Patent Publication Number: US-11646567-B2

Title: Solid state circuit interrupter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority under 35 U.S.C. § 120 from, U.S. patent application Ser. No. 16/775,976, filed Jan. 29, 2020, entitled “SOLID STATE CIRCUIT INTERRUPTER”, the contents of which are incorporated herein by reference. 
     This application is related to commonly assigned U.S. patent application Ser. No. 16/775,985, filed Jan. 29, 2020, and entitled “SOLID STATE CIRCUIT INTERRUPTER”. 
    
    
     BACKGROUND 
     Field 
     The disclosed concept relates generally to circuit interrupters, and in particular, to solid state circuit interrupters. 
     Background Information 
     Circuit interrupters, such as for example and without limitation, circuit breakers, are typically used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition, a short circuit, or another fault condition, such as an arc fault or a ground fault. Solid state circuit interrupters use solid state components, e.g., semiconductor devices, to switch on and off current flowing from a power source to a load. 
     Solid state circuit interrupters provide faster tripping than conventional mechanical circuit interrupters. However, these capabilities have not been optimally utilized. Additionally, solid state circuit interrupters provide different safety and wellness concerns than conventional mechanical circuit interrupters. There is considerable room for improvement in solid state circuit interrupters. 
     SUMMARY 
     In accordance with an aspect of the disclosed concept, a circuit interrupter structured to electrically connect between a power source and a load comprises: a current sensor structured to sense current flowing through the circuit interrupter and having a normal sensor output proportional to the current flowing through the circuit interrupter and an over current detection (OCD) output that changes to an on state when the current flowing through the circuit interrupter reaches a second threshold level; a solid state switch module structured to have a closed state to allow current to flow through the circuit interrupter and an open state to interrupt current flowing through the circuit interrupter; a gate driver structured to control the solid state switch module to interrupt current flowing through the circuit interrupter, wherein the gate driver includes a desaturation (DESAT) function output that changes to an on state when the current flowing through the circuit interrupter reaches a third threshold level, and wherein the gate driver is structured to cause the solid state switch module to interrupt current flowing through the circuit interrupter when the DESAT function output changes to the on state; and an analog trip circuit structured to receive the normal sensor output and the OCD output and to output a trip signal to the gate driver when the normal sensor output reaches a first threshold level or the OCD output changes to the on state, wherein the trip signal causes the gate driver to control the solid state switch module to interrupt current flowing through the circuit interrupter. 
     In accordance with an aspect of the disclosed concept, a circuit interrupter structured to electrically connect between a power source and a load comprises: separable contacts structured to open to provide galvanic isolation between the power source and the load; an operating mechanism structured to open and close the separable contacts; a first position sensor structured to sense a position of the separable contacts; a solid state switch module structured to have a closed state to allow current to flow through the circuit interrupter and an open state to interrupt current flowing through the circuit interrupter; and an electronic trip unit structured to control the solid state switch module to change between the open state and the closed state and to control the operating mechanism to open the separable contacts, wherein, based on an output of the first position sensor, the electronic trip unit is structured to control the solid state switch module to control the solid state switch module to change from the open state to the closed state when the separable contacts are in a closed position. 
     In accordance with an aspect of the disclosed concept, a solid state switch assembly for use in a circuit interrupter comprises: an input terminal; a first conductor; an output terminal; a second conductor; a solid state switch module electrically connected to the input terminal with the first conductor and electrically connected to the output terminal with the second conductor and including at least one solid state switch; a heat sink attached to the solid state switch module; a current sensor structured to sense current flowing through the solid state switch module; and a number of metal oxide varistors (MOVs). 
     In accordance with an aspect of the disclosed concept, a circuit interrupter comprises: a frame including a number of compartments; and a number of solid state switch assemblies, each solid state switch assembly disposed in a corresponding one of the number of compartments and including: an input terminal; a first conductor; an output terminal; a second conductor; a solid state switch module electrically connected to the input terminal with the first conductor and electrically connected to the output terminal with the second conductor and including at least one solid state switch; a heat sink; a current sensor structured to sense current flowing through the solid state; and a number of metal oxide varistors (MOVs). 
     In accordance with an aspect of the disclosed concept, a method of operating a circuit interrupter having a solid state switch module including a solid state switch comprises: monitoring a characteristic of the solid state switch; determining that the characteristic of the solid state switch meets or exceeds a predetermined threshold; and providing an indication in response to determining that the characteristic of the solid state switch meets or exceeds the predetermined threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG.  1    is a schematic diagram of a circuit interrupter in accordance with an example embodiment of the disclosed concept; 
         FIG.  2    is a circuit diagram of a power supply in accordance with an example embodiment of the disclosed concept; 
         FIGS.  3 A and  3 B  are a circuit diagram of an analog trip circuit in accordance with an example embodiment of the disclosed concept; 
         FIGS.  4 A and  4 B  are a circuit diagram of a gate driver circuit in accordance with an example embodiment of the disclosed concept; 
         FIGS.  5 A and  5 B  are partial assembly views of a circuit interrupter in accordance with an example embodiment of the disclosed concept; 
         FIGS.  6 A and  6 B  are partial assembly views of a circuit interrupter in accordance with an example embodiment of the disclosed concept; 
         FIG.  7    is a view of a partially disassemble circuit interrupter in accordance with an example embodiment of the disclosed concept; 
         FIG.  8    is a partial internal side view of a circuit interrupter in accordance with an example embodiment of the disclosed concept; 
         FIGS.  9 A-C  are views of a solid state switch assembly in accordance with an example embodiment of the disclosed concept; 
         FIGS.  10 A-D  are views of a heat sink and solid state switch module in accordance with an example embodiment of the disclosed concept; 
         FIGS.  11 A-B  are views of a frame housing solid state switch assemblies in accordance with an example embodiment of the disclosed concept; and 
         FIG.  12    is a flowchart of a method of operating a circuit interrupter in accordance with an example embodiment of the disclosed concept. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
     As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. 
       FIG.  1    is a schematic diagram of a circuit interrupter  10  (e.g., without limitation, a circuit breaker) in accordance with an example embodiment of the disclosed concept. The circuit interrupter  10  in some example embodiments is a 100 A (I n =100 A) rated device (i.e., the rated current I n  is 100 A). The circuit interrupter  10  is structured to be electrically connected between a power source  2  and a load  4 . The circuit interrupter  10  is structured to trip open or switch open to interrupt current flowing to the load  4 , for example, in the case of a fault condition (e.g., without limitation, an overcurrent condition) to protect the load  4 , circuitry associated with the load  4 , as well as the components within the circuit interrupter  10 . 
     The circuit interrupter  10  includes a solid state switch assembly  200  including a solid state switch module  202  and a current sensor  206 . The circuit interrupter  10  also includes a gate driver circuit  204  and an analog trip circuit  208  associated with the solid state switch assembly  200 . The circuit interrupter  10  further includes an operating mechanism  300 , separable contacts  302 , and an electronic trip unit  304 , as well as a power supply  100 . Additionally, the circuit interrupter  10  includes positon sensors  500 ,  502 ,  504 , and close and open buttons  506 , 508 . It will be appreciated by those having ordinary skill in the art that the circuit interrupter  10  need not include all these components. For example, in example embodiments, the circuit interrupter  10  may only include a subset of these components without departing from the scope of the disclosed concept. 
     The circuit interrupter  10  is structured to provide solid state circuit interruption via the solid state switch assembly  200  and galvanic isolation via the separable contacts  302 . The solid state switch module  202  includes one or more solid state switches (e.g., without limitation, metal-oxide-semiconductor field-effect transistors (MOSFETS), insulated-gate bipolar transistors (IGBTs), or other suitable types of solid state switches) electrically connected between the power source  2  and the load  4 . The solid state switch module  202  has a closed state in which power is allowed to flow through the solid state switch module  202  between the power source  2  and the load  4  and an open state in which power is prevented from flowing between the power source  2  and the load  4 . 
     The gate driver circuit  204  is structured to control the state of the solid state switch module  202 . The gate driver circuit  204  has a desaturation function (DESAT) that changes from an off state to an on state when current flowing through the solid state switch module  202  reaches a predetermined threshold level. In an example embodiment, the predetermined threshold level is about 2250 A (22.5×I n ). The DESAT function operates by monitoring a forward voltage drop of a solid state switch in the solid state switch module  202 . When the forward voltage drop reaches a threshold level, the DESAT function changes to the on state and the gate driver circuit  204  responsively causes the solid state switch module  202  to change to the open state, interrupting current flowing through the circuit interrupter  10 . In an example embodiment, the DESAT function has a threshold voltage of 9V. Based on the on-resistance of a silicon-carbide (SiC) MOSFET, the forward voltage drop will reach 9V when the current level is about 2250 A. Thus, the DESAT function will change to the on state when the current flowing through the solid state switch module  202  reaches about 2250 A. It will be appreciated that these threshold values are merely provided as an example. Different threshold values may be employed without departing from the scope of the disclosed concept. 
     Using the DESAT function of the gate driver circuit  204  to cause the solid state switch module  202  to open allows for very fast interruption of the current flowing through the circuit interrupter  10 . In some example embodiments of the disclosed concept, interruption based on the DESAT function can be within 0.5 microseconds. In some example embodiments of the disclosed concept, the gate driver circuit  204  includes a capacitor structured to change the interruption based on the DESAT function. For example, the time to interrupt based on the DESAT function is based on the capacitance of the capacitor. In this manner, the interruption time based on the DESAT function can be easily adjusted by changing the capacitor. 
     In some example embodiments, the current sensor  206  is structured to provide a normal sensor output that is proportional to the current flowing through the circuit interrupter  10  and an overcurrent detection (OCD) output that changes to an on state when the current flowing through the circuit interrupter  10  reaches a threshold level. In an example embodiment, the current sensor  206  is a Hall-effect sensor. 
     The analog trip circuit  208  is structured to receive the normal sensor output and the OCD output from the current sensor  206 . The analog circuit  208  is electrically connected to the gate driver circuit  204  and is structured to output a trip signal to the gate driver circuit  204 . In response to the trip signal, the gate driver circuit  204  controls the solid state switch module  202  to change to the open state, interrupting current flowing through the circuit interrupter  10 . The analog trip circuit  208  is structured to output the trip signal in response to the normal sensor output reaching a threshold level or the OCD output changing to the on state. The analog trip circuit  208  is structured to output the trip signal in response to the OCD output changing to the on state within a first predetermined amount of time and to output the trip signal in response to the normal sensor output reaching the threshold level within a second predetermined amount of time. In an example embodiment, the first predetermined amount of time is less than the second predetermined amount of time. In an example embodiment, the first predetermined amount of time is 10 nanoseconds and the second predetermined amount of time is 100 nanoseconds. However, it will be appreciated that other predetermined amounts of time may be employed without departing from the scope of the disclosed concept. In an example embodiment, interruption of current flowing through the circuit interrupter  10  based on the normal sensor output reaching the threshold level occurs within 4 microseconds and interruption based on the OCD output occurs within 2 microseconds. However, it will be appreciated that these are example times and other times may be employed without departing from the scope of the disclosed concept. In some example embodiments, the threshold level associated with the normal current sensor output is within a range of about 200 (2×I n ) to 750 A (7.5×I n ) and the threshold level associated with the OCD output is about 750 A (7.5×I n ). However, it will be appreciated that these are just example values and may be adjusted without departing from the scope of the disclosed concept. 
     With the analog trip circuit  208  and the DESAT function of the gate driver circuit  204 , a three-level interruption logic is able to be employed within the circuit interrupter  10 . The DESAT function provides the fastest interruption based on the highest current threshold, the OCD output provides the second fastest interruption based on the second highest current threshold, and the normal sensor output provides the third fastest interruption based on the third highest current threshold. In an example embodiment, the highest current threshold is about 2250 A (22.5×I n ) and the fastest interruption is within 0.5 microseconds, the second highest current threshold is about 750 A (7.5×I n ) and the second fastest interruption is within 2.5 microseconds, and the third highest current threshold is selected from within a range of about 200 (2×I n )-750 A (7.5×I n ) and the third fastest interruption is within 4 microseconds. With the analog trip circuit  208  and the DESAT function of the gate driver circuit  204 , interruption is able to occur faster than through digital circuit protection, such as that provided by the electronic trip unit  304 . 
     In some example embodiments of the disclosed concept, the electronic trip unit  304  is also structured to output a trip signal to the gate driver circuit  204  to cause the gate driver circuit  204  to control the solid state switch module  202  to change to the open state. The electronic trip unit  304  may output the trip signal based on current thresholds below the third highest current threshold associated with trips based on the normal sensor output by the analog trip circuit  208 . The electronic trip unit  304  may be structured to output the trip signal based on an I-t trip curve such that when the electronic trip unit  304  detects a fault condition based on the normal sensor output of the current sensor  206 , the electronic trip unit  304  will output the trip signal to the gate driver circuit  204  at the time associated with the current level based on the I-t trip curve. 
     The circuit interrupter  10  also includes the operating mechanism  300  and separable contacts  302 . The separable contacts  302  are structured to open to provide galvanic isolation between the power source  2  and the load  4 . The operating mechanism  300  is structured open and close the separable contacts  302 . For example, the operating mechanism  300  may include a movable arm, which when moved causes the separable contacts  302  to open or close. The electronic trip unit  304  is structured to control the operating mechanism  300  to open the separable contacts  302 . For example, the electronic trip unit  304  may be structured to control the operating mechanism  300  to open the separable contacts  302  only after the solid state switch module  202  has changed to the open state. For example, in a mechanical circuit interrupter, the separable contacts are designed to interrupt current flowing through the circuit interrupter and have associated components such as an arc chute to manage arcing as a result of circuit interruption. The circuit interrupter  10  is a solid state circuit interrupter in which current is interrupted by the solid state switch module  202 . The separable contacts  302  need not be designed to interrupt the current and need not have an associated arc chute or other components, as they are only intended to open after the solid state switch module  202  has interrupted the current. As such, the electronic trip unit  304  may be structured to control the operating mechanism  300  to open the separable contacts  302  only after the solid state switch module  202  has changed to the open state. Similarly, the electronic trip unit  304  may be structured to cause the gate driver circuit  204  to change the solid state switch module  202  to the closed state only after the separable contacts  302  are closed. In this manner, bounce arc due to bouncing of the separable contacts  302  is prevented. In some example embodiments, the separable contacts  302  are closed with manual intervention by a user through, for example, a reset switch. In some example embodiments, the operating mechanism  300  is structured to close the separable contacts  302  in response to a close signal from the electronic trip unit  304 . 
     In some example embodiments of the disclosed concept, the circuit interrupter  10  includes a position sensor  500 . The position sensor  500  is structured to sense whether the separable contacts  302  are in the open position or the closed position. The output of the position sensor  500  may be provided to the electronic trip unit  304 . Based on the output of the position sensor  500 , the electronic trip unit  304  is able to determine the position of the separable contacts  302 . Similarly, the electronic trip unit  304  unit may receive an output of the gate driver circuit  204  indicative of the state of the solid state switch module  202 . With these outputs, the electronic trip unit  304  may ensure that the separable contacts  302  are opened only after the solid state switch module  202  has changed to the open state and that the solid state switch module  202  is changed to the closed state only after the separable contacts  302  are closed. 
     In some example embodiments, the circuit interrupter  10  includes a close button  506  and an open button  508 . It will be appreciated that buttons are used as an example. It will be appreciated that any user actuatable element may be employed without departing from the scope of the disclosed concept. In an example embodiment, the electronic trip unit  304  is structured to control the operating mechanism  300  to close the separable contacts  302  to close and then output a close signal to the gate driver circuit  204  to cause the gate driver circuit  204  to change the solid state switch module  202  to the closed state in response to actuation of the close button  506 . In an example embodiment, the electronic trip unit  304  is structured to output the trip signal to the gate driver circuit  204  to cause the gate driver circuit  204  to change the solid state switch module  202  to the open state and then control the operating mechanism  300  to open the separable contacts  302  in response to actuation of the open button  508 . In some example embodiments, a position sensor  502  may be used to sense actuation of the close button  506  and a position sensor  504  may be used to sense actuation of the open button  508 . The electronic trip unit  304  may be structured to receive outputs of the position sensors  502 , 504  and sense actuation of the close and open buttons  506 , 508  based on outputs of the position sensors  502 , 504 . 
     The position sensors  500 , 502 , 504  may be any suitable type of sensor for sensing the position of a component. As an example, the position sensors  500 , 502 , 504  may be micro switches that are actuated by movement of their corresponding component. For example, the position sensor  500  may be a micro switch disposed by a movable arm of the operating mechanism  300  such that movement of the moveable arm to open or close the separable contacts  302  actuates the position sensor  500 , and based on the output of the position sensor  500 , the electronic trip unit  304  is able to sense the current position of the separable contacts  302 . Similarly, the position sensors  502 , 504  may be micro switches disposed such that actuation of the on and off buttons  506 , 508 , respectively, actuates the position sensors  502 , 504 . 
     The power supply  100  is structured to receive power from the power source  2  and convert the power from the power source  2  to power usable by components of the circuit interrupter  10 . For example, the power supply  100  may convert alternating current power from the power source  2  to direct current power usable by components of the circuit interrupter  10 . The power from the power supply  100  may provide power to operate components such as, without limitation, the electronic trip unit  304 , the gate driver circuit  204 , the operating mechanism  300  (e.g., a solenoid included in the operating mechanism), the current sensor  206 , and the analog trip circuit  208 ). The power supply  100  may generate direct current power at multiple voltages (e.g., without limitation, 24V, 15V, 5V, and 3.3V). In an example embodiment, the power supply  100  may be omitted and power to operate the components of the circuit interrupter  10  may be provided by an external power supply. In some example embodiments, the electronic trip unit  304  is structured to cause the solid state switch module  202  to change to the open state and the separable contacts  302  to open if power is unavailable from the power supply  100  or an external power supply. In some example embodiments, the power supply  100  is structured to use line-line voltage from the power source  2  to generate the direct current power for use by the components of the circuit interrupter  10 . For example, rather than being connected between line and neutral conductors, the power supply  100  is instead connected between multiple line conductors. While  FIG.  1    shows a single pole of the circuit interrupter  10 , it will be appreciated that the circuit interrupter  10  may have multiple poles in which multiple line phases of power flow through the circuit interrupter  10  with the power supply  100  being connected to the multiple line phases. 
       FIG.  2    is a circuit diagram of the power supply  100  in accordance with an example embodiment of the disclosed concept. In this example embodiment, the power supply  100  includes a three-phase line input  110 , a rectifier diode bridge  120 , a filtering circuit  130 , a DC/DC converter  140 , and an output  150 . The three-phase line input  110  receives power from multiple lines phases and provides a line-to-line AC voltage input to the rectifier diode bridge  120 . The rectifier diode bridge  120  converts the AC voltage to DC voltage and outputs the DC voltage into the filtering circuit  130 . The filtering circuit  130  limits the current input, thereby protecting the power supply circuit  100  from rushing in of the current input, and filters the DC voltage via the current dividers (C 10 , C 11 , C 12 , C 13 , R 1 , R 2 , R 3 , and R 4 ). The DC/DC converter  140  receives the filtered DC voltage from the filtering circuit  130  and converts the filtered high DC voltage to low DC voltage, e.g., 24V, 15V, 5V, or 3.3V. The DC/DC converter  140  then outputs the low DC voltage to provide power for components of the circuit interrupter  10 . The line voltage is stepped down to, e.g., 24, 15, 5, or 3.3V DC, to fulfill the voltage requirements of the electrical components of the circuit interrupter  10 . When the line to line voltage is not available, an external 24V power supply may be used. If there is neither the external power nor the line to line voltage, the solid state switch module  202  may be changed to the open state. While  FIG.  2    illustrates an example of circuitry used within the power supply  400 , it will be appreciated that  FIG.  2    is merely an example embodiment. Circuit components may be rearranged, added to, subtracted from, or implemented differently without departing from the scope of the disclosed concept. 
       FIGS.  3 A and  3 B  are a circuit diagram of the analog trip circuit  208  in accordance with an example embodiment of the disclosed concept. The analog trip circuit  208  includes a normal sensor input  210  and an OCD input  212 . The normal sensor input  210  is structured to receive the normal sensor output of the current sensor  206 , which is proportional to current flowing through the circuit interrupter  10 . The OCD input  212  is structured to receive the OCD output of the current sensor  206 . The analog trip circuit  208  also includes a trip signal output  214  that is electrically connected to the gate driver circuit  204 . In response to the normal sensor output reaching a threshold level or the OCD output changing to an on state, the analog trip circuit  208  is structured to output the trip signal at the output  214 . The analog trip circuit  208  is structured to compare the normal sensor output to the threshold level while the OCD output is not needed to be compared to the threshold level. By bypassing this check with the OCD output, the analog trip circuit  208  is able to output the trip signal based on the OCD output faster than the trip signal based on the normal sensor output.  FIGS.  3 A and  3 B  illustrates an example of logic circuitry used in the analog trip circuit  208 . However, it will be appreciated that the example shown in  FIGS.  3 A and  3 B  is merely an example implementation of the analog trip circuit  208 . It will be appreciated that the circuit components may be rearranged, added to, subtracted from, or implemented differently without departing from the scope of the disclosed concept. 
       FIGS.  4 A and  4 B  are a circuit diagram of the gate driver circuit  204  in accordance with an example embodiment of the disclosed concept. The gate driver circuit  204  includes an enable input  216  and a DESAT input  222 . The gate driver circuit  204  also includes a driver output  224  and fault output  218 . The gate driver circuit  204  further includes a driver  220  and a capacitor  226 . The enable input  216  is electrically connected to the analog trip circuit  208  and the electronic trip unit  304 . The driver output  224  and the DESAT input  222  are electrically connected to the solid state switch module  202 . The fault output  218  is electrically connected to the electronic trip unit  218 . The solid state switch module  202  is structured to change between the open state and the closed state based on the driver output  224 . The driver  220  is structured to control the state of the driver output  224  based on the trip signal received at the enable input  216  or the DESAT input  222 . The driver  220  is structured to implement the DESAT function based on the DESAT input  222 . The timing associated with changing the driver output  224  based on the DESAT input  222  is based in part on the capacitance of the capacitor  226 . The driver  220  is also structured to control the state of the fault output  218  such that the electronic trip unit  304  may be notified when the gate driver circuit  204  has controlled the solid state switch module  202  to change to the open or closed state. It will be appreciated that the example shown in  FIGS.  4 A and  4 B  is merely an example implementation of the gate driver circuit  204 . It will be appreciated that the circuit components may be rearranged, added to, subtracted from, or implemented differently without departing from the scope of the disclosed concept. 
       FIGS.  5 A and  5 B  are partial assembly views of the circuit interrupter  10  in accordance with an example embodiment of the disclosed concept.  FIGS.  5 A and  5 B  show an example of the close and open buttons  506 , 508 , the position sensors  502 , 504 , part of the operating mechanism  300 , and part of the separable contacts  302 . In the example shown in  FIGS.  5 A and  5 B , a three pole operating mechanism  300  is shown with movable rotary arms that move the separable contacts  302  in conjunction. The position sensors  502 , 504  are associated with the close and open buttons  506 , 508 , respectively, such that actuation of the on and off buttons  506 , 508  causes actuation of the position sensors  502 , 504 . For example, protrusions are attached to the on and off buttons  506 , 508  and move in conjunction with actuation of the close and open buttons  506 , 508 . As an example, the protrusion associated with the on button  508  may move against the position sensor  504  when the close button  508  is actuated.  FIGS.  5 A and  5 B  show part of the separable contacts  302 . In particular,  FIGS.  5 A and  5 B  show the moveable contact of the separable contacts  302 . It will be appreciated that a stationary contact is associated with the moveable contact. Moving the moveable contact away from the stationary contact opens the separable contacts  302 . 
       FIGS.  6 A and  6 B  are partial assembly views of the circuit interrupter  10  in accordance with an example embodiment of the disclosed concept.  FIG.  6 A  shows part of the operating mechanism  300  and the separable contacts  302  in the closed position.  FIG.  6 B  shows part of the operating mechanism and the separable contacts  302  in the open position.  FIGS.  6 A and  6 B  also show the position sensor  500  which is structured to sense whether the separable contacts  302  are in the closed or open position. The position sensor  500  may be associated with part of a moveable arm of the operating mechanism  300  such that the moveable arm abuts against the position sensor when the separable contacts  302  are in the closed position and moves away from the positon sensor  500  when the separable contacts  302  are in the open position. 
       FIG.  7    is a partially disassembled elevation view of the circuit interrupter  10  in accordance with an example embodiment of the disclosed concept.  FIG.  7    shows the close and open buttons  506 , 508 , as well as a status indicator  510  that indicates the position of the separable contacts  302  in accordance with an example embodiment of the disclosed concept. 
       FIG.  8    is a partial internal side view of the circuit interrupter  10  in accordance with an example embodiment of the disclosed concept. A current path  600  through the circuit interrupter is designated with arrows. As shown in  FIG.  8   , current flowing through the circuit interrupter  10  from the power source  2  first flows through the separable contacts  302 . The current then continues through the solid state switch assembly  200  and the current sensor  206  disposed proximate the output of the solid state switch assembly  200 , where it is then provided to the load  4 . 
       FIGS.  9 A-C  are views of the solid state switch assembly  200  in accordance with an example embodiment of the disclosed concept. The solid state switch assembly  200  includes the solid state switch module  202  and the current sensor  206 . The solid state switch assembly  200  also includes an input terminal  250  and an input conductor  252 . The input terminal  250  is structured to receive power from the power source  2  via the separable contacts  302  and provide it to the solid state switch module  202  via the input conductor  252 . The solid state switch assembly  200  also includes an output terminal  256  and an output conductor  254 . When the solid state switch module  202  is in the closed state, power flows through the solid state switch module  202  to the load conductor  254  and subsequently to the output terminal  256 . The output terminal  256  is structured to be electrically connected to the load  4 . The solid state switch assembly  200  also includes a module cover  258 . 
     In  FIG.  9 C , the module cover  258  is omitted. The solid state switch assembly  200  also includes MOVs  262 , shown in  FIG.  9 C , that are covered by the module cover  258 . 
     The solid state switch assembly  200  further includes a heat sink  260 . The heat sink  260  is attached to the solid state switch module  200  and is described further with respect to  FIGS.  10 A-D . 
       FIGS.  10 A and  10 B  are views of the heat sink  260  in accordance with an example embodiment of the disclosed concept and  FIGS.  10 C and  10 D  are views of the solid state switch module  202  attached to the heat sink  260  in accordance with an example embodiment of the disclosed concept. The heat sink  260  includes a first planar member  264  and a second planer member  268  that extends from one side of the first planar member  268 . The heat sink  260  also includes multiple prongs  270  that extend from an opposite side of the first planar member  264 . 
     The solid state switch member  202  is structured to attach to the second planar member  268 , as shown in  FIGS.  10 C and  10 D . In an example embodiment, fasteners  272  may be used to attach the solid state switch member  202  to the second planar member  268 . The heat sink  260  may be composed of a metallic material and is operable to dissipate heat generated by the solid state switch module  202 . 
       FIGS.  11 A and  11 B  are views of a frame  280  for housing the solid state switch assemblies  200  in accordance with an example embodiment of the disclosed concept. The frame  280  includes compartments  282 , each housing one solid state switch assembly  200 . In the example embodiment shown in  FIGS.  11 A and  11 B , the frame  280  includes three compartments  282  and houses three solid state switch assemblies  200 . Each solid state switch assembly  200  may correspond to a pole of the circuit interrupter  10 . The frame  280  is thus suitable for use in a 3-pole circuit interrupter. However, it will be appreciated that the frame  280  may be modified to have a different number of compartments  282  without departing from the scope of the disclosed concept. 
     The solid state switch assembly  200  has a modular design. Components of the solid state switch assembly  200  may be substituted for other similar shaped components depending on the application of the solid state switch assembly  200 . For example, the solid state switch module  202  may be substituted with another solid state switch module  202  for an application with different voltage and current requirements. The remaining components of the solid state switch assembly  200  may remain unchanged, thus allowing a wider application of the solid state switch assembly  200  without the need to redesign the whole solid state switch assembly  200 . Similarly, the current sensor  206  may be replaced with another current sensor  206  in applications with different current requirements. Similarly, the other components of the solid state switch assembly  200  may be replaced. 
       FIG.  12    is a flowchart of a method of operating a circuit interrupter in accordance with an example embodiment of the disclosed concept. The method may be implemented, for example, in the circuit interrupter  10  described herein. Solid state circuit interrupters, such as the circuit interrupter  10 , present new concerns regarding health and remaining life compared to mechanical circuit interrupters. For example, monitoring the health of solid state switches differs from monitoring the health of mechanical switches. However, in both cases, it is important to monitor when the switch is reaching the end of its lifespan and becomes at risk of failure. 
     The method of  FIG.  12    begins at  700  with monitoring a characteristic of the solid state switch assembly  200 . In some example embodiments, a solid state switch the solid state switch module  202  is monitored. In some example embodiments, the MOVs  262  are monitored. It will be appreciated that both may be monitored. The monitored characteristic may be a junction temperature, a forward volt drop (in the case of an IGBT solid state switch), a body diode forward volt drop (in the case of a MOSFET solid state switch), a gate threshold voltage (in the case of a MOSFET solid state switch), or a gate leakage current (in the case of a MOSFET solid state switch) of the solid state switch. The monitored characteristic may also be a voltage across the MOVs  262 . 
     At  702 , it is determined whether the monitored characteristic exceeds a threshold level. The threshold level may be selected based on the monitored characteristic and the device being monitored. In the case of the voltage across the MOVs  262 , the threshold may be a time-varying range. For example, the voltage across the MOVs  262  may be monitored for a period of time after the solid state switch is opened. The threshold range changes over the period of time and it is determined whether the voltage across the MOVs  262  goes outside that threshold range at a particular time. If the characteristic does not exceed the threshold level, the method returns to  700 . However, if the characteristic exceeds the threshold level, the method proceeds to  704 . 
     At  704 , an indication is provided. The indication may be via a display on the circuit interrupter  10  or any other suitable type of indication such as for example, an LED indicator, a wired or wireless communication to an external device, etc. The indication notifies a user or technician that the component needs to be serviced or replaced. It will be appreciated that additional method steps may be employed such as servicing or replacing a component or controlling the circuit interrupter  10  to trip open in response to determining that the monitored characteristic exceeds the threshold level. 
     The junction temperature is an indicator of the wellness of a solid state switch. As an example, some solid state switches should be kept under a threshold junction temperature of 150 degrees Celsius. If the junction temperature reaches this threshold, then the solid state switch may become damaged and fail. Thus, junction temperature of the solid state switch is a useful characteristic to monitor. 
     The forward volt drop or body diode forward volt drop are also indicators of the wellness of a solid state switch. When the forward volt drop or body diode forward volt drop reach its threshold when operating at rated current, the solid state switch can become damaged and fail. The forward volt drop or body diode forward volt drop can be caused by a number of factors such as high current, bad heat conduction, or bad thermal management. Thus, the forward volt drop and body diode forward volt drop are useful characteristics to monitor. 
     The gate threshold voltage or gate leakage current are also useful characteristics of the solid state switch to monitor. The gate threshold voltage or gate leakage current exceeding their threshold levels can damage or cause the solid state switch to fail. The gate leakage current is more sensitive to degradation of the solid state switch and is possible to monitor while the solid state switch is closed and conducting current, which makes it more practical to monitor than the gate threshold voltage. However, both the gate threshold voltage and gate leakage current are useful characteristics to monitor to determine the wellness of the solid state switch. 
     When the MOVs  262  begin to degrade, the voltage across the MOVs  262  will increase or decrease. The MOVs  262  clamp voltage in a period of time after the solid state switch is opened, and thus this is the relevant time period to monitor the voltage across the MOVs  262 . An example threshold range may be ±10% of the MOVs  262  normal clamp voltage. For example, voltage across the MOVs  262  drifting more than 10% from their normal clamp voltage is an indication that the MOVs  262  are degrading and should be serviced or replaced. Thus, the voltage across the MOVs  262  is another useful characteristic to monitor. 
     While some examples of characteristics to monitor have been described, it will be appreciated that other characteristics may be monitored without departing from the scope of the disclosed concept. It will also be appreciated that additional action in addition to or in place of providing an indication may be performed in response to a characteristic exceeding its threshold. 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.