Patent Application
20130096853
The subject matter disclosed herein relates generally to electrical contacts, and more particularly to systems and methods for monitoring electrical contacts on a continuous or periodic basis.
Electrical connections typically have a useful life. Over time, the contacts of the electrical connections can degrade, which can result in the partial or total loss of the functioning of the connections. The contacts can also degrade suddenly after an operation of the device. If not effectively monitored, the degradation of these connections within different components can adversely affect the performance characteristics of these components and reduce the reliability of associated systems. To maintain adequate performance of an electrical system, the components are often monitored along with system performance to determine if some type of maintenance, repair or replacement action should be taken. Components may be monitored continuously or via periodic prophylactic examinations consisting of visual inspection or a series of test using appropriate instruments. The gradual degradation of contact surfaces can cause conduction problems resulting in local temperature rise, which may affect system performance, and lead to further degradation. Contacts can also degrade suddenly from a single, or few operations under extremely adverse conditions. The degree of degradation is often not obvious to the user and whether the device can be put back into useful operation cannot be easily determined. This then requires a battery of manual tests and close observation after putting the device back in service, or the device is replaced “just in case”.
In some conventional electrical contact monitoring systems, the determination of the contact condition of circuit breakers is by means that connect special instruments designed for low resistance measurement to the contacts (to provide a line test of low resistance) or using infrared scans to provide online measuring of temperature.
These conventional electrical contact monitoring systems may not satisfactorily identify the degradation of the electrical contacts, such as a progressive degradation of the electrical contacts. Accordingly, late detection or poor sensitivity may result when using these systems.
In accordance with one embodiment, a method is provided that includes calculating an impedance of an electrical contact based on an electrical signal applied to the electrical contact and a measured electrical signal after passing through the electrical contact. The method also includes determining a condition of the electrical contact using the calculated impedance.
In accordance with another embodiment, a system is provided that includes a receiving unit configured to receive electrical signal information, the electrical signal information including information for an electrical signal applied to an electrical contact and a measured electrical signal after passing through the electrical contact. The system also includes a processing unit configured to calculate an impedance of the electrical contact using the measured electrical signal information to determine a condition of the electrical contact.
In accordance with still another embodiment, a circuit breaker is provided that includes one or more pairs of contacts and a signal generator for generating an electrical signal having at least one frequency, wherein the electrical signal is applied to the pair(s) of contacts. The circuit breaker also includes a processing unit configured to measure the applied electrical signal after the signal passes through the pair(s) of contacts and determine a change between the applied electrical signal and the measured electrical signal. The processing unit is further configured to determine an impedance of the contacts using the determined to determine a condition of the pair(s) of contacts.
The drawings, in which like numerals represent similar parts, illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
The foregoing summary, as well as the following detailed description of certain embodiments of the subject matter set forth herein, will be better understood when read in conjunction with the appended drawings. As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the subject matter disclosed herein may be practiced. It is to be understood that the embodiments may be combined or that other embodiments may be utilized, and that structural, logical, and electrical variations may be made without departing from the scope of the subject matter disclosed herein. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the subject matter disclosed herein is defined by the appended claims and their equivalents. In the description that follows, like numerals or reference designators will be used to refer to like parts or elements throughout. In this document, the terms “a” or “an” are used to include one or more than one and the term “or” is used to refer to a nonexclusive “or”, unless otherwise indicated.
The electrical contact monitoring system 100 includes a signal generator 102 (e.g., an alternating signal generator) that generates an electrical signal 103 at one or more frequencies. In one embodiment, the signal generator 102 generates the electrical signal 103, which is applied across an electrical contact, illustrated as a contact pair 104 (e.g., a contact pair of a circuit breaker) and wherein the electrical signal 103 includes one or more frequencies.
The contact pair 104, in various embodiments, forms a part of a circuit 105, for example, an electrical circuit (not shown) beyond points 1 and point 2 as shown in
The contact pair 104 is any device capable of providing electrical contact such that an electrical path or connection is provided. For example, the contact pair 104 may be any suitable electrical contacts employed in relays or switches.
In operation, in one embodiment, the signal generator 102 generates an electrical signal 103 having a single frequency signal. In other embodiments, the signal generator 102 generates an electrical signal 103 having a frequency range that includes a plurality of different frequencies. For example, the signal generator 102 may generate an electrical signal 103 with a frequency range that is between 1 kHz to 1 MHz. Accordingly, the signal generator 102 may generate an electrical signal 103 with a single frequency or multiple frequencies between 1 kHz to 1 MHz and the like. However, other ranges are contemplated. For example, the signal generator 102 may generate an electrical signal 103 with frequencies up to 20 MHz. It should be noted that the one or more frequencies may be based on a particular contact condition to be monitored or identified. In various embodiments, the frequency of the electrical signal 103 is a higher frequency than a supply frequency for the circuit 105.
The electrical signal 103 may be different types of signals. In one embodiment, the electrical signal 103, which is applied across the contact pair 104, is an alternating current signal. For example, the alternating current signal may have a current value up to 100 Ampere (A). The electrical signal 103 also may have different voltages, for example, a voltage up to 10 Volts. Again, the current and voltage of the electrical signal 103 may be higher or lower, such as based on the particular application.
The electrical signal 103 generated by the signal generator 102 (illustrated by the arrows showing electrical flow 106) to the contact pair 104, which includes the electrical contacts under inspection or that are being monitored. In one embodiment, to limit or prevent the flow 106 of the electrical signal 103 from leaking into the circuit 105 and to direct the flow 106 through the contact pair 104, an inductor 108 may be provided to the circuit 105. For example, the inductor 108 may be positioned within the circuit 105 before the contact pair 104 (toward Point 1 in
In various embodiments, the generated electrical signal 103 is periodically injected through (or applied to) the contact pair 104. The electrical signal 103 may be injected at predetermined intervals, which may be fixed or variable. The electrical signal 103 also may be applied continuously during some or all of the period when the contact pair 104 is being monitored. When the electrical signal 103 passes through the contact pair 104, the resulting measured signal at one or more frequencies may vary with the surface condition of the contact pair 104. For example, different surface conditions of the contact pair 104 may affect the response of the electrical signal 103 at different frequencies, such as pitting, dust deposits, roughness of the surface of the contact pair 104, carbon deposits, sulphide corrosion, rust, moisture, decay, deterioration, and/or oxidation, among others. In various embodiments, the response, such as the resulting or measured electrical signal is used to determine and identify the surface condition of the contact pair 104. For example, based on the injected frequencies and the measured responses, electrical impedance spectroscopy (EIS) as described in more detail herein, may be used to determine the particular condition (and the extent of the condition) affecting the surface of the contact pair 104. For example, variations or changes in the impedance of the measured signal at one or more frequencies may be analyzed to determine a condition of the contact pair 104.
In one embodiment, a blocking capacitor 112 also is provided to limit or prevent the in-situ operational current of the circuit 105 from leaking into the electrical contact monitoring system 100. However, the blocking capacitor 112 also allows the electrical signal 103 generated by the signal generator 102 to pass therethrough. To limit or prevent the electrical signal 103 from leaking into the circuit 105 after the electrical signal 103 passes through the contact pair 104, an inductor 114 may be added to the circuit 105. The inductor 114 may be positioned in the circuit 105 after the contact pair 104 (toward Point 2 in
Additionally, a current sensor 116 is provided in some embodiment where the applied electrical signal 103 is a voltage applied across the electrical contact pair 104 and a resulting electrical current is measured. In one embodiment, the applied electrical signal 103 may be a current signal and the current sensor 116 measures the applied current signal. The measurement by the current sensor 116, when the applied electrical signal 103 is a current, may be used as a feedback to the signal generator 102 to tune or calibrate the applied electrical signal 103, such as to a predetermined value. In another embodiment, the feedback may be used to monitor the functioning of a blocking capacitor 112 to prevent in-situ current from leaking to a processing unit 118. For example, when the current sensor 116 detects a high input current leaking into the electrical contact monitoring system 100, the current sensor 116 may break circuit connectivity and provide an alarm (e.g., an audible or visible alarm to an operator).
Thus, an electrical signal, as the applied electrical signal 103 passes through the contact pair 104 (and in some cases the current sensor 116), and an electrical signal 120 is measured (also referred to as a measured electrical signal) in response thereto, which may be provided as an input to the processing unit 118 for processing, such as to perform contact condition detection. The processing unit 118 may be any type of processor or computing machine, which may be embodied in hardware, software or a combination thereof. It should be noted that the processing unit 118 may include a receiving unit (or other receiver) to receive the electrical signal 120 (or information relating to the electrical signal 120), as well as other signals or data, for example, the frequency and value of the applied electrical signal 103.
For example, the processing unit 118 also receives the electrical signal 103 generated by the signal generator 102. In this signal path, another blocking capacitor 122 and current sensor 124 may be used to limit or prevent the in-situ operational current of the circuit 105 from leaking to the processing unit 118. The operation of the blocking capacitor 122 and current sensor 124 are similar to the operation of the blocking capacitor 112 and current sensor 116 as described above.
In one embodiment, the processing unit 118 analyzes the received signals, namely the electrical signals 103 and 120 using EIS techniques to determine one or more contact conditions. For example, the processing unit 118 may analyze the received signals to monitor changes between the applied signal and the resulting measured signal at one or more frequencies, for example, between the applied electrical signal 103 and the electrical signal 120. In one embodiment, the processing unit 118 may be calibrated to an original contact pair 104 condition, that is, the surface condition of the contact pair existing when the contact pair 104 is new. The applied electrical signal 103 may also be used to calibrate the processing unit 118. Alternatively, the processing unit 118 may be calibrated for other contact conditions or any other factor. The calibration of the processing unit 118 in some embodiments allows the electrical contact monitoring system 100 to reduce or avoid false positives in identifying or predicting contact pair 104 conditions by defining a baseline measurement. The processing unit 118 may also be used to compute the real part of the impedance and the imaginary part of the impedance from the applied electrical signal 103 and the measured electrical signal 120.
Thus, in various embodiments, the electrical signal 103 is applied across electrical contacts, for example, the contact pair 104, as an applied electrical signal. The applied electrical signal 103 has at least one frequency. A response is then measured or monitored, for example, the electrical signal 120, which is a measured electrical signal, and is measured as the applied electrical signal 103 passes through the electrical contact. The processing unit 118 then may use the applied and measured signals at different frequencies to determine a condition of the contact pair 104. In various embodiments, the processing unit 118 may calculate an impedance, for example, a complex impedance including at least one of a resistive property, a capacitive property or an inductive property of the electrical contact at one or more frequencies as described in more detail herein to determine a condition of the electrical contact. For example, the applied electrical signal 103 may be an electrical voltage signal and the measured electrical signal 120 may be an electrical current. In other embodiments, the applied electrical signal 103 may be an electrical current signal and the resulting electrical voltage measured.
In various embodiments, the processing unit 118 may analyze the spectroscopic signatures of the contact pair 104 to determine different contact conditions. For example, the processing unit 118 may determine a resistive property, a capacitive property or an inductive property of the contact pair using the electrical signal 120 to identify a particular contact condition corresponding to the signature of the electrical signal 120. For example, multiple points along one or more curves may be analyzed or compared or a morphology type analysis may be performed. It should be noted that a capacitance spectroscopy of a new contact pair may include both a contact pair resistance and an air capacitance.
When the contact pair 104 is in use, the contact pair 104 generally experiences a continuous time dependant degradation of the contact pair material, such that the impedance spectroscopy of the contact pair 104 may include a resistance, capacitance and/or inductance due to the surface condition of the contact pair 104. The change in signature of the electrical signal 120 correlates or corresponds to different types and levels of degradation of the contact pair 104.
For example, the signature of the electrical signal 120 after a period of use may have a capacitive signature with an increased resistance. In one embodiment, the capacitive property of the contact pair 104 may be calculated such that the capacitive property includes a combination of a real capacitive part and an imaginary capacitive part. The capacitance of the contact pair 104 may be represented by the following equation:
Z=R+jXc Equation 1
where Z represents a total capacitance for the contact pair 104, R represents the real capacitive part, and Xc represents the imaginary capacitive part.
Alternatively, an impedance plot of the response of the contact pair 104 may be used. The signature of the electrical signal 120 after a period of use has an inductance signature with an increased resistance. In one embodiment, the inductance property of the contact pair 104 may be calculated such that the inductance property includes a combination of a real inductive part and an imaginary inductance part. The inductance of the contact pair 104 may be represented by the following equation:
L=Rl+jXl Equation 2
where L represents a total inductance for the contact pair 104, Rl represents the real inductance part, and Xl represents the imaginary inductance part.
Referring again to
In various embodiments, the processing unit 118 analyzes the received signal at one or more frequencies as generally illustrated in
In various embodiments, the processing unit 118 may also predict the condition of the contact pair 104 based on a predefined model, wherein the predefined model includes using at least one of the frequency, impedance, phase angle, voltage, or a current of the measured electrical signal 120. In some cases, the processing unit 118 may predict the contact pair 104 condition based on a predefined model, wherein the model is created using different voltage signals, wherein the signal has a frequency range or may have a single frequency, and an EIS phase response of the received signal in relation to the applied signal using data such as shown in
In one embodiment, the processing unit 118 may indicate a progressive degradation of the contact pair 104 using at least one of the response of the measured electrical signal 120, an impedance of the measured electrical signal 120, a phase angle of the measured electrical signal 120, a voltage of the measured electrical signal 120, or a current of the measured electrical signal 120. For example, as the contact pair 104 degrades, the EIS phase angle of the measured electrical signal 120 decreases, which may be determined using any suitable EIS analysis technique (e.g., comparing a measured response to a predicted response from a forward model). Using the results of the change in the phase angle of the EIS of the contact pair 104, the processing unit determines the progressive degradation or damage to the contact pair 104 based on, for example, a point along the spectroscopic impedance signature curve or a comparison with predicted values.
The various embodiments may provide a notification of a particular contact pair condition or level of degradation. For example, returning to
The information provided by the processing unit 118 may be an analog or a digital signal. The signal may be communicated over a wired or a wireless network. The processing unit 118 may transmit the information to a central monitoring location wherein similar signals are received from a plurality of monitored contact pairs 104 of a plurality of electrical contact monitoring systems 100. In another embodiment, the processor 118 may transmit the measured electrical signal 120 to a central monitoring location, wherein the measured electrical signal 120 may be used for further processing, such as to notify a technician that a circuit breaker needs to be changed. Alternatively, the electrical signal 120 may be sent to another system. For example, the other system may be a circuit breaker switch system.
The electrical contact monitoring system 100 also may be used when the circuit 105 is off-line. The circuit 105 may be off-line when the circuit 105 is not operating and/or has no electrical current. Alternatively, the electrical contact monitoring system 100 may be used when the circuit 105 is in-situ operation or is a live circuit. A circuit is in-situ or a circuit is live when the circuit is operatively connected to a power source.
In some embodiments, the electrical contact monitoring system 100 may simultaneously or concurrently monitor multiple contact pairs 104. For example, the contact pair 104 may be connected in a series or parallel connection with a plurality of other contact pairs 104. In an arrangement for monitoring the operation of a plurality of contact pairs 104 connected in parallel, wherein each contact pair 104 may have a substantially different impedance when the contacts are closed, a separate electrical contact monitoring system 100 may be provided for connection with each such plurality of contact pairs 104. A single electrical contact monitoring system 100 may simultaneously or concurrently monitor a plurality of circuits with each of the plurality of circuit having a plurality of contact pairs 104. The electrical contact monitoring system 100 may monitor the plurality of contact pairs 104 and report a combined result of the condition of all or a subset of the contact pairs 104.
At 606, a change between the applied electrical signal and the measured electrical signal, for example the electrical signal 120, is monitored. The monitoring of the change may be at multiple frequencies, for example, using the processing unit 118. Then at 608, at least one of a resistive property, an inductive property and/or a capacitive property of the contact pair is determined using the measured electrical signal that includes one or more frequency components that may be separated using any suitable signal frequency separation technique.
At 610, the measured electrical signal may be calibrated to a predefined contact pair condition. For example, the surface condition of the contact pair existing when the contact pair is new may be used for calibration, namely to set baseline measurements and a frequency response. The applied electrical signal may be used for calibration to limit or avoid a false positive determination of the contact pair condition as described herein.
Thereafter, at 612, at least one contact pair condition is determined or predicted using EIS. For example, the contact pair condition may be one of pitting, dust deposits, roughness of the surface of the contact pair, carbon deposits, sulphide corrosion, rust, moisture, decay, deterioration, and/or oxidation, among others.
The EIS analysis may include one or more different determinations at steps 614, 616 and/or 618. For example, in a new contact pair, an impedance spectroscopy includes mainly contact pair resistance and an air capacitive property. However, in a contact pair that is not new an impedance spectroscopy may include a contact pair resistance and a capacitive property due to the surface conditions of the contacts. It should be noted that the capacitive property may include a combination of a real capacitive part and an imaginary capacitive part as described herein.
Thus, at 614 at least one condition of the contact pair may be determined using a change between the applied electrical signal and the measured electrical signal. Additionally or alternatively, at least one condition may be determined using the determined resistive property, a determined inductive property or a determined capacitive property at 616. At least one condition may be determined at 618 using the response of the measured electrical signal, the contact impedance, a phase angle, a voltage, or a current of the measured electrical signal or any combination thereof. For example, as described herein, these determinations may be based on spectroscopic impedance signatures or predicted values, among other information.
It should be noted that the determination may be of a present state of the contact pair or may include indicating a progressive degradation of the contact pair, such as based on a position of the current measurement along a spectroscopic impedance signatures curve
The method 600 may be performed off-line when the circuit having the monitored contact pair is not in an operating state. Alternatively, the method 600 may be performed in-situ wherein the contact pair is operatively connected within the circuit.
The determination may be made based on a single frequency response or a multiple frequency response, which may correspond to one or more monitored contact pairs. The responses may be compared to predetermined or modeled responses to identify a particular condition or the level of the condition.
Once the various determinations are made with respect to the condition of contact pair, at 620 a notification may be provided upon detecting at least one predefined contact pair condition. For example, the condition might indicate that the contact pair is within ten percent of an overall useful life based upon a position along a predicted curve. The notification, as well as general monitoring information, may be transmitted to a central monitoring location, wherein the information is processed for various contact pair conditions. Thus, the determination may be made locally or remotely.
In various embodiments, determining the impedance includes determining one or more, or at least two, of a resistive property, an inductive property or a capacitive property, at one or more frequencies. In some embodiments, the voltage and current are combined at multiple frequencies. In some embodiments, plots of resistance, capacitance and/or inductance as a function of frequency are used, for example, to determine a change or shift in a plotted curve. Also, the signature of degradation may be analyzed using the measured or resulting signals only, or bother the applied and measured signals.
At least one technical effect of various embodiments is an improved determination of the condition of a contact and/or an improved ability to predict the condition of a contact.
The various embodiments and/or components, for example, the modules, elements, or components and controllers therein, also may be implemented as part of one or more computers or processors. The computer or processor may include a computing device, an input device, a display unit and an interface, for example, for accessing the Internet. The computer or processor may include a microprocessor. The microprocessor may be connected to a communication bus. The computer or processor may also include a memory. The memory may include Random Access Memory (RAM) and Read Only Memory (ROM). The computer or processor further may include a storage device, which may be a hard disk drive or a removable storage drive such as an optical disk drive, solid state disk drive (e.g., flash RAM), and the like. The storage device may also be other similar means for loading computer programs or other instructions into the computer or processor.
As used herein, the term “computer” or “module” may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), graphical processing units (GPUs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “computer”.
The computer or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within a processing machine.
The set of instructions may include various commands that instruct the computer or processor as a processing machine to perform specific operations such as the methods and processes of the various embodiments of the invention. The set of instructions may be in the form of a software program, which may form part of a tangible non-transitory computer readable medium or media. The software may be in various forms such as system software or application software. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to operator commands, or in response to results of previous processing, or in response to a request made by another processing machine.
As used herein, the terms “software”, “firmware” and “algorithm” are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments of the invention without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments of the invention, the embodiments are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
This written description uses examples to disclose the various embodiments of the invention, including the best mode, and also to enable any person skilled in the art to practice the various embodiments of the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments 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 the examples have structural elements that do not differ from the literal language of the claims, or if the examples include equivalent structural elements with insubstantial differences from the literal languages of the claims.
