Abstract:
An electronic trip unit for a circuit breaker includes: a microprocessor, the microprocessor programmed to determine an overcurrent condition of the circuit breaker; a nonvolatile memory in electronic communication with the microprocessor; a module plug releasably engaged with the microprocessor, the module plug includes an identification register; wherein the microprocessor reads the identification register, the identification register including an identification number; wherein the microprocessor accesses one of a plurality of programs in the nonvolatile memory based the identification number; and wherein the one of a plurality of programs instructs the microprocessor to perform steps necessary to operate one or more functions of the module plug.

Description:
BACKGROUND OF INVENTION 
     Electronic trip units (trip units) for actuating the separable contacts in a circuit breaker are well known. An electronic trip unit typically comprises voltage and current sensors that provide analog signals indicative of current or voltage in a power distribution circuit. The analog signals are converted by an A/D (analog/digital) converter to digital signals that are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. The ROM includes trip unit application code, e.g., main functionality trip setting values, including initializing parameters, boot code, and operational parameters (e.g., trip setting instructions). Operational parameters for the application code are also stored in the EEPROM. An output of the electronic trip unit actuates a trip module, such as a solenoid, that trips a mechanical operating mechanism. The mechanical operating mechanism, in turn, separates a pair of main contacts within the circuit breaker. When the contacts open, circuit current is prevented from flowing from one contact to the other, and electrical current is prevented from flowing to a load that is connected to the breaker. The electronic trip unit initiates a trip for instantaneous, short time, long time, ground fault, and manual conditions. 
     Circuit breakers having electronic trip units are described in U.S. Pat. No. 4,672,501 entitled “Circuit Breaker and Protective Relay Unit”. Such trip units often include a specific interface for a specific plug in module. One such example of a specific interface is a keypad along with a display for accessing the processor and for entering and changing the trip unit settings as described within U.S. Pat. No. 4,870,531 entitled “Circuit Breaker With Removable Display &amp; Keypad”. Other functional modules cannot be plugged into the place where this specific plug is received within the electronic trip unit. Thus, in order for the operator to receive additional functions for the trip unit, the operator would have to order the additional functions prior to the electronic trip unit being shipped to the operator. The operator could not install these additional functions in the field. 
     SUMMARY OF INVENTION 
     The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a module plug for an electronic trip unit. In an exemplary embodiment of the invention, an electronic trip unit for a circuit breaker includes: a microprocessor, the microprocessor programmed to determine an overcurrent condition of the circuit breaker; a nonvolatile memory in electronic communication with the microprocessor; a module plug releasably engaged with the microprocessor, the module plug includes an identification register; wherein the microprocessor reads the identification register, the identification register including an identification number; wherein the microprocessor accesses one of a plurality of programs in the nonvolatile memory based the identification number; and wherein the one of a plurality of programs instructs the microprocessor to perform steps necessary to operate one or more functions of the module plug. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures: 
     FIG. 1 is a perspective view of a circuit breaker including an electronic trip unit with a module plug; 
     FIG. 2 is the electronic trip unit with the module plug of FIG. 1; 
     FIG. 3 is a schematic block diagram of the electronic trip unit with the module plug of FIG. 2 in the circuit breaker of FIG. 1; and 
     FIG. 4 is a flow chart providing an operation of the module plug and the electronic trip unit of FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a molded case circuit breaker  20  employing an electronic trip unit  22  is generally shown. Circuit breakers of this type have an insulated case  24  and a mid-cover  26  that house the components of circuit breaker  20 . A handle  28  extending through an aperture  30  of a cover  32  gives the operator the ability to turn circuit breaker  20  “on”, which allows electricity to flow through circuit breaker  20 , turn circuit breaker  20  “off”, which prevents electricity from flowing through circuit breaker  20 , or “reset” circuit breaker  20  after a fault. A plurality of electrically conducting load side contact straps (load straps)  40 ,  42 , and  44  at a load side  46  of circuit breaker  20  extend within case  24 . Line side contact straps  50 ,  52 ,  54  (shown on FIG. 3) are located on a line side  48  of circuit breaker and also extend within case  24 . Circuit breaker  20  illustrates a typical three-phase configuration, however, the present disclosure is not limited to this configuration but may be applied to other configurations, such as one, two or four phase circuit breakers. Removably disposed at electronic trip unit  22  is a module plug  60 , as will be described in further detail hereinafter. 
     Electronic trip unit  22  also includes a cover  126  that has transparent windows  130  that enables the operator to view module plug  60  without removing cover  126 . Module plug  60  is flush with the face of electronic trip unit  22  so that cover  126  can be closed with module plug  60  in place in electronic trip unit  22 . Preferably, cover  126  has hinges  128  so that cover can be swung open and the operator may easily access module plug  60 . Cover  126  may also be locked to prevent tampering by unauthorized personnel. 
     FIG. 2 illustrates electronic trip unit  22  removed from circuit breaker  20 . Electronic trip unit  22  includes a printed circuit board  61  to which a plug-in battery  62 , a plug-in rating plug  64 , and module plug  60  are removably mounted. Rating plug  64  allows the circuit interruption rating to be set by replacing rating plug  64  with a different rating plug. For instance, rating plug  64  may be used to set circuit breaker at 800 amperes maximum current. Rating plug  64  may be subsequently changed to set the maximum rating to 1200 amperes. Battery  62  supplies either a primary source or an alternative source of power to electronic trip unit  22 . 
     Module plug  60  is a small electronic assembly, which may be approximately one inch square and approximately about one-half inch deep. Module plug  60  provides for an operator interface in the form of dials  66 , push buttons (not shown), rotary switches (not shown), and the like. Module plug  60  may also include an LCD or LED display  68  that provides the operator with information regarding circuit breaker  20  (shown in FIG. 1) (e.g., whether the circuit breaker is on, off, or tripped), or electronic trip unit  22  (e.g., the trip setting), or the power distribution circuit to which circuit breaker  20  (shown in FIG. 1) is connected (e.g., voltage, power, or current). Module plug  60 , battery  62 , and rating plug  64  each include a means for removably connecting to printed circuit board  61 . Such means includes a pin connector  69  (shown on FIG.  3 ), an input/output port (not shown), or the like. 
     Referring to FIG. 3, a general schematic of a portion of circuit breaker  20  is shown. In circuit breaker  20 , load straps  40 ,  42 , and  44  are electrically connected to line straps  50 ,  52 , and  54  via electrical contacts  70 ,  72 ,  74 . Electrical contacts  70 ,  72 , and  74  are arranged so that each electrical contact  70 ,  72 , and  74  can be separated to stop the flow of electrical current from line straps  50 ,  52 , and  54  to load straps  40 ,  42 , and  44 . Electrical contacts  70 ,  72 , and  74  are mechanically connected to an operating mechanism  80 , which is a spring-loaded latching mechanism for separating contacts  70 ,  72 , and  74 . A trip actuator  82  is positioned to trip (unlatch) operating mechanism  80  in response to receiving an electrical trip signal from electronic trip unit  22  via line  84 . When operating mechanism  80  is tripped by trip actuator  82 , operating mechanism  80  separates each electrical contact  70 ,  72 , and  74  to stop the flow of electrical current from line straps  50 ,  52 , and  54  to load straps  40 ,  42 , and  44 . 
     Load straps  40 ,  42 , and  44  are configured for electrical connection to a three-phase power source exemplified by phases A, B, and C. Load straps  40 ,  42 , and  44  are coupled to current transformers  90 ,  92 ,  94 , respectively, which are then connected by lines  100 ,  102 , and  104  to a rectifier  106 . Rectifier  106  is electrically connected by line  108  to a microprocessor  110  mounted to printed circuit board  61  of electronic trip unit  22 . 
     Electronic trip unit  22  includes microprocessor  110 , a random access memory (RAM)  112 , a read only memory (ROM)  114 , and a nonvolatile memory  115 . RAM  112  is coupled with microprocessor via a bus  117  and is used for the temporary storage of current and voltage data and as a scratch pad memory. ROM  115  is coupled with microprocessor via bus  117  and contains boot code data. Nonvolatile memory  115  is also coupled with microprocessor via bus  117  and stores a control program  116  that instructs microprocessor  112  to perform certain functions such as overcurrent protection, metering, protective relaying and communications. Nonvolatile memory  115  also stores a plurality of programs  120  that implement module plug  60  functions and a look-up table  121  that maps each program  120  with a corresponding module plug identification number. Microprocessor  110  controls RAM  112 , ROM  114 , nonvolatile memory  115 , and bus  117 . 
     Electronic trip unit  22  is coupled with module plug  60  by pin connector  69 . Pin connector  69  is coupled with microprocessor  110  by a lead  122 . Module plug  60  includes an identification register  118 , dials  66 , and display  68 , all of which are coupled with pin connector  69  via lead  123 . Stored in identification register  118  is a binary representation of the module plug identification number unique to the type of module plug  60 . Rating plug  64  is also coupled with microprocessor  110  by a lead  124  and a pin connector  125 . 
     Referring to FIGS. 3 and 4, module plug  60  and electronic trip unit  22  function as follows. Control program  116  instructs microprocessor  110  to perform a process  200 , which is started when microprocessor  110  is first booted up (block  202 ). An operator (not shown) plugs module plug  60  into pin connector  69 , which couples module plug  60  with microprocessor  110 . Control program  116  instructs microprocessor  110  to periodically read identification register  118  located at module plug  60  (block  204 ). Control program  116  determines whether a new identification number is present (block  206 ). If a new identification number is not present, control program  116  instructs microprocessor  110  to read identification register  118  (block  204 ). If a new identification number is present, then control program  116  instructs microprocessor  110  to compare the identification number read from identification register  118  with the identification numbers listed in lookup table  121  and determine the program  120  associated with the identification number (block  208 ). Control program  116  then instructs microprocessor to retrieve and execute the associated program  120  (block  210 ). 
     Depending on which program  120  is accessed, program  120  will instruct microprocessor  110  to perform steps necessary to operate functions of module plug  60  (block  212 ). Such functions include accepting input from module plug  60 , such as reading input values from dials  66 , and providing output data to module plug  60 , such as providing signals to display  68 . Some examples of the functions module plug  60  can perform include displaying the current being measured by electronic trip unit  22 , changing the trip parameters stored in remote access memory  112 , displaying overload pick-up times, displaying instantaneous tripping values and energy values, and the like. When a specific module plug  60  is not desired, a blank module plug should be connected to electronic trip unit  22  to protect electronic trip unit  22 . In addition, microprocessor  110  reads the number associated with the blank module and determines that no additional function is required. 
     Module plug  60  and electronic trip unit  22  provide the operator with a flexible electronic trip unit. The operator will be able to upgrade the electronic trip unit after purchasing the electronic trip unit. The operator will also be able to change the capability of the electronic trip unit easily by changing the module plug in the electronic trip unit. Thus, additional options and functions can be installed by the operator in the field. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.