Patent Publication Number: US-9897643-B2

Title: Apparatuses, systems and methods for detecting corona

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation patent application Ser. No. 14/202,940, filed Mar. 10, 2014, which claims the benefit of U.S. provisional patent application Ser. No. 61/781,496, and is a continuation in part of U.S. national phase application Ser. No. 13/825,451 based on International Application PCT/US2011/001632, filed Sep. 22, 2011, each of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present application relates to the detection of corona using audio data. Some illustrative embodiments of the present invention relate to the detection of corona on power transmission lines using audio data. 
     BACKGROUND OF THE INVENTION 
     Power Grids 
       FIGS. 1-4  illustrate related art disclosed in U.S. Pat. No. 8,002,592.  FIG. 1  shows a transmission tower  200  which is used to suspend power transmission lines  202  above the ground. The tower  200  has cantilevered arms  204 . Insulators  206  extend down from the arms  204 . One or more suspension clamps  208  are located at the bottom ends of the insulators  206 . The lines  202  are connected to the suspension clamps. The clamps  208  hold the power transmission lines  202  onto the insulator  206 . 
       FIGS. 2-4  illustrate an example of a suspension clamp  208 , which generally comprises an upper section  210  and a lower support section  212 . These two sections  210 ,  212  each contain a body  214 ,  216  which form a suspension case. The bodies  214 ,  216  each comprise a longitudinal trough (or conductor receiving area)  215 ,  217  that allow the transmission conductor  202  to be securely seated within the two sections when the two sections are bolted (or fastened) together by threaded fasteners  201  (not shown). This encases the transmission conductor  202  between the two bodies to securely contain the transmission conductor  202  on the clamp  208 . Threaded fasteners are not required and any other suitable fastening configuration may be provided. 
     The two bodies  214 ,  216  connected together are suspended via a metal bracket  218  that attaches to the lower body  216  at points via bolt hardware  220 . 
     The lower body, or lower body section,  216  comprise a first end  219  and a second end  221 . The conductor receiving area (or conductor contact surface)  217  extends from the first end  219  to the second end  221  along a top side of the lower body  216 . The conductor receiving area, including longitudinal trough  217 , forms a lower groove portion for contacting a lower half of the conductor  202 . A general groove shape is not required, and any suitable configuration may be provided. 
     In one implementation, the upper and lower sections  210 ,  212  each have embedded within their respective bodies  214 ,  216  one-half of a current transformer  222 ,  224  that is commonly referred to in the industry as a split core current transformer. When these components  222 ,  224  are joined, they form an electromagnetic circuit that allows, in some applications, the sensing of current passing through the conductor  202 . In one implementation, the current transformer is used for power sensing, data collection, data analysis and data formatting devices. In some implementations the current transformer may be located outside of the clamp or similar device or, in some implementations, power may be provided by another means. 
     The body  214  of the upper section  210  contains a first member  232  and a second member  234  forming a cover plate. The first member  232  comprises a first end  233 , a second end  235 , and a middle section  237  between the first end  233  and the second end  235 . The conductor receiving area (or conductor contact surface)  215  extends from the first end  233  to the second end  235  along a bottom side of the first member  232 . The conductor receiving area  215  forms an upper groove portion for contacting an upper half of the conductor  202 . A general groove shape is not required, and any suitable configuration may be provided. In one implementation, the first member  232  further comprises a recessed cavity  226  at the middle section  237  that effectively contains an electronic circuit  228 . In this implementation, the electronic circuit  228  is designed to accept inputs from several sensing components. This cavity  226  may be surrounded by a faraday cage  230  to effectively nullify the effects of high voltage EMF influence from the conductor  202  on the circuitry  228 . The faraday cage may also surround the current transformer  222 . The cover plate, or cover plate member,  234  can cover the top opening to the cavity  226  to retain the electronic circuit inside the body, or upper body section,  214 . The electronics may be housed in a metal or plastic container, surrounded by the noted faraday cage, and the entire assembly can be potted, such as with epoxy for example. 
     The electronic circuit  228  can accept and quantify in a meaningful manner various inputs for monitoring various parameters of the conductor  202  and the surrounding environment. The inputs can also be derived from externally mounted electronic referencing devices/components. The inputs can include, for example: Line Current reference (as derived from the Current transformer  222 ,  224  or other means); Barometric pressure and Temperature references—internal and ambient (as derived from internal and external thermocouples  236 ,  238  or other means); Vibration references of the conductor (as derived from the accelerometer  240 , such as a 0.1-128 Hz sensor, for example, or other means); and Optical references (as derived from the photo transistor  242  in a fiber optic tube or other means). The optical reference portion may, for example, allow the clamp to look up and see flashes of light from corona if the insulator starts to fail, or lightening indication storm activity, and/or tensile references (as derived from the tension strain device  244  which may be included in certain implementations). The tensile references from the tensile indicators  244  may, for example, provide information indicating that ice is forming as the weight of the conductor increases due to ice build up. 
     Supervisory Control And Data Acquisition (SCADA) generally refers to an industrial control system such as a computer system monitoring and controlling a process. Information derived by the electrical/electronic circuitry can exit the circuit  228  via a non-conductive fiber optic cable  246  and be provided up and over to the transmission tower  200  and ultimately at the base of the tower and fed into the user&#39;s SCADA system to allow the end user to access and view electrical and environmental conditions at that sight, or the information can be transmitted to a remote or central site. The suspension clamp or other sensing device may be alternatively configured to wirelessly transmit information from the electronic circuit  228  to a receiver system. 
     Problems Associated with Corona and Conventional Corona Detection Systems 
     Corona is a type of electrical discharge which will corrode or eat away at wire, insulators, and anything else in the vicinity. Conventional methods of corona detection involve ultraviolet and ultrasonic detection. Both suffer from a high cost of implementation and various disadvantages. For example, power lines can generate corona that can be seen by using special cameras operating in the ultraviolet spectrum. However, such cameras are large and expensive. The cameras are generally sent to places where an insulator appears to be eaten away, but may not be effective since corona can be intermittent and is affected by many environmental conditions such as moisture and air pressure. Further, conventional ultraviolet detectors require a user to manually operate a device and aim at an area suspected to contain corona. As such, these detectors are cumbersome and not autonomous. Furthermore, conventional ultrasonic detectors employ nondiscriminatory means of detecting corona, seeking any noise in a given ultrasonic frequency range. Thus, these detectors are often not sufficiently accurate. 
     Repair or Servicing a Transmission Line 
     Initially, one must locate where a power transmission line is broken. However, power transmission lines can run hundreds of miles between substations, and the only information generally available is that one substation is supplying power and the next one is not receiving the supplied power. Accessibility to power transmission lines may vary. In some cases, the power transmission lines may be accessible by motorized ground vehicles. In other cases, lines may only be accessible by helicopter, wherein a service technician must hang under the helicopter to service or repair a line. Such repairs or maintenance can be very expensive. Accordingly, preventative methods of detecting problems such as corona are needed. 
     Conventional Communication Protocols 
     In order to retrieve information about the system, rapid and secure communication is necessary. Radio communication via Ethernet is one option. However, organizing an Ethernet network requires the use of devices known as routers or switches. Each router or switch will look at an Ethernet packet of information and make note of the source address and the destination address as the packet arrives at a port. If the destination is known, the packet is forwarded to only one port which is known to be connected to that destination device. If it is not a known address, it is repeated to all ports except the port where it arrived. When the destination device responds, the source address will appear in a packet on a single port which permit the router or switch to learn where to send the next packet with that particular destination address. 
     There are specific protocols which optimize the route for delivering a packet and to remove the opportunity for a packet to become repeated in a loop in the network. Some of the more common protocols are Spanning Tree Protocol and Rapid Spanning Tree Protocol. A popular radio protocol for packet-based transmission is Zigbee which is described in standard IEEE 802.15.4, but it is only useful in networks in a small geographic area. 
     There is a need for accurate, inexpensive, small and easy-to-implement systems and methods for detecting corona. These may allow for fast analysis of any actual or potential repair problems and power optimization capabilities along transmission lines, with lower costs of repair, better preventative maintenance, and faster restore times. A need also exists for a way of collecting and communicating data by a widespread installation of sensing devices such as corona sensors over large geographic areas (such as power line grids). 
     SUMMARY OF THE INVENTION 
     Illustrative embodiments of the present invention address at least the above problems and/or disadvantages, and provide at least the advantages described below. 
     An illustrative method and system for detecting corona can be operable to obtaining audio data by a detector near an electrical conductor; and process the audio data using a fundamental frequency corresponding to the AC power signal in the conductor and a selected number of harmonic frequencies of the audio data by a processor to detect corona indicative of a corona condition, wherein thresholds are designated for each of the harmonic frequencies relative to the fundamental frequency and need to be met to detect a corona condition. 
     In accordance with one or more of the following aspects of the illustrative embodiments, or different combinations thereof, the method and system for detecting corona can process the audio data by 
     determining a first indicator of the energy at a substantially fundamental frequency in the audio data from an audio detector deployed to detect corona generated by an alternating current (AC) system, 
     determining a second indicator of the energy at a plurality of harmonic frequencies in the audio data, 
     determining a third indicator of noise energy in the audio data, 
     determining a normalized indicator of the energy at each of the harmonic frequencies in the audio data by dividing the energy at each of the harmonic frequencies by the first indicator, and 
     detecting a corona event if:
         the second indicator, which corresponds to the sum of the energy at each of the harmonic frequencies, is greater than the third indicator of the noise energy in the audio data; and   each normalized indicator of the energy at each of the harmonic frequencies in the audio data is within a range of acceptable levels.       

     With regard to the method and system for detecting corona the fundamental frequency of the audio data is within an frequency range audible to human beings. 
     The method and system for detecting corona can also communicate an alert on corona event detection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other illustrative features, aspects and advantages of the present invention will become more apparent from the following detailed description of certain illustrative embodiments thereof when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of a transmission tower supporting transmission lines connected via suspension clamps; 
         FIG. 2  is a perspective view of a suspension clamp; 
         FIG. 3  is a cross section view of the suspension clamp shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of a first member of the suspension clamp shown in  FIG. 2 ; 
         FIG. 5  illustrates a signal-to-noise-ratio versus frequency graph of the frequency responses of an example set of narrowband bandpass filters according to an illustrative embodiment of the present invention; 
         FIG. 6  illustrates a signal-to-noise-ratio versus frequency graph of an example frequency mask for a corona detector according to an illustrative embodiment of the present invention; 
         FIG. 7 a    illustrates a block diagram of the operation of an example comb filter according to an illustrative embodiment of the present invention; 
         FIG. 7 b    illustrates a gain-to-frequency graph of the frequency response of an example comb filter according to an illustrative embodiment of the present invention; 
         FIG. 8 a    illustrates an example process for detecting corona using audio data according to an illustrative embodiment of the present invention; 
         FIG. 8 b    shows a block diagram of an illustrative apparatus for detecting corona using audio data according to an illustrative embodiment of the present invention; 
         FIG. 9  illustrates a block diagram of an example of a method and a system processing audio data to detect corona according to an illustrative embodiment of the present invention; and 
         FIGS. 10 a - c    show illustrative apparatuses for detecting corona using audio data according to illustrative embodiments of the present invention. 
     
    
    
     Throughout the drawings, like reference numerals will be understood to refer to like elements, features and structures. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     This description is provided to assist with a comprehensive understanding of illustrative embodiments of the present invention described with reference to the accompanying drawing figures. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the illustrative embodiments described herein can be made without departing from the scope and spirit of the present invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. Likewise, certain naming conventions, labels and terms as used in the context of the present disclosure are, as would be understood by skilled artisans, non-limiting and provided only for illustrative purposes to facilitate understanding of certain illustrative implementations of the embodiments of the present invention. 
     Generally referring to  FIGS. 5-9 , various apparatuses, systems and methods can detect or assist in the detection of corona according to illustrative embodiments of the present invention. For example, power lines can generate corona that can sometimes be heard in the audio spectrum as a sizzling sound. Briefly, audio data can be collected on site (e.g., a location or installation where corona may be present) using audio sensors in accordance with illustrative embodiments of the present invention. The audio data, including frequency properties of the audio data (e.g., fundamental and harmonic frequencies) can be processed locally and/or remotely with respect to the site. Corona can be detected using the sensed audio data and audio signatures of corona or threshold characteristics, for example. If corona is detected, such detection can be indicative of a corona condition of a conductor, and can be documented using time stamps, durations, and/or other parameters relating to the detected corona event. For example, other parameters can include information about a level of corona detection, frequency of corona detection, or a percentage of time corona is detected over a selected period of time. 
     An audio spectrum is usually generated along with a corona in or near high power environments, such as, for example, electrical power lines, step-down transformers, high power closets or substations or other power sources for cranes or industrial sites, and neon lamps. While such high power environments are typically associated with voltages of about 12,000 V or more, some illustrative embodiments of the present invention may be applicable to environments associated with any voltage level. 
     A corona discharge can be created in an alternating current (AC) system at a voltage peak, that is, either at a positive voltage peak or at a negative voltage peak, but generally not both. Consequently, at most one discharge generally occurs per AC cycle. The discharge generally does not persist as the voltage drops. The polarity of the discharge generally depends on the shape of an electrode from which corona originates. Since at most one discharge usually occurs per AC cycle, an AC system generally creates an audio spectrum with a fundamental frequency equal to the frequency of the AC system. For example, a 60 Hz AC system can create an audio spectrum with a fundamental frequency of 60 Hz. It is however possible for corona to be discharged at both positive and negative voltage peaks. It is also possible that some AC cycles create audio spectra with fundamental frequency different from the frequency of the AC system. Accordingly, a fundamental frequency can be arrived at or varied prior, during or after various elements, process(es) or modules employed by the methods or systems according to the present invention. For example, stored corona detection data can be used to determine a desired fundamental frequency. 
     An audio spectrum can refer to a portion of the audible frequency range at which typical human beings can hear. This range can span, for example, from 20 Hz to 20,000 Hz. An advantage of using audio data over ultrasound data to detect corona is the superior affordability of audio data detectors, such as conventional audio microphones and other audio detectors, over ultrasound detectors. 
     Another advantage of using audio data over ultraviolet data to detect corona can also be the smaller size, the ease of implementation and the autonomy of systems using conventional microphones and audio detectors, according to some illustrative embodiments of this invention, versus expensive, large, non-autonomous ultraviolet cameras described above. 
     A further advantage of illustrative embodiments of the present invention disclosed herein is a higher accuracy in the audio spectrum detection of corona than conventional corona detection methods. While conventional methods, such as, for example, methods using ultrasound detection, do not discriminate among different inputs, some illustrative embodiments disclosed herein can seek particular frequency and amplitude patterns in processed audio data. Signal processing of audio data according to illustrative embodiments of the present invention, including, for example, analysis of harmonic frequencies of audio data, results in more accurate detection of corona. As a result of this higher accuracy, corona detection can be more reliably implemented as a preventative measure for preserving the integrity of conductors such as power transmission lines. 
     A further advantage of illustrative embodiments of the present invention disclosed herein is calibration of evaluation criteria. For example, based on historic data gathered using illustrative embodiments of systems and methods according to the present invention, frequencies or other parameters can be calibrated to provide more accurate corona detection. Further, audio signatures of corona or threshold characteristics can be provided or varied prior, during or after various elements, process(es) or operation(s) or modules employed by the illustrative methods or systems according to the present invention. Stored corona detection data can be used to determine and then calibrate desired audio signatures of corona or threshold characteristics for corona detection purposes (e.g., pre-calibrated data for deployment in a corona detection system). 
     As described below, illustrative methods or systems according to the present invention look for a specific pattern of harmonic peaks relative to the fundamental in audio data to detect corona, and employ a mask for the expected pattern and a range for the mask. An example frequency mask is described below with reference to  FIGS. 6 and 9  (e.g., step  960 ). 
       FIG. 5  illustrates a signal-to-noise-ratio versus frequency graph  500  of the frequency responses of an example set of narrowband bandpass filters. A series of evenly spaced narrow pulses with equal signal-to-noise ratios, from an audio spectrum generated by an AC system, can produce a frequency spectrum with a spike at the fundamental frequency and spikes of equal signal-to-noise ratios at each harmonic. Similar spectra can be detected by applying a set of narrowband bandpass filters with frequency responses as shown in  FIG. 5 . Digital signal processing can allow for the creation of accurate filters with bands that can be as narrow as required for a given application. 
       FIG. 6  illustrates a signal-to-noise-ratio versus frequency graph  600  of an example frequency mask for a corona detector as employed in accordance with illustrative embodiments of the present invention. The mask assumes the level of each harmonic is about the same, but the higher harmonics are permitted to be more attenuated than the lower order harmonics. In other words, as the widths of pulses from an audio spectrum generated by an AC system increase, the signal-to-noise ratios of the harmonics may decline at higher frequencies. The harmonics at lower frequencies may not be substantially affected by nominal variations in the pulse width. Accordingly, example methods and systems according to illustrative embodiments of the present invention use the fundamental and the next 11 harmonics. Other illustrative implementations of the present invention can use any number of harmonics or frequency range of harmonic frequencies besides an illustrative range of 10-12 harmonics (i.e., that were selected in view of the dynamic range of an illustrative 16-bit converter). While the range of harmonics to be used can range from one to an upper range defined by a range of a detector, it may be preferable to use at least four harmonics. As stated above, when using a mask (e.g., step  960 ), one may assume the signal-to-noise ratios of the harmonics to be approximately uniform, although harmonics at higher frequencies can be more attenuated than harmonics at lower frequencies without disturbing the process. Alternatively, a number of harmonics can be provided or varied prior, during or after various elements, process(es) or operation(s) or modules employed by the illustrative methods or systems according to the present invention. For example, stored corona detection data can be used to determine and then designate a desired number of harmonics. 
     A spectrum having harmonics with energies essentially equal to the energy between harmonics is generally insufficient to establish a detection of a corona event, because such a pattern can be produced by background or white noise. Rather, a spectrum having more energy in harmonics than energy between harmonics, or more energy than a multiple of the noise energy between harmonics, is generally a better indicator of corona events. Thus, the illustrative methods or systems according to present invention can use total energy between harmonics to determine corona in the presence of noise and do not require determining energy in respective harmonic frequencies or specific energy between two harmonic frequencies to overcome the effects of noise when detecting corona. The total noise energy between harmonics can be obtained, for example, with a comb filter, as illustrated in  FIGS. 7 a   - b.    
       FIG. 7 a    illustrates a block diagram  700  of the operation of an example comb filter according to an illustrative embodiment of the present invention, and  FIG. 7 b    illustrates a gain-to-frequency graph  750  of the frequency response of an example comb filter according to an illustrative embodiment of the present invention. Any comb filter known in the art can be implemented to determine the total noise energy between harmonics in an audio spectrum generated by an AC system. For example, a feedforward notch filter can be implemented with a delay equal to a period of a fundamental frequency of the audio spectrum. By way of example, an illustrative implementation can use a sample rate of 8820 samples per second for a 60 Hz AC system and 7350 samples per second for a 50 Hz AC system. This can result in a 147-sample delay for either frequency. The input data can be subtracted from the delayed data, resulting in a gain at the fundamental and each harmonic. The gain can be 2 between harmonics. 
     In an example method, the total energy of the harmonics can be compared to the total energy between the harmonics. An example algorithm (e.g., employed by a processor  854 ) can require the harmonic energy to be at least 4 times higher than the noise energy, such that the gain can be approximately 6 dB. Alternative example algorithms can require the harmonic energy to be greater than any desired multiple of the noise energy. This amount of gain can be adequate to reliably detect most significant corona. 
       FIG. 8 a    illustrates a block diagram  800  of a process according to an illustrative embodiment of the present invention for detecting corona using audio data. Briefly, by way of an example, this illustrative method can include obtaining audio data (e.g., near an electrical conductor) at step  810 , processing audio data using audio signatures or threshold characteristics at step  820 , and communicating an alert on corona event detection at step  830 . 
       FIG. 8 b    shows a block diagram of an illustrative apparatus  850  for detecting corona using audio data according to an illustrative embodiment of the present invention. Apparatus  850  can include audio detector  852 , processor  854 , memory  856  and communication system  858 . Audio detector  852 , processor  854 , memory  856  and communication system  858  can be electrically or communicatively coupled, can be configured in the same housing or be separate (e.g., the detector  852  and/or the communication system can be separate from the processor  854  and memory  856 ), and can be configured to perform steps substantially similar to any of the steps in example method  800 . Additional illustrative embodiments of the present invention can include components that are enclosed or partially exposed, and can be located in or near a high power environment, on or near a suspension clamp. The apparatus  850  can be connected to a power source available at the site being monitored or can comprise a battery. 
     At step  810 , a detector  852  can obtain audio data, for example, near an electrical conductor, which can be deployed over relatively large geographic distances. The detector  852  can be located near, on or inside a clamp, in a closet, or anywhere with power conductor(s) or other component(s) that are being monitored for corona. Audio data can be obtained using, for example, a microphone, or any other audio data detector known in the art. For example, a conventional microphone can be used, which can be less costly than ultrasonic detectors required by conventional methods of detecting corona. 
     At step  820 , the audio data can be processed using, for example, audio signatures of corona or threshold characteristics. The audio data can be processed using, for example, a digital signal processor (DSP) or any other processor  854  known in the art. The DSP or other processor  854  can be local or remote. Audio signatures of corona or threshold characteristics can be stored or determined, locally or remotely, using a computer, machine-readable media, or other electronic circuitry. Alternatively, audio signatures of corona or threshold characteristics can be provided or varied prior, during or after element(s), process(es) or operation(s) or modules employed by the illustrative methods or systems according to the present invention. For example, stored or collected corona detection data can be used to determine and then calibrate desired audio signatures of corona or threshold characteristics. 
     The output of the microphone  852  can be continually or periodically sampled by the DSP or other processor  854 . The sampled audio data can be processed using the DSP or other processor using audio signatures of corona or threshold characteristics. 
     At step  830 , an alert signal or message can be communicated (e.g., by communication system  858 ) each time a corona event is detected, for example, or after a particular number of detected corona events has occurred, for example, to assist with calibrating the DSP or other processor  854  to more accurately characterize sounds as corona events. The DSP or other processor can then determine (e.g. using designated audio signatures of corona or threshold characteristics) whether an alert should be generated indicating that a corona event has occurred. The alert signal or message can be communicated using any communication method or systems known in the art, such as, for example, at least one of wired or wireless communication, cell communication, Bluetooth®, ZigBee®, LAN, WLAN, RF, IR, or any other communication method or system known in the art. A communication can be in the form of at least one of an email, a binary code, an e-mail message, an SMS message, a phone communication, a facsimile, or any other form of communication known in the art. Each clamp in a power system can, for example, be configured to send a message (e.g., a short e-mail message) to programmable e-mail addresses in case of events such as current surges, excessive conductor temperature, excessive vibration, corona, and the like to ensure rapid and intelligent response to serious conditions. In an illustrative embodiment of the present invention, a small message containing corona information can be sent, for example, using geographically distributed arrays over long distances. Radio protocols for very large networks can be used to communicate alerts, for example, using methods and systems disclosed in commonly-owned International Application PCT/US2011/001632, filed Sep. 22, 2011. The collected and/or analyzed and/or reported corona event data can include, but is not limited to, time stamps, level, duration, periodicity/patterns, and correlation to coincident temperature, humidity and/or other conditions. 
       FIG. 9  is a block diagram of an example of a method and a system  900  for processing audio data to detect corona according to an illustrative embodiment of the present invention. For example, block diagram  900  shows an example of a system and method for performing step  820  described above. An illustrative method and system  900  for processing audio data can include such elements or modules as a bandpass filter  901 , a low-pass filter  902 , a square root filter  903 , a square filter  904 , a comb filter  905 , a division  906 , an adder  907 , and a multiplier  908 . Briefly, in an illustrative implementation, a method and system  900  for processing audio data to detect corona can include determining bandwidth limited audio data at step  910 , determining an indicator of the energy at a fundamental frequency at step  920 , determining an indicator of the energy at each of a plurality of harmonic frequencies at step  930 , determining an indicator of the noise energy at step  940 , determining a comparison indicator at step  950 , determining an example mask or masking indicator at step  960 , and determining a corona detection indicator at step  970 . It will be understood by a person skilled in the art that some of these steps can be performed in any order. 
     In an illustrative method and system  900  for processing audio data to detect corona according to an illustrative embodiment of the present invention, a processor  854  with or without memory  856  can perform steps substantially similar to any of steps  910 - 970  using software, or discrete components (e.g., filters) can be used, or a combination of both. The system and method  900  for processing audio data to detect corona according to illustrative embodiments the invention can be implemented using software and/or hardware components. 
     In the illustrative implementations, at steps  920 ,  930  and  940 , the root mean square of the energy from each filter (e.g., respective bandpass filters  910  in steps  920  and  930 , and comb filter  905  in step  940 ) is computed by squaring the data  904 , performing a low pass filter  902  to get an average, and then taking the square root  903 . With regard to steps  930  and  960 , the results for each harmonic is then normalized to the energy from the fundamental frequency using a division  906  as shown in step  960 . The output of each divider  906  provides the energy in each harmonic as a fraction of the energy in the fundamental frequency. An alternative implementation to using the root mean square function is described below. 
     As stated above, audio data can include, for example, audio data obtained from an audio detector (e.g., a microphone) deployed with respect to an alternating current (AC) system. Audio data from the audio detector can be analog-to-digital converted. In illustrative implementations, at step  910 , bandwidth limited audio is provided to a system  900  to reduce the processing requirements. The lower bandwidth signal can be decimated (reduced sampling rate) before sampling. By way of example, an illustrative implementation may reduce the sample rate from 44,100 samples per second to 8820 samples per second (⅕ th  rate) for a 60 Hz AC system and 7350 samples per second (⅙ th  rate) for a 50 Hz AC system. 
     As explained above, the AC system will typically generate significant energy at the fundamental frequency of the audio data and further energy at harmonics. For a power system, its fundamental frequency will usually contain the majority of the energy. As each frequency is analyzed, the root mean square of the energy is computed. As described above, with reference to steps  920 ,  930  and  960 , the energy at each harmonic frequency separated by the bandpass filters is referenced to the energy at the fundamental frequency using a division  906  to normalize the measured energy. 
     In illustrative implementations, at step  920 , the energy of the fundamental frequency is measured and used as a normative reference for other measurements. The bandpass filter  901  isolates energy at fundamental frequency. In a typical AC power system, the fundamental frequency would be 60 Hz in the United States and other countries and 50 Hz in Europe and other countries. The computation in step  920  (e.g. by processor  854 ) performs a root means square (rms) measurement. The data is squared, integrated, and a square root results in rms measurement. The low pass filter  902  in step  920  is, essentially, an integration. The output of step  920  is the energy at the fundamental frequency. This is used as a reference. That is, the energy of the harmonics is computed relative to the energy in the fundamental. 
     In illustrative implementations, at step  930 , the energy at each harmonic is computed using the root mean square. While the illustrated embodiment in  FIG. 9  shows each bandpass filter is a multiple of 60 Hz, the implementation in a 50 Hz system would use bandpass filters which are multiples of 50 Hz. The corner frequency of the 40 Hz low pass filters (e.g., integrators  901  in step  930 ) would change to 33.3 Hz for a 50 Hz system (i.e., 40 Hz*50/60=33.3 Hz). The output of each harmonics&#39; section within step  930  produces the rms energy at that harmonic. 
     In illustrative implementations, at step  940 , the energy between the bandpass filters implemented in steps  930  and  920  is measured. In the case where the input signal is simply white noise, energy will be detected in all of the bands, which might be erroneously considered a positive indication. By looking at energy between the harmonics, the illustrative implementation of the method and system  900  can determine a noise floor for the corona detection algorithm or system  900  (e.g., performed by processor  854 ). The energy in the harmonics must be substantially above the noise floor for the corona detection to be created. The implementation uses, for example, a comb filter with notches at the fundamental and all of the designated harmonics. The peak response of the comb filter will occur at (n+0.5)*fundamental frequency. For a 60 Hz fundamental, the peaks will be at 90 Hz, 150 Hz, 210 Hz, and so forth up to 750 Hz. Above 780 Hz there will be little energy due to the 780 Hz bandpass filter in step  910 . 
     In illustrative implementations, at step  950 , a comparison indicator is generated. The indicators of the energy at each harmonic frequency detected at step  930  are summed together in step  960  (e.g., using a processor  854  and a memory  856 ), and this total energy is compared with, for example, double the noise energy. If the sum of the indicators of the energy at each harmonic frequency is greater than the indicator of twice the noise energy, a comparison indicator is set high. If not, the comparison indicator  950  is set low. If the total energy from the harmonics exceeds twice the noise measured between the harmonics, the signal may be considered for creation of a corona event (with further evaluation). If twice the noise energy exceeds the energy in the harmonics, the signal will be disqualified as corona. 
     In illustrative implementations, at step  960 , a masking indicator can be determined. Normalized indicators of the energy at each harmonic frequency can be determined by dividing each indicator of the energy at each harmonic frequency by the indicator of the energy at the fundamental frequency. A mask can be applied to the normalized indicators of the energy at each harmonic frequency, comparing each normalized indicator of the energy at each harmonic frequency with a range of acceptable levels. A range of acceptable levels can be uniform across frequencies or can vary as a function of frequency. For example, a minimum value in a range of acceptable levels can range linearly or nonlinearly from about 15 dB for the lowest harmonic frequency to about 5 dB for the highest harmonic frequency. Any other range of acceptable levels can be used. Alternatively, a range of acceptable levels can be provided or varied prior, during or after operation using methods or systems according to the present invention. For example, stored corona detection data can be used to determine and then calibrate a desired range of acceptable levels. 
     If all levels are within the mask, the masking indicator  960  can be set high. If not, the masking indicator can be set low. The masking indicator  960  can be, for example, a mask block output. 
     In illustrative implementations, at step  970 , a corona detection indicator can be determined. A corona detection indicator  970  can be, for example, a corona detection bit, which can be output by an AND gate. If both the comparison indicator  950  and the masking indicator  960  are high, the AND gate output can be set high. If not, the AND gate output can be set low. 
     An alternative illustrative implementation can use absolute value functions in place of square functions at steps  930  and  920 . The low-pass filter may need a lower corner frequency, but the square root at step  930  may not be needed. Even with such narrow filters, the output may not be a sine; consequently, the root mean square may be a more accurate method of measuring energy than the filtered absolute value, though the filtered absolute value may be good enough. 
     In an alternative illustrative method of processing audio data to detect corona, at least some of steps  910 - 970  can be performed using a processor and a memory, without using some of blocks or modules  901 - 908  illustrated in  FIG. 9 . Indicators in steps  910 - 970  can be variables. 
       FIGS. 10 a - c    show illustrative apparatuses  1000 ,  1020  and  1040  for detecting corona using audio data according to illustrative embodiments of the present invention, which can include processor  854  and audio detector  852 . Processor  854  and audio detector  852  can be electrically or communicatively coupled, and can be configured to perform steps substantially similar to any of the steps in example method  800 . 
       FIG. 10 a    shows an illustrative stand-alone apparatus  1010  for detecting corona using audio data according to an illustrative embodiment of the present invention, which can include processor  854  having an integral or separate memory  856  and audio detector  852 . 
       FIG. 10 b    shows an illustrative apparatus  1020  for detecting corona using audio data according to an illustrative embodiment of the present invention, on a suspension clamp substantially similar to the suspension clamp illustrated in  FIGS. 2-4  described above. In illustrative apparatus  1020 , processor  854  and audio detector  852  can be electrically or communicatively coupled to electronic circuit  228 . In an alternative illustrative embodiment of the present invention, electronic circuit  228  can include a processor adapted to perform steps substantially similar to steps that processor  854  is adapted to perform. 
       FIG. 10 c    shows an illustrative apparatus  1040  for detecting corona using audio data according to an illustrative embodiment of the present invention, on a clamp assembly. The clamp assembly  1041  on a conductor  1042  can include a clamp body  1043 , a keeper body  1044  resting on the clamp body  1043 , an electronics housing  1045 , and a heat shield  1046  that protects the electronic components in the electronics housing  1045 . In illustrative apparatus  1040 , processor  854  and audio detector  852  can be electrically or communicatively coupled to an electronic circuit disposed within electronics housing  1045 . 
     The components of the illustrative devices, systems and methods employed in accordance with the illustrated embodiments of the present invention can be implemented, at least in part, in digital electronic circuitry, analog electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. These components can be implemented, for example, as a computer program product such as a computer program, program code or computer instructions tangibly embodied in an information carrier, or in a machine-readable storage device, for execution by, or to control the operation of, data processing apparatus such as a programmable processor, a computer, or multiple computers. Examples of the computer-readable recording medium include, but are not limited to, read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices. It is envisioned that aspects of the present invention can be embodied as carrier waves (such as data transmission through the Internet via wired or wireless transmission paths). A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. The computer-readable recording medium can also be distributed over network-coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments for accomplishing the present invention can be easily construed as within the scope of the invention by programmers skilled in the art to which the present invention pertains. Method steps associated with the illustrative embodiments of the present invention can be performed by one or more programmable processors executing a computer program, code or instructions to perform functions (e.g., by operating on input data and/or generating an output). Method steps can also be performed by, and apparatus of the invention can be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example, semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in special purpose logic circuitry. 
     The above-presented description and figures are intended by way of example only and are not intended to limit the present invention in any way except as set forth in the following claims. It is particularly noted that persons skilled in the art can readily combine the various technical aspects of the various elements of the various exemplary embodiments that have been described above in numerous other ways, all of which are considered to be within the scope of the invention. 
     The above-described illustrative embodiments of an apparatus, system and method can include program instructions, which can be stored on non-transient computer-readable media to implement various operations performed by a processor, such as microprocessor or computer. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. The media and program instructions may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM disks and DVD; magneto-optical media such as optical disks; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like. The media may also be a transmission medium such as optical or metallic lines, wave guides, and so on, and is envisioned include a carrier wave transmitting signals specifying the program instructions, data structures, and so on. The computer-readable recording medium can also be distributed over network-coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. The described hardware devices may be configured to act as one or more software modules in order to perform the operations of the above-described embodiments of the present invention. 
     Although illustrative embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope of the present invention. Therefore, the present invention is not limited to the above-described embodiments, but is defined by the following claims, along with their full scope of equivalents.