Abstract:
A circuit breaker includes a set of separable contacts moveable between a closed position and an open position, an operating mechanism configured to open the set of contacts, a conductor coupled to the set of contacts, a current transformer coupled to the conductor, and a trip circuit coupled to the operating mechanism and to the current transformer and configured to cause the operating mechanism to open the set of contacts when a current through the conductor exceeds a current threshold that is greater than a saturation threshold of the current transformer. The trip circuit is further configured to vary the current threshold during an interval following a closure of the set of the contacts and to provide a fixed current threshold thereafter.

Description:
BACKGROUND 
       [0001]    The present inventive subject matter relates generally to circuit breakers and methods of operating the same and, more particularly, to circuit breakers including current transformers and electronic trip units. 
         [0002]    Circuit breakers are commonly used to protect circuitry, such as distribution wiring, from overheating due to short circuits or overloads. Circuit breakers typically include at least one set of contacts that is configured to be opened and closed by an actuator mechanism. The actuator mechanism is typically configured open and close the contacts in response to a manual or other mechanical input (e.g., by movement of a motorized actuator), and is further configured to rapidly open in response to an input from a trip unit. 
         [0003]    Circuit breaker trip units may operate in a number of ways. For example, trip units for thermal magnetic breakers typically trip breaker contacts in response to current in and temperature of conductors in the breaker. Such trip units may use current transformers to sense currents for so-called “instantaneous” current-level tripping, and may use mechanical and/or electromechanical devices to provide thermal tripping. 
       SUMMARY 
       [0004]    According to example embodiments of the present inventive subject matter, a circuit breaker may include a set of separable contacts moveable between a closed position and an open position, an operating mechanism configured to open the set of contacts, a conductor coupled to the set of contacts, a current transformer coupled to the conductor, and a trip circuit coupled to the operating mechanism and to the current transformer. The trip circuit may be configured to cause the operating mechanism to open the set of contacts when a current level through the conductor exceeds a current threshold that is greater than a saturation threshold of the current transformer. 
         [0005]    In example embodiments of the present inventive subject matter, the circuit breaker may include a power supply circuit coupled to the current transformer. The power supply circuit may be configured to supply power to the trip circuit from the current transformer. 
         [0006]    In example embodiments of the present inventive subject matter, the trip circuit may be configured to vary a level of the current threshold based on a state of the set of contacts. 
         [0007]    In example embodiments of the present inventive subject matter, the trip circuit may be configured to vary the current threshold during an interval following a closure of the set of contacts and to provide a fixed current threshold thereafter. 
         [0008]    In example embodiments of the present inventive subject matter, the trip circuit may include a current detection circuit coupled to the current transformer, a reference signal generator circuit, and a trip signal generator circuit. The current detection circuit may be configured to generate a current detection signal responsive to the current transformer. The reference signal generator circuit may be configured to generate a reference signal that varies during the interval following the closure of the set of contacts. The trip signal generator circuit may be configured to generate a trip signal responsive to a comparison of the current detection signal to the reference signal. 
         [0009]    In example embodiments of the present inventive subject matter, the reference signal generator circuit may include a voltage regulator, a first resistor and a first capacitor connected in parallel, and a second resistor and a second capacitor connected in parallel. The voltage regulator may have an input voltage coupled to an output of the current transformer and an output voltage coupled to a first node. The first resistor and the first capacitor may be coupled to the first node and to a second node. The second resistor and the second capacitor may be coupled to the second node and to ground. 
         [0010]    In example embodiments of the present inventive subject matter, the trip signal generator circuit may include a first variable resistor coupled to the current detection signal, and an instantaneous trip comparator with a first input coupled to the second node and a second input coupled to the first variable resistor. The trip signal may be an output of the instantaneous trip comparator. 
         [0011]    In example embodiments of the present inventive subject matter, the circuit breaker may include a thermal sensor thermally coupled to the conductor. The thermal sensor may be configured to generate a temperature signal. The trip circuit may be further configured to open the set of contacts responsive to the temperature signal. 
         [0012]    In example embodiments of the present inventive subject matter, the thermal sensor may include a thermal diode. The trip circuit may be further configured to open the set of contacts responsive to a voltage across the thermal diode. 
         [0013]    In example embodiments of the present inventive subject matter, the thermal sensor may include a first thermal sensor that generates a first temperature signal. The circuit breaker may also include a second thermal sensor. The second thermal sensor may be configured to generate a second temperature signal indicating an ambient temperature of the circuit breaker. The trip circuit may be further configured to open the set of contacts responsive to the first and second temperature signals. 
         [0014]    In example embodiments of the present inventive subject matter, the trip circuit may be configured to open the set of contacts responsive to a comparison of the first temperature signal to a reference temperature signal. The trip circuit may be configured to vary the reference temperature signal responsive to the second temperature signal. 
         [0015]    In example embodiments of the present inventive subject matter, the trip circuit may further include a peak detection circuit. The peak detection circuit may be configured to detect a peak value of an output current from the current transformer which exceeds a reference peak value. The reference peak value may correspond to the current level through the set of contacts at which the trip circuit is configured to cause the operating mechanism to open the set of contacts. 
         [0016]    In example embodiments of the present inventive subject matter, the reference peak value may be configured to rise from an initial reference peak value to a steady-state reference peak value when power is applied to the circuit breaker. 
         [0017]    In example embodiments of the present inventive subject matter, the rise of the reference peak value from the initial reference peak value to the steady-state reference peak value may be responsive to a charging of a capacitor by an output of the current transformer. 
         [0018]    In example embodiments of the present inventive subject matter, the steady-state reference peak value may be configured to be dynamically adjustable by altering a variable resistor element within the trip circuit. 
         [0019]    According to example embodiments of the present inventive subject matter, a circuit breaker may include a set of separable contacts moveable between a closed position and an open position, an operating mechanism configured to open the set of contacts, a conductor coupled to the set of contacts, a thermal diode thermally coupled to the conductor, and a trip circuit coupled to the operating mechanism and to the thermal diode. The trip circuit may be configured to cause the operating mechanism to open the set of contacts responsive to the thermal diode. 
         [0020]    In example embodiments of the present inventive subject matter, the circuit breaker may include an ambient thermal sensor. The ambient thermal sensor may be configured to measure an ambient temperature of the circuit breaker. The trip circuit may be configured to cause the operating mechanism to open the set of contacts responsive to the thermal diode and the ambient thermal sensor. 
         [0021]    In example embodiments of the present inventive subject matter, the trip circuit may be configured to open the set of contacts responsive to a comparison of a temperature signal from the thermal diode to a reference temperature signal. The trip circuit may be configured to vary the reference temperature signal responsive to an ambient temperature signal from the ambient thermal sensor. 
         [0022]    In example embodiments of the present inventive subject matter, the reference temperature signal can be configured to be dynamically adjusted by altering a variable resistor element within the trip circuit. 
         [0023]    In example embodiments of the present inventive subject matter, the trip circuit may be a first trip circuit. The first trip circuit may include a current transformer coupled to the conductor, and a second trip circuit coupled to the current transformer and the operating mechanism. The second trip circuit may be configured to cause the operating mechanism to open the set of contacts responsive to a current level through the set of contacts that is greater than a saturation level of the current transformer. 
         [0024]    In example embodiments of the present inventive subject matter, the first trip circuit and the second trip circuit may be powered by the output of the current transformer. 
         [0025]    According to example embodiments of the present inventive subject matter, a circuit breaker may include a set of separable contacts moveable between a closed position and an open position, an operating mechanism configured to open the set of contacts, a conductor coupled to the set of contacts, a first thermal sensor thermally coupled to the conductor, a second thermal sensor, and a trip circuit coupled to the operating mechanism and to the first and second thermal sensors. The first thermal sensor may be configured to generate a first temperature signal indicating a temperature of the conductor. The second thermal sensor may be configured to generate a second temperature signal indicating an ambient temperature of the circuit breaker. The trip circuit may be configured to cause the operating mechanism to open the set of contacts responsive to the first and second temperature signals. 
         [0026]    In example embodiments of the present inventive subject matter, the trip circuit may be configured to open the set of contacts responsive to a comparison of the first temperature signal to a reference temperature signal. The trip circuit may be configured to vary the reference temperature signal responsive to the second temperature signal. 
         [0027]    In example embodiments of the present inventive subject matter, the reference temperature signal may be configured to be dynamically adjusted by altering a variable resistor element within the trip circuit. 
         [0028]    In example embodiments of the present inventive subject matter, the trip circuit may be a first trip circuit. The first trip circuit may further include a current transformer coupled to the conductor, and a second trip circuit coupled to the current transformer and the operating mechanism. The second trip circuit may be configured to cause the operating mechanism to open the set of contacts responsive to a current level through the set of contacts that is greater than a saturation level of the current transformer. 
         [0029]    In example embodiments of the present inventive subject matter, the circuit breaker may further include an ambient temperature circuit, a transistor, and a trip comparator. The ambient temperature circuit may include a controllable voltage source integrated circuit with a first input coupled to a reference voltage, a second input coupled to ground and a first output coupled to an output node of the ambient temperature circuit, a variable resistor coupled to the reference voltage and to the output node of the ambient temperature circuit, and an ambient thermal diode coupled to the output node of the ambient temperature circuit and to ground. The transistor may have a drain coupled to the reference voltage, a source coupled to ground and a gate coupled to a voltage across a thermal diode. The trip comparator may have a first input coupled to the output node of the ambient temperature circuit and a second input coupled to the drain of the transistor. An output of the trip comparator may be configured to cause the operating mechanism to open the set of contacts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The above and other features and advantages of the present inventive subject matter will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which: 
           [0031]      FIG. 1  is a block diagram of a circuit breaker according to some embodiments of the present inventive subject matter; 
           [0032]      FIG. 2  illustrates a three dimensional view of a bus bar according to some embodiments of the present inventive subject matter. 
           [0033]      FIG. 3  illustrates a circuit breaker according to further embodiments of the present inventive subject matter. 
           [0034]      FIG. 4  illustrates a circuit to provide power to circuit breakers according to some embodiments of the present inventive subject matter. 
           [0035]      FIG. 5  illustrates an input delay circuit which may be used in some embodiments of the present inventive subject matter. 
           [0036]      FIG. 6  illustrates an instantaneous trip circuit according to some embodiments of the present inventive subject matter. 
           [0037]      FIG. 7  illustrates a reference voltage transition from an initial period to a steady-state period according to some embodiments of the present inventive subject matter. 
           [0038]      FIG. 8  illustrates an overload trip circuit according to some embodiments of the present inventive subject matter. 
           [0039]      FIG. 9  illustrates a trip generation circuit according to some embodiments of the present inventive subject matter. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0040]    Advantages and features of the present inventive subject matter and methods of accomplishing the same may be understood more readily by reference to the following detailed description of preferred embodiments and the accompanying drawings. The present inventive subject matter may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the present inventive subject matter to those skilled in the art, and the present inventive subject matter will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification. 
         [0041]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present inventive subject matter. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0042]    It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on”, “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0043]    It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present inventive subject matter. 
         [0044]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present inventive subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0045]      FIG. 1  is a block diagram of a circuit breaker according to some embodiments of the present inventive subject matter. The circuit breaker  100  may be configured to open a set of contacts  150  to interrupt current flow through a set of conductors  181 ,  182 ,  183  in response to certain predetermined conditions. The contacts  150  may be opened by an actuator  120 . In some embodiments of the present inventive subject matter, the conductors  181 ,  182 ,  183  may represent phases of a multi-phase circuit. 
         [0046]    The actuator  120  may be controlled by a driver circuit  110  which is configured to trip the actuator  120  to open the sets of contacts  150  in response to certain conditions, such as a short circuit or overload condition. The driver circuit  110  may control the actuator  120  in response to inputs provided by an instantaneous trip circuit  130  and an overload trip circuit  140 . The instantaneous trip circuit  130  and the overload trip circuit  140  are two examples of inputs in to the driver circuit  110 . The driver circuit  110  may also control the actuator  120  in response to other inputs. 
         [0047]    The instantaneous trip circuit  130  may be configured to trip the circuit breaker  100  when an instantaneous value of the current flowing through a conductor exceeds a predetermined value. This may indicate that a short circuit has occurred. The instantaneous trip circuit  130  may be connected to current transformers  191 ,  192 ,  193  which may be operatively coupled to at least one conductor. For example, the current transformers  191 ,  192 ,  193  may be operatively coupled to three conductors  181 ,  182 ,  183 , as shown in  FIG. 1 , where each conductor can represent one phase of a three-phase power circuit. The conductors  181 ,  182 ,  183  may be coupled, for example, to connectors or terminal blocks that are configured to be connected to external wires or cables protected by the circuit breaker  100 . The current transformers  191 ,  192 ,  193  may be configured to generate an induced current i CT  in response to the current flowing through the conductors  181 ,  182 ,  183 . The induced current i CT  may be proportional to the current flowing through the conductors  181 ,  182 ,  183 . For example, a higher magnitude of alternating current flowing through the conductors  181 ,  182 ,  183  can result in a higher induced alternating current i CT  being generated by the current transformers  191 ,  192 ,  193 . A lower magnitude of alternating current flowing through the conductors  181 ,  182 ,  183  can result in a lower induced alternating current i CT  being generated by the current transformers  191 ,  192 ,  193 . 
         [0048]    The induced current i CT  from the current transformers  191 ,  192 ,  193  may be sensed by the instantaneous trip circuit  130 . The instantaneous trip circuit  130  can be configured to monitor the induced current i CT  to determine if the current flowing through the conductors  181 ,  182 ,  183  has exceeded a predetermined limit. If the instantaneous trip circuit  130  determines that the current flowing through the conductors  181 ,  182 ,  183  exceeds the predetermined limit, the instantaneous trip circuit  130  can provide an input to the driver circuit  110 , which can cause the actuator  120  to open the contacts  150 . 
         [0049]    The current transformers  191 ,  192 ,  193  may also be used to power the circuit breaker  100 . In particular, the current transformers  191 ,  192 ,  193  can provide power to the other elements of the circuit breaker  100  to facilitate the operation thereof. 
         [0050]    The overload trip circuit may be configured to trip the circuit breaker  100  when a cumulative value of the current flowing through a conductor exceeds a predetermined level. This can indicate that a cumulative load on the circuit breaker  100  exceeds the rating of the circuit breaker  100 , such as when the circuit is overloaded. 
         [0051]    The overload trip circuit  140  may receive input from thermal diodes  171 ,  172 ,  173 . The thermal diodes  171 ,  172 ,  173  may be placed internal to, or external to, the circuit breaker  100 . While  FIG. 1  shows three thermal diodes, the overload trip circuit  140  may accept input from more than three or fewer than three temperature sensors. The thermal diodes  171 ,  172 ,  173  may be configured so that there is one thermal diode for conductor, i.e., there may be a thermal diode associated with each phase, such that thermal diode  171  corresponds to conductor  181 , thermal diode  172  corresponds to conductor  182 , and thermal diode  173  corresponds to conductor  183 . The thermal diodes  171 ,  172 ,  173  may be placed at any of a variety of different positions on the conductors  181 ,  182 ,  183 . In some embodiments, multiple thermal diodes may be thermally coupled to each of the conductors  181 ,  182 ,  183 . The thermal diodes  171 ,  172 ,  173  may also be placed so that some conductors  181 ,  182 ,  183  have a thermal diode placed on them while other conductors do not. 
         [0052]    The overload trip circuit  140  can use the input from the thermal diodes  171 ,  172 ,  173  to determine if the load served by the conductors  181 ,  182 ,  183  has exceeded a predetermined limit. If the overload trip circuit  140  determines that the load exceeds the predetermined limit, the overload trip circuit  140  can provide input to the driver circuit  110 . The driver circuit  110  may then engage the actuator  120  to open the contacts  150 . 
         [0053]    The overload trip circuit  140  may also receive input from an ambient temperature compensation circuit  160 . The ambient temperature compensation circuit can provide an estimate of an ambient temperature of the circuit breaker  100 . The overload trip circuit  140  can use the input of the ambient temperature compensation circuit  160  to adjust the predetermined limit at which the overload trip circuit  140  trips. 
         [0054]    Based on the input of the ambient temperature compensation circuit  160 , the overload trip circuit  140  may alter the predetermined limit at which the circuit breaker  100  is tripped. For instance, if the ambient temperature compensation circuit  160  provides input corresponding to a higher ambient temperature, the overload trip circuit  140  may increase the conductor temperature (as sensed by the thermal diodes  171 ,  172 ,  173 ) at which the circuit breaker  100  will be tripped. In other embodiments, in response to a higher temperature reported by the ambient temperature compensation circuit  160 , the overload trip circuit  140  may decrease the conductor temperature at which the circuit breaker  100  will be tripped. 
         [0055]    The ambient temperature compensation circuit  160  may use thermal sensors such as those employed by the overload trip circuit  140  to determine the ambient temperature. In some embodiments, the ambient temperature compensation circuit  160  may use thermal sensors different than those employed by the overload trip circuit  140 . 
         [0056]      FIG. 2  illustrates a three dimensional view of a bus bar that may be used for the conductors  181 ,  182 ,  183  according to some embodiments of the present inventive subject matter. The bus bar  200  may comprise a top portion  210  and a bottom portion  220 . The thermal diode  171  may be attached to the top portion  210 . The top portion  210  may be connected to the bottom portion  220  through a cylindrical connector  230 . The cylindrical connector  230  may pass through a current transformer  191  such that the current transformer  191  encloses the cylindrical connector  230 . 
         [0057]    Current flowing through the bus bar  200  may flow through the top portion  210 , the cylindrical connector  230  and the bottom portion  220 . Multiple bus bars  200  may be utilized by the circuit breaker  100 . For example, the circuit breaker  100  may comprise three bus bars  200 , one for each phase of a three-phase power system. The example embodiment illustrated in  FIG. 2  is an example bus bar of the present inventive subject matter only and the present inventive subject matter is not limited thereto. A person of skill in the art will recognize that there are multiple configurations of bus bars using thermal diodes and current transformers which can embody the present inventive subject matter 
         [0058]      FIG. 3  illustrates a circuit breaker according to further embodiments of the present inventive subject matter. The circuit breaker  100  may include bus bars  200  such as those illustrated in  FIG. 2 . The circuit breaker  100  may also include a switch handle  310 . The switch handle  310  position can correspond to the position of the contacts  150  illustrated in  FIG. 1 . When the contacts  150  are closed, the switch handle  310  may be closed and when the contacts  150  are open, the switch handle  310  may be open. The switch handle  310  may be manually moved to the open or closed position. Additionally, the switch handle  310  may be automatically moved to the open position by the circuit breaker  100  when the circuit breaker  100  is tripped. 
         [0059]      FIG. 4  illustrates a circuit to provide power to circuit breakers according to some embodiments of the present inventive subject matter. 
         [0060]    As shown  FIG. 4 , the current transformer  191  can be coupled to a power supply generating circuit  400  that receives an induced current i CT  from the current transformer. While a single current transformer  191  is illustrated, multiple current transformers, such as, for example, current transformers  191 ,  192 ,  193 , may be coupled together to provide power to the circuit. In particular, the power supply generating circuit  400  may accept the power input from multiple current transformers  191 ,  192 ,  193 . A single current transformer  191  coupled to a single conductor, such as the conductor  181  in  FIG. 1 , is shown for illustrative purposes only. 
         [0061]    The current transformer  191  can be coupled to the power supply generating circuit  400 , such as through connector  410 , to name one example. The induced current i CT  can flow between the current transformer  191  and the power supply generating circuit  400 . 
         [0062]    As shown in  FIG. 4 , the power supply generating circuit  400  can include a full wave rectifier  420 . The output of the full wave rectifier  420  can be coupled both to energy storage capacitors  430 ,  440  and the peak detection circuit  500 . The peak detection circuit  500  will be discussed in more depth with respect to  FIG. 5 . 
         [0063]    The charge capacitors  430 ,  440  can charge to a voltage V chg  based on the output of the full wave rectifier  420 . By way of example,  FIG. 4  shows a charge voltage of 24V being stored across charge capacitors  430 ,  440 . 
         [0064]    The power stored in the power supply generating circuit  400  can be utilized in multiple ways by the circuit breaker  100 . In some examples of embodiments of the present inventive subject matter, this stored charge can be used to generate other power supply voltages for use in the circuit breaker  100 . For example, the 24V stored across charge capacitors  430 ,  440  could be converted to 5V secondary output voltage  480  for use in other areas of the circuit breaker  100 . 
         [0065]    The secondary voltage conversion to 5V illustrated in  FIG. 4  can be accomplished by a voltage regulation integrated circuit  450 . The voltage regulation integrated circuit  450  can be coupled to the charge capacitors  430 ,  440  such that the charge stored in the charge capacitors  430 ,  440  can be an input into the voltage regulation integrated circuit  450 . An output of the voltage regulation integrated circuit  450  can be used to power other parts of the circuit breaker  100 . As an example only,  FIG. 4  illustrates a secondary output voltage  480  of 5V being provided as output of the power supply generating circuit  400 . 
         [0066]    The magnetizing coils of the current transformer  191  may experience saturation from currents within the conductor  181 , such as where a short circuit occurs in the wiring protected by the breaker. When saturation occurs, the correspondence between the induced current i CT  and the current passing the conductor  181  may change. Because the circuit breaker  100  is designed to detect such high currents as part of its operation, the coils of the current transformer  191  can saturate. In some embodiments, the current transformer  191  may saturate at relatively low current levels. This saturation may not affect the capability of the current transformer  191  to provide power to both the circuit and the charge capacitors  430 ,  440 . Embodiments of the circuit breaker  100  can include additional circuitry to discharge the current transformer  191  and demagnetize the coils of the current transformer  191  in the event the circuit breaker  100  trips. 
         [0067]    The secondary output voltage conversion illustrated in  FIG. 4  is provided for example purposes only and is not meant to be limiting. Some embodiments of the present inventive subject matter can provide power to the control circuit in ways other than the capacitor and voltage regulator shown. 
         [0068]      FIG. 5  illustrates an input delay circuit  500  which may be used in some embodiments of the present inventive subject matter. 
         [0069]    For ease of identification,  FIG. 5  includes the full wave rectifier  420  and connector  410  discussed with respect to  FIG. 4 . The output of the full wave rectifier  420  may be coupled to the input delay circuit  500 . The output of the full wave rectifier  420  generates a current in current sense resistor  510  contained in the input delay circuit  500 . 
         [0070]    The current through the current sense resistor  510  may also be coupled to delay transistor  520 . The delay transistor  52 Q functions in conjunction with delay capacitors  530 ,  540  to delay a peak level corresponding to the current flowing through sense resistor  510 . 
         [0071]    The input delay circuit  500  may allow for the peak level of the current flowing through the sense resistor  510  to be delayed for a period of time while the current flowing through the sense resistor  510  continues to transition. The input delay circuit  500  may introduce a delay of one to two milliseconds. The delayed signal can then fed into an input of the signal amplifier  550 . The output of the signal amplifier  550  may be output from the input delay circuit (shown as ISP in  FIG. 5 ) to other parts of the circuit breaker  100 . 
         [0072]      FIG. 6  illustrates an instantaneous trip circuit  600  according to some embodiments of the present inventive subject matter. The instantaneous trip circuit  600  may receive as input the output of the input delay circuit  500 . This input is illustrated, for example, as ISP in  FIG. 6 . 
         [0073]    The instantaneous trip circuit  600  can generate an instantaneous trip signal  650  via the use of an instantaneous trip comparator  640 . The instantaneous trip comparator  640  takes as input an adjusted value of output of the input delay circuit  500  and an output of a reference voltage generating circuit  660 . 
         [0074]    The output of the input delay circuit  500  may be coupled to a variable instantaneous trip resistor  610 . The variable instantaneous trip resistor  610  may allow for adjustment of the output of the input delay circuit  500  being input into the instantaneous trip comparator  640 . In other words, by adjusting the resistance value of the variable instantaneous trip resistor  610 , the value of a signal being input into the instantaneous trip comparator  640  may be made higher or lower depending on the adjustment. In this way, the current level at which the instantaneous trip function of the circuit breaker  100  will be activated can be adjusted. The variable instantaneous trip resistor  610  may be configured so that it can be adjusted during fabrication and/or by a user of the circuit breaker  100 . Further embodiments of the present inventive subject matter may replace the variable instantaneous trip resistor  610  with a resistor that is not adjustable. 
         [0075]    As noted, the second input into the instantaneous trip comparator  640  may be the output of the reference voltage generating circuit  660 . The reference voltage generating circuit  660  may be composed of a voltage divider comprising reference voltage capacitors  620 , 630 . The reference voltage generating circuit  660  is configured to store a reference voltage on the reference voltage capacitors  620 , 630  based on the secondary output voltage  480 . As illustrated in  FIG. 1  and  FIG. 4 , the secondary output voltage  480  corresponds to the current provided by the current transformers  191 ,  192 ,  193 . 
         [0076]    In  FIG. 6 , the input voltage is shown, by way of example, as the 5V secondary output voltage  480 . As illustrated in  FIG. 4 , some embodiments of the present inventive subject matter can generate the 5V secondary output voltage  480  from a voltage of greater magnitude provided by the current transformers  191 ,  192 ,  193 . Though a 5V signal is illustrated in  FIG. 6 , the input voltage can be a different level and the present inventive subject matter is not limited thereto. 
         [0077]    The reference voltage generating circuit  660  may store a charge on the reference voltage capacitors  620 , 630  and the voltage stored on the reference voltage capacitors  620 , 630  may become an input into the instantaneous trip comparator  640 . In a steady-state operation, the voltage stored on the reference voltage capacitors  620 , 630  may be relatively constant, which may allow for a level at which the circuit breaker  100  will trip to remain constant as well. 
         [0078]    However, in an initial period of the circuit breaker  100 , the circuit breaker  100  may be closed onto a set of conductors  181 ,  182 ,  183  which are already shorted. As shown in  FIG. 4 , the peak value of the induced current i CT  from the current transformers  191 ,  192 ,  193  may be determined by the primary current through the conductors  181 ,  182 ,  183  and the bus voltage (charge capacitors  430 ,  440 ). During the initial period, the bus voltage may increase from a start-up level (e.g., zero volts) as power is applied. During steady state operation after the initial period, the bus voltage may be relatively constant. The induced current i CT  may be smaller in the initial period than in the steady state operation. A circuit which compared a detected peak value to a static predetermined value could fail to trip the circuit breaker  100  during the initial period when the circuit voltages are lower than the steady state values. In other words, the initial stages of a monitoring circuit experiencing an instantaneous trip may require a lower instantaneous trip value than may be required in the same circuit during steady state operation. Such a lower instantaneous trip value may not be provided by a circuit which uses a static comparison to determine whether the circuit breaker  100  should be tripped. 
         [0079]    Embodiments of the present inventive subject matter can address this issue by determining whether the circuit breaker  100  should be tripped based on a comparison of the induced current i CT  with the reference voltage generating circuit  660  as illustrated in  FIG. 6 . In the initial stages of operation for the circuit breaker  100 , the voltage divider circuit comprising reference voltage capacitors  620 , 630  may be charged by the secondary output voltage  480 , which may be generated by the power supply generating circuit  400  illustrated in  FIG. 4 . 
         [0080]    During the initial time, the voltage stored in the reference voltage capacitors  620 , 630  may also decrease and rise, respectively. As a result, the voltage provided as input to the instantaneous trip comparator  640  may also rise. In this way, the level at which the instantaneous trip circuit  600  can trip will start at a lower level and rise to a higher steady state level. This operation can allow the beneficial result that the instantaneous trip circuit  600  can detect early phases of an instantaneous trip condition that could otherwise be missed. 
         [0081]    As illustrated in  FIG. 6 , the output of the instantaneous trip circuit  600  may be an instantaneous trip signal  650 . This signal can be provided to other elements of the circuit breaker  100  as described herein. 
         [0082]      FIG. 7  illustrates a reference voltage transition from an initial period to a steady-state period according to some embodiments of the present inventive subject matter. 
         [0083]      FIG. 7  illustrates the rising reference voltage  710  during the initial period of the charging of the reference voltage capacitors  630 ,  63 Q, as described herein. The reference voltage  710  will rise from a lower level during an initial period to a higher level during a steady-state period such that the circuit breaker  100  can correctly trip in early stages of operation. 
         [0084]      FIG. 8  illustrates an overload trip circuit  800  according to some embodiments of the present inventive subject matter. 
         [0085]    The overload trip circuit  800  can include an overload trip comparator  810 . The overload trip comparator  810  may take as input the output of a temperature measurement circuit  830  and an ambient adjustment circuit  820 . The ambient adjustment circuit  820  is a reference circuit with an ambient temperature adjustment function. The overload trip circuit  800  may be powered by the secondary output voltage  480  illustrated in  FIG. 4 . 
         [0086]    The temperature measurement circuit  830  can take as input the signal from a temperature sensor. The temperature sensor  815  can be connected to the temperature measurement circuit  830 , for example, at the temperature connectors  840  illustrated in  FIG. 8 . The temperature sensor can be either internal or external to the circuit breaker  100 . That is to say that the signal from the temperature sensor  815  may be provided to the circuit breaker  100  by an external temperature sensor rather than being generated from within the circuit breaker  100 . 
         [0087]    Though a single temperature sensor  815  is illustrated in  FIG. 8 , multiple temperature sensors could be used. 
         [0088]    The temperature transistor  845  can be configured to latch the output of the temperature sensor  815 . When the signal as provided by the temperature sensor  815  exceeds a predetermined limit, the temperature transistor  845  and circuit elements will transition the signal provided to the overload trip comparator  810 . 
         [0089]    The second input to the overload trip comparator  810  can be the output of an ambient adjustment circuit  820 . The ambient adjustment circuit  820  may be configured to provide a signal to the overload trip comparator  810  corresponding to an ambient temperature measurement. 
         [0090]    The ambient adjustment circuit  820  may contain an ambient thermal diode  850  which is configured to alter its resistance in response to a change in temperature. Though the ambient thermal diode  850  is illustrated as an example for generating an ambient thermal measurement, those of ordinary skill in the art will recognize that the ambient thermal diode  850  could be replaced by other temperature sensors. In addition, the ambient thermal diode  850  could be either internal or external to the circuit breaker  100 . Similarly, the measurement provided by the ambient thermal diode  850  could be provided by more than one thermal diode, or via a combination of ambient thermal sensors. 
         [0091]    The ambient thermal diode  850  may be coupled to a controllable voltage source integrated circuit  860  which regulates the output provided to the overload trip comparator  810  based on the voltage of the ambient thermal diode  850  as well as other elements of the ambient adjustment circuit  820 . 
         [0092]    Some embodiments of the present inventive subject matter may allow the output provided to the overload trip comparator  810  by the ambient adjustment circuit  820  to be altered by adjustment of a variable ambient resistor  870 . In other words, by adjusting the resistance value of the ambient resistor  870 , the value of a signal being input into the overload trip comparator  810  may be made higher or lower depending on the adjustment. In this way, the level at which the overload function of the circuit breaker  100  will be engaged can be adjusted. The variable ambient resistor  870  may be configured so that it can be adjusted manually by a user of the circuit breaker  100 . Alternatively, the variable ambient resistor  870  may not allow for adjustment once it has been initially set to a value. Further embodiments of the present inventive subject matter may replace the variable ambient resistor  870  with a resistor that is not adjustable. 
         [0093]    As illustrated in  FIG. 8 , the output of the overload trip circuit  800  may be an overload trip signal  890 . This signal can be provided to other elements of the circuit breaker  100  as described herein. 
         [0094]      FIG. 9  illustrates a trip generation circuit  900  according to some embodiments of the present inventive subject matter. 
         [0095]    The trip generation circuit  900  can be coupled to the actuator  120  so as to enable the opening of the contacts  150  as illustrated in  FIG. 1 . The actuator  120  can be connected to the trip generation circuit  800 , for example, via connectors such as the trip connectors  940  illustrated in  FIG. 8 . 
         [0096]    The trip generation circuit  900  can take as inputs the instantaneous trip signal  650  illustrated in  FIG. 6  and the overload trip signal  790  illustrated in  FIG. 7 . The trip generation circuit  900  can energize the actuator  120  when either of the instantaneous trip signal  650  or the overload trip signal  890  is activated. 
         [0097]    While only the instantaneous trip signal  650  and the overload trip signal  890  are illustrated in  FIG. 9 , those of ordinary skill in the art will recognize that additional signals could be provided to activate the trip generation circuit  900  without impacting the present inventive subject matter. Similarly, some embodiments of the present inventive subject matter could also involve the use of only the instantaneous trip signal  650  or only the overload trip signal  890 . 
         [0098]    As illustrated in  FIG. 9 , the activation of the actuator  120  can be controlled by a MOSFET  930 . The input voltage to the MOSFET  930  can be coupled to signal diodes  910 , 920  which are coupled to the instantaneous trip signal  650  and the overload trip signal  890 , respectively. The signal diodes  910 , 920  can be configured to perform a logical OR operation such that if either the instantaneous trip signal  650  or the overload trip signal  890  is activated, the secondary output voltage  480  can be provided to the input of the MOSFET  930 . A trip capacitor  960  can thus be charged to provide a current through the MOSFET  930  to energize the actuator  120 . 
         [0099]    The foregoing is illustrative of the present inventive subject matter and is not to be construed as limiting thereof. Although a few embodiments of the present inventive subject matter have been described, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the present inventive subject matter. Accordingly, all such modifications are intended to be included within the scope of the present inventive subject matter as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present inventive subject matter and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The present inventive subject matter is defined by the following claims, with equivalents of the claims to be included therein.