Patent Description:
A system for measuring leakage current of an electrical power cable that is providing operating power to a powered electrical system according to the invention is defined in independent claim <NUM>.

Further, a method for measuring leakage current of an electrical power cable that is providing operating power to a powered electrical system according to the invention is defined in independent claim <NUM>.

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> is a schematic diagram of an aircraft equipped with a system for measuring leakage current of a sensor resistive heating element. In <FIG>, aircraft <NUM> includes engine <NUM>, which drives electrical generator <NUM> so as to provide electrical operating power to various powered electrical systems aboard aircraft <NUM>. Aircraft <NUM> is also equipped with various sensors, including sensor <NUM>. Sensor <NUM> is an electrical system powered by power source <NUM>, which is configured to convert power provided by electrical generator <NUM> to that power specifically required by sensor <NUM>. Sensor <NUM> received operating power from power source <NUM> via electrical power cable <NUM>. Aircraft <NUM> is also equipped with leakage-current detector <NUM>, 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 <NUM>.

Although leakage-current detector <NUM> can be used to detect leakage current in a variety of powered electrical systems, in the depicted embodiment, sensor <NUM> 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 <NUM> is a Pitot tube airspeed detector that includes resistive heating element <NUM>, and ram pressure sensor <NUM>. Resistive heating element <NUM> is configured to prevent icing of sensor <NUM> when aircraft <NUM> is operating in an atmosphere in which ice accretion can occur.

Leakage-current detector <NUM> has first transformer <NUM>, second transformer <NUM>, inducer <NUM>, signal sensor <NUM>, and controller <NUM>. First transformer <NUM> has primary winding <NUM> about first magnetic core <NUM> having first passageway <NUM> through which electrical power cable <NUM> passes. By passing through first passageway <NUM>, electrical power cable <NUM> functions as a secondary winding of first transformer <NUM>. Second transformer <NUM> has secondary winding <NUM> about second magnetic core <NUM> having second passageway <NUM> through which electrical power cable <NUM> passes. By passing through second passageway <NUM>, electrical power cable <NUM> functions as a primary winding of second transformer <NUM>. Inducer <NUM> is conductively coupled to primary winding <NUM> of first transformer <NUM>. Inducer <NUM> generates a high-frequency excitation signal into primary winding <NUM> of first transformer <NUM>. Signal sensor <NUM> is conductively coupled to secondary winding <NUM> of second transformer <NUM>. Signal sensor <NUM> senses a high-frequency response signal induced, in response to the high-frequency excitation signal, into secondary winding <NUM> of second transformer <NUM>. Controller <NUM> performs a signal comparison of a high-frequency reference signal and the high-frequency response signal sensed by signal sensor <NUM>. Controller <NUM> generates a signal indicative of leakage current based on the signal comparison.

<FIG> is a schematic diagram of system for measuring leakage current for a powered electrical system. In <FIG>, sensor <NUM> and leakage-current detector <NUM> of <FIG> are depicted in more schematic detail. Sensor <NUM> includes resistive heating element <NUM> and impedance components <NUM> and <NUM>, which correspond to a leakage condition of resistive heating element <NUM>. For example, resistive heating element <NUM> 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 <NUM> and/or capacitor <NUM>. As such impedance changes, as represented by changes in resistor <NUM> and/or capacitor <NUM>, the electrical dynamics change for a powered electrical system, which in the depicted embodiment includes power source <NUM> electrical power cable <NUM>, heating resistive heating element <NUM>, resistor <NUM> and capacitor <NUM>.

When resistor <NUM> and/or capacitor <NUM> is present, leakage path <NUM> 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 <NUM> 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 <NUM> 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 <NUM> and/or capacitor <NUM>, 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 <NUM>.

As described above with reference to <FIG>, leakage-current detector <NUM> induces (via primary winding <NUM> of first transformer <NUM>) a high-frequency excitation signal into the conductors (operating as a secondary winding of first transformer <NUM>) of electrical power cable <NUM> at a first location where first transformer <NUM> 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 <NUM> of first transformer <NUM>) of first transformer <NUM>. Such impedance changes with changing resistance and/or capacitance of resistor <NUM> and/or capacitor <NUM>, respectively. For example, a normally high impedance can be significantly reduced with increasing values of capacitance of capacitor <NUM> and/or decreasing values of resistance of resistor <NUM>.

The high-frequency excitation signal induced into electrical power cable <NUM> 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 <NUM> and at location of resistor <NUM> and capacitor <NUM>) along electrical power cable <NUM> to a second location where electrical power cable <NUM> passes through second magnetic core <NUM> of second transformer <NUM>. 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 <NUM>) to signal sensor <NUM> coupled to secondary winding <NUM> via second transformer <NUM>. The high-frequency response signal is then sensed by signal sensor <NUM> and communicated to controller <NUM>, 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 <NUM>, <NUM>, <NUM>, <NUM>, 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 <NUM> passes through passageways <NUM> and <NUM> of first and second transformers <NUM> and <NUM> one or more times. For example, electrical power cable <NUM> can be wrapped around first magnetic core <NUM> and/or second magnetic core <NUM> more than one times, thereby increasing the coupling between the primary and secondary windings of the first <NUM> and/or second <NUM> transformers.

<FIG> are graphs exhibiting examples of a high-frequency excitation signal, a high-frequency response signal, and a high-frequency reference signal. In <FIG>, graph <NUM> includes horizontal axis <NUM>, vertical axis <NUM> and amplitude/time relations <NUM>, <NUM>, and <NUM>. Horizontal axis <NUM> is indicative of time, and vertical axis <NUM> is indicative of signal amplitude. Amplitude/time relation <NUM> corresponds to an example of a high-frequency excitation signal, as generated by inducer <NUM> (as depicted in <FIG>) and induced, via first transformer <NUM>, into electrical power cable <NUM> (at the first location where electrical power cable <NUM> passes through magnetic core <NUM> of first transformer <NUM>).

Amplitude/time relation <NUM> corresponds to the high-frequency response signal generated, in response to the high-frequency excitation signal, at the second location of electrical power cable <NUM> (as depicted in <FIG>), where electrical power cable <NUM> passes through magnetic core <NUM> of second transformer <NUM>. Initially, amplitude of amplitude/time relation <NUM> is at a first level Ii, and then at time TDEGRADE, amplitude of amplitude/time relation <NUM> is attenuated to a lower level I<NUM>. 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 <NUM> 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 <NUM> (as depicted in <FIG>), where electrical power cable <NUM> passes through magnetic core <NUM> of second transformer <NUM>. In the depicted embodiment, the amplitude/time relation <NUM> has substantially the same phase and amplitude as amplitude/time relation <NUM> during the period of time before TDEGRADE. But after time TDEGRADE both amplitude and phase of amplitude/time relation <NUM> differ from amplitude and phase of amplitude/time relation <NUM>.

In some embodiments, controller <NUM> generates a signal indicative of leakage if a ratio of amplitudes of amplitude/time relation <NUM> and amplitude/time relation <NUM> is less than <NUM>, <NUM>, <NUM>, <NUM>, or less. In some embodiments, controller <NUM> generates a signal indicative of leakage if a difference in phases of amplitude/time relation <NUM> and amplitude/time relation <NUM> is greater than <NUM>°, <NUM>°, <NUM>°, or <NUM>°. Such a generated signal indicative of leakage can then be communicated to the pilot and/or a health monitoring system of aircraft <NUM>, for example.

A system as defined in independent claim <NUM>.

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.

A method as defined in independent claim <NUM>.

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.

Claim 1:
A system for measuring leakage current of an electrical power cable that is providing operating power to a powered electrical system, the system comprising:
a first transformer (<NUM>) having a primary winding (<NUM>) about a first magnetic core (<NUM>) having a first passageway (<NUM>) providing passage therethrough for both a power conductor and a return conductor of the electrical power cable (<NUM>);
a second transformer (<NUM>) having a secondary winding (<NUM>) about a second magnetic core (<NUM>) having a second passageway (<NUM>) providing passage therethrough for both the power conductor and the return conductor of the electrical power cable (<NUM>);
wherein the electrical cable (<NUM>) operates as a secondary winding for the first transformer (<NUM>) and a primary winding for the second transformer (<NUM>) when passing through both the first and second passageways (<NUM>, <NUM>);
an inducer (<NUM>) conductively coupled to the primary winding (<NUM>) of the first transformer (<NUM>), the inducer (<NUM>) generating a high-frequency excitation signal into the primary winding (<NUM>) of the first transformer (<NUM>);
a signal sensor (<NUM>) conductively coupled to the secondary winding (<NUM>) of the second transformer (<NUM>), the signal sensor (<NUM>) sensing a high-frequency response signal induced, in response to the high-frequency excitation signal, into the secondary winding (<NUM>) of the second transformer (<NUM>);
characterised in that the system further comprises
a controller (<NUM>) that performs a signal amplitude and/or phase comparison of a high-frequency reference signal and the high-frequency response signal sensed by the signal sensor, the controller generating a signal indicative of leakage based on the signal amplitude and/or phase comparison.