Patent Publication Number: US-2023133287-A1

Title: Trip unit with high-load analysis

Description:
BACKGROUND 
     Field 
     The disclosed concept relates generally to circuit interrupters, and in particular, to capturing information about high-load events in a circuit interrupter. 
     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. Circuit breakers typically include separable contacts. The separable contacts may be operated either manually by way of an operator handle or automatically in response to a detected fault condition. Typically, such circuit breakers include an operating mechanism, which is designed to rapidly open and close the separable contacts, and a trip mechanism, such as a trip unit, which senses a number of fault conditions to trip the breaker automatically. Upon sensing a fault condition, the trip unit causes the operating mechanism to trip open the separable contacts. 
     One type of event that can cause a circuit breaker trip unit to initiate a trip is a high load that draws current in excess of the rated breaker current. Circuit breakers typically include some type of mechanism for indicating that a high load condition has occurred, however, these mechanisms generally only indicate the time of the occurrence and a snapshot of RMS currents measured at the starting time of the high load condition. These snapshots do not provide detailed information about the duration of the high-load condition or the characteristics of the current profile over that duration. Such detailed information is important to have, as sustained high load conditions are likely to be indicative of more serious issues with the circuit breaker load setup than transient high load conditions are. 
     There is thus room for improvement in capturing information about high load events in circuit interrupters. 
     SUMMARY 
     These needs and others are met by embodiments of the disclosed concept in which an electronic trip unit for a circuit interrupter provides detailed information about conditions present during high load events in a circuit interrupter. The trip unit compiles the metrics of a high load event using data collected throughout the duration of the event. 
     In accordance with one aspect of the disclosed concept, an electronic trip unit for a circuit interrupter comprises: a processor with a timer and structured to receive an output of a current sensor sensing current flowing through a busbar of the circuit interrupter, and a user interface. The processor is configured to detect a high load condition in the circuit interrupter based on the sensed current, and to capture a plurality of metrics of the high load condition. The plurality of metrics are based on data captured throughout the entire duration of the high load condition, and the processor is configured to display the plurality of metrics on the user interface. 
     In accordance with another aspect of the disclosed concept, a circuit interrupter comprises: a first terminal and a second terminal; a busbar disposed between the first terminal and the second terminal; separable contacts structured to be moveable between a closed position and an open position, the first and second terminals being electrically disconnected from each other when the separable contacts are in the open position; an operating mechanism structured to open and close the separable contacts; a current sensor configured to sense current flowing through the busbar; a user interface; and an electronic trip unit structured to actuate the operating mechanism. The electronic trip unit comprises a processor with a timer and is structured to receive an output of the current sensor. The processor is configured to detect a high load condition in the circuit interrupter based on the sensed current, and to capture a plurality of metrics of the high load condition. The plurality of metrics are based on data captured throughout the entire duration of the high load condition, and the processor is configured to display the plurality of metrics on the user interface. 
     In accordance with another aspect of the disclosed concept, a method of informing a user of a circuit interrupter that a high load condition is present in the circuit interrupter comprises: providing a current sensor structured to sense current flowing through a busbar of the circuit interrupter; providing an electronic trip unit, the electronic trip unit being structured to receive an output of the current sensor, and comprising a processor with a timer and a user interface; detecting, with the processor, a high load condition in the circuit interrupter based on the sensed current; capturing, with the processor, a plurality of metrics of the high load condition; and displaying the plurality of metrics on the user interface, wherein the plurality of metrics are based on data captured throughout the entire duration of the high load condition. 
    
    
     
       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 including a high load event detector in accordance with an example embodiment of the disclosed concept; 
         FIG.  2    is an illustrative example of a trip curve that can be used by the high load event detector shown in  FIG.  1    in accordance with an example embodiment of the disclosed concept; 
         FIG.  3    is a graph of two current-time curves corresponding to two different high load events, 
         FIG.  4 A  shows a waveform capture of a high load event provided to a user of the circuit interrupter shown in  FIG.  1   , in accordance with an example embodiment of the disclosed concept; 
         FIG.  4 B  shows a RMS capture of a high load event provided to a user of the circuit interrupter shown in  FIG.  1   , in accordance with an example embodiment of the disclosed concept; 
         FIG.  4 C  shows an additional RMS capture of a high load event provided to a user of the circuit interrupter shown in  FIG.  1   , in accordance with an example embodiment of the disclosed concept; and 
         FIG.  5    is a flow chart of a method for providing detailed information about high load events to a user of a circuit interrupter in accordance with example embodiments 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 used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. 
     As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. As used herein, “directly coupled” means that two elements are directly in contact with each other. As used herein, “fixedly coupled” or “fixed” means that two components are coupled so as to move as one while maintaining a constant orientation relative to each other. As used herein, “movably coupled” means that two components are coupled so as to allow at least one of the components to move in a manner such that the orientation of the at least one component relative to the other component changes. 
     As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
     As employed herein, the term “processor” shall mean a programmable analog and/or digital device that can store, retrieve and process data; a controller; a control circuit; a computer; a workstation; a personal computer; a microprocessor; a microcontroller; a microcomputer; a central processing unit; a mainframe computer; a mini-computer; a server; a networked processor; or any suitable processing device or apparatus. 
       FIG.  1    is a schematic diagram of a circuit interrupter  10  in accordance with an example embodiment of the disclosed concept. The circuit interrupter  10  includes a first terminal  11 , a second terminal  12 , a line conductor  14  connecting the first terminal  11  and second terminal  12 , separable contacts  16 , and an operating mechanism  18 . The line conductor  14  may be comprised of one or more busbars. The separable contacts  16  are disposed along the line conductor  14  such that tripping open the separable contacts  16  stops current from flowing through the line conductor  14  from the first terminal  11  to the second terminal  12 . The operating mechanism  18  is structured to trip open the separable contacts  16 . 
     The circuit interrupter  10  also includes a current sensor  20  structured and disposed to sense current flowing through the line conductor  14  (i.e., the busbars of the line conductor  14 ). However, it will be appreciated that the current sensor  20  may also be employed to sense current flowing through a neutral conductor without departing from the scope of the disclosed concept. The circuit interrupter  10  further includes an electronic trip unit  22  with a processor  24 . Processor  24  may comprise, for example and without limitation, a microprocessor. The processor  24  includes a high load event detection module  26  with a timer  28  and sampling device  30  (detailed further herein), and is structured to receive the output of the current sensor  20  and to detect faults in the circuit interrupter  10  based on the sensed current. In response to detecting a fault, the electronic trip unit  22  is structured to cause the operating mechanism  18  to trip open the separable contacts  16 . The high load event detection module  26  encompasses software and/or firmware instructions for executing high load event detection functions, as detailed herein with respect to the remaining figures. The data determined during high load event detection can be presented to a user of the circuit interrupter  10  by a user interface  32  configured to be in electrical communication with the trip unit processor  24 . The user interface  32  may comprise, for example and without limitation, either a hardware component of the circuit interrupter  10  or a remote dashboard accessed via a remote computing device, or both. 
     Referring now to  FIG.  2   , a graph of a high load trip curve  40  is shown. The high load detector  26  of circuit interrupter  10  is configured to determine, in accordance with a trip curve such as trip curve  40 , how long a high load condition should be permitted to persist before the electronic trip unit  22  initiates a trip. The trip curve  40  plots time against RMS current (I RMS ) and depicts how quickly a trip will be initiated at various high load current levels. It should be noted that trip curve  40  is plotted logarithmically on both the x- and y-axes. The x-axis depicts current levels that are expressed as multiples of the current rating of circuit interrupter  10  such that, for a current rating of R, each increment on the x-axis can be expressed as nR, wherein n is an integer. The y-axis denotes the amount of time that has elapsed since the current flowing through the circuit interrupter  10  has reached a given amperage. 
     Still referring to  FIG.  2    and trip curve  40 , three different types of data points reflecting events captured by a high load detector  26  are displayed on the graph, as noted in the legend. The three types of data points displayed are: high load no trip (referred to hereinafter as “high load”), short delay fault no trip (referred to hereinafter as “short delay fault”), and trip. It should be noted that any values falling below trip curve  40  are indicative of current levels and durations that do not cause the trip unit  22  to initiate a trip, and that any values occurring above trip curve  40  are indicative of current levels and durations that do cause the trip unit  22  to initiate a trip. It will be appreciated that it is often desirable for circuit interrupters such as circuit interrupter  10  to have either or both short delay and long delay settings activated so that transient overcurrent conditions do not cause the circuit interrupter to trip, and the presence of both high load and short delay fault data points in  FIG.  2    indicates activation of both short delay and long delay settings. 
     It will be further appreciated that relatively lower overcurrent conditions can be permitted to persist for a longer period of time before initiating a trip, and that relatively higher overcurrent conditions should only be permitted to persist for a short period of time before initiating a trip. In addition, the processor  24  may optionally be configured to store more than one trip curve  40  in memory such that a user may choose a trip curve  40  corresponding to a particular use or application of the circuit interrupter  10 . The relatively lower overcurrent conditions that can persist for a longer period of time are referred to hereinafter as high load events, and the relatively higher overcurrent conditions that should only persist for a shorter period of time are referred to hereinafter as short delay faults. The left-hand portion of the trip curve  40  as denoted by reference number  42  is the region in which high load events occur, as data points falling under the trip curve  40  in this region have lower amperage values and correspond to more time having elapsed relative to the right-hand side of the curve  40 . The right-hand portion of trip curve  40  denoted by reference number  44  is the region in which short delay faults occur, as data points falling under the trip curve  40  in this region have higher amperage values and correspond to less time having elapsed relative to the left-hand side of the curve  40 . The innovations of the present disclosure are directed toward activity occurring in the high load region  42  rather than in the short delay fault region  44 . 
     As previously stated, the high load detector  26  of circuit interrupter  10  is configured to determine, in accordance with a trip curve such as trip curve  40 , how long an overcurrent condition should be permitted to persist before the electronic trip unit  22  initiates a trip. It is expected that current levels occurring above trip curve  40  may cause irreparable damage to components of the circuit interrupter  10  within a relatively short amount of time, which is why the trip data points in  FIG.  2    occur just above the trip curve in both the high load region  42  and the short delay fault region  44 . Current that reaches the magnitude of a predetermined threshold monitoring level triggers the timer  28  of high load detector  26 . For each given level of current within the area under the trip curve  40  in  FIG.  2   , the given current level can continue to flow for a predetermined length of time (in accordance with the trip curve  40 ), as monitored by timer  28 , before the trip unit  22  initiates a trip. The timer  28  is configured to run for as long as the current remains at or above the threshold monitoring level. In addition, the length of time that a given level of overcurrent can flow encompasses a tolerance level, as denoted by the thickness T of curve  40 . For example and without limitation, if a high load current of 200 A should generally only be allowed to flow for 100 seconds before the trip unit  22  initiates a trip, for a chosen tolerance level of ±10%, a current of 200 A may cause a trip after flowing for as little as 90 seconds (90% of 100 s) or could flow for as long as 110 seconds (110% of 100 s) before causing a trip, depending on what other factors the trip unit  22  is programmed to take into account before initiating a trip. 
     Referring to  FIG.  3   , two curves i 1  and i 2  are shown on a graph plotting current against time. Both curves i 1  and i 2  depict high load currents. Two levels of current, High Load and Pickup, are marked on the y-axis. High Load denotes an amperage level that is detected by the high load detector  26 , and Pickup denotes an amperage level that will cause the trip unit  22  to initiate a trip. It will be appreciated that the regions of the graph in  FIG.  3    can be related to the regions of the graph in  FIG.  2   . Specifically, current that reaches the High Load amperage level but does not reach the Pickup amperage level in  FIG.  3    corresponds to the high load region  42  of  FIG.  2   , while current that reaches the Pickup amperage level in  FIG.  3    corresponds to the values on the trip curve  40  in  FIG.  2   , and current that exceeds the Pickup amperage level in  FIG.  3    corresponds to the region above the trip curve  40  in  FIG.  2   . 
     However, there is a notable difference between the data presented in the graph of  FIG.  2    and the graph of  FIG.  3   . While the data points plotted in  FIG.  2    depict the highest level of current that was reached before the overcurrent condition ceased or before a trip was initiated, existing electronic trip units only provide information about the overcurrent condition from time t 1  of the graph in  FIG.  3   . That is, if an existing trip unit were to report the high load events depicted by i 1  and i 2  (referred to hereinafter as “event i 1 ” and “event i 2 ”, respectively), for either of event i 1  or event i 2 , said existing trip unit would simply report that a high load event occurred at time t 1 , i.e. the time when the curve i 1  or i 2  crossed the High Load threshold, and would provide a snapshot of the RMS current of event i 1  or i 2  at the starting time t 1  of the high load condition. So, even though curve i 1  and curve i 2  follow significantly different trajectories after time t 1 , the information presented to a user by an existing trip unit would make it appear that event i 1  and event i 2  were nearly identical. In contrast and as detailed further herein, the electronic trip unit  22  of the disclosed circuit interrupter  10  performs an extended capture of the high load event and informs the user of various metrics of the high load event such as the maximum amperage reached during the event (i.e. the data presented in the High Load region  42  of  FIG.  2   ) and the average high load current for the duration of the event, thus providing an improvement over high load monitoring performed by existing trip units. 
     Referring now to  FIGS.  4 A,  4 B, and  4 C , various data captures of an example high load 60 Hz current are shown, in accordance with exemplary embodiment of the disclosed concept. The captures shown in  FIGS.  4 A- 4 C  are representative of data captured by the sampling device  30  of the electronic trip unit  22 .  FIG.  4 A  shows an abbreviated waveform capture of the high load current. Specifically,  FIG.  4 A  depicts 0.6 seconds of AC waveform data such that 36 cycles of the 60 Hz current are depicted. The sampling device  30  samples at a rate of 80 samples/cycle.  FIGS.  4 B and  4 C  depict alternative metrics of the high load current, with each figure showing an abbreviated graph of metered values of the high load current, i.e. a collection of RMS values for a given interval of time. Specifically, for  FIG.  4 B , each data point in the graph denotes the RMS value of each individual cycle within a 6-second interval of the high load current signal. For  FIG.  4 C , the graph depicts an interval of 60 seconds divided into 200-ms periods, and each data point in the graph denotes the RMS value of the high load current for a corresponding 200-ms period. 
     It will be appreciated that the combination of the three different data captures shown in  FIGS.  4 A- 4 C  provides a well-rounded depiction of the high load event, as the three measurements encompass varying degrees of the trade-off between data resolution and duration. It will be appreciated that time intervals and sampling rates used in  FIGS.  4 A- 4 C  are intended to be non-limiting illustrative examples, and that time intervals and sampling rates other than those used to generate the data captures shown in  FIGS.  4 A- 4 C  can be used to generate useful data captures without departing from the scope of the disclosed concept. 
     Detailed high load data determined by the high load event detector  26 , such as the waveform captures and RMS metered values shown in  FIGS.  4 A- 4 C , can be displayed on the user interface  32 . In particular, said detailed high-load data can be displayed in graphical format alongside the relevant trip curve  40 , allowing the high-load data to be easily compared to the trip curve  40 . Presenting said detailed high load data and/or presenting a comparison against a trip curve  40  constitutes a significant benefit provided by the systems and methods disclosed herein, as existing circuit breaker trip units provide limited information about high load conditions. In existing breakers, the presence of a high-load current is indicated, but these captures only denote the time of the entry into the high-load condition and a snapshot of the RMS current at the time of entry into the high load condition. In these existing systems, a user is presented with nearly identical high load event captures for two drastically differing high load currents, as previously detailed with respect to curves i 1  and i 2  in  FIG.  3   . This limited data capture provided by existing trip units leaves a significant gap in the information available to the user, as the user cannot tell whether the high load condition was relatively transient or whether the high-load current steadily increased in RMS value over the duration of the event. Furthermore, it should be noted that the plurality of event metrics discussed herein, i.e. waveform captures and multiple groups of metered RMS value data points for a given high load event, are generated by the single sampling device  30  of processor  24 . The ability of the single sampling device  30  to generate both waveform captures and multiples groups of metered RMS value data points for a given high load event, rather than necessitating multiple sampling devices, is another benefit provided by the systems and methods disclosed herein relative to existing trip units. 
     Referring now to  FIG.  5   , a flowchart of a method  100  for informing a user of a circuit interrupter of the details of high-load conditions is shown, in accordance with an example embodiment of the disclosed concept. The method of  FIG.  5    may be employed, for example, with the circuit interrupter  10  shown in  FIG.  1    and the user interface  32  shown in  FIG.  1   , with trip curves such as trip curve  40  shown in  FIG.  2   , and with data captures such as those shown in  FIGS.  4 A- 4 C , and the method is described in conjunction with the circuit interrupter  10 , user interface  32 , trip curve  40 , and data captures shown in  FIGS.  1 ,  2 ,  3 , and  4 A- 4 C . However, it will be appreciated that the method may be employed in other devices as well without departing from the scope of the disclosed concept. 
     The method begins at  101  where the current sensor  20  is provided and disposed around the line conductor busbar  14  of the circuit interrupter  10  in order to sense the current flowing through the busbar  14 . At  102 , the electronic trip unit  22  is provided such that the high load event detector  26  is configured to receive the output of the current sensor  20 , and the high load event detector  26  is programmed with a number of stored preset high load delays and a corresponding number of trip curves  40  such that each preset delay has an associated trip curve  40 . At  103 , the high load event detector  26  detects a high load condition in the circuit interrupter  10  based on the sensed current and in accordance with the trip curve corresponding to the preset delay chosen by the user. At  104 , the high load event detector  26  performs an extended capture of the high load event. Performing said extended capture may comprise, for example and without limitation, sampling data points from the high load current AC waveform and producing metered RMS values for various intervals of time, in order to obtain the data needed to produce graphs such as the graphs shown in  FIGS.  4 A- 4 C . 
     At  105 , after the current exits the high load condition, the high load event detector  26  displays a number of metrics of the high load event on the user interface  32 , said metrics being based on the data collected during the extended capture performed at step  104 . Said metrics displayed at step  105  may, for example and without limitation, be presented in the form of waveform and/or meter captures, such as those shown in  FIGS.  4 A- 4 C , and may also include information such as the maximum high load current reached during the high load event, or the average high load current calculated for the duration of the high load event. It will be appreciated that the current can exit the high-load condition either by decreasing below the high load threshold amperage, or by increasing to a pickup level amperage that causes the trip unit  22  to initiate a trip. In the event that exiting the high load condition constitutes the current decreasing below the high load threshold, the duration of the high load event spans from the time that the current meets the high load threshold to the time that the current decreases below the high load threshold. In the event that exiting the high load condition constitutes the current increasing until a trip is initiated, the duration of the high load event spans from the time that the current meets the high load threshold to the time that the trip is initiated. 
     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.