubber grommets are required to prevent the vibration within the circuit breaker interior from interfering with the operation of the flux shift unit 43 that controls the movement of the flux shift plunger 19, described earlier. The bottom shelf 46 includes apertures 49 for connection of the mounting bracket with the circuit breaker accessory bracket 32, as shown in FIG. 1. The connector link 26 is pivotally attached to the reset arm 27 by screw 39 and nut 40. The position of the flux shifter reset bracket 47 is determined by the flux shifter reset spring 48 in the manner described in the aforementioned U.S. patent application Ser. No. 08/551,640. Upon displacement of the connector link 26 by the circuit breaker crossbar 30 in FIG. 1, the reset arm 27 and return spring 28 rotate flux shifter reset bracket 47 against the return bias of the flux shifter reset spring 48 to return the plunger 19 to the home position as shown in solid lines. 
     An electronic trip unit conversion kit in the form of trip unit having automatic reset facility has herein been described. The conversion kit is mounted within the circuit breaker enclosure without requiring disassembly of any of the circuit breaker components.