Method, apparatus and computer readable medium for detecting movement of an electrical cable

Abstract

A method (900) for detecting movement of an electrical cable including at least one core includes transmitting (S91) a time domain reflectometry (TDR) signal from a measurement point along each core of the cable. Reflections of the TDR signal from each core are received (S92) at the measurement points, and a reflectogram for each core is generated (S93) by correlating the TDR signal with the reflections. Each reflectogram is a waveform of relative impedance change versus distance from the measurement point. Movement of the cable is detected by comparing (S94) the reflections generated for each core to a reference reflectogram for the corresponding core, where each reference reflectogram was previously obtained when the cable was in a baseline position.

Description

[Technical field]

[0001] The present disclosure relates generally to monitoring cable movement. A non-limiting example of the present disclosure relates to monitoring the movement of submarine power cables using time domain reflectometry. [Background technology]

[0002] Submarine power cables are used to transmit electricity generated by offshore wind turbines to onshore power grids. However, submarine cables are subject to forces from the ocean that can cause the cables to fail over time. For example, tides and eddies can cause submarine cables to move, and over a long enough period of time, such movement can deteriorate the cable's conductors and / or insulation, eventually causing them to fail. Such failures can be difficult to locate, expensive to repair, and disrupt the power supply.

[0003] To facilitate repairs and minimize the costs of operating and maintaining submarine cables, non-destructive monitoring systems are used to identify the presence and location of faults. For example, the applicant's earlier US Pat. No. 6,399,433 describes a submarine cable monitoring device capable of outputting a signal indicative of the integrity of a submarine cable. The device uses time domain reflectometry to help pinpoint the exact location of a fault.

[0004] To prevent failures in cables, such as submarine power cables, it is desirable to identify potential faults before they occur so that preventative maintenance can be performed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 2339359 Summary of the Invention

[0006] The present disclosure provides methods and apparatus for detecting movement of an electrical cable. By detecting movement of the cable and monitoring such movement over time, movement that may ultimately lead to failure of the cable can be detected. Furthermore, by detecting movement that may lead to failure of the cable, preventative maintenance can be performed to prevent such failure.

[0007] According to a first aspect, there is provided a method of detecting movement of an electrical cable, the electrical cable including at least one core, the method comprising transmitting a time-domain reflectometry (TDR) signal from a measurement point along each core of the cable, receiving one or more reflections of the TDR signal from each core at the measurement points, generating reflectometry data for each core by correlating the TDR signal transmitted along each core with one or more reflections of the TDR signal received from a corresponding core, the reflectometry data indicative of impedance changes at each of a plurality of points along the corresponding core, and detecting movement of the cable by comparing the generated reflectometry data for each core to reference reflectometry data for the corresponding core.

[0008] The inventors have discovered that cable movement causes a measurable change in the impedance of the core of the cable. The inventors have further discovered that cable movement can be detected using time domain reflectometry; that is, that time domain reflectometry is sensitive enough to detect minute changes in impedance caused by cable movement, and that changes in impedance caused by cable movement can be distinguished from changes in impedance due to other causes.

[0009] The techniques disclosed herein can be used to detect movement of a cable even when the cable is energized (i.e., connected to a voltage and / or carrying current) without interfering with the normal operation of the cable. Thus, the techniques are suitable for long-term non-invasive monitoring of cables to identify movements that may lead to cable failure.

[0010] The electrical cable may be any suitable type of cable. For example, the electrical cable may be an underwater power cable, such as a submarine power cable. However, the cable need not be installed underwater, and the techniques disclosed herein are also applicable to cables installed underground, on land, or in the air (e.g., overhead cables).

[0011] The measurement point may be any point on the cable, although in practice it is typically at one end of the cable. For example, for an umbilical power cable connecting offshore generating equipment to the onshore power grid, the measurement point is typically at the onshore end of the cable. A signal generator that generates the TDR signal and a signal processor that receives the reflections of the TDR signal are typically located at the measurement point.

[0012] The techniques disclosed herein detect cable movement relative to a baseline position of the cable. The baseline position may be any position of the cable and need not be known precisely. In particular, the cable need not be straight when it is in the baseline position. However, for a particular position of the cable to be considered a baseline position, reference reflectance measurement data must have been previously acquired with the cable at that position. The reference reflectance measurement data may have been generated in the same manner as that generated to detect cable movement, i.e., by transmitting one or more time domain reflectance measurement signals from measurement points along each core of the cable, receiving one or more reflections of the TDR signal from each core, and correlating the TDR signals transmitted along each core with one or more reflections of the TDR signal received from the corresponding core.

[0013] Typically, electrical cables have multiple cores. By generating reflectance measurement data for only a single core, it is possible to detect movement of the cable. However, as described further below, by generating reflectance measurement data for multiple cores (in some instances, all of the multiple cores of the cable), it is possible to distinguish between different types of movement.

[0014] Typically, the geometry of the cable is known, e.g., the number of cores is known, and the position of each core relative to the other cores is known. Each core used for time domain reflectometry is conductive, but this does not prevent the use of the technique with cables that additionally contain other types of cores (e.g., optical fiber cores).

[0015] In some embodiments, detecting the movement of the cable includes identifying bending, stretching, contraction and / or twisting of the cable.

[0016] The techniques disclosed herein can detect and distinguish between various types of cable movement, particularly bending, elongation (and conversely, contraction), and / or twisting. As used herein, "bending" refers to the deviation of the cable (the longitudinal axis) from a straight path. Bending is caused by an external force applied perpendicular to the longitudinal axis of the cable. As used herein, "elongation" refers to the lengthening of the cable along the longitudinal axis of the cable, and "contraction" refers to the shortening of the cable along the longitudinal axis of the cable. "Elongation" and "contraction" are caused by external tensile or compressive forces applied along the longitudinal axis of the cable, respectively. As used herein, "twisting" refers to the twisting of the cable about its longitudinal axis. Twisting is caused by an external torque applied about the longitudinal axis of the cable.

[0017] In some embodiments, transmitting the TDR signals includes transmitting a plurality of TDR signals along each core of the cable from the measurement point, each of the plurality of TDR signals being transmitted at a corresponding one of the plurality of times; receiving one or more reflections includes receiving a plurality of reflections from each core, each of the plurality of reflections corresponding to a TDR signal of the plurality of TDR signals; and generating the reflectivity measurement data includes correlating each TDR signal transmitted along each core to its corresponding reflection.

[0018] By repeatedly generating reflectance measurement data covering a period of time, the movement of the cable can be monitored over time and / or the frequency of the movement of the cable can be determined.

[0019] Producing the reflectometry data may include generating a plurality of reflectograms, each reflectogram being a waveform of impedance change versus distance along a corresponding core. Each reflectogram corresponds to a corresponding one of the plurality of TDR signals, i.e., each TDR signal transmitted along a core produces a single reflectogram. The method may further include monitoring movement of the cable over a period of time by comparing each of the plurality of reflectograms generated for each core to a reference reflectogram for the corresponding core.

[0020] Monitoring the movement of a cable over a period of time can aid in preventive maintenance of the cable, for example by detecting movement that may ultimately lead to failure of the cable, allowing the cable to be repaired or replaced before a failure occurs.

[0021] The reference reflectometry data may include a reference reflectogram for each core, i.e., the reference reflectometry data may include a plurality of reflectograms, where each reflectogram quantifies the variation in impedance as a function of distance along a corresponding core when the cable is in a baseline position.

[0022] The method may further include selecting a measurement section for each core from the reflectance measurement data, where the measurement section includes measurements of impedance change over time at a given point on the core. Detecting cable movement may include comparing the measurement section for each core to a reference time series, where the reference time series includes measurements of impedance change over time at a given point on the core when the cable was in a baseline position.

[0023] For example, the reflectivity measurement data may include a multi-dimensional time series for each core, where the multi-dimensional time series includes measurements of impedance change at each of a plurality of points on the core, each measurement made at a corresponding one of a plurality of time points. Selecting a measurement interval may include selecting a measurement interval of the multi-dimensional time series for each core, where the measurement interval is taken across a time axis of the multi-dimensional time series for the core to obtain a waveform of impedance change over time.

[0024] Comparing the measurement interval to the reference time series may include applying a dynamic time warping algorithm to the measurement interval and / or the reference time series.

[0025] The propagation velocities of the TDR signals and their reflections may change due to external factors such as the temperature of the cable. A more accurate measurement of cable movement can be achieved by using a dynamic time warping algorithm that corrects for differences in the propagation velocities of the signals between the measurement section and the reference time series. The dynamic time warping algorithm may be applied to either the measurement section or the reference time series, or to both.

[0026] In some embodiments, the method may further include determining a frequency of the cable movement. Determining the frequency of the cable movement may include analyzing the reflectometry data to identify time-dependent impedance changes of the at least one core.

[0027] In some embodiments, the cable includes a first core and a second core, and the method further includes identifying a type of movement of the cable by comparing the reflectance measurement data of the first core and the reflectance measurement data of the second core.

[0028] Each type of cable movement (e.g., bending, stretching, contraction, and twisting) induces a characteristic change in the impedance of the different cores. Therefore, by comparing the reflectance measurement data of different cores of a multi-core or multi-conductor cable, different types of movement can be distinguished. For cables with more than one core, the reflectance measurement data for all cores can be compared. In general, the greater the number of cores for which reflectance measurement data is considered, the more accurately the cable movement can be identified.

[0029] Identifying a type of cable movement may include determining that the first core exhibits a greater impedance change than the second core, and identifying a bend in the cable when the first core exhibits a greater impedance change than the second core.

[0030] Specifically, a bend in the cable can be identified if both cores exhibit a change in impedance relative to the reference reflectance measurement data at corresponding points along their length (e.g., at a common distance from the measurement point), but one core exhibits a larger change in impedance than the other core. Such an impedance change is characteristic of a bend in the cable because the core located toward the inside of the bend experiences a larger bend than the core located toward the outside of the bend, causing the core located toward the inside of the bend to exhibit a larger change in impedance than the other core.

[0031] The method may further include determining a direction of a bend in the cable.Alternatively or additionally, the method may include determining a position of a bend in the cable.

[0032] The method may further include virtually reconstructing the shape of the cable relative to the baseline position.

[0033] In some embodiments, the TDR signal is a spread spectrum time domain reflectometry signal.

[0034] The present disclosure may be implemented using any suitable time-domain reflectometry technique, such as sequence time-domain reflectometry (STDR) or spread spectrum time-domain reflectometry (SSTDR). SSTDR is considered practical because the TDR signal injected into each core can be easily cross-correlated with its reflections. Furthermore, such cross-correlation essentially cancels electrical noise in the cable, so that SSTDR-based implementations of the present disclosure can detect very small impedance changes whose amplitudes are comparable to the noise floor of the measurement system. This allows the techniques disclosed herein to detect very small movements of the cable.

[0035] According to a second aspect, there is provided an apparatus configured to perform any of the methods disclosed herein.

[0036] According to a third aspect, there is provided a computer readable medium comprising instructions which, when executed by a computer, cause the computer to perform any of the methods disclosed herein. [Brief description of the drawings]

[0037] For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

[0038] [Figure 1] 1 illustrates an example of a power cable connected to an analytical system according to the present disclosure. [Figure 2(a)] Measured and reference reflectograms obtained from the cable are shown. [Figure 2(b)] The difference between the measured reflectogram and the reference reflectogram in FIG. 2(a) is shown. [Diagram 3] All SSTDR reflectograms obtained over time in the example measurement are shown. [Figure 4] An example of an SSTDR reflectogram in a measurement example is shown. [Diagram 5] Shows bending of a 4-core cable. [Figure 6] 6 shows the equivalent circuit of two of the four cores of the cable shown in FIG. [Figure 7] This shows the change in impedance over time when the four-core cable shown in FIG. 5 is bent. [Figure 8] FIG. 1 is a flow diagram of a method for detecting cable movement in accordance with the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The present disclosure involves using time domain reflectometry to detect movement in electrical cables.

[0040] Reflectometry involves injecting an electromagnetic test signal into a system, such as a transmission line or cable. The test signal is partially reflected at each impedance discontinuity in the cable. Each reflection of the test signal is determined by a change in impedance, which is measured by the voltage reflection coefficient:

number

[0041] Here, V reflected is the reflected voltage, V test is the voltage of the test signal that caused the reflection, and Zo is the characteristic impedance of the transmission line, and Z L is the impedance of the load or other impedance discontinuity. Z o and Z L The greater the change in impedance between the open circuit (Z L =∞) and short circuit (Z L = 0) results in maximum reflection, while the smaller the change in impedance, the smaller the reflection coefficient.

[0042] By analyzing the reflections of the test signal, the presence of impedance discontinuities in the transmission line can be identified, and the location of each impedance discontinuity can be estimated based on the estimated propagation speed of the test signal and the time interval between injecting the test signal and receiving its reflection.

[0043] There are many types of reflectometry, each using a different type of test signal. These include time domain reflectometry (TDR), sequence time domain reflectometry (STDR), and spread spectrum time domain reflectometry (SSTDR). In SSTDR, the test signal comprises a pseudorandom noise signal modulated onto a carrier signal. By multiplying the pseudorandom noise signal by the received reflections, each test signal can be correlated to its reflections, which can be used to estimate the location of the impedance discontinuity that caused each reflection.

[0044] As mentioned above, submarine power cables may be subject to movement. For example, eddies in the water may induce unwanted movement in the cable. This movement may include tension being applied to the cable such that the cable is stretched. As a result, the cross-sectional area of ​​the cable, and therefore each core of the cable, decreases as the cable adapts to maintain the same volume. The reduction in cross-sectional area creates an impedance mismatch within the core.

[0045] Motion due to e.g. vortexes can also cause bending of the cable. This motion can result in a single bend of the cable away from its normal direction. Alternatively, multiple bending movements of the cable can occur when the cable is moved in the transverse direction. Bending of the core causes an impedance mismatch since the cross-sectional area of ​​the core changes in the vicinity of the bend. In addition, bending of the cable causes a change in the mutual coupling of the core with other cores or the exterior of the cable, which also causes an impedance change.

[0046] According to the present disclosure, movement of an electrical cable is detected using a TDR to identify changes in impedance caused by such movement.

[0047] 1 shows an example of an electrical cable 1 connected to an analysis system that includes a signal generator 2 and a processor 3. The processor 3 optionally includes a controller and an analog-to-digital converter (ADC). Although FIG. 1 shows the signal generator 2 and the processor 3 as separate units, in some implementations the signal generator 2 and the processor 3 are provided as a single unit.

[0048] In the example shown in Figure 1, the electric cable 1 is a four-core cable having cores 4, 5, 6 and 7. Each of the cores 4, 5, 6 and 7 includes two conductors that are connected in use to phase voltages and neutral terminals. Each core further includes one or more insulating layers, which surround the conductors and insulate them from each other and from the other cores of the cable 1. The four cores 4, 5, 6, 7 are surrounded by an armor layer 8 that protects the cable from damage. Between the cores 4, 5, 6, 7, the electric cable includes non-metallic material (sometimes referred to as "filler") and, optionally, one or more signal cables. The signal cables may be electrical signal cables, optical fibers, or a combination of both.

[0049] The electrical cable 1 shown in FIG. 1 is intended as only one example of a cable whose movement can be detected using the techniques disclosed herein. The techniques disclosed herein can be used to detect the movement of electrical cables having more or fewer cores and / or different structures. In general, the structure of the electrical cable 1 is known in advance; that is, the number of cores is known, and the positions of the cores relative to each other are known. Prior knowledge of other structural features of the cable is beneficial to improve the accuracy of the analysis of the reflectometry data. Such structural features may include, but are not limited to, the distance between the cores, the material of each component of the cable, whether the cable has a shield, and / or the cross-sectional area of ​​the cable.

[0050] 1, an SSTDR signal generator 2 is connected to one end of a cable 1. Specifically, the SSTDR signal generator 2 is connected to at least one core 4, 5, 6, 7 of the cable 1. In some implementations, multiple signal generators 2 are used, with each signal generator connected to a different core 4, 5, 6, 7. In other implementations, a single signal generator 2 is used, with a multiplexer provided to connect the signal generator to each core 4, 5, 6, 7 in turn.

[0051] A test signal is selected in the signal generator 2. In the example of FIG. 1, the signal generator 2 is an SSTDR generator and the test signal is an SSTDR signal. However, other suitable types of TDR signal generators, such as an STDR signal generator, may be used instead. In selecting the test signal, parameters such as the amplitude of the test signal, the length of the pseudorandom code, the carrier frequency, and the scan rate are selected. The amplitude of the test signal is typically in the range of 0.1 to 10 volts. The length of the pseudorandom (PN) code is typically in the range of 28-1 to 216-1 bits. The length of the PN code is limited by the processing capabilities of the system, the longer the code the higher the signal-to-noise ratio. The carrier frequency is typically in the range of 1 to 100 MHz. The scan rate is typically in the range of 10 to 100 Hz. That is, 10 to 100 test signals are transmitted along each core per second. It will be appreciated that other suitable values ​​for these parameters may be used, depending on the capabilities of the signal generator 2. One example of an SSTDR generator is the Viper Innovations SSTDR S100 unit (https: / / www.viperinnovations.com / sstdr-s100 / ).

[0052] The signal generator 2 generates a TDR test signal and transmits the TDR signal along at least one core 4, 5, 6, 7 of the cable 1. The same TDR signal may be transmitted along each core 4, 5, 6, 7, or a different signal may be transmitted along each core 4, 5, 6, 7. The TDR signal is reflected at each impedance discontinuity along the length of the at least one core 4, 5, 6, 7. The resulting reflections of the TDR signal are received by the signal generator 2. The signal generator 2 generates reflectometry data for each core 4, 5, 6, 7 by correlating (e.g. cross-correlating) the TDR signal transmitted along each core with the reflections received from the corresponding core. The reflectometry data is then transmitted to the processor 3 for further analysis.

[0053] Figures 2(a) and 2(b) show examples of reflectance measurement data generated by the SSTDR generator 2. The Y-axis shows the relative level of impedance change. The X-axis shows the distance along the cable from the measurement point in meters. The plots shown in Figures 2(a) and 2(b) are example reflectograms. Figure 2(a) shows a reference reflectogram, which is obtained when cable 1 is in a baseline position. Figure 2(a) also shows a measured reflectogram, which is obtained after cable 1 has moved. Both the reference and measured reflectograms shown in Figure 2(a) were obtained from the same core of cable 1. Figure 2(b) shows the difference between the reference and measured reflectograms. It can be seen that the movement of cable 1 has introduced new impedance discontinuities that were not present when cable 1 was in the baseline position. By analyzing these new impedance discontinuities, the movement of cable 1 can be detected. Optionally, the impedance discontinuities introduced by movement of cable 1 can be analyzed to identify the type of movement (e.g., bending, stretching, contraction and / or twisting), determine the frequency or frequency of the movement, and / or quantify the magnitude of the movement (e.g., measuring the amount that cable 1 is bent).

[0054] The resulting measurement reflectograms can be organized into a multi-dimensional time series, as shown in Figure 3. Each measurement reflectogram represents a measurement corresponding to a different time point. By combining these waveforms over time, the impedance change of the core (or a section thereof) over time can be shown and analyzed.

[0055] Figure 3 shows all SSTDR reflectograms obtained over time for the example measurement. The x-axis represents distance and corresponds to the x-axis in Figures 2(a) and 2(b). The y-axis represents relative impedance change and corresponds to the y-axis in Figures 2(a) and 2(b). The z-axis represents time in seconds.

[0056] By taking a subset (or measurement interval) of data points on the x-axis (distance) and a slice across the z-axis (time), the monitored core can be divided into measurement intervals for analysis. Each measurement interval represents a section along the length of the cable 1 from the measurement point (i.e., the end connected to the signal generator). The length of each measurement interval depends on the resolution of the signal generator 2 in the time domain. As the time domain resolution of the signal generator 2 increases, the length of each measurement interval can be shortened, so that each measurement interval begins to approximate a single point on the cable. Long measurement intervals can also be chosen such that the measurement interval refers to a region extending along the length of the cable 1.

[0057] The measurement section may then be compared to a reference time series that includes measurements of impedance change over time when cable 1 is in a baseline position, the measurements of the reference time series being taken from the same point on cable 1 (or the same longitudinal region of cable 1) as the measurement section.

[0058] In one embodiment, for each measurement section, the overall similarity of the measured waveform to the reference time series can be calculated using dynamic time warping. Dynamic time warping is an algorithm used to measure the similarity between two time series. It is used to dynamically compare time series data when the time indices between the compared data points do not match perfectly. By applying dynamic time warping, the measurement section (described in detail above) is converted into a list of discrete numbers, each number representing the level of impedance change for a given cable section compared to a reference point.

[0059] Figure 4 shows another example of reflectance measurement data. In particular, Figure 4 shows a reference reflectogram, a measured reflectogram, and a differential reflectogram, which is the difference between the measured reflectogram and the reference reflectogram. Each reflectogram in this example plots the relative impedance change (Y-axis) against sample number (Y-axis) or ID of the SSTDR trace, which can be converted to distance based on the frequency of the applied test signal.

[0060] By monitoring multiple cores of a cable of known geometry, further information regarding the motion can be obtained. Figure 5 shows a four-core cable having cores 51, 52, 54 and 54 and an armor layer 55. The cable is bent in the direction of the arrow, i.e., toward the right. The cross-sectional area of ​​each core 51, 52, 53, 54 is strained as the core is bent. This strain is a narrowing of the cross-sectional area of ​​the core at the bend, resulting in an increase in the resistance, and therefore the impedance, of the core at the bend.

[0061] Cores 51 and 54 undergo greater bending than cores 52 and 53 and therefore undergo greater changes, i.e., reductions, in their cross-sectional areas, than cores 52 and 53. In addition to changes in the physical shape of the cores, the relative capacitive coupling between the cores and between each core and sheath 55 also changes with bending.

[0062] FIG. 6 shows an equivalent circuit of two of the four cores of the cable 50 shown in FIG. 5. The cores 51, 52 of the cable 50 are capacitively coupled to each other, represented by the capacitor C1. Additionally, each core 51, 52 is also capacitively coupled to the armor 55, represented by the capacitors C2 and C3, respectively. When the cable is bent in the direction of the arrow, i.e., towards the right, physical changes occur in the cores 61, 62, as described above in terms of cross-sectional area. There is also a physical change in the armor 55 around the bend. These physical changes in the cores 51, 52 and armor 55 change the values ​​of the capacitors C1, C2, C3, which results in a change in impedance that can be detected using TDR. It should be understood that while FIG. 6 shows only two cores of the cable 50 for the sake of simplicity, each core 53, 54 shown in FIG. 5 is similarly capacitively coupled to every other core and armor layer 55 of the cable.

[0063] Figure 7 shows how the impedance of each of the cores 51, 52, 53, 54 changes when the cable 50 shown in Figure 5 is bent. In the example of Figure 7, a bending force is applied to the cable 50 between 0 and 5 seconds, and the bending force is released after 5 seconds. After 10 seconds, the cable 50 has returned to its baseline position.

[0064] In Figure 7, when bent towards the right, cores 51 and 54 experience a larger relative impedance change than cores 52 and 53. This indicates the direction of the bend. Cores towards the outside of the bend experience a larger impedance change or discontinuity than cores towards the inside of the bend. Thus, the direction of the bend can be detected when a first core is closer to the outside of the bend than a second core, and the second core is closer to the inside of the bend than the first core.

[0065] These principles can be extended to detect other types of motion of an electrical cable, in particular stretching, contracting and twisting of the cable. Each type of motion results in a characteristic change in the impedance of each core of the cable. By measuring the change in impedance of each core, different types of motion can be distinguished from one another. Furthermore, the controller 3 can be calibrated so that the magnitude of each type of motion can be determined based on the reflectometry data.

[0066] These principles can be further extended so that the shape of the cable at any given time can be virtually reconstructed relative to a baseline position. In particular, the reflectometry data can be analyzed section by section, where each section is a finite region extending along the length of the cable. For each section, the reflectometry data can be analyzed to determine whether the cable has moved, and if so, the type of movement the cable has undergone, and the magnitude of that movement. By considering each section of the cable in turn, the overall movement of the cable relative to the baseline position can be determined, and the shape of the cable relative to the baseline position can be determined.

[0067] 8 is a flow diagram of a method 80 for detecting movement of an electrical cable 1 according to the present disclosure. The method begins with S81 in which a TDR signal is transmitted from a measurement point along each core 4, 5, 6, 7 of the cable 1. The measurement point is an end of the cable 1 to which a signal generator 2 is connected. The TDR signal may be transmitted by the signal generator 2 along each core 4, 5, 6, 7.

[0068] At S82, one or more reflections of the TDR signal from each core are received at a measurement point. The reflections may be received by a signal generator 2.

[0069] At S83, reflectance measurement data is generated for each core 4, 5, 6, 7. The reflectance measurement data is generated by correlating the TDR signal transmitted along each core with one or more reflections of the TDR signal received from the corresponding core. The reflectance measurement data is indicative of impedance changes at each of a plurality of points along the corresponding core. The reflectance measurements may include one or more reflectograms. The reflectance measurement data may be generated by a signal generator 2.

[0070] In S84, cable movement is detected by comparing the reference reflectance measurement data generated for each core with reference reflectance measurement data for the corresponding core, the reference reflectance measurement data having been previously acquired when cable 1 was in the baseline position (i.e., acquired at a time prior to performing operation S81). Cable movement may be detected in S84 by controller 3.

[0071] The method 80 may be performed by instructions stored on a processor-readable medium. The processor-readable medium may be a read-only memory (including a PROM, EPROM, or EEPROM), a random access memory, a flash memory, an electrical, electromagnetic, or optical signal, a magnetic, optical, or magneto-optical storage medium, one or more registers of a processor, or any other type of processor-readable medium. In alternative embodiments, the present disclosure may be implemented as control logic in hardware, firmware, software, or any combination thereof. The signal generator 2 and / or the controller 3 may be implemented by dedicated hardware, such as one or more application specific integrated circuits (ASICs) or appropriately connected discrete logic gates. An appropriate hardware description language may be used to implement the methods described herein in dedicated hardware.

[0072] A first example use of the techniques disclosed herein is to monitor the health of submarine power cables. A significant percentage of cable failures in submarine environments are due to repeated exposure to Vortices Induced Vibrations (VIV), which have characteristic frequencies that can be identified from reflectometry data according to the present disclosure. By monitoring the reflectometry data over time, it is possible to identify when a cable has been exposed to vortices induced vibrations that lead to failure. Submarine power cable operators can be alerted before the cable fails, reducing potential downtime in power generation.

[0073] A second example use of the techniques disclosed herein is to aid in the design and testing of cables. Currently, new cable designs are tested by manufacturers to ensure that they can withstand a certain number of bending cycles. However, these tests provide very limited information at the end of the test cycle other than a binary answer of whether the cable survived the test or not. The techniques disclosed herein allow cable manufacturers to better understand the characteristics of the cable under test and understand the factors that lead to cable failure.

[0074] Measurements given throughout the specification or in the figures are for illustrative purposes only and other dimensions may be used.

[0075] It will be understood that the invention has been described above purely by way of example and that modifications in detail are possible within the scope of the appended claims. In particular, the sequence of operations shown in Figure 8 is merely exemplary. Any of the operations shown in method 80 may be performed in a different order that achieves substantially the same result.

Claims

1. 1. A method for detecting movement of an electrical cable, the electrical cable including at least one core; The method comprises: transmitting time domain reflectometry (TDR) signals from measurement points along each core of the cable; receiving one or more reflections of the TDR signal from each core at the measurement point; generating reflectometry data for each core by correlating the TDR signal transmitted along each core with the one or more reflections of the TDR signal received from a corresponding core, the reflectometry data indicative of impedance changes at each of a plurality of points along the corresponding core; detecting movement of the cable by comparing the reflectance measurement data generated for each core with reference reflectance measurement data for the corresponding core, the reference reflectance measurement data having been previously obtained when the cable was in a baseline position; A method comprising:

2. The method of claim 1 , wherein detecting the movement of the cable includes identifying bending, stretching, contraction, and / or twisting of the cable.

3. transmitting the TDR signal includes transmitting a plurality of TDR signals from the measurement point along each core of the cable, each of the plurality of TDR signals being transmitted at a corresponding one of a plurality of times; receiving the one or more reflections includes receiving a plurality of reflections from each core, each of the plurality of reflections corresponding to a TDR signal of the plurality of TDR signals; 3. The method of claim 1 or claim 2, wherein generating the reflectometry data comprises correlating each TDR signal transmitted along each core with its corresponding reflection.

4. generating the reflectometry data includes generating a plurality of reflectograms, each reflectogram being a waveform of impedance change versus distance along a corresponding core, each reflectogram corresponding to a respective one of the plurality of TDR signals; 4. The method of claim 3, further comprising monitoring movement of the cable over a period of time by comparing each of the plurality of reflectograms generated for each core with a reference reflectogram for the corresponding core.

5. selecting a measurement section for each core from the reflectance measurement data, the measurement section including a measurement of change in impedance over time at a given point on the core; 5. The method of claim 3 or claim 4, wherein detecting movement of the cable includes comparing the measurement section for each core to a reference time series, the reference time series comprising measurements of impedance change over time at the given point on the core when the cable was in the baseline position.

6. The method of claim 5 , wherein comparing the measurement interval to a reference time series comprises applying a dynamic time warping algorithm to the measurement interval and / or the reference time series.

7. The method of claim 1 , further comprising determining a frequency of movement of the cable.

8. The method of claim 7 , wherein determining a frequency of the cable movement comprises analyzing the reflectometry data to identify time-dependent impedance changes of at least one core.

9. 9. The method of claim 1, wherein the cable includes a first core and a second core, the method further comprising identifying a type of movement of the cable by comparing reflectance measurement data for the first core with reflectance measurement data for the second core.

10. Identifying a type of movement of the cable includes: determining that the first core exhibits a greater impedance change than the second core; identifying a bend in the cable when the first core exhibits a greater impedance change than the second core; 10. The method of claim 9, comprising:

11. The method of claim 10 further comprising determining a direction of a bend in the cable.

12. 12. The method of claim 10 or claim 11, further comprising determining a location of a bend in the cable.

13. The method of claim 1 , further comprising virtually reconstructing a shape of the cable relative to the baseline position.

14. The method of any one of claims 1 to 13, wherein the TDR signal is a spread spectrum time domain reflectometry signal.

15. Apparatus configured to perform the method of any one of claims 1 to 14.

16. A computer readable medium comprising instructions which, when executed by a computer, cause the computer to perform the method of any one of claims 1 to 14.

Images