Abstract:
Predictive maintenance systems and methods are described. A method includes measuring environmental conditions using a plurality of sensors within the IED, processing the environmental measurements to determine long-term exposure factors representing historical operating conditions of the IED, applying a reliability model to the long-term exposure factors, determining a numerical measure of IED life based on the long-term exposure factors and the reliability model, comparing the numerical measure of IED life to preselected boundary values, and signaling if the numerical measure of IED life is outside of the preselected boundary values.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates generally to maintenance of intelligent electronic devices used in rugged environments and, more particularly, to systems and methods for facilitating predictive maintenance of intelligent electronic devices based on continuous monitoring of operating conditions, exposure to external factors, and reliability models embedded within the devices. 
         [0002]    Electrical grids including incorporated generation, transmission, distribution, and energy conversion means are often operated with the aid of intelligent electronic devices (IEDs). Such devices protect against faults and other abnormal conditions, monitor and meter energy usage, and control other aspects of electrical grid operations. Intelligent electronic devices include, but are not limited to including, protective relays, remote terminal units, programmable logic controllers (PLCs), meters, local human machine interfaces (HMIs), Ethernet switches and/or routers, modems, and other similar devices. 
         [0003]    Intelligent electronic devices are often installed and operated in harsh environments, such as high voltage substation control houses, medium voltage switchgear, power plants, industrial plants, and motor control centers. As such, IEDs are exposed to conditions such as extreme temperatures, electromagnetic interference, electrical surges, mechanical shocks and vibration, and chemical agents. At least some known IEDs are designed to withstand such conditions as prescribed by industry standards, established design practices, and/or based on competition between manufacturers. 
         [0004]    At least some known IEDs perform critical functions within an electrical grid, such as protection functions and/or control functions. As such, IEDs are needed that remain fully functional during a commissioned time. To ensure that the IEDs retain their desired functions and perform when and as necessary, the IEDs are periodically checked and/or maintained. Periodic maintenance procedures have changed since the use of a previous generation of protection, control, and/or metering devices that included electro-mechanical and analog technologies. At least some known periodic maintenance procedures include visually inspecting an IED for signs of problems and periodically taking the IED out of service, isolating the IED from the rest of the system to which it belongs, and testing the functionality of the IED. The maintenance intervals of such periodic maintenance procedures may be between 2 and 5 years, and are based on factors such as past experience of a given user, a make of the IED being inspected, average operating conditions, a criticality of the application, and other related factors. 
         [0005]    Such periodic maintenance procedures, however, are not optimized to consider IEDs having different life expectancies and/or failure rates. IEDs may be installed in operating conditions that differ considerably when compared to average expected operating conditions. Variable operating conditions include easily verifiable factors such as average ambient temperature, and hidden factors such exposure to electromagnetic interference and local operating temperature. Often, all IEDs in a given facility are maintained, regardless of the make and/or operating conditions of the IEDs. As a result, some percentage of IEDs are “over maintained” and some are “under maintained,” causing unexpected failures to occur. 
         [0006]    Such periodic maintenance procedures miss a significant potential for cost savings to users and/or operators of IEDs. For example, maintenance is an expensive operation due to the amount of associated labor and, in cases where device redundancy has not been employed, the maintenance may require shutting down protected and/or controlled processes and/or assets. In addition, unexpected failures of IEDs require emergency-style responses that involve unscheduled work, unscheduled spare material usage, additional urgency and a need to work without proper preparation, and/or unscheduled shutdowns of protected and/or controlled assets, which may then trigger shutdowns of associated process steps. 
         [0007]    At least some known IEDs include microprocessors that enable the IEDs to collect and analyze information from the sensors. However, systems and/or methods are needed that employ information collection and analysis to understand the operating conditions and exposures of IEDs in combination with an embedded knowledge of the life expectancies of the IEDs, such as a reliability model, to generate predictive maintenance requests and/or signals. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    In one aspect, a method for predicting maintenance of an intelligent electronic device (IED) is provided. The method includes measuring environmental conditions using a plurality of sensors within the IED, processing the environmental measurements to determine long-term exposure factors representing historical operating conditions of the IED, applying a reliability model to the long-term exposure factors, determining a numerical measure of IED life based on the long-term exposure factors and the reliability model, comparing the numerical measure of IED life to preselected boundary values, and signaling if the numerical measure of IED life is outside of the preselected boundary values. 
         [0009]    In another aspect, a system is provided for establishing and maintaining reliability models for a plurality of intelligent electronic devices (IEDs). The system includes an acquisition unit configured to acquire long-term exposure factors from the plurality of IEDs, an input unit configured to receive failure information from failed IEDs of the plurality of IEDs, and a processor configured to be coupled to the acquisition unit and the input unit. The processor is programmed to determine a reliability of each IED and derive a reliability model that correlates between the exposure factors and the reliability of each IED. 
         [0010]    In another aspect, a system is provided for monitoring operating conditions of an intelligent electronic device (IED) having a plurality of sensors therein for acquiring environmental data. The system includes an acquisition unit configured to acquire long-term exposure factors from the IED, an input unit configured to receive failure information the IED, and a processor configured to be coupled to the acquisition unit and the input unit. The processor is programmed to determine a reliability of the IED, derive a reliability model that correlates between the exposure factors and the reliability of the IED, compare the numerical measure of IED life to preselected boundary values, and generate a signal if the numerical measure of IED life is outside of the preselected boundary values. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The detailed description below explains the exemplary embodiments of the systems and methods described herein, including advantages and features, by way of example with reference to the drawings. 
           [0012]      FIG. 1  is a schematic diagram of an exemplary intelligent electronic device (IED) that may be used to monitor operating temperatures; 
           [0013]      FIG. 2  is a schematic diagram of an exemplary IED that may be used to monitor and/or measure electrical surges; 
           [0014]      FIG. 3  is a schematic diagram of an exemplary IED that may be used to detect improper grounding of inputs in relation to a grounding point; and 
           [0015]      FIG. 4  is a flowchart showing an exemplary predictive maintenance method. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Although the embodiments described below describe monitoring intelligent electronic device (IED) life based on environmental factors such as temperature, surges, and grounding, one of ordinary skill in the art would understand that other environmental factors may also be monitored. Moreover, one of ordinary skill in the art would understand that effects due to environmental factors may change due to flows in engineering or construction, unexpected events, and/or due to intentional use by a user that subjects the IED to accelerated wear. Further, it should be understood that miniaturization and/or integration enables an IED to include one sensor as described below, or a plurality of sensors, such that each IED may monitor multiple environmental factors concurrently. For example, and not by way of limitation, an IED may include a plurality of sensors that enable the IED to concurrently monitor mechanical shock, vibration, humidity, exposure to chemical factors, power supply levels, and/or radiated and/or conducted electromagnetic interference. 
         [0017]      FIG. 1  is a schematic diagram of an exemplary intelligent electronic device (IED)  100  that may be used to monitor operating temperatures. IED  100  includes a chassis  102  having a plurality of components  104  and at least one temperature sensor  106 . In the exemplary embodiment, components  104  are critical components within IED  100  such as, but not limited to, a capacitor, a microcontroller, a graphical display, and/or a communication transceiver. Temperature sensor  106  is positioned within IED  100  such that temperature sensor  106  may monitor temperature points inside IED  100  as well as a temperature of ambient air  108 . More specifically, temperature sensor  106  is positioned to facilitate an accurate estimation of a temperature of each component  104  and ambient temperature  108  in order for a processor  110  to determine a temperature gradient between each component  104  and ambient temperature  108 . 
         [0018]    During operation, and under steady state conditions, a temperature measured by temperature sensor  106  remains at a substantially constant offset ΔTA with respect to ambient temperature  108 . Moreover, the temperature measured by temperature sensor  106  remains at a substantially constant offset with respect to each component  104 . For example, the temperature measured by temperature sensor  106  remains at a substantially constant first offset ΔT 1  with respect to a first component  112 , and remains at a substantially constant second offset ΔT 2  with respect to a second component  114 . Each offset ΔTA, ΔT 1 , ΔT 2  is determined via calculations and/or measurements during IED construction and/or IED post-construction testing. 
         [0019]    In the exemplary embodiment, temperature sensor  106  measures a temperature within IED  100 . Temperature sensor  106  generates a signal representative of the measured temperature, and transmits the signal to processor  110 . Processor  110  determines an estimated temperature of each component  104  by adding or subtracting the known temperature offset. For example, processor  110  determines an estimated temperature of first component  112  by adding or subtracting ΔT 1 , as appropriate, from the temperature measured by temperature sensor  106 . Moreover, processor  110  determines an estimated temperature difference between an interior operating temperature of IED  100  and ambient temperature  108  by adding or subtracting ΔTA, as appropriate, from the temperature measured by temperature sensor  106 . 
         [0020]    One of ordinary skill in the art will understand that external conditions such as a style of mounting used for each component  104  and/or temperature sensor  106 , patterns of circulating air, and the like, may change a temperature profile within IED  100 , thereby affecting the accuracy of the estimation of the temperature of each component  104 . 
         [0021]      FIG. 2  is a schematic diagram of an exemplary IED  200  that may be used to monitor and/or measure electrical surges. IED  200  includes a plurality of inputs  202 , at least one grounding point  204 , and a plurality of surge suppressing circuits  206  that are coupled at a first end  208  to an input  202 . Each surge suppressing circuit  206  is also coupled at a second end  210  a shunt  212  to facilitate generating a measurable voltage across shunt  212 . Moreover, each surge suppressing circuit  206  is implemented using capacitors and/or non-linear resistors. Shunt  212  may be implemented by, for example and not by way of limitation, a resistor or an RLC circuit that is designed to capture desired frequency components in a surge current. In the exemplary embodiment, the voltage generated across shunt  212  is measured by a surge measuring circuit  214 . Surge measuring circuit  214  generates a signal representative of the measured voltage and transmits the signal to a processor  216 . The surge current that generated the measured surge voltage is then shunted by shunt  212  to grounding point  204 . In an alternative embodiment, shunt  212  is embodied by a plurality of capacitors to integrate high frequency components into a signal representative of the surge current, and surge measuring circuit  214  is implemented by a plurality of standard amplifiers. In such an embodiment, surge measuring circuit  214  amplifies the signal and transmits the signal to an analog-to-digital (A/D) converter (not shown) that digitizes the signal and transmits the digital signal to processor  216 . The remaining components of the surge current are shunted by shunt  212  to grounding point  204 . 
         [0022]    During operation, surge suppressing circuits  206  create a bypass path for high frequency signal components and shunt these components to grounding point  204  without exposing other internal circuitry (not shown) of IED  200  to excessive electrical stress. In the exemplary embodiment, a surge current flows into IED  200  through inputs  202 . The surge current flows from each input  202  through an associated surge suppressing circuit  206 , thereby bypassing the other internal IED circuitry. The surge current then flows through shunt  212 , generating a surge voltage that is proportional to the surge current and a resistance of shunt  212 . The surge current then flows to grounding point  204 . The surge voltage is measured by surge measurement circuit  214 . Surge measurement circuit  214  generates a signal representative of the surge voltage and transmits the signal to processor  216 . In an alternative embodiment, the surge current flows through shunt  212 , which generates a signal representative of the surge current. Surge measurement circuit  214  amplifies the signal and transmits the signal to processor  216 . 
         [0023]      FIG. 3  is a schematic diagram of an exemplary IED  300  that may be used to detect improper grounding of inputs in relation to a grounding point. Where an IED, such as IED  300 , is coupled to secondary generators of current and/or voltage, generally at least one wire carrying the secondary current and/or secondary voltage is grounded. An example of a secondary generator is a high voltage instrument transformer. Grounding the wire facilitates preventing capacitive coupling with primary generators of current and/or voltage. 
         [0024]    In the exemplary embodiment, IED  300  includes a high voltage current transformer  302  and a voltage transformer  304 , which are both coupled to respective inputs  306  and  308 . Specifically, current input  306  includes input terminal  310 , and voltage input  308  includes input terminal  312 . IED  300  also includes grounded input terminals  314  and  316 , each of which correspond to a respective input  306  and  308 . Current transformer  302  includes a primary circuit  318  and a secondary circuit  320  that is coupled to grounded input terminal  314 . Similarly, voltage transformer  304  includes a primary circuit  322  and a secondary circuit  324  that is coupled to grounded input terminal  316 . Grounding both secondary circuits  320  and  324  maintains grounded input terminals  314  and  316  at ground potential, and the non-grounded input terminals  310  and  312  at a relatively low voltage compared to ground potential. An impedance of current inputs  306  facilitates maintaining both input terminal  310  and grounded input terminal  314  at a potential nearly equal to ground potential. Moreover, an impedance of voltage inputs  308  facilitates maintaining both input terminal  312  and grounded input terminal  316  to within a relatively low voltage difference, such as 10.0 Volts (V) or 100.0 V. In the exemplary embodiment, IED  300  also includes a ground terminal  326 , which also facilitates maintaining current input terminal  310  near ground potential with respect to ground terminal  326 . Moreover, ground terminal  326  facilitates maintaining voltage input terminal  312  at a low potential with respect to ground terminal  326 . 
         [0025]    In the exemplary embodiment, IED  300  also includes a plurality of voltage detector circuits  328  that monitor voltages between current inputs  306  and voltage inputs  308 . More specifically, a first voltage detector circuit  330  monitors a voltage between current input terminal  310  and ground terminal  314 , and a second voltage detector circuit  332  monitors a voltage between voltage input terminal  312  and ground terminal  316 . Voltage detector circuits  328  are designed so as to respond to high frequency components of signals input into inputs  306  and  308 , as well as to system frequency components of approximately 50.0 Hertz (Hz) and approximately 60.0 Hz. Each voltage detector circuit  328  generates a signal representative of a detected voltage, digitizes the signal, and transmits the digitized signal to a processor  334 . 
         [0026]    During operation, high voltage current transformer  302  and voltage transformer  304  generate input signals and transmit the input signals to current inputs  306  and voltage inputs  308 , respectively. A voltage across the terminals of each input  306  and  308  is monitored by a voltage detector circuit  328 . More specifically, first voltage detector circuit  330  monitors a voltage between current input terminal  310  and ground terminal  314 , and second voltage detector circuit  332  monitors a voltage between voltage input terminal  312  and ground terminal  316 . Each voltage detector circuit  328  generates a signal representative of the detected voltage, digitizes the signal, and transmits the digitized signal to processor  334 . 
         [0027]      FIG. 4  is a flowchart showing an exemplary predictive maintenance method  400  using an IED. Although the IED is designed to withstand such factors as temperature extremes, electrical surges, improper grounding and exposure to elevated voltages, and the like, per applicable standards and design practices, such factors add wear to the IED and affect the life expectancy of the IED accordingly. Moreover, repetitive exposure of such factors shorten the life expectancy of the IED. As such, method  400  uses measured data, as described above, and applies the measured data to a reliability model developed for the IED. Although method  400  is described below in relation to IED  100  (shown in  FIG. 1 ), it should be understood that method  400  is applicable to predicting maintenance for any IED. 
         [0028]    In the exemplary embodiment, a reliability model is developed  402 . For example, an integrated circuit, such as a microcontroller, typically exhibits a temperature-reliability relationship with a decline in reliability as the operating temperature exceeds a particular value. Such information is typically available from the integrated circuit manufacturer and may be verified by testing. For example, an integrated circuit that is operated with an internal temperature of 115° C. may have a life expectancy that is half of an expected life-expectancy when operated with an internal temperature of 75° C. A manufacturer of IED  100  may derive the internal operating temperature for each component  104  (shown in  FIG. 1 ) based on a temperature profile of IED  100  and/or by directly measuring one or more points within IED chassis  102  (shown in  FIG. 1 ), as described above. In one embodiment, the reliability model applied to the long-term exposure factors is a deterministic reliability model. In an alternative embodiment, the reliability model is a stochastic reliability model. In further alternative embodiments, the reliability model may be based on, for example, fuzzy mathematics and/or an artificial neural network. In one embodiment, the reliability model is integrated into an operating code of IED  100 . In an alternative embodiment, the reliability model is stored by IED  100  as a data entity. Storing the reliability model facilitates enabling an IED operator to upgrade the reliability model. For example, the operator may manually upgrade the reliability model at an TED installation site, or the reliability model may be upgraded from a centrally located application that is remote to the IED. 
         [0029]    Next, environmental factors are measured  404  within IED  100  using, for example, temperature sensor  106  (shown in  FIG. 1 ). The measured environmental factors are then processed  406  to determine long-term exposure factors that represent historical operating conditions of IED  100 . More specifically, processor  110  (shown in  FIG. 1 ) determines raw measurements, an integral, an average value of raw measurements, and/or a maximum value of raw measurements. For example, a set of internal temperature readings as recorded by temperature sensor  106  are sorted into temperature bands such as −40.0° C. to −25.0° C., −25.0° C. to 0° C., 0° C. to 25.0° C., 25.0° C. to 30.0° C., 30.0° C. to 35.0° C., and so on. A total operating time in each temperature band is accumulated by processor  110 . 
         [0030]    In the exemplary embodiment, the long-term exposure factors are then applied  408  to the reliability model of IED  100  and/or each component  104 . By using the temperature-reliability relationship, or reliability model, a remaining life of each component  104  and/or a probability of a failure may be calculated by processor  110  based on the long-term exposure factors. More specifically, processor  110  determines  410  a numerical measure of remaining IED life based on the long-term exposure factors and the reliability model. Examples of a numerical measure include, but are not limited to including, a remaining life of IED  100 , a used life of IED  100 , and a rate of wear of IED  100 . In one embodiment, the used life of IED  100  may be expressed in a number of time units such as hours, days, weeks, months, and/or years. Further examples of a numerical measure include a ratio of actual wear to normal wear. In one embodiment, the rate of wear of IED  100  is based on operating conditions that are outside a specified range of acceptable operating conditions for IED  100 . In one embodiment, the long-term exposure factors are transmitted to a centrally located application that is remote to IED  100 , such that the central application applies the long-term exposure factors received from a plurality of IEDs to one or more reliability models and determines a numerical measure of remaining IED life for each of the plurality of IEDs and/or for each individual IED. 
         [0031]    In the exemplary embodiment, processor  110  compares  412  the numerical measure of remaining IED life to a preselected remaining life value. If the numerical measure of remaining IED life is less than the preselected remaining life value, processor  110  generates  414  a signal, such as an alarm. The signal may be based on, for example, the determined remaining life of IED  100 , the determined used life of IED  100 , the determined rate of wear, and/or exceeded operating conditions. In one embodiment, the signal is a visual indication provided to an IED operator by, for example, an alphanumeric message, a light-emitting diode (LED), and the like. In an alternative embodiment, the signal is a physical on/off output. In another alternative embodiment, the signal may be a virtual point created by processor  110  in an operating code and/or programming code of IED  100 . For example, in such an embodiment, a maintenance output relay, or fail safe relay, may be opened, thereby de-energizing the relay to signify to the IED operator that IED  100  is in need of attention and/or repair. In such a case, IED  100  may continue to function while signifying to the IED operator that environmental conditions are not normal. Moreover, the opened relay may signify that IED  100  is experiencing wear at an accelerated rate and/or a remaining life of IED  100  has reached a level at which service is necessary. In the exemplary embodiment, sensitivity and/or functionality of the signal may be selected via user settings. 
         [0032]    In one embodiment, upon a failure of IED  100  and/or a particular component  104 , the long-term exposure factors determined for IED  100  are stored in a memory (not shown) such that the long-term exposure factors may be extracted by, for example, a service technician. Alternatively, the long-term exposure factors may be transmitted by processor  110  to a remote storage device (not shown) for storage. If IED  100  is sent for repair and/or refurbishment, for example after a failure of IED  100  and/or a particular component  104 , the stored long-term exposure factors may be augmented to reflect an actual wear of IED  100  in order to reflect the improved operation status of IED  100  due to the repair and/or refurbishment. In addition, the reliability model may be updated to reflect data, such as long-term exposure data, collected by a technician during repair. Upon a significant change in reliability data, a manufacturer of IED  100  may update the reliability model in newly manufactured devices. 
         [0033]    The systems and methods described herein facilitate predicting needed maintenance of intelligent electronic devices (IEDs) by using sensors and/or processors to enable the IEDs to collect and analyze information from the sensors. Collecting and analyzing the information facilitates understanding the operating conditions and exposures of IEDs in combination with an embedded knowledge of the life expectancies of the IEDs, such as a reliability model, to generate predictive maintenance requests and/or signals. 
         [0034]    When introducing elements of aspects of the invention or embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0035]    Exemplary embodiments of systems and methods for predicting maintenance of an intelligent electronic device (IED) are described above in detail. The systems and methods are not limited to the specific embodiments described herein but, rather, steps of the methods and/or components of the system may be utilized independently and separately from other steps and/or components described herein. Further, the described steps and/or components may also be defined in, or used in combination with, other systems and/or methods, and are not limited to practice with only the systems and methods as described herein. 
         [0036]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.