Patent Publication Number: US-2022221525-A1

Title: Detecting leakage currents in a powered electrical system

Description:
BACKGROUND 
     Powered electrical systems are ubiquitous in our technological society. They can be found in homes, businesses, vehicles, and spacecrafts. Some powered electrical systems operate in environments that are quite severe, such as very high or very low temperatures, high pressures, corrosive chemicals or particles, etc. Furthermore, failure of some powered electrical systems can present dangers to persons or property. For example, aircrafts have many powered electrical systems that are operated so as to maintain safe flight operations. Numerous sensors provide metrics used by pilots and/or various systems, which respond to such metrics so as to properly control the aircraft. Air data sensors, for example provide metrics of altitude, airspeed, angle-of-attack, etc., all of which are used by pilots and other systems to maintain safe operation of the aircraft. Some air data sensors have resistive heating elements to prevent icing during operation within cloud atmospheres where icing conditions are present. Should such resistive heating elements fail, the metrics obtained by the associated sensor might no longer be usable. Identification of resistive heating element degradation before failure of the resistive heating element is therefore desirable. 
     SUMMARY 
     Apparatus and associated methods relate to a system for measuring leakage current. The system includes first and second transformers, an inducer, a signal sensor and a controller. The first transformer has a primary winding about a first magnetic core having a first passageway configured to provide passage therethrough for an electrical cable. The second transformer has a secondary winding about a second magnetic core having a second passageway configured to provide passage therethrough for the electrical cable. The electrical cable operates as a secondary winding for the first transformer and a primary winding for the second transformer when passing through both the first and second passageways. The inducer conductively couples to the primary winding of the first transformer. The inducer generates a high-frequency excitation signal into the primary winding of the first transformer. The signal sensor is conductively coupled to the secondary winding of the second transformer. The signal sensor senses the high-frequency response signal induced, in response to the high-frequency excitation signal, into the secondary winding of the second transformer. The controller performs a signal comparison of a high-frequency reference signal and the high-frequency response signal sensed by the signal sensor. The controller generates a signal indicative of leakage based on the signal comparison. 
     Some embodiments relate to a method for measuring leakage current. The method includes coupling, via a first transformer having a primary winding about a first magnetic core having a first passageway configured to provide passage therethrough for an electrical cable, the electrical cable with the secondary winding of the electrical transformer. The method include coupling, via a second transformer having a secondary winding about a second magnetic core having a second passageway configured to provide passage therethrough for the electrical cable, the primary winding of the second transformer and the electrical cable. The method includes generating, via an inducer conductively coupled to the primary winding of the first transformer, a high-frequency excitation signal into the primary winding of the first transformer. The method includes sensing, via a sensor conductively coupled to the secondary winding of the second transformer, a high-frequency response signal induced into the secondary winding of the second transformer. The method includes performing, via a controller, a signal comparison of a high-frequency reference signal and the high-frequency response signal sensed by the sensor. The method also includes generating, via the controller, a signal indicative of leakage based on the signal comparison. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an aircraft equipped with a system for measuring leakage current of a sensor resistive heating element. 
         FIG. 2  is a schematic diagram of system for measuring leakage current for a powered electrical system. 
         FIG. 3  are graphs exhibiting examples of a high-frequency excitation signal, a high-frequency response signal, and a high-frequency reference signal, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     Apparatus and associated methods relate to detecting leakage current in a powered electrical system. Such leakage current can be detected by changes in a high-frequency response signal within an electrical power cable that provides operating power to the powered electrical system. A high-frequency excitation signal is induced into the electrical power cable at a first location along the electrical power cable, and a high-frequency response signal is sampled at a second location along the electrical power cable. The electrical power cable includes a plurality of conductive wires for providing a closed-circuit path for operating current to and from the powered electrical system. The high-frequency response signal can be compared with a high-frequency reference signal to determine whether changes in the high-frequency response signal (e.g., changes indicative of leakage) have occurred. The high-frequency reference signal can be a high-frequency response signal obtained at an earlier time. For example, the high-frequency reference signal can be obtained at a time of calibration, at a time of initial operation of the powered electrical system, or at any time of system operation with no leakage current (i.e., a time of proper functioning of the powered electrical system). 
     The high-frequency response signal can change over time in response to changes in the powered electrical system. Should the powered electrical system become degraded in some fashions, leakage paths can develop. For example, electrical insulators can degrade causing changes to impedances between components of the powered electrical system and a grounded nearby chassis. Such impedance changes can then present differences in the electrical dynamics of the powered electrical system as such electrical dynamics relate to an induced high-frequency excitation signal. 
       FIG. 1  is a schematic diagram of an aircraft equipped with a system for measuring leakage current of a sensor resistive heating element. In  FIG. 1 , aircraft  10  includes engine  12 , which drives electrical generator  14  so as to provide electrical operating power to various powered electrical systems aboard aircraft  10 . Aircraft  10  is also equipped with various sensors, including sensor  16 . Sensor  16  is an electrical system powered by power source  18 , which is configured to convert power provided by electrical generator  14  to that power specifically required by sensor  16 . Sensor  16  received operating power from power source  18  via electrical power cable  20 . Aircraft  10  is also equipped with leakage-current detector  22 , which is configured to detect leakage current of a powered electrical system. In the depicted embodiment, leakage-current detector is configured to detect leakage current of sensor  16 . 
     Although leakage-current detector  22  can be used to detect leakage current in a variety of powered electrical systems, in the depicted embodiment, sensor  16  senses air pressure. Various air data sensors sense air pressure for the purpose of determining various air data metrics, such airspeed, altitude sensor, angle-of-attach, etc. In the depicted embodiment, sensor  16  is a Pitot tube airspeed detector that includes resistive heating element  24 , and ram pressure sensor  26 . Resistive heating element  24  is configured to prevent icing of sensor  16  when aircraft  10  is operating in an atmosphere in which ice accretion can occur. 
     Leakage-current detector  22  has first transformer  28 , second transformer  30 , inducer  32 , signal sensor  34 , and controller  36 . First transformer  28  has primary winding  38  about first magnetic core  40  having first passageway  42  through which electrical power cable  20  passes. By passing through first passageway  42 , electrical power cable  20  functions as a secondary winding of first transformer  28 . Second transformer  30  has secondary winding  44  about second magnetic core  46  having second passageway  48  through which electrical power cable  20  passes. By passing through second passageway  48 , electrical power cable  20  functions as a primary winding of second transformer  30 . Inducer  32  is conductively coupled to primary winding  38  of first transformer  28 . Inducer  32  generates a high-frequency excitation signal into primary winding  38  of first transformer  28 . Signal sensor  34  is conductively coupled to secondary winding  44  of second transformer  30 . Signal sensor  34  senses a high-frequency response signal induced, in response to the high-frequency excitation signal, into secondary winding  44  of second transformer  30 . Controller  36  performs a signal comparison of a high-frequency reference signal and the high-frequency response signal sensed by signal sensor  34 . Controller  36  generates a signal indicative of leakage current based on the signal comparison. 
       FIG. 2  is a schematic diagram of system for measuring leakage current for a powered electrical system. In  FIG. 2 , sensor  16  and leakage-current detector  22  of  FIG. 1  are depicted in more schematic detail. Sensor  16  includes resistive heating element  24  and impedance components  50  and  52 , which correspond to a leakage condition of resistive heating element  24 . For example, resistive heating element  24  can be electrically isolated from a nearby grounded chassis by an insulative member. When such insulative member degrades, the impedance parameters at the location of such degradation can change. Such impedance parameters can include capacitance and/or resistive components, as represented by resistor  50  and/or capacitor  52 . As such impedance changes, as represented by changes in resistor  50  and/or capacitor  52 , the electrical dynamics change for a powered electrical system, which in the depicted embodiment includes power source  18  electrical power cable  20 , heating resistive heating element  24 , resistor  50  and capacitor  52 . 
     When resistor  50  and/or capacitor  52  is present, leakage path  54  for the powered electrical system is created. Normally, when no leakage path is present, a sum of currents in the conductors of electrical power cable  20  is zero. Such a sum (i.e., zero) indicates that any positive current provided by one or more conductors is matched by return current carried by other conductors. Leakage path  54  provides a return path of current that is conducted by various conductive members not part of the powered electrical system. Such members can include metal chassis, metal airframes, other conductive structural elements, etc. Changes in resistance and/or capacitance of resistor  50  and/or capacitor  52 , respectively, also change the electrical dynamics of the powered electrical system, which affects the high-frequency response signal generated for leakage-current-detection purposes by leakage-current detector  22 . 
     As described above with reference to  FIG. 1 , leakage-current detector  22  induces (via primary winding  38  of first transformer  28 ) a high-frequency excitation signal into the conductors (operating as a secondary winding of first transformer  28 ) of electrical power cable  20  at a first location where first transformer  28  is located. Such induction of the high-frequency excitation signal is a function of the impedance of the powered electrical system as seen from the secondary winding (i.e., the location along electrical power cable where it passes through first magnetic core  40  of first transformer  28 ) of first transformer  28 . Such impedance changes with changing resistance and/or capacitance of resistor  50  and/or capacitor  52 , respectively. For example, a normally high impedance can be significantly reduced with increasing values of capacitance of capacitor  54  and/or decreasing values of resistance of resistor  52 . 
     The high-frequency excitation signal induced into electrical power cable  20  at the first location is then communicated (e.g., conductively and/or inductively as well as by reflection at a terminating locations, such as at a location or power source  18  and at location of resistor  50  and capacitor  52 ) along electrical power cable  20  to a second location where electrical power cable  20  passes through second magnetic core  46  of second transformer  30 . There, at the second location, a high-frequency response signal is generated by such conduction and reflection. This high-frequency response signal is then coupled by electrical power cable (operating as a primary winding of second transformer  30 ) to signal sensor  34  coupled to secondary winding  44  via second transformer  30 . The high-frequency response signal is then sensed by signal sensor  34  and communicated to controller  36 , which compares the sensed high-frequency response signal to a high-frequency reference signal. Various metrics of comparison can be used. For example, steady-state amplitude, amplitude variation, phase difference, etc. can be used as metrics for comparison between the sensed high-frequency response signal and the high-frequency reference signal. 
     In some embodiments, the high-frequency excitation signal is a steady-state high-frequency signal. The steady-state high-frequency excitation signal can have a frequency of at least 100 kHz, 1 MHz, 10 MHz, 100 MHz, or greater. In other embodiments, the high-frequency excitation signal can be a short duration pulse containing high-frequency components. The metrics used in such a pulsed operation, for example, can include time difference between excitation time and response time, the presence of addition echo responses, pulse amplitudes of response pulse and/or echo responses, etc. 
     In some embodiments, electrical power cable  20  passes through passageways  42  and  48  of first and second transformers  28  and  30  one or more times. For example, electrical power cable  20  can be wrapped around first magnetic core  40  and/or second magnetic core  46  more than one times, thereby increasing the coupling between the primary and secondary windings of the first  28  and/or second  30  transformers. 
       FIG. 3  are graphs exhibiting examples of a high-frequency excitation signal, a high-frequency response signal, and a high-frequency reference signal. In  FIG. 3 , graph  56  includes horizontal axis  58 , vertical axis  60  and amplitude/time relations  62 ,  64 , and  66 . Horizontal axis  58  is indicative of time, and vertical axis  60  is indicative of signal amplitude. Amplitude/time relation  62  corresponds to an example of a high-frequency excitation signal, as generated by inducer  32  (as depicted in  FIGS. 1-2 ) and induced, via first transformer  28 , into electrical power cable  20  (at the first location where electrical power cable  20  passes through magnetic core  40  of first transformer  28 ). 
     Amplitude/time relation  64  corresponds to the high-frequency response signal generated, in response to the high-frequency excitation signal, at the second location of electrical power cable  20  (as depicted in  FIGS. 1-2 ), where electrical power cable  20  passes through magnetic core  46  of second transformer  30 . Initially, amplitude of amplitude/time relation  64  is at a first level I 1 , and then at time TDEGRADE, amplitude of amplitude/time relation  64  is attenuated to a lower level I 2 . Such attenuation of the signal amplitude can be indicative of a sudden degradation of the powered electrical system. Although depicted as a sudden event, more commonly, degradation of the powered electrical system is of a slow long-term nature. 
     Amplitude/time relation  66  corresponds to an example of a high-frequency reference signal. Such a high-frequency reference signal can be a high-frequency response signal that is obtained at a time at which the powered electrical system is operating properly. Thus, such a high-frequency reference signal corresponds to the high-frequency response signal generated, in response to the high-frequency excitation signal, at the second location of electrical power cable  20  (as depicted in  FIGS. 1-2 ), where electrical power cable  20  passes through magnetic core  46  of second transformer  30 . In the depicted embodiment, the amplitude/time relation  66  has substantially the same phase and amplitude as amplitude/time relation  64  during the period of time before TDEGRADE. But after time TDEGRADE both amplitude and phase of amplitude/time relation  66  differ from amplitude and phase of amplitude/time relation  64 . 
     In some embodiments, controller  36  generates a signal indicative of leakage if a ratio of amplitudes of amplitude/time relation  64  and amplitude/time relation  66  is less than 0.9, 0.8, 0.5, 0.3, or less. In some embodiments, controller  36  generates a signal indicative of leakage if a difference in phases of amplitude/time relation  64  and amplitude/time relation  66  is greater than 15°, 30°, 45°, or 60°. Such a generated signal indicative of leakage can then be communicated to the pilot and/or a health monitoring system of aircraft  10 , for example. 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     Apparatus and associated methods relate to a system for measuring leakage current. The system includes first and second transformers, an inducer, a signal sensor and a controller. The first transformer has a primary winding about a first magnetic core having a first passageway configured to provide passage therethrough for an electrical cable. The second transformer has a secondary winding about a second magnetic core having a second passageway configured to provide passage therethrough for the electrical cable. The electrical cable operating as a secondary winding for the first transformer and a primary winding for the second transformer when passing through both the first and second passageways. The inducer conductively couples to the primary winding of the first transformer. The inducer generates a high-frequency excitation signal into the primary winding of the first transformer. The signal sensor is conductively coupled to the secondary winding of the second transformer. The signal sensor senses the high-frequency response signal induced, in response to the high-frequency excitation signal, into the secondary winding of the second transformer. The controller performs a signal comparison of a high-frequency reference signal and the high-frequency response signal sensed by the signal sensor. The controller generates a signal indicative of leakage based on the signal comparison. 
     The system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A further embodiment of the foregoing system, wherein the electrical cable connecting the resistive heating element to the power source can include a plurality of conductors. 
     A further embodiment of any of the foregoing systems can further include the electrical cable. 
     A further embodiment of any of the foregoing systems, wherein the electrical cable can connect a power source to a resistive heating element. 
     A further embodiment of any of the foregoing systems, wherein the resistive heating element, when in good working condition, can be electrically isolated from a ground reference. 
     A further embodiment of any of the foregoing systems, wherein the first and second transformers can be spaced apart from one another. 
     A further embodiment of any of the foregoing systems, wherein the sensor can sense the high-frequency reference signal at a reference time. 
     A further embodiment of any of the foregoing systems, wherein the reference time can be a time of calibration. 
     A further embodiment of any of the foregoing systems, wherein the reference time can be a time of first operation. 
     Some embodiments relate to a method for measuring leakage current. The method includes coupling, via a first transformer having a primary winding about a first magnetic core having a first passageway configured to provide passage therethrough for an electrical cable, the electrical cable with the secondary winding of the electrical transformer. The method include coupling, via a second transformer having a secondary winding about a second magnetic core having a second passageway configured to provide passage therethrough for the electrical cable, the primary winding of the second transformer and the electrical cable. The method includes generating, via an inducer conductively coupled to the primary winding of the first transformer, a high-frequency excitation signal into the primary winding of the first transformer. The method includes sensing, via a sensor conductively coupled to the secondary winding of the second transformer, a high-frequency response signal induced into the secondary winding of the second transformer. The method includes performing, via a controller, a signal comparison of a high-frequency reference signal and the high-frequency response signal sensed by the sensor. The method also includes generating, via the controller, a signal indicative of leakage based on the signal comparison. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A further embodiment of the foregoing method, wherein the electrical cable connecting the resistive heating element to the power source can include a plurality of conductors. 
     A further embodiment of any of the foregoing methods can further include transmitting, via the electrical cable, the high-frequency electrical signal along a length of the electrical cable. 
     A further embodiment of any of the foregoing methods, wherein the electrical cable can connect a power source to a resistive heating element. 
     A further embodiment of any of the foregoing methods, wherein the resistive heating element, when in a degraded condition where leakage current results, can be conductively and/or capacitively coupled to a ground reference. 
     A further embodiment of any of the foregoing methods, wherein the first and second transformers can be spaced apart from one another. 
     A further embodiment of any of the foregoing methods, wherein the sensor can sense the high-frequency reference signal at a reference time. 
     A further embodiment of any of the foregoing methods, wherein the reference time can be a time of calibration. 
     A further embodiment of any of the foregoing methods, wherein the reference time can be a time of first operation. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.