Patent Publication Number: US-11650264-B2

Title: Capacitance-coupled voltage transformer monitoring

Description:
RELATED APPLICATION 
     This application claims benefit as a continuation-in-part of, and claims priority to, U.S. patent application Ser. No. 16/396,939 filed on 29 Apr. 2019, titled “Capacitance-Coupled Voltage Transformer Monitoring” naming Travis C. Mallett and Robert Lopez Jr. as inventors, which is incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to monitoring the operation of a capacitance-coupled voltage transformer (CCVT or CVT). In particular, this disclosure relates to obtaining primary and secondary signals from a CCVT and monitoring performance of the CCVT using the primary and secondary signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the disclosure are described, including various embodiments of the disclosure with reference to the figures, in which: 
         FIG.  1    illustrates a simplified diagram of a system including a CCVT and an intelligent electronic device (IED) consistent with the present disclosure. 
         FIG.  2 A  illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  2 B  illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  2 C  illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  3    illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  4 A  illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  4 B  illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  4 C  illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  5    illustrates a theoretical block diagram of electrical measurements useful for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  6    illustrates a plot of current ratio vs primary voltage. 
         FIG.  7    illustrates a plot of current ratio vs a change in capacitance. 
         FIG.  8 A  illustrates a functional block diagram of a device for monitoring a CCVT. 
         FIG.  8 B  illustrates a circuit diagram of a device for monitoring a CCVT. 
         FIG.  8 C  illustrates a plot of CCVT secondary voltage versus time. 
         FIG.  8 D  illustrates a plot of current versus time. 
         FIG.  8 E  illustrates a plot of current versus time. 
         FIG.  8 F  illustrates a plot of voltage magnitudes versus time. 
         FIG.  8 G  illustrates a plot of voltage ratio versus time. 
         FIG.  8 H  illustrates a plot of a warning signal versus time. 
         FIG.  9    illustrates a simplified block diagram of a device for monitoring a CCVT. 
         FIG.  10    illustrates a simplified diagram of a three-phase CCVT system and monitoring system in accordance with the embodiments herein. 
         FIG.  11    illustrates a functional block diagram of a system for monitoring a CCVT. 
         FIG.  12 A  illustrates a theoretical block diagram of electrical measurements useful for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  12 B  illustrates a simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  12 C  illustrates another simplified diagram of a system to obtain measurements for monitoring of a CCVT consistent with embodiments of the present disclosure. 
         FIG.  13    illustrates a functional block diagram of a device for monitoring a CCVT. 
         FIG.  14    illustrates a plot of angle difference vs change in inductance. 
         FIG.  15 A  illustrates a plot of a waveform capture of two currents obtained for monitoring a CCVT. 
         FIG.  15 B  illustrates a plot of waveform capture of two currents over a number of decomposition levels for monitoring a CCVT. 
         FIG.  15 C  illustrates a health factor for several decomposition levels for monitoring a CCVT. 
     
    
    
     DETAILED DESCRIPTION 
     Electric power delivery systems are expected to operate reliably, safely, and economically. To meet those objectives, systems are closely monitored to determine operating conditions, detect anomalies, and effect protective actions on the electric power delivery system. Monitoring typically involves obtaining current and voltage measurements from various pieces of equipment of the electric power delivery system and using the current and voltage measurements in various monitoring and protection functions. Portions of the electric power delivery system may be operated at a sufficiently high voltage that a capacitively-coupled voltage transformer (CCVT) is used to obtain voltage measurements. 
     CCVTs are used to reduce high-voltage signals to a low voltage for monitoring by an intelligent electronic device (IED). Over time, CCVT components may degrade, resulting in errors in the measured voltage, failure of the CCVT, or even catastrophic events such as CCVT explosion. Errors in the measured voltage may result in misoperation of the IED. Catastrophic events may lead to injury or system failure. What is needed is a system to monitor CCVT for component degradation such that the CCVT may be repaired or replaced before significant misoperation or a catastrophic event occurs. 
     Most methods of CCVT monitoring require knowledge of the power system behavior or analysis of CCVT transients. These methods are sometimes complex because data about the CCVT health must be extracted from the CCVT secondary voltage and/or other power system equipment such as CCVTs on other phases. Time-domain and frequency-domain characteristics of CCVT secondary voltages are highly complex. Traditional CCVT monitoring techniques suffer from the resulting complexity. Furthermore, single-phase CCVTs are often not monitored because of the difficulty in obtaining a reliable reference quantity. What is needed is a system for monitoring a single-phase CCVT without requiring knowledge of the power system behavior or analysis of CCVT transients. 
     Accordingly, disclosed herein are improvements to IEDs that use signals from CCVTs to monitor the CCVT itself for component degradation. In various embodiments, the IED may perform monitoring functions on the electric power delivery system and monitoring functions on the CCVT. 
       FIG.  1    illustrates a simplified diagram of a system  100  including a CCVT consistent with the present disclosure. A capacitor stack  113  is in electrical communication with a high voltage portion  102  and a low voltage portion  103  and is connected between a primary voltage terminal  101  and a substation ground  104 . A primary current measurement device  115  may be used to obtain current measurements from a line such as a transmission or distribution line, bus, or the like. 
     The capacitor stack  113  creates a capacitive voltage divider and produces an intermediate voltage at the tap terminal  105 . In various embodiments, the primary voltage may be 110 kV and above, and may include 750 kV and 1 MV networks. The intermediate voltage may be in the range of 5-30 kV. A step-down transformer  107  further steps down the intermediate voltage to a standard secondary voltage at the output CCVT terminals  109 . The standard secondary voltage may be in the range of 60-250 V in various embodiments. 
     A direct connection of a step-down transformer to a capacitor stack may introduce an angle measurement error. To reduce that error, a tuning reactor  106  may be connected in series between the intermediate voltage terminal  105  in the capacitive divider and the step-down transformer  107 . A connection of the step-down transformer  107  and the capacitors  102  and  103  would create a danger of ferroresonance. A ferroresonance is a self-exciting and potentially destructive oscillation between the non-linear magnetizing branch of the step-down transformer  107  and the capacitors  102  and  103 . A ferroresonance suppression circuit (FRSC)  108  is connected to the secondary winding of the step-down transformer  107  to prevent ferroresonance. The output voltage at the CCVT secondary terminals  109  is connected via control cables  110  to the input terminals  111  of the end device  112  such as an IED. The connection at the end device  112  typically includes a safety ground  124 . 
     System  100  acts inadvertently as a band-pass filter. System  100  passes the fundamental frequency component (typically 50 or 60 Hz) at the nominal transformation ratio and with small magnitude and angle errors. The components of system  100  considerably attenuate frequencies below the nominal power system frequency as well as high frequencies. In addition, the CCVT produces transient components in the spectrum close to the nominal frequency that may impair the operation of the power system monitoring as mentioned above. 
     For very high frequency components, such as voltage traveling waves, an ideal tuning reactor  106  behaves as an open circuit, and therefore it does not pass any very high frequency signals to the step-down transformer  107 . Similarly, an ideal step-down transformer  107  is an open circuit for very high frequencies, and as such, it also prevents any high-frequency signals from being passed to the low voltage side  109  of the step-down transformer  107 . As a result, the IED  112  may not receive high-frequency signals, such as may be associated with traveling waves at its terminals  111 . In practice, however, the tuning reactor  106  has some parasitic inter-turn capacitance, which may also be called stray capacity. Similarly, the windings of the step-down transformer  107  also include parasitic capacitance. 
     Various embodiments consistent with the present disclosure may use measurements from the electric power delivery system such as measurements from primary current measurement device  115  along with additional measurements associated with capacitor stack  113  to monitor performance of the CCVT. Such systems and methods may also use signals obtained from the CCVT and CT  115  to monitor and protect a larger electric power delivery system. For the purposes of the present disclosure, additional current measurements from the capacitor stack  113  may be used to monitor the CCVT for degradation. For various implementations, a second CT may be used. For example, to obtain high-fidelity voltage signals, a second CT may be used to obtain a second current signal. The second CT may also be useful for monitoring and protection of the CCVT according to several embodiments described herein. 
       FIG.  2 A  illustrates a simplified diagram of a system  200  to determine a voltage signal based on current measurements in a CCVT consistent with embodiments of the present disclosure. The current signals may be used to monitor the CCVT. In the illustrated embodiment, a first current transformer  204  is installed in series with the low voltage capacitor  203  in a CCVT. A second current transformer  206  is located in the return connection from a step-down transformer  209 . The current transformers  204  and  206  may be installed near the ground  208  for various reasons, including the low electrical potential and the accessibility of the wires. One or both of current transformers  204  and  206  may be embodied as a clamp-on transformer or other current measurement device in various embodiments. 
     Using Kirchoff&#39;s current law, the current i C1    201  through capacitor  202  may be expressed as a function of the currents through the current transformers  204  and  206 , as shown in Eq. 1.
 
 i   C1   =i   2   +i   3   Eq. 1
 
     The current i C2    205  through capacitor  203  is measured directly by current transformer  204 , as it is equal to i 2    215 . Having the currents i C1    201  and i C2    205  in capacitors  202  and  203 , the voltage may be calculated using Eq. 2. 
     
       
         
           
             
               
                 
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                   = 
                   
                     
                       
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                     + 
                     
                       
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                           2 
                         
                       
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     Eq. 2 provides an accurate representation of the voltage in a wide frequency range. While Eq. 2 represents an ideal voltage calculation, it is understood that Eq. 2 may be modified to apply to only certain frequency ranges. For example, if calculation of only high-frequency voltages is required, the integration in Eq. 2 may be implemented on only high-frequencies by means of a digital or analog low-pass filter, as a non-limiting example. 
       FIG.  2 B  illustrates a simplified diagram of a system  280  to determine a voltage signal based on current measurements in a CCVT consistent with embodiments of the present disclosure. In contrast to system  200  illustrated in  FIG.  2 A , system  280  has a different grounding configuration. 
       FIG.  2 C  illustrates a simplified diagram of a system  290  to determine a voltage signal based on current measurements in a CCVT consistent with embodiments of the present disclosure. In contrast to system  200  illustrated in  FIG.  2 A , the capacitors  202  and  203  are shown with equivalent series resistances R 1   232  and R 2   233  and equivalent series inductances L 1   222  and L 2   223 . In some embodiments, Eq. 2 may not be valid over a frequency range of interest, and integration of currents through ideal capacitors C 1   212  and C 2   213  may not be an accurate representation of the voltage across the capacitors. Accordingly, a more accurate model of the CCVT may be employed such as illustrated in  FIG.  2 C . The voltage may be calculated as shown in Eq. 3. 
     
       
         
           
             
               
                 
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     Although  FIG.  2 C  illustrates a particular embodiment of a system to determine a voltage signal based on current measurements in a CCVT, different embodiments are contemplated. For example, instead of modeling the CCVT capacitors as a series R-L-C circuit, other models may be used which may employ any number of elements in any configuration. 
       FIG.  3    illustrates a simplified diagram of a system  300  to determine a voltage signal based on a current measurement in a CCVT consistent with embodiments of the present disclosure. In contrast to system  200  illustrated in FIG.  2 A, system  300  illustrated in  FIG.  3    has the first current transformer  310  installed in the ground connection rather than in the low portion of the capacitor stack. 
     Using Kirchoff&#39;s current law, the current i C1    201  through capacitor  202  may be expressed as a function of the current through transformer  310 , as shown in Eq. 4.
 
 i   C1   =i   1   Eq. 4
 
The current through capacitor  203  may be expressed using Eq. 5.
 
 i   C2   =i   1   −i   3   Eq. 5
 
Equation 5 may be used with Equation 4 and Equation 2 to determine a voltage signal for use in connection with the systems and methods disclosed herein.
 
       FIG.  4 A  illustrates a simplified diagram of a system  400  to determine a voltage signal based on a current measurement in a CCVT and to obtain measurements useful to monitor CCVT health consistent with embodiments of the present disclosure. In comparison to system  200  illustrated in  FIG.  2 A , system  400  has a different grounding configuration. 
     Using Kirchoff&#39;s current law, the current i C1    201  through capacitor  202  may be expressed as a function of the current through transformer  416 , as shown in Equation 6.
 
 i   C1   =i   1   Eq. 6
 
The current through capacitor  203  i C2    205  may be expressed using Equation 7.
 
 i   C2   =i   2   Eq. 7
 
     Equations 6, 7, and 2 may be used to determine a voltage signal from the current signals determined by current transformers  204  and  416 . In connection with the systems illustrated in  FIGS.  2 A,  2 B,  2 C,  3 ,  4 A,  4 B,  4 C,  8 ,  9 ,  10  and  11   , other current measurement devices, such as current transformers, resistive shunts, or capacitive shunts may be utilized. Such currents may be used to monitor health of a CCVT. 
       FIG.  4 B  illustrates a simplified diagram of a system  401  to determine a voltage signal based on a current measurement in a CCVT and to obtain measurements useful to monitor CCVT health consistent with embodiments of the present disclosure. In comparison to  FIG.  4 A , the system  401  illustrates parasitic capacitance  403  which conducts current i 4    407 . The parasitic current is measured using current transformer  409 . Using Kirchoff&#39;s current law, the current through capacitor  202  i C1  may be expressed as a function of the current through transformers  206  and  409 , as shown in Equation 8.
 
 i   C1   =i   1   +i   4   Eq. 8
 
     While  FIG.  4 B  illustrates a parasitic capacitance of the step-down transformer  209 , it is understood that other parasitic current paths may exist and can be measured to improve the calculation of current through the CCVT capacitors  202  and  203 . Alternatively, some CCVTs may have internal ground connections or other non-parasitic components which operate as current paths to ground. Measurement of other currents and voltages in the CCVT may be required to accurately calculate a current through a capacitor element of the capacitor stack. Furthermore, some current paths may be predictable, and their effects on the current in the capacitor stack may be calculated or estimated indirectly rather than measured. 
       FIG.  4 C  illustrates a diagram of a system  402  to determine a voltage signal based on a current measurement in a CCVT and to obtain measurements useful to monitor CCVT health consistent with embodiments of the present disclosure. In comparison to  FIG.  4 B , the system  402  illustrates parasitic capacitances  403 ,  404 ,  405 , and  406  which collectively conduct current from capacitor  202  to CCVT secondary terminal box  421 . Furthermore, several non-parasitic connections  410 ,  411 , and  412  conduct current from capacitor  202 . The CCVT secondary terminal box  421  may be divided into accessible region  423  and inaccessible region  422 . Accordingly, it may be difficult to measure the effects of current paths in the inaccessible region  422  such as current through chassis connections  412  and  413 . The CCVT secondary terminal box  421  is connected to ground  208  through an external ground lead  450 . In this embodiment, current transformer  416  measures current i 1    431  through the ground lead  450 . This allows the currents through all parasitic and non-parasitic chassis connections  410 ,  411 ,  430 ,  412 , and  413  to be measured and used to accurately calculate the current i 1    431  through capacitor  202 . 
     Using Kirchoff&#39;s current law, the current through capacitor  202  i C1  may be expressed as a function of the current through transformer  416 , as shown in Equation 9.
 
 i   C1   =i   1   Eq. 9
 
The current through capacitor  203  i C2    205  may be expressed as the current through transformer  417  using Equation 10.
 
 i   C2   =i   2   Eq. 10
 
Equations 9, 10, and 2 may be used to determine a voltage signal from the current signals determined by current transformers  416  and  417 .
 
       FIG.  5    illustrates a representative circuit of a CCVT useful to illustrate monitoring a CCVT using current signals therefrom in accordance with several embodiments. A CCVT may be modeled in the frequency domain as a current divider with frequency-dependent impedances Z 1    504 , Z 2    514 , and Z 3    518 . Currents to ground  508  through leads may be different, depending on the frequency content of the signal. However, at a single frequency, the impedances Z 1    504 , Z 2    514 , and Z 3    518  will remain constant under ideal conditions. Accordingly, changes in the relative impedances at a single frequency or frequency range may indicate degradation of the components of the CCVT. 
     The current through C 2  (represented by I 2    512  in  FIG.  5   ) may be calculated using Equation 11: 
                     I   2     =         I   1     ⁡     (         Z   2     ⁢             ⁢     Z   3         Z   2       )       =       I   1     ⁡     (       Z   3         Z   2     +     Z   3         )                 Eq   .           ⁢   11               
where I 1  represents current through C 1 . Similarly, the current I 3    516  through the current transformer  206  (or through impedance Z 3    518 ) may be calculated using Equation 12:
 
                     I   3     =         I   1     ⁡     (         Z   2     ⁢             ⁢     Z   3         Z   3       )       =       I   1     ⁡     (       Z   2         Z   2     +     Z   3         )                 Eq   .           ⁢   12               
Finally, the ratio of current I 2  to I 3  may be calculated using Equation 13:
 
     
       
         
           
             
               
                 
                   
                     
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     Impedances Z 3  and Z 2  are not constant over a range of frequencies, but at any given frequency, the impedances Z 3  and Z 2  are constant. As can be seen from Equation 13, measuring the currents I 2  and I 3  may be useful to determine a ratio of impedances Z 3  and Z 2 . The ratio of the impedances Z 3  and Z 2  at a single frequency remains constant unless the health of the CCVT changes. Accordingly, the currents I 2  and I 3  at a single frequency or frequency range may be measured, and the ratio of I 2  to I 3  may be monitored. If the ratio changes, it may be an indication of a change in the capacitor stack or step-down transformer  209 . In particular, a change or drift of the ratio of currents I 2  to I 3  outside of an acceptable band may indicate degradation of the CCVT. 
       FIG.  6    illustrates a ratio of currents I 2  to I 3  at a single frequency (60 Hz) across a range of voltages from 100 V to 115 kV. It can be seen that the ratio of the currents I 2  to I 3  at a single frequency holds constant.  FIG.  7    illustrates the ratio of the currents I 2  to I 3  at a single frequency (60 Hz) as the capacitance of the CCVT changes. Accordingly, a change in the ratio of the currents I 2  to I 3  may be used to indicate a change in the CCVT, even if the various capacitor stacks of the CCVT change by the same percentage in the same direction. The change in capacitance of the CCVT may be indicative of decreased health of the CCVT. Accordingly, systems and methods herein may monitor the ratio of the currents I 2  to I 3  at a single frequency to monitor the health of the CCVT. 
     While Equations 11-13 are developed with reference to a single frequency common to both Z 3  and Z 2 , it is understood that the merits of Equations 11-13 can be utilized with respect to ranges of frequencies. 
     Accordingly, a ratio of measurements (currents, impedances, or even voltages calculated by integrating the currents) may be determined and monitored to determine a health of the CCVT. As used herein, the ratio of measurements may be referred to as a health factor of the CCVT. Thus, embodiments herein may monitor the health of a CCVT by calculating a health factor from measurements representing current through different portions of the CCVT. In several embodiments, the health factor may be a ratio of currents at a particular frequency or range of frequencies. In other embodiments, the health factor may be a ratio of impedances at a particular frequency or range of frequencies. In other embodiments, the health factor may be a ratio of voltages calculated from currents at a particular frequency or range of frequencies. In still other embodiments, the health factor may be other quantities calculated using measurements from different portions of the CCVT. 
       FIG.  8 A  illustrates a functional block diagram of a system  800  for monitoring a CCVT in accordance with several embodiments herein. The system includes a device  850  such as an IED for monitoring the CCVT. The device  850  obtains current signals from CT  204  and CT  206  which are in electrical communication with the ground leads of the CCVT and the step-down transformer  206 . Signals from the CTs  204 ,  206  may be filtered using cosine filters  852 ,  854 . As stated above, the impedances Z 2  and Z 3 , and the ratio of the impedances Z 2  and Z 3  are constant for a healthy CCVT. Following Equation 13, the ratio of the currents I 2  to I 3  at a single frequency may be used in place of the ratio of the impedances to monitor the health of the CCVT. Accordingly, the cosine filters  852 ,  854  may be used to extract phasors of the current signals from CTs  204 ,  206  at a single frequency, such as, for example, the fundamental frequency. 
     Magnitudes of the outputs of the cosine filters  852 ,  854  may be determined using magnitude calculators  856 ,  858 . Thus, a ratio of the magnitudes of the current signals from CTs  206  and  204  at a single frequency may be determined using ratio calculator  860 . As has been illustrated above, for a healthy CCVT, the ratio at a single frequency should be constant. Accordingly, comparators  862 ,  864  may be used to determine whether the ratio remains within a healthy range. In comparator  862  the ratio is compared against a maximum limit  866 ; and in comparator  864  the ratio is compared against a minimum limit  868 . The maximum limit  866  and minimum limit  868  may be predetermined limits. In various embodiments, the maximum limit  866  and the minimum limit  868  may be calculated using values of the ratio from calculator  860  during healthy-state operation of the CCVT. The maximum limit  866  and minimum limit  868  may be calculated based on a percentage of the healthy-state operation of the CCVT. For example, a healthy value of the ratio may be predetermined or calculated using an output of ratio calculator  860  during healthy-state operation of the CCVT. The maximum limit  866  may be calculated as 10% above the healthy value of the ratio, and the minimum limit  868  may be calculated as 10% below the healthy value of the ratio. Various other minimum and maximum limits may be used. 
     If the ratio from ratio calculator  860  is greater than the maximum limit  866 , comparator  862  asserts its output to the input of OR gate  870 . If the ratio from the ratio calculator  860  is less than the minimum limit  868 , then comparator  864  asserts its output to the input of OR gate  870 . The OR gate  870  asserts a CCVT failure signal  872  upon assertion from either of the comparators  862 ,  864 . The CCVT failure signal  872  may be used to notify operators of a status of the CCVT operating outside of the predetermined healthy condition. The system may display or send an alert of the CCVT operating outside of the predetermined healthy condition. The system may take a protective action upon assertion of the CCVT failure signal  872  such as, for example, opening a circuit breaker to remove power to the CCVT. 
     As capacitor elements in the CCVT capacitor stack begin to fail, increased voltage and stress is applied to the remaining healthy capacitors. This can lead to an increased rate of failure over time producing an avalanche failure mode and a possible explosion. Although the ratio from ratio calculator  860  may be within the maximum limit  866  and minimum limit  868 , the ratio rate of change may exceed a rate of change limit which indicates likely CCVT failure. Accordingly, the device  850  may employ a rate of change calculator  861  which calculates the rate of change of the ratio from the ratio calculator  860 . The ratio calculator may compute the difference between consecutive samples of the ratio or may compare the current ratio to a record of ratio values over time to determine a rate of change. The rate of change is compared to a maximum rate of change limit  869  using comparator  871 . If the rate of change exceeds the maximum rate of change limit  869 , then the comparator  871  asserts a CCVT warning signal  873  which can alert the user to an imminent CCVT failure. 
     Although  FIG.  8 A  illustrates a particular embodiment of a system to monitor a CCVT, different embodiments are contemplated. For example, instead of determining a ratio of magnitudes of the current signals at a single frequency, and comparing the ratio against minimum and maximum limits, the system may calculate voltages from the CTs  204 ,  206  by integrating the current signals from CTs  204 ,  206 , and comparing a ratio of the voltage magnitudes. In other embodiments, the device  850  may be implemented to monitor the power system using high-fidelity voltage signals from the current signals from CTs  204 ,  206 . These voltage measurements may then be differentiated to calculate current signals, which may then be used in cosine filters, magnitude calculators, ratio calculator, and comparators as illustrated in  FIG.  8 A . 
       FIG.  8 B  illustrates a schematic diagram  801  for simulating a system to monitor a CCVT in accordance with several embodiments herein. The capacitor stack  810  comprises a high voltage capacitor consisting of capacitor elements C 1   A    811  and C 1   B    812  and a low voltage capacitor C 2   813 . A step-down transformer  814  is electrically connected to the capacitor stack  810 . A normally open voltage-controlled switch  815  is electrically connected to the high voltage capacitor element C 1   B    812 , and the voltage-controlled switch  815  is programmed to close at 100 ms, causing a short circuit across the terminals of high voltage capacitor element C 1   B    812 . When the switch  815  closes, the short circuit simulates a failure of a capacitor in the capacitor stack  810 . 
     A current measurement module  816  measures current i 2    817  from the current stack  810  to ground and current i 3    818  from the step-down transformer  814  to ground by means of shunt devices R 2   819  and R 3   820 . A current magnitude calculator module  821  computes quantities representing magnitudes of the currents i 2    817  and i 3    818 . As illustrated here, the magnitudes are calculated for a range of frequencies using bandpass filters  822 . A ratio calculator  823  computes the ratio  824  of the magnitudes from the current magnitude calculator module  821 . Finally, a ratio comparison module  825  compares the ratio  824  to a predetermined range comprising a maximum ratio  826  (which may be set at around 200 mV) and a minimum ratio  827  (which may be set at around 100 mV). If the ratio  824  exceeds the range, the ratio comparison module  825  asserts a CCVT warning signal  828 . 
       FIG.  8 C  illustrates a plot  829  of the CCVT voltage  830  from the CCVT secondary  831  in the schematic diagram  801  in  FIG.  8 B . At 100 ms, the CCVT voltage  830  has an increase in magnitude due to the failure in the capacitor stack  810  simulated by switch  815 . An IED monitoring the CCVT secondary voltage  831  cannot determine whether the step at 100 ms in the plot  829  represents a failure of the electronic delivery system (i.e., a change in the primary voltage V PRI    832 ), a failure of the capacitor stack  810 , or a failure of the step-down transformer  814 . The CCVT voltage  830  also exhibits a CCVT transient after the simulated capacitor failure at 100 ms. 
       FIG.  8 D  illustrates a plot  833  of the current  834 , which is equal to i 3    818  through the step-down transformer  814 , measured through current shunt R 3   820 . The similarities between the CCVT voltage  830  in  FIG.  8 C  and the current  834  through the step-down transformer  814  in  FIG.  8 D  are noted. In particular, the similarities between the current  834  and voltage  830  illustrate that a failure of the step-down transformer  814  has not occurred and may allow an IED to limit diagnosis of the event occurring at 100 ms to either a failure of the capacitor stack  810  or a change in primary voltage  832 . In some embodiments, the IED may calculate a health supervisory signal using the secondary voltage of the CCVT and a current associated with the CCVT such as i 1 , i 2 , or i 3 . The secondary voltage and the current may be at a common frequency. The health supervisory signal may be a ratio of the magnitudes of the secondary voltage and the current at a common frequency. The IED may compare the health supervisory signal against an acceptable range, which may be predetermined, static, or dynamic based on operating conditions. When the health supervisory signal does not exceed the acceptable range, then the IED may determine that a failure of the step-down transformer  814  has not occurred, such that when the health factor does exceed its acceptable range (the CCVT_WARN signal is issued), then the IED may determine that the failure is in the capacitor stack  810  or a change in the primary voltage. When both the health supervisory signal exceeds its acceptable range and the health factor exceeds its acceptable range, then the IED may determine that the failure may be in the capacitor stack  810 , the step-down transformer  814 , a change in primary voltage, or the like. Finally, when the health supervisory signal exceeds its acceptable range but the health factor does not exceed its acceptable range, then the IED may determine that the failure is outside of the capacitor stack  810 . 
       FIG.  8 E  illustrates a plot  835  of the current  836  through the capacitor stack  810 , measured through current shunt R 2   819 . 
       FIG.  8 F  illustrates a plot  837  of voltage quantities representing magnitudes of currents i 2    817  and i 3    818 . The voltage magnitude  838  related to i 2  shows a large increase immediately following the simulated failure of the capacitor stack  810 . The voltage magnitude  839  related to i 3  shows an increase after the simulated failure of the capacitor stack  810 , but the increase in the voltage magnitude  839  related to i 3  is significantly lower than the increase in the voltage magnitude  838  related to i 2 . 
       FIG.  8 G  illustrates a plot  840  of the ratio voltage  824  (e.g. from the ratio calculator  823 , where the ratio voltage is related to a ratio of the currents at a particular frequency). Also shown are the plots of the maximum ratio  826  and minimum ratio  827 . The health range is illustrated between the maximum ratio  826  and minimum ratio  827 . After 100 ms, ratio voltage  824  drops below the minimum ratio threshold  827 . Although descriptions of the ratio as developed in Equations 11-13 assume ideal cases where the ratio is constant, it is clear that the health factor may take many forms and may not be constant when computed from a range of frequencies or from non-ideal magnitude calculations. In various embodiments, the health range is predetermined. The maximum ratio  826  and minimum ratio  827  may be constant, and in various embodiments may be predetermined. Furthermore, it is contemplated that the maximum ratio  826  and minimum ratio  827  values may not be constant and may be adjusted dynamically based on various measurements, calculations, or conditions, resulting in a dynamic health range. By means of example, the acceptable health range may be adjusted based on a temperature measurement of the CCVT. Additionally, the acceptable health range may be adjusted with time to adjust for the aging of the CCVT. The acceptable health range may also be adjusted based on the rate of ratio change. 
       FIG.  8 H  illustrates a plot  844  of the CCVT warning signal  828 . After 100 ms, the warning signal asserts indicating a failure of the CCVT. According to the embodiments illustrated in  FIGS.  8 A,  8 B,  8 C,  8 D,  8 E,  8 F, and  8 G , an IED may correctly identify a failure of the CCVT capacitor stack  810 . In contrast, prior methods of single-phase CCVT monitoring cannot distinguish between a failure a change in the primary voltage V PRI    832 , a failure of the capacitor stack  810 , or a failure of the step-down transformer  814 . 
       FIG.  9    illustrates a block diagram of a system  900  to monitor a CCVT consistent with the present disclosure. The system may further be configured to monitor an electric power delivery system using voltage signals from a CCVT. Two current transformers  901  and  902  are in electrical communication with the CCVT and the CCVT secondary voltage  904 . Current transformers typically do not generate large signals, and accordingly, the length of their leads connecting to the device implementing the present invention may be limited. As a result, the IED  909  may be installed in a proximity to the CCVT. In one embodiment, the IED  909  may be installed in the substation switchyard. 
     In the illustrated embodiment, power for an IED  909  is drawn from the secondary voltage output of the CCVT  904 . In alternative embodiments, power may be provided by other sources. As illustrated, a power supply  905  may provide power to other components in system  900 . Power supply  905  may be designed to accept CCVT output voltage without introducing any consequential distortions to this voltage, and therefore not impacting accuracy of other end devices in system  900  or other devices connected to the same voltage  904 . The connection from the secondary CCVT output to the device may be fused, but the fuse is not shown in in the interest of simplicity. A typical CCVT is rated for a burden of upwards of 100 W. The actual burden created by IED  909  may be much lower and therefore a CCVT can provide several Watts of power to power the device in system  900 . In some embodiments, secondary voltage from all three power system phases may be used to power the device, thus distributing the load. 
     IED  909  may obtain current signals from the CCVT as described hereinabove using CTs  901  and  902 . The current signals may be received by a measurement system  906  of the IED. Measurement system  906  may include an ADC to create digitized representations of the signals from current transformers  901  and  902 . 
     The measurements are provided to a processing system  907 . Processing system  907  may analyze the measurements and generate alarms and or control actions. For example, the processing system  907  may transmit the high-fidelity voltage, the secondary voltage, the alarm signal, and the trip signal using a communication system  908 . Communication system  908  may communicate using a variety of communication media and protocols. In some embodiments, communication system  908  provides a representation of the high-fidelity full-scale voltage signal as an output. Still further, communication system  908  may provide a representation of the voltage derivative directly as a representation of a voltage traveling waves. In some embodiments, communication system  908  may communicate via a fiber optic medium. Other forms of communication media may also be used. 
     In some embodiments, the measurements from communication system  908  may be used by other IEDs to perform monitoring functions such as electric power system monitoring or CCVT monitoring. In other embodiments, the IED  909  may be configured to apply monitoring functions to CCVT as described herein. For example, the processing system  907  may be configured to determine a ratio of current magnitudes at a single frequency from CTs  901  and  902  or voltage magnitudes to determine a ratio and compare the ratio against predetermined maximum and minimum limits as described herein. 
     The secondary voltage output  904  of the CCVT is proportional to the current through CT  902 . In some embodiments, the IED  909  may compare the difference between current through CT  902  and the secondary voltage output of the CCVT  904  with predetermined maximum and minimum limits. The IED may use this comparison to warn of secondary transformer  911  failure or may use the information to validate other CCVT monitoring functions. For example, a loss of potential (LOP) monitoring method may be commonly employed by other IEDs monitoring the secondary voltage output of the CCVT  904 . If an IED reports a LOP, the monitoring IED  909  may report the failure location. If, for example, the ratio of current magnitudes at a single frequency from CTs  901  and  902  are within the predetermined maximum and minimum limits, then the failure may be reported to occur on the secondary side of the CCVT transformer  911 . 
       FIG.  10    illustrates a representation of the placement of a system consistent with respect to a CCVT consistent with embodiments of the present disclosure. A CCVT monitoring system  1006  consistent with the present disclosure may be disposed in a substation switchyard in proximity to the marshaling cabinet  1005 . The signals of interest may be provided to other devices, via a communication channel  1007 . In some embodiments, the other devices may be located in the control house. The communication channel  1007  may be embodied as a fiber optic connection or other type of communication media. 
     The marshaling cabinet  1005  is typically a part of a practical CCVT installation. It allows a cross-connection and demarcation point between the voltage control cables that run toward the control house and the single-phase CCVTs  1001 A,  1001 B, and  1001 C in the switchyard. These CCVTs serve the A, B, and C phases of the three-phase power system, and may have their own cabinets  1002 A,  1002 B, and  1002 C at the bottom. A CCVT monitoring system consistent with the present disclosure may place the current transformers inside the  1002 A,  1002 B, and  1002 C cabinets and may be connected via shielded twisted-pair cables  1003 A,  1003 B, and  1003 C to the marshaling cabinet  1005 , using a similar path and conduits—if possible—as the secondary voltage cables. The secondary voltages may be connected to the marshaling cabinet  1005  with the single-phase voltage cables  1004 A,  1004 B, and  1004 C. The CCVT monitoring system  1006  may be placed inside the marshaling cabinet  1005  if space permits, or in its own cabinet mounted in proximity to the marshaling cabinet  1005 . 
       FIG.  11    illustrates a functional block diagram of a system  1100  for detecting and locating faults using traveling waves consistent with embodiments of the present disclosure. System  1100  includes a communications interface  1116  to communicate with devices and/or IEDs. In certain embodiments, the communications interface  1116  may facilitate direct communication with other IEDs or communicate with systems over a communications network. Consistent with the embodiments of this disclosure the interface  1116  may include communications with the CCVT high-fidelity voltage IED with the intent to receive the high-fidelity voltage, the secondary CCVT voltage, voltage TWs, CCVT alarm and trip signals, or a combination of the above. Also, the communications interface  1116  may provide the said CCVT information to other devices. Communications interface  1116  may facilitate communications through a network. System  1100  may further include a time input  1112 , which may be used to receive a time signal (e.g., a common time reference) allowing system  1100  to apply a time-stamp to the acquired samples. In certain embodiments, a common time reference may be received via communications interface  1116 , and accordingly, a separate time input may not be required for time-stamping and/or synchronization operations. One such embodiment may employ the IEEE 1588 protocol. A monitored equipment interface  1108  may receive status information from, and issue control instructions to, a piece of monitored equipment, such as a circuit breaker, conductor, transformer, or the like. 
     Processor  1124  may process communications received via communications interface  1116 , time input  1112 , and/or monitored equipment interface  1108 . Processor  1124  may operate using any number of processing rates and architectures. Processor  1124  may perform various algorithms and calculations described herein. Processor  1124  may be embodied as a general-purpose integrated circuit, an application-specific integrated circuit, a field-programmable gate array, and/or any other suitable programmable logic device. 
     In certain embodiments, system  1100  may include a sensor component  1110 . In the illustrated embodiment, sensor component  1110  gathers data directly from conventional electric power system equipment such as a conductor (not shown) using potential transformers and/or current transformers. In various embodiments, sensor component  1110  may be in electrical communication with a clamp-on CT in a CCVT as described in connection with various embodiments of the present disclosure. The sensor component  1110  may use, for example, transformers  1102  and  1114  and A/D converters  1118  that may sample and/or digitize filtered waveforms to form corresponding digitized current and voltage signals provided to data bus  1122 . A/D converters  1118  may include a single A/D converter or separate A/D converters for each incoming signal. A current signal may include separate current signals from each phase of a three-phase electric power system. A single line diagram is shown only for the sake of clarity. 
     A/D converters  1118  may be connected to processor  1124  by way of data bus  1122 , through which digitized representations of current and voltage signals may be transmitted to processor  1124 . In various embodiments, the digitized current and voltage signals may be used to calculate time-domain quantities for the detection and the location of a fault on an electric power system as described herein. 
     A computer-readable storage medium  1130  may be the repository of various software modules to perform any of the methods described herein. A data bus  1142  may link monitored equipment interface  1108 , time input  1112 , communications interface  1116 , and computer-readable storage medium  1130  to processor  1124 . 
     Communications module  1132  may allow system  1100  to communicate with any of a variety of external devices via communications interface  1116 . Communications module  1132  may be configured for communication using a variety of data communication protocols (e.g., UDP over Ethernet, IEC 61850, etc.). 
     Data acquisition module  1140  may collect data samples such as the current and voltage quantities. The data samples may be associated with a timestamp and made available for retrieval and/or transmission to a remote IED via communications interface  1116 . Data acquisition module  1140  may operate in conjunction with CCVT monitoring module  1134 . Data acquisition module  1140  may control recording of data used by the CCVT monitoring module  1134 . According to one embodiment, data acquisition module  1140  may selectively store and retrieve data and may make the data available for further processing. Such processing may include processing by CCVT monitoring module  1134 , which may determine the occurrence of a fault within an electric power distribution system. 
     A protective action module  1152  may implement a protective action based on a declaration of a fault and/or a signal of failing CCVT health from the CCVT monitoring module  1134 . In various embodiments, a protective action may include tripping a breaker, selectively isolating a portion of the electric power system, etc. In various embodiments, the protective action module  1152  may coordinate protective actions with other devices in communication with system  1100 . 
       FIG.  12 A  illustrates a representative circuit of a CCVT useful to illustrate monitoring a CCVT using current and voltage signals associated with the CCVT in accordance with several embodiments. An IED (not separately illustrated in  FIG.  12 A ) may obtain both current associated with the CCVT as described above and secondary voltage from the CCVT using, for example, voltage terminals  1222 ,  1224 . The IED may compare the current and secondary voltage to monitor the health of the CCVT. Health of a CCVT may be monitored using current and secondary voltage because the secondary voltage of a CCVT is proportional to a current such as current I 3    516  at a single frequency, and the proportion remains relatively constant during normal operation of the CCVT. Thus, the secondary voltage V SEC  of the CCVT may be represented as a function of the current I 3    516  using Equation 14, where ƒ is the transfer function of the CCVT secondary transformer  209 . The current I 3    516  can be expressed as a function of the secondary voltage V SEC    1220  of the CCVT as shown in Equation 15 where it is noted that the inverse transfer function ƒ −1  is simply a scalar a when evaluated at a single frequency.
 
 V   SEC =ƒ( I   3 )  Eq. 14
 
 I   3 =ƒ −1 ( V   SEC )=α V   SEC   Eq. 15
 
Finally, the ratio of current I 2    512  to the secondary voltage V SEC    1220  of the CCVT may be calculated using Equation 16:
 
                       I   2       V     S   ⁢   E   ⁢   C         =         I   2         1   α     ⁢     I   3         =       α   ⁢       I   2       I   3         =     α   ⁢       Z   3       Z   2                     Eq   .           ⁢   16               
A health factor may be determined as the ratio of current I 2    512  to the secondary voltage V SEC  of the CCVT, and should remain relatively constant at a single frequency during normal operation of the CCVT. Thus, in operation, a health factor which is constant at a single frequency may be determined by measuring a single current and comparing with the secondary voltage of the CCVT. If the ratio changes, it may be an indication of a change in the capacitor stack or step-down transformer  209 . In particular, a change or drift of the ratio of current I 2    512  to V SEC    1220  outside of an acceptable band may indicate degradation of the CCVT. This method has a major advantage of simplifying the retrofitting process as illustrated in  FIG.  12 B  and the accompanying description. In particular, the inaccessible region of the CCVT need not be accessed in order to install equipment needed to obtain the necessary measurements for monitoring the health of the CCVT.
 
       FIG.  12 B  illustrates a representative circuit of a CCVT useful to illustrate monitoring a CCVT using current and voltage signals therefrom in accordance with several embodiments. IED  1209  may obtain appropriate current and voltage signals from the CCVT for monitoring the health thereof. In some embodiments, the CCVT ground current I 1    431  is electrically conducted to ground  208  through an external ground lead  450  as illustrated in  FIG.  12 B . The CCVT ground current  431  may be measured using a clamp-on CT  416  which allows the ground current to be measured with no wiring modifications to the CCVT. In some embodiments, this may allow the health monitoring system  1285  to be installed on a live CCVT circuit and provide additional flexibility for installation outside of scheduled line outages. In other embodiments, an IED  1209  may measure both the CCVT ground current  431  and the secondary voltage of the CCVT V SEC    1220 . The IED  1209  may calculate a health factor based on a current and/or voltage measurement associated with the CCVT. 
     In the embodiment illustrated in  FIG.  12 B , the CCVT ground current  431  is the summation of I 2    432  and I 3    516 . The ratio of I 1    431  to V SEC    1220  is shown in Equation 17 using the substitution for I 3  given in Equation 15. 
     
       
         
           
             
               
                 
                   
                     
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     As illustrated in Equation 17, the ratio of I 1    431  to V SEC    1220  is a scalar multiple of the ratio of Z 3  to Z 2 , which may serve as a health factor at a single frequency. A change or drift of the ratio of current I 1  to V SEC  outside of an acceptable band may indicate degradation of the CCVT. 
       FIG.  12 C  illustrates a representative circuit of a CCVT useful to illustrate monitoring a CCVT using current and voltage signals therefrom in accordance with several embodiments. In  FIG.  12 C , the current sensor  206  measures current I 3    516 . As shown in Equation 15, current I 3    516  is proportional to the secondary voltage of the CCVT  1220  at a single frequency. Thus, the ratio of I 3    516  to the secondary voltage of the CCVT  1220  may be calculated by an IED  1209  to indicate the health of the CCVT as shown in Equation 18. 
     
       
         
           
             
               
                 
                   
                     
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     In particular, the embodiment of  FIG.  12 C  may be used to determine the health of the secondary transformer of the CCVT. When used in combination with other embodiments, a comparison of I 3    516  to the secondary voltage V SEC    1220  of the CCVT may differentiate CCVT capacitor stack failures from a failure of the secondary transformer  209  of the CCVT. For example, the IED  1209  may also measure I 1    431  (as illustrated in  FIG.  12 B ) and calculate a health factor of the CCVT in combination with the current measurement of current I 3    516 . A change or drift in the health factor of the CCVT based a calculation from currents I 1    431  and I 3    516  may indicate a failure of either a CCVT capacitor or a secondary transformer  209  of the CCVT. A failure can be determined to be in the capacitor stack if the health factor based on a calculation from I 3    516  and secondary voltage V SEC    1220  of the CCVT indicates the secondary transformer of the CCVT is healthy. Alternatively, a failure may be determined to be present in the secondary transformer  209  but not the capacitor stack if the health factor based on a calculation from currents I 1    431  and I 3    516  indicates the capacitor stack is healthy when a health factor based on a calculation from I 3    516  and secondary voltage V SEC    1220  of the CCVT indicates the secondary transformer  209  of the CCVT is unhealthy. 
     Several embodiments herein are described as using current magnitudes or current and voltage magnitudes obtained from a CCVT to monitor the health of the CCVT. In various embodiments, the phases of current and/or voltages may be used to monitor the health of a CCVT.  FIG.  13    illustrates a functional block diagram of a device for monitoring a CCVT  1302  using phases of electrical power system measurements in accordance with several embodiments herein. The system includes a device  1350  such as an IED for monitoring the CCVT  1302 . The device  1350  obtains electrical signals from the CCVT  1302  such as, for example, current and/or voltage signals as described herein. The electrical signals may be filtered  1352 ,  1354 . As described above, the electrical signals at a single frequency may be used. In various embodiments, the filters  1352 ,  1354  may be cosine filters to extract phasors of the electrical signals at a single frequency, such as the fundamental frequency. The phase of each electrical signal may be determined  1356 ,  1358 . 
     As stated above, a health indicator may be a difference in phase, which should remain relatively constant for a healthy CCVT  1302 . Accordingly, the health indicator may be determined as a difference  1360  between the phases calculated in  1356 ,  1358 . The health indicator may be compared  862 ,  864  with a maximum limit  866  and a minimum limit  868  to determine CCVT failure  872 ; and a rate of change may be calculated  861  and compared  871  with a rate of change limit  869 , in order to determine a CCVT warning signal  873 . In other embodiments, an absolute value of the difference from  1360  may be compared with a single maximum or minimum limit to determine the CCVT failure  872 . 
       FIG.  14    illustrates the difference between the phase of current I 3  and the secondary voltage V SEC  of the CCVT at a single frequency (60 Hz) across a range of secondary transformer inductance values. As can be seen, a change in the phase difference of I 3  to V SEC  may be used to indicate a change in the CCVT. The change in inductance of the secondary transformer  209  of the CCVT may be indicative of decreased health of the CCVT. Accordingly, systems and methods herein may monitor the phase difference of various voltages and currents associated with a CCVT to determine the health of a CCVT. In some embodiments a phase difference outside a predefined, calculated, and/or measured limit may indicate a failure of the CCVT. 
     In some embodiments a change in the phase difference between currents and/or voltages associated with a CCVT may be used to differentiate between failures in the capacitor stack versus failures of a secondary transformer associated with the CCVT. For example, a change or drift of the ratio of currents I 2  to I 3  may indicate a failure of the capacitor stack and/or a secondary transformer of the CCVT. In this case, the phase difference between the phase of current I 3  and the secondary voltage V SEC  of the CCVT may be examined to determine whether the failure is in the capacitor stack or the secondary transformer of the CCVT. 
     Although  FIG.  14    illustrates a plot of phase difference between a current and a voltage to show a change in health of a CCVT, the present embodiments are also applicable to phase differences in current measurements. As discussed above, a ratio of current measurement magnitudes may be used to determine a health of a CCVT. Similarly, a difference in current phases may be used to determine a health of a CCVT. For example, the difference in current phases may be a difference in the current phases of I 2  and I 3 . 
     Several embodiments herein describe use of current and/or voltage measurements from a CCVT to monitor health of the CCVT by comparing the currents or current and voltage (magnitude or phase) ratio in the frequency domain (or even at a single frequency), and monitoring changes in the ratio. In addition to monitoring at a single frequency, a time-frequency, multiresolution, or multiscale approximation analysis of the current ratios or current-voltage ratios may be used to monitor health of the CCVT. For example, the time-domain data of the currents and/or voltages may be obtained and then decomposed using a wavelet analysis such as the Haar wavelet analysis to produce a number of decomposition levels. Other types of wavelet analyses may also be used to produce a number of decomposition levels. For example, the Daubechies, Biorthogonal, Coiflets, Symlets, Morlet, Mexican Hat, and/or Meyer wavelets may be employed in various embodiments. A health factor may then be calculated for each decomposition level to monitor the health of the CCVT. The multiple decomposition level health factors may be used to monitor the health of the CCVT over a wide range of CCVT characteristics. 
       FIG.  15 A  illustrates a plot of time domain measurement of currents I 2    1502  and I 3    1304  from a CCVT. At around 50,000 samples, a high frequency signal  1501  is injected on the CCVT primary. In some embodiments, switching noise on the primary voltage line can periodically inject high frequency signals into the CCVT, and this noise may be used to determine the health of the CCVT. In some embodiments, switching noise may provide frequencies otherwise unavailable for health factors calculated from power system fundamental frequencies or harmonics thereof. In other embodiments, higher or lower frequencies may be intentionally injected on the power system for the purposes of determining CCVT health factors. For example, a power system may contain multiple CCVTs, and a utility may inject a high-frequency signal onto the primary power line to determine the health of all CCVTs connected to the system. In some embodiments of the disclosure, multiple frequencies may be used simultaneously to calculate a health factor of the CCVT. 
     In some embodiments, frequencies higher and/or lower than the power system fundamental frequency may be injected onto the power line for purposes other than determining a CCVT&#39;s health. For example, power-line communication transmit data on a conductor that is also used for electric power transmission. For example, a medium frequency power-line carrier may transmit data across a power system conductor that is also used for electric power transmission at a frequency of 100 kHz. In some embodiments, the CCVT health can be calculated based on the power-line communication frequencies. In some embodiments consistent with this disclosure, a burst of data may be measured by the CCVT as a transient event consistent with the data captured in  FIG.  15 A . A time-frequency analysis or other analysis such as the Short-Time Fourier transform may be used to calculate one or more CCVT health factors. In some embodiments, data from a power-line communication may be encoded, such as with a Manchester code or phase encoding to provide a constant fundamental data transmission frequency that can be used to calculate CCVT health factors consistent with embodiments described in this disclosure. 
       FIG.  15 B  illustrates a multiresolution analysis of the time domain data of  FIG.  15 A  using a discrete wavelet transform with the Haar wavelet. Multiresolution analysis such as a discrete wavelet transform may be used to divide complex currents and voltage measurements associated with a CCVT into several simpler ones associated with various frequency domains. In  FIG.  15 B , lower decomposition levels such as 1 may contain higher frequency content than coarser decomposition levels such as level  13 . In  FIG.  15 B , the high frequency signal  1520  injected on the CCVT primary is clearly visible in levels  1 , through  7  but is highly attenuated in levels  8  through  13 . In some embodiments, there may be a predictable mathematical relationship between the magnitude of the wavelet coefficients of currents and/or voltages of a CCVT. In other embodiments, a short time Fourier analysis may be used to determine the magnitudes of multiple frequencies of currents and/or voltage associated with a CCVT to calculate a health factor of a CCVT. 
       FIG.  15 C  illustrates a health factor calculated from the wavelet decomposition of  FIG.  15 B . A time-domain function y s (t)∈W s  may be written as a summation of coefficients {w k,s } k∈l  multiplied by a wavelet Ψ(t)∈L 2  as shown in Equation 18 where s represents the multiresolution scale level. 
     
       
         
           
             
               
                 
                   
                     
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     The magnitude of the absolute value of the wavelet coefficients of I 2  is divided by the magnitude of the absolute value of the wavelet coefficients of I 2  for each decomposition level and plotted in  FIG.  15 C . In some embodiments, a multiresolution analysis may be used to calculate a health factor of the CCVT and compare against an acceptable range to determine the health of the CCVT. By calculating a health factor for each resolution level, a full range of CCVT characteristics, including parasitics, may be monitored. Other embodiments may calculate a multi-frequency health factor of a CCVT using time-frequency techniques such as the Short-Time Fourier Transform. 
     In some embodiments a neural network such as a Generative Adversarial Network (GAN) may be used to discriminate between transients in the data and degradations of the CCVT health. For example, a GAN may be trained to detect CCVT degradations based on a variant of the wavelet transform, such as a cross wavelet transform, of currents and/or voltage associated with a CCVT. 
     The embodiments of the disclosure will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the disclosed embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the systems and methods of the disclosure is not intended to limit the scope of the disclosure, as claimed, but is merely representative of possible embodiments of the disclosure. In addition, the steps of a method do not necessarily need to be executed in any specific order, or even sequentially, nor must the steps be executed only once, unless otherwise specified. 
     In some cases, well-known features, structures or operations are not shown or described in detail. Furthermore, the described features, structures, or operations may be combined in any suitable manner in one or more embodiments. It will also be readily understood that the components of the embodiments as generally described and illustrated in the figures herein could be arranged and designed in a wide variety of different configurations. 
     Several aspects of the embodiments described may be implemented as software modules or components. As used herein, a software module or component may include any type of computer instruction or computer executable code located within a memory device and/or transmitted as electronic signals over a system bus or wired or wireless network. A software module or component may, for instance, comprise one or more physical or logical blocks of computer instructions, which may be organized as a routine, program, object, component, data structure, etc., that performs one or more tasks or implements particular abstract data types. 
     In certain embodiments, a particular software module or component may comprise disparate instructions stored in different locations of a memory device, which together implement the described functionality of the module. Indeed, a module or component may comprise a single instruction or many instructions, and may be distributed over several different code segments, among different programs, and across several memory devices. Some embodiments may be practiced in a distributed computing environment where tasks are performed by a remote processing device linked through a communications network. In a distributed computing environment, software modules or components may be located in local and/or remote memory storage devices. In addition, data being tied or rendered together in a database record may be resident in the same memory device, or across several memory devices, and may be linked together in fields of a record in a database across a network. 
     Embodiments may be provided as a computer program product including a non-transitory computer and/or machine-readable medium having stored thereon instructions that may be used to program a computer (or other electronic device) to perform processes described herein. For example, a non-transitory computer-readable medium may store instructions that, when executed by a processor of a computer system, cause the processor to perform certain methods disclosed herein. The non-transitory computer-readable medium may include, but is not limited to, hard drives, floppy diskettes, optical disks, CD-ROMs, DVD-ROMs, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, solid-state memory devices, or other types of machine-readable media suitable for storing electronic and/or processor executable instructions. 
     While specific embodiments and applications of the disclosure have been illustrated and described, it is to be understood that the disclosure is not limited to the precise configurations and components disclosed herein. Accordingly, many changes may be made to the details of the above-described embodiments without departing from the underlying principles of this disclosure. The scope of the present invention should, therefore, be determined only by the following claims.