System and method for detecting insulation defects in underground power cables

Abstract

The invention relates to a system (2) for detecting insulation defects in an underground power cable (12) comprising one or more single conductors (16, 18, 20) surrounded by an electrically conductive shield (22). The system (2) comprises one or more external clamp-on sensors (4, 4', 4", 4"') clamped to the outside of the power cable (12) or arranged in the vicinity of the power cable (12). The clamp-on sensors (4, 4', 4", 4"') are configured to provide two or more current measurements from the outside of the power cable (12) without being electrically connected to any of the one or more single conductors (16, 18, 20) of the power cable (12). The system (2) comprises a signal processing unit (50). The clamp-on sensors (4, 4', 4", 4"') are configured to detect partial discharge events (6, 6', 6", 6"', 6""). The signal processing unit (50) is adapted to use a mathematical statistical model (52) that processes the measurements made by the clamp-on sensors (4, 4', 4", 4"') to identify whether the current measurements are caused by a partial discharge event (6, 6', 6", 6"', 6"") caused by a leakage structure (46) in the power cable (12).

Description

Technical Field

[0001] This invention relates to systems for partial discharge analysis and methods for performing partial discharge analysis. More specifically, this invention relates to systems and methods for detecting insulation defects in underground power cables. Background Technology

[0002] According to the International Electrotechnical Commission (IEC), partial discharge is defined as: "Partial discharge, which only partially bridges the insulation between conductors, and which may or may not occur near the conductors."

[0003] Partial discharge occurs when impurities or cavities inside the conductor's insulation or external protrusions create a stress zone. This stress zone can be formed by sharp edges or protrusions around the conductor.

[0004] Partial discharge in power cables includes several types of discharge phenomena, such as surface discharge occurring at the boundaries of different insulating materials and internal discharge occurring in gaps or cavities within solid or liquid dielectrics.

[0005] The detection and measurement of discharges are based on the energy exchange that occurs during the discharge. These exchanges manifest as electrical pulse currents.

[0006] However, existing solutions are both difficult and expensive to install because they require an electrical connection to the power cable. Therefore, the power cable needs to be disconnected when these solutions are applied. This has been a major unresolved challenge for decades.

[0007] Existing partial discharge analysis tools are expensive because they require costly clamp sensors, and because these sensors need to be mounted via electrical connections to or around a single conductor. Therefore, these analysis tools are not suitable for use.

[0008] Technicians are increasingly facing decisions about whether to replace some of the older cables in their underground distribution systems. Partial discharge measurements are used to identify whether the cables should be replaced with new ones or repaired if possible.

[0009] However, research indicates that it is difficult to definitively identify whether power cables should be replaced using measurements of partial discharge in them. Removing these cables based solely on partial discharge measurements may not be guaranteed, as external events (e.g., lightning or network switching) and leaks in the power cable insulation can cause partial discharge events. The problem with existing solutions is that they cannot distinguish whether a partial discharge event is caused by an external event (e.g., lightning) or a leak in the power cable.

[0010] US20090177420A1 discloses an apparatus for detecting, locating, and interpreting partial discharges occurring along an electrical device at a partial discharge site. However, this apparatus is not suitable for determining partial discharges with sufficiently high accuracy.

[0011] Therefore, systems and methods that reduce or even eliminate the drawbacks of existing technological solutions are desired. Improved devices and methods for detecting, locating, and interpreting partial discharges are also desired.

[0012] Therefore, the object of the present invention is to provide a system that reduces or even eliminates the aforementioned disadvantages of the prior art.

[0013] The purpose of this invention is to provide a system and method for detecting, locating, and interpreting partial discharges in multi-conductor cables. Summary of the Invention

[0014] The object of the present invention can be achieved by a power quality analysis system and method. Preferred embodiments are explained in the following description and illustrated in the accompanying drawings.

[0015] The system according to the invention is a system for detecting insulation defects in an underground power cable, the underground power cable comprising one or more single conductors surrounded by a conductive shield, wherein the system includes one or more clamp sensors clamped to or disposed near the exterior of the power cable, wherein the clamp sensors are configured to provide one or more current measurements from the exterior of the power cable without being electrically connected to any of the one or more single conductors of the power cable, wherein the system includes a processing unit, wherein the clamp sensors are configured to detect partial discharge events, and wherein the system includes a signal processing unit adapted to process the current measurements taken by the clamp sensors using a mathematical statistical model to identify whether the current measurements are caused by a partial discharge event resulting from a leakage structure in the power cable. In one embodiment, the mathematical statistical model is configured to linearly project the current in the single conductors and the conductive shield, wherein the mathematical statistical model is defined as:

[0016]

[0017] in It is a vector that determines the observation process at time t, including observation data (S1, S2, ..., S...) from the clamp sensor. n ); It is a vector that determines the potential process at time t, including the potential process data; that is, the currents originating from the conductor and shield of the power cable (12), respectively; It is a regression matrix that determines the linear relationship between the potential process and the observed process at time t; It is an evolutionary matrix that determines the transition from time t-1 to time t in the potential process; and These are the random noise vectors of the observation process and the potential process, respectively; It is the observation variance-covariance matrix, and It is the evolutionary variance-covariance matrix.

[0018] Therefore, a system can be provided that can measure partial discharge in power cables in a manner that enables predictive and proactive maintenance; that is, to definitively identify whether the power cable should be replaced.

[0019] The system is configured to detect insulation defects in underground power cables comprising a single conductor surrounded by a conductive shield. Both the single conductor and the surrounding conductive shield constitute the conductor. Therefore, the single conductor surrounded by the conductive shield is a two-conductor cable.

[0020] Existing solutions are not configured to detect insulation defects in underground power cables comprising at least one single conductor surrounded by a conductive shield. The problem is that the number of equations is less than the number of unknowns. Therefore, due to the existence of an infinite number of solutions, it is impossible to provide a unique solution, and thus impossible to determine whether the current measurement is caused by a partial discharge event from a leaking structure in the power cable or from a partial discharge event originating from the conductive shield, by using the magnetic field detected by a clamp-on sensor placed outside the power cable.

[0021] However, this invention employs a mathematical statistical model to identify whether the current measurement is caused by a partial discharge event resulting from a leakage structure in the power cable or the conductive shield. This is accomplished by arranging a sufficiently large number of sub-sensors on or near the outer surface of the power cable to provide a sufficiently large number of equations. Thus, multiple measurements detected by multiple different sensors (a main sensor and multiple sub-sensors) can be provided, with the sensors arranged in a manner where their relative positions to each other are known (this can be accomplished by arranging the sensors in a predetermined mounting structure).

[0022] The mathematical model is used to estimate the transfer function from the conductor and screen to the main sensor and sub-sensors as a linear projection and random noise component.

[0023] If it is necessary to inspect insulation defects in an underground power cable consisting of three single conductors (where the single conductors are electrically insulated from each other) and a conductive shield, the currents flowing in the conductors of the power cable will be represented as I1, I2, and I3, and the currents flowing in the conductive shield will be represented as I4.

[0024] The signals B1, B2, B3, B4… measured by the main sensor and sub-sensors can be calculated as the superposition of the magnetic fields generated by the currents I1, I2, I3, I4, as the superposition equation: (1)

[0025] Among them B j It is j th Signal (by j) th (Sensor measurement), and d ij The calculation can be performed using a simple projection. The calculation can be accomplished using a simple projection because the coordinates of the six cylinders (from the center of each of the three single conductors to the three distances to the clamp sensor in question and the angular position of the sensor) are known.

[0026] According to Ampere's law, at a distance r from the center of a conductor carrying a flowing current I, the magnetic field B is defined by the following equation: (2) or (3)

[0027] in It is the permeability of free space.

[0028] Example 1 In an underground power cable with three single conductors surrounded by a conductive shield, there will be seven unknown parameters that need to be estimated using superposition equations from the main sensor and the sub-sensor (assuming that the distances from the main sensor and the sub-sensor to the center of the power cable are known).

[0029] If we have one main sensor and eleven sub-sensors, then we have 12 - 7 = 5 degrees of freedom. In reality, the currents have three degrees of freedom, and therefore two degrees of freedom in the set of 12 equations. In this specific example, the currents I1, I2, I3, and I4 can therefore be estimated and differentiated by a multiple linear regression with two degrees of freedom.

[0030] The number of sub-sensors required depends on the number of conductors.

[0031] In one embodiment, the main sensor and the additional sub-sensor include coils. Therefore, when current flows through a single conductor or conductive shield of the power cable, a current will be induced in each coil.

[0032] In one embodiment, the system is configured to detect insulation defects in an underground power cable comprising a plurality of single conductors surrounded by a conductive shield.

[0033] The system includes one or more external clamp sensors that are clamped to the outside of or located near the power cable. In one embodiment, the sensor can be attached to the power cable using a mechanical attachment structure. In one embodiment, the mechanical attachment structure is a cable strap.

[0034] Clamp-on sensors are configured to provide one or more current measurements from outside the power cable without being electrically connected to any of the one or more single conductors of the power cable. This is a major advantage because it makes it possible to retrofit clamp-on sensors onto existing power cables, both underground and above ground.

[0035] The system includes a signal processing unit adapted to use a mathematical statistical model to process measurements taken by a clamp sensor to identify whether the current measurement is caused by a partial discharge event resulting from a leakage structure in the power cable. Therefore, the sensor is able to detect partial discharge events. The system is configured to perform partial discharge analysis of the power cable and thereby detect insulation defects in the power cable.

[0036] In one embodiment, the power cable comprises a plurality of single conductors.

[0037] In one embodiment, the system includes a plurality of spaced-apart clamp sensors arranged along the conductive shield of a power cable. This allows the location of a leaking structure within the power cable to be detected. The more sensors present, the more accurately the location of the leaking structure in the power cable can be detected. A leaking structure in the power cable will cause a partial discharge event, which can be detected by sensors within a certain distance of the leaking structure's location in the power cable. The clamp sensor closest to the leaking structure will detect a higher signal than a clamp sensor positioned at a greater distance from the leaking structure. Therefore, the clamp sensor placed at the shortest distance from the leaking structure in the power cable can be located. Thus, the location of the leaking structure in the power cable can be determined.

[0038] In one embodiment, the system includes a plurality of clamp sensors arranged and configured to determine the location of a partial discharge event. Since the signal strength and frequency / wavelength of the partial discharge event depend on the distance between the sensor and the event location, the strengths of the sensor signals can be compared, and thus it can be determined which sensor is placed at the shortest distance to the event.

[0039] In one embodiment, the system includes a main sensor component and one or more additional sensor components arranged circumferentially along a conductive shield of a power cable, wherein the sensor components are tangentially spaced apart.

[0040] Therefore, the sensor can detect whether a partial discharge event is caused by a leaking structure without knowing the internal location of the conductor in the power cable.

[0041] It is important to emphasize that the main sensor component and one or more additional sensor components can be positioned at a short distance from the conductive shielding of the power cable. In one embodiment, the main sensor component and one or more additional sensor components are attached to the conductive shielding of the power cable. The attachment of the main sensor component and one or more additional sensor components to the conductive shielding of the power cable can be accomplished using cable ties or other mechanical attachment structures.

[0042] In one embodiment, the system includes a calibration unit configured to perform calibration of one or more clamp sensors so that the system can detect whether the detected signal is a partial discharge signal caused by a leakage structure in the power cable or a similar signal caused by an external event such as lightning or switching of the power grid (noise).

[0043] Calibration is performed by applying a difference in signals between the main sensor and one or more additional sensors (sub-sensors) to distinguish currents operating in one or more single conductors from currents operating in a surrounding conductive shield.

[0044] In one embodiment, the calibration process includes a step of training a mathematical model, wherein differences between clamp sensor signals detected by different sensors are used as input. After training, the mathematical model will be able to classify any signal as: a) The first portion originating from the current flowing in one or more single conductors, and b) The second portion originates from the current flowing in the surrounding conductive shielding.

[0045] In one embodiment, the mathematical model is a mathematical statistical model configured to estimate the signal portions of the clamp sensor that flow through one or more single conductors and a conductive shield, respectively. A time-correlation transformation of the sensor S1 measurement can be performed to correct for the actual environment of the sensor S1.

[0046] By using mathematical statistical models to estimate whether time-independent transformations can be used, a method with lower computer requirements can be obtained.

[0047] Using time-independent transformations instead of fully mathematical statistical models for operational measurements from sensor S1 may be advantageous.

[0048] Sometimes it may be beneficial to test whether the accuracy of the transformation is acceptable, and if necessary, to use a mathematical statistical model to update it.

[0049] The necessary number of samples can be obtained by estimating the measurement error of the transformation. In this way, the results can be retained until the desired accuracy is achieved.

[0050] The following describes a preferred method for estimating latent processes using mathematical statistical models. The latent process can be modeled, for example, by a state-space model defined as follows: (4)

[0051] (5)

[0052] in It is a vector that determines (e.g., describes or defines) the observation process at time t, including observation data (S1, S2, ..., S...) from the clamp sensor. n ); It is a vector that determines the potential process at time t, including potential process data; that is, currents originating from the main conductor of the power cable, the conductive shield, or from external electromagnetic radiation, respectively; It is a regression matrix that determines the linear relationship between the potential process and the observed process at time t; It is the evolutionary matrix that determines the linear transition from time t-1 to time t in the potential process; and These are the zero-mean multivariate Gaussian noise vectors of the observed process and the potential process, respectively. It is the observation variance-covariance matrix; It is the evolutionary variance-covariance matrix.

[0053] Model parameter matrix and Estimation can be performed using, for example, a Kalman filter with prior data from a modeling system and / or similar systems, including data provided by users and / or field experts. Standard statistical methods can be used to infer information about the process (e.g., to estimate information). This information can be, for example, estimated signals (e.g., trends) and / or predictions (e.g., prognoses) of the process, along with the relevant distributions of estimates, variances, and / or confidence intervals. Using these types of estimates, it is easy, for example, to issue warnings and / or alerts. For example, if the probability of an observed deviation in the process is less than 0.1%, an alert can be selected.

[0054] The above model framework is a special case of a more general model framework: (6)

[0055] (7)

[0056] in and It is a general function. and It is the general statistical distribution, and all other terms as described above.

[0057] Inferences about this more general model framework can be made, for example, by an extended Kalman filter when the relationship between the latent process and the observed process is nonlinear, and by a Kalman-Busch filter when time is defined (e.g., described) on a continuous scale.

[0058] Other time series analysis methods and / or multivariate data analysis methods, such as analysis of variance (ANOVA), Markov models, generalized linear models (GLM), and multivariate Gaussian models, can also be used to estimate the underlying process and infer the information.

[0059] Applying additional sensors may be advantageous, as it can accelerate the training process. Switching events in one or more conductors of the power cable can be used to perform calibration (through the training process).

[0060] The main advantage of using clamp sensors in the systems and methods according to the present invention is that they do not need to bypass power cables.

[0061] In one embodiment, the system includes a calibration unit configured to perform calibration of one or more clamp sensors to calibrate the system to its physical location on the power cable and in the environment. This allows for the initial calibration of the sensors (during sensor installation).

[0062] In one embodiment, the calibration unit is separate from the clamp sensor.

[0063] In one embodiment, the system includes multiple clamp sensors and a single centrally located calibration unit configured to receive and process data from the clamp sensors.

[0064] In one embodiment, the calibration unit is integrated into each clamp sensor.

[0065] In one embodiment, the calibration unit is configured to calibrate the clamp sensor as the main sensor component and several additional sensor components of the clamp sensor move along the periphery of the power cable.

[0066] This can be achieved by detecting several locations where there is a local maximum sensor signal amplitude. At these locations, one of the main sensor components or an auxiliary sensor component (sub-sensor) should be positioned. This process can be performed manually or using a calibration tool that tracks the location and the corresponding clamp sensor signal.

[0067] In one embodiment, one or more external clamp sensors include an energy harvester.

[0068] In one embodiment, one or more external clamp sensors are electrically connected to the energy harvester.

[0069] In one embodiment, the energy harvester includes a thermoelectric generator or an electric field energy harvesting device.

[0070] In one embodiment, the system includes: The communication unit extends from the clamp sensor toward the ground plane, and An antenna configured to transmit wireless signals. The system is configured to wirelessly transmit measurements taken by clamp sensors via an antenna.

[0071] This allows sensor signals to be detected and wirelessly transmitted to a receiving device.

[0072] In one embodiment, the communication unit is configured to communicate wirelessly with the antenna.

[0073] In one embodiment, the system includes a wired connection between a communication unit and an antenna.

[0074] In one embodiment, the antenna is powered by an energy harvester, preferably a thermoelectric generator.

[0075] In one embodiment, the antenna is integrated into an antenna assembly that includes an energy harvester, preferably a thermoelectric generator or a solar cell.

[0076] In one embodiment, the shielding structure surrounds a portion of the entire circumference of the clamp sensor and the power cable, where the clamp sensor extends, and the shielding structure is electromagnetic shielding.

[0077] In one embodiment, the shielding structure is formed as a magnetically conductive shielding structure, which is configured to surround a portion of the entire circumference of the clamp sensor and the power cable extending from the clamp sensor.

[0078] Therefore, electromagnetic shielding can be provided.

[0079] This can reduce the impact of electromagnetic radiation.

[0080] In one embodiment, the processing unit includes a peak detector configured to analyze current measurements and detect any current peaks.

[0081] In one embodiment, the processing unit includes a high-pass filter configured to perform high-pass filtering on the current measurement.

[0082] In one embodiment, the processing unit includes an algorithm configured to automatically identify whether the current measurement is caused by a partial discharge event resulting from a leakage structure in the power cable.

[0083] The method according to the invention is a method for detecting insulation defects in an underground power cable, the underground power cable comprising one or more single conductors surrounded by a conductive shield, wherein the method includes the steps of: clamping one or more external clamp sensors to the outside of the power cable or arranging one or more external clamp sensors near the power cable, wherein the electrical conductors of the clamp sensors are configured to provide one or more current measurements from the outside of the power cable without being electrically connected to any of the one or more single conductors of the power cable, wherein the method includes the step of applying a signal processing unit to process data, wherein the clamp sensors are configured to detect partial discharge events, wherein the step of applying the signal processing unit to process data is performed by using a mathematical statistical model that processes the measurements taken by the clamp sensors to identify whether the current measurements are caused by a partial discharge event caused by a leakage structure in the power cable, wherein in one embodiment, the method applies a mathematical statistical model for linearly projecting the current in the single conductors and the conductive shield, wherein the mathematical statistical model is defined as:

[0084]

[0085] in It is a vector that determines the observation process at time t, including observation data (S1, S2, ..., S...) from the clamp sensor. n ); It is a vector that determines the potential process at time t, including the potential process data; that is, the currents originating from the single conductor and the conductive shield of the power cable (12), respectively; It is a regression matrix that determines the linear relationship between the potential process and the observed process at time t; It is an evolutionary matrix that determines the transition from time t-1 to time t in the potential process; and These are the random noise vectors of the observation process and the potential process, respectively; It is the observation variance-covariance matrix, and It is the evolutionary variance-covariance matrix.

[0086] Therefore, a method can be provided to measure partial discharge in power cables, enabling definitive identification of whether the power cable should be replaced / repaired. Thus, this method allows for the determination of when a power cable should be removed based on the partial discharge measurement performed using this method.

[0087] In one embodiment, the power cable comprises a plurality of single conductors.

[0088] In one embodiment, the method includes the following steps: Exposing a portion of the power cable at one or more locations along its length; At each location, one or more external clamp sensors are clamped to the outside of the power cable or placed near the power cable; A connection is established between each external clamp sensor and the signal processing unit.

[0089] Therefore, this method can be used to retrofit existing power cables with sensors, thereby allowing the method to be used to detect insulation defects in underground power cables.

[0090] In one embodiment, the method includes the step of calibrating a clamp sensor.

[0091] In one embodiment, the method includes the step of calibrating a clamp sensor using a calibration unit configured to calibrate the clamp sensor by moving a main sensor component and several additional sensor components of the clamp sensor along the periphery of a power cable.

[0092] By detecting several locations where local maximum sensor signal amplitude exists, the most promising locations for arranging the main sensor component and one or more auxiliary sensor components can be identified. Therefore, either the main sensor component or one of the auxiliary sensor components (sub-sensors) should be positioned at these locations. This process can be performed manually or using a calibration tool that tracks the positions and corresponding clamp sensor signals.

[0093] In one embodiment, each clamp sensor includes a main sensor component and one or more additional sensor components, wherein the method includes arranging the main sensor component and the additional sensor components tangentially spaced along the circumference of a conductive shield of a power cable.

[0094] In one embodiment, the method includes the step of applying a clamp sensor configured to measure both the magnetic field and the electric field of a power cable.

[0095] In one embodiment, the sensor is configured to communicate wirelessly with one or more external devices.

[0096] In one embodiment, at least some of the sensors are powered by at least one energy harvesting device. Attached Figure Description

[0097] The invention will become more comprehensive from the detailed description given below. The accompanying drawings are given by way of illustration only and therefore do not limit the invention. In the drawings: Figure 1 A schematic diagram of a system according to the invention is shown, the system comprising a plurality of external clamp sensors clamped to the outside of an underground power cable; Figure 2A The curve depicting the current changing over time is shown, which illustrates the partial discharge signal; Figure 2B The curve depicting the change of current over time is shown, in which no partial discharge signal is present; Figure 3 A schematic diagram of a system according to the invention is shown, the system including an external clamp sensor clamped to the outside of an underground power cable; Figure 4A A clamp sensor according to the present invention is shown; Figure 4B The power cable is shown; Figure 4C It shows the attachment to Figure 4B The power cable shown Figure 4A The clamp sensor shown; Figure 5A A power cable including a leakage structure is shown; Figure 5B It shows Figure 5A The power cable shown has had its leaking structure replaced by a fused section. Figure 6A A clamp sensor according to the present invention is shown; Figure 6B The power cable is shown; Figure 6C It shows the attachment to the power cable. Figure 6A The clamp sensor shown; Figure 7A The partial discharge currents operating in a single conductor and a conductive shield are shown, respectively. Figure 7B A clamp sensor according to the present invention is shown; Figure 7C Another sensor according to the present invention is shown; Figure 8 A flowchart illustrating the method according to the present invention is shown; Figure 9A A clamp sensor according to the present invention is shown; Figure 9B The diagram shows an attachment to a power cable comprising three single conductors and a conductive shield. Figure 9A The clamp sensor shown; Figure 9C A clamp sensor according to the invention is shown clamped to the outside of a power cable; Figure 9D Another sensor according to the invention is shown clipped to the outside of a power cable; Figure 10A A clamp sensor according to the invention is shown arranged on the outer surface of a power cable; Figure 10B Another sensor according to the invention is arranged on the outer surface of a power cable; Figure 10C A clamp sensor according to the invention is arranged on the outer surface of a multi-conductor power cable; and Figure 10D The method according to the invention is shown as being used in a manner that treats the conductor as a single conductor. Detailed Implementation

[0098] To illustrate preferred embodiments of the invention, reference will now be made in detail to the accompanying drawings. Figure 1 A schematic diagram of a system according to the present invention is shown. The system includes a plurality of external clamp sensors 4, 4', 4”, 4”', 4”” that are clamped to the outside of an underground power cable 12.

[0099] Clamp sensors 4, 4', 4”, 4”', 4”” are spaced apart from each other. Therefore, clamp sensors 4, 4', 4”, 4”', 4”” will pick up signals at different locations along the power cable 12.

[0100] Under each clamp sensor 4, 4', 4”, 4”', 4””, the detected sensor signals 6, 6', 6”, 6”', 6””, which have been processed by the signal processing unit, are plotted relative to time. The sensor signals 6, 6', 6”', 6”', 6”” are processed by the signal processing unit to remove the main signal (e.g., 50Hz AC) and partial discharge events caused by switching events. This processing may include one or more filtering processes.

[0101] Clamp sensors 4, 4', 4”, 4”', and 4”” are configured to detect current. Therefore, the graph depicts the relationship between current and time. It can be seen that clamp sensors 4” and 4”', located at the shortest distance to partial discharge event 10, indicated by the thick arrow, detect a larger signal than the other clamp sensors 4, 4', and 4”” located at a greater distance from partial discharge event 10.

[0102] Therefore, clamp sensors 4, 4', 4”, 4”', 4”” can be used to identify the location of partial discharge event 10. By comparing the amplitudes of the processed sensor signals 6, 6', 6”, 6”', 6””, the location of partial discharge event 10 can be identified.

[0103] Figure 2A A curve 54 depicting the current as a function of time is shown. It indicates the partial discharge signal caused by a leakage structure in the underground power cable. The partial discharge signal is generated by... Figure 1 The clamp sensor measurement is schematically shown in the diagram. The frequency of the partial discharge signal is much higher than the frequency of the "main signal" (e.g., 50Hz AC). Therefore, the partial discharge signal is shown as the peak value.

[0104] Figure 2B Curve 54', depicting the current as a function of time, is shown where no partial discharge signal is present. Therefore, curve 54' corresponds to curve 54 in the modified version, where the partial discharge signal has been removed.

[0105] Figure 3 A schematic diagram of system 2 according to the present invention is shown. System 2 includes an external clamp sensor 4 clamped to the outside of an underground power cable 12. System 2 is configured to detect insulation defects in the power cable 12.

[0106] The power cable 12 includes three single conductors 16, 18, and 20 surrounded by a conductive shield 22. Although not shown, the system 2 may include multiple external clamp sensors 4, which are clamped to the outside of the power cable 12 or arranged in the vicinity of the power cable 12.

[0107] Clamp-on sensor 4 is configured to provide one or more current measurements from outside the power cable 12, without being electrically connected to any one of the one or more single conductors 16, 18, 20 of the power cable 12. Clamp-on sensor 4 is configured to detect partial discharge events. This is accomplished by measuring the magnetic field generated by the current flowing in the single conductors 16, 18, 20 and the conductive shield 22. Since each clamp-on sensor 4 can only measure the superimposed magnetic field (the sum of the magnetic fields caused by the current flowing in the single conductors 16, 18, 20 and the conductive shield 22), additional information must be provided.

[0108] The system 2 includes a signal processing unit 50 configured to provide the required additional information. The signal processing unit 50 is adapted to use a mathematical statistical model 52. The mathematical statistical model 52 is configured to process measurements taken by the clamp sensor 4 of the system 2 to identify the origin of the magnetic field measured by the clamp sensor 4. This means that the signal processing unit 50 can divide the measurement signal into: a) The current flowing in single conductors 16, 18, and 20, and b) Current flowing in the conductive shield 22.

[0109] Therefore, the signal processing unit 50 is able to identify whether the current measurement value is caused by a partial discharge event caused by a leakage structure in the power cable 12.

[0110] The power cable is connected to a connection assembly located in power station 8. It can be seen that the conductive shield 22 is grounded. Lightning 14 strikes power station 8, causing a partial discharge event. Therefore, a partial discharge event current flows in the single conductors 16, 18, and 20. Since the conductive shield 22 is conductive and surrounds the single conductors 16, 18, and 20, a current is induced in the conductive shield 22. However, due to the capacitive coupling between the single conductors 16, 18, and 20 and the surrounding conductive shield 22, the induced current caused by the partial discharge event current (caused by lightning) will be delayed by 90 degrees (or a fourth wavelength). Therefore, by comparing the partial discharge event current in the conductive shield 22 with the partial discharge event current in the single conductors 16, 18, and 20, it is possible to identify whether the partial discharge event current is caused by a leakage structure in the power cable 12.

[0111] The system 2 is able to detect whether the current measurement value is caused by a partial discharge event caused by a leakage structure in the power cable 12.

[0112] The system includes an antenna 28 and a communication unit 24, which is arranged to transmit signals detected by the clamp sensor 4 to the antenna 28. The communication unit 24 can be configured to transmit signals to the antenna 28 via a wired connection or a wireless connection.

[0113] Antenna 28 transmits wireless signal 30, which is received by signal processing unit 50. Wireless signal 30 is transmitted via Internet 26.

[0114] In one embodiment, the clamp sensor 4 and / or communication unit 24 includes or is electrically connected to an energy harvester arranged and configured to harvest energy and thereby supply electrical energy to the clamp sensor 4 and / or communication unit 24. In one embodiment, the energy harvester includes a thermoelectric generator or an electric field energy harvesting device. In one embodiment, the energy harvester includes a solar panel.

[0115] Figure 4A A clamp sensor 4 according to the present invention is shown. The clamp sensor 4 includes a main sensor component 34 and a plurality of additional sensor components (sub-sensors) 36, 36', 36”, 36”'. The main sensor component 34 is electrically connected to the additional sensor components 36, 36', 36”, 36”' via an electrical connector 38.

[0116] Each of the main sensor component 34 and the auxiliary sensor components 36, 36', 36" and 36"' is configured to detect the magnetic field caused by the current running in the underlying structure. By having the main sensor component 34 and the auxiliary sensor components 36, 36', 36" and 36"', the main sensor component 34 and the auxiliary sensor components 36, 36', 36" and 36"' can be arranged at different tangential positions around the power cable 12, such as... Figure 4C As shown. Therefore, data from the main sensor component 34 and the additional sensor components 36, 36', 36"' can be processed (e.g., via reference as shown in the figure). Figure 3 The signal processing unit 50 interprets the signal so that it can separate the measured signal into the current running in one or more single conductors of the power cable and the current running in the conductive shield of the power cable.

[0117] In one embodiment, the main sensor component 34 includes an integrated communication unit (not shown). In one embodiment, the main sensor component 34 is configured to receive signals from the auxiliary sensor components 36, 36', 36"', 36"', and to transmit the signals measured by the main sensor component 34 and the signals from the auxiliary sensor components 36, 36', 36"' to a receiving device via a wired or wireless connection.

[0118] Figure 4B A power cable 12 according to the present invention is shown. The power cable 12 corresponds to a reference. Figure 5A The type of power cable 12 is shown and explained.

[0119] Figure 4C It shows the attachment to Figure 4B The power cable 12 shown Figure 4A The clamp sensor 4 is shown. The clamp sensor 4 can be attached to the power cable 12 using any suitable attachment structure. In one embodiment, the clamp sensor 4 is attached to the power cable 12 via one or more cable straps (not shown). A shielding structure 60 surrounds the clamp sensor 4 and a portion of the power cable 12 extending from the clamp sensor 4, covering the entire circumference. The shielding structure 60 is for electromagnetic shielding.

[0120] The shielding structure 60 is used to electrically isolate the clamp sensor 4 and the power cable 12 from the environment through which the power cable 12 passes. In one embodiment, the shielding structure 60 is a conductive shell for blocking electrostatic fields.

[0121] Figure 5AAn underground power cable 12 is shown, positioned below ground level 32. The power cable 12 comprises three single conductors 16, 18, and 20. Each of the three single conductors 16, 18, and 20 is surrounded by an insulator 42. The insulator 42 of the three single conductors 16, 18, and 20 is surrounded by an insulating structure 44. The insulating structure 44 is surrounded by a filler 40. The filler 40 is surrounded by a conductive shield 22.

[0122] As can be seen, the power cable 12 is damaged and includes a leakage structure 46 (enlarged for illustration). The leakage structure 46 extends through the conductive shield 22. Therefore, water and moisture can enter the power cable 12 through the leakage structure 46. The leakage structure 46 extends through the filler 40, the insulation structure 44, and the insulator 42. Therefore, when water or moisture enters the leakage structure 46, the impedance along the path of the leakage structure 46 decreases to the point that a short circuit (current traveling along an unintended path along the leakage structure 46) is generated.

[0123] During a short circuit, the current is at its maximum, causing the temperature within the leakage structure 46 to rise. Therefore, a short circuit typically leads to the melting of the leakage structure 46, resulting in a fusion region 48, such as... Figure 5B As shown. The fusion zone 48 can be used to simultaneously seal the damaged structure of the power cable (leaking structure 46). Therefore, several short circuits can occur before the power cable 12 must be replaced, as shown in the reference. Figure 5A As explained.

[0124] Figure 6A A clamp sensor 4 according to the present invention is shown. The clamp sensor 4 includes a main sensor component 34 and a single auxiliary sensor component (sub-sensor) 36. The main sensor component 34 is electrically connected to the auxiliary sensor component 36 via an electrical connector 38.

[0125] The main sensor component 34 and the auxiliary sensor component 36 are configured to detect the magnetic field caused by the current flowing in the underlying structure. By having the main sensor component 34 and the auxiliary sensor component 36, the main sensor component 34 and the auxiliary sensor component 36 can be arranged at different tangential positions around the power cable 12, such as... Figure 4C As shown. Therefore, data from the main sensor component 34 and the additional sensor component 36 can be processed (e.g., via reference as shown in the figure). Figure 3 The signal processing unit 50 interprets the signal and thereby separates the measured signal into currents operating in one or more single conductors of the power cable and currents operating in the conductive shield of the power cable.

[0126] In one embodiment, the main sensor component 34 includes an integrated communication unit (not shown). In one embodiment, the main sensor component 34 is configured to receive signals from the additional sensor component 36 and transmit the signals measured by the main sensor component 34 and the signals from the additional sensor component 36 to a receiving device via a wired or wireless connection.

[0127] Figure 6B A power cable 12 according to the present invention is shown. The power cable 12 includes a single conductor 16 surrounded by an insulator 42. The insulator 42 is surrounded by an insulating structure 44. A filler 40 is disposed between the insulating structure 44 and the surrounding conductive shield 22.

[0128] Figure 6C It shows the attachment to Figure 6B The power cable 12 shown Figure 6A The clamp sensor 4 is shown. The clamp sensor 4 can be attached to the power cable 12 using any suitable attachment structure. In one embodiment, the clamp sensor 4 is attached to the power cable 12 via one or more cable straps (not shown).

[0129] Figure 7A The first curve 56 is shown, which depicts the situation during a partial discharge event, such as... Figure 5A The diagram shows the relationship between the current flowing in a single conductor of a power cable and time, where the corresponding... Figure 4C or Figure 6C The clamp sensor shown is used to detect current. Figure 7 also shows a second dashed curve 58, which depicts the relationship between the current flowing in the conductive shield of the power cable and time during a partial discharge event.

[0130] The first curve 56 has an amplitude A2 that is greater than the amplitude A1 of the second dashed curve 58. Furthermore, the second dashed curve 58 is delayed.

[0131] Because the conductive shielding is conductive and surrounds the single conductor of the power cable (see...) Figure 5A Therefore, when current flows in a single conductor, a current is induced in the conductive shield. Due to capacitive coupling between the single conductor and the surrounding conductive shield, the induced current in the conductive shield is delayed by 90 degrees (or the fourth wavelength λ). Therefore, compared to the first curve 56, the second dashed curve 58 (showing the induced current in the conductive shield caused by an external partial discharge event current) is delayed by 90 degrees. Thus, by comparing the first solid curve 56 and the second dashed curve 58, the sequence of partial discharge event currents will reveal whether the partial discharge event current is caused by a leakage structure in the power cable. Figure 7A Curves 56 and 58 shown reveal partial discharge events occurring in a single conductor of a power cable.

[0132] Figure 7B A clamp sensor 4 according to the present invention is shown. The clamp sensor 4 substantially corresponds to... Figure 6A The clamp sensor is shown. However, the main sensor component 34 includes a signal processing unit 50. The signal processing unit 50 applies an algorithm using a mathematical statistical model 52 according to the present invention. In another embodiment, the signal processing unit 50 and the mathematical statistical model 52 may be located in an additional sensor component 36 or in a separate device (not shown) of the clamp sensor 4.

[0133] Figure 7C Another clamp sensor 4' according to the invention is shown. The clamp sensor 4 essentially corresponds to Figure 4A The clamp sensor is shown. However, the main sensor component 34 includes a signal processing unit 50. The signal processing unit 50 applies an algorithm using the mathematical statistical model 52 according to the invention. In another embodiment, the signal processing unit 50 and the mathematical statistical model 52 may be located in one of the additional sensor components 36, 36', 36" or in a separate device (not shown) of the clamp sensor 4'.

[0134] Figure 8 A flowchart illustrating the method according to the invention is shown. The first step of the method is to detect the signal measured by a clamp sensor. The clamp sensor will provide different data because the clamp sensor is located in different positions.

[0135] The data detected by the clamp sensor is processed. The processing includes filtering using a high-pass filter. The processing also includes signal amplification.

[0136] The next step is to determine whether the detected signal is caused by partial discharge from a damaged power cable (with a leaky structure). This can be done by using a reference... Figure 3 The interpretation is completed by the processing unit.

[0137] In one embodiment, these steps are repeated to continuously monitor the power cable.

[0138] In one embodiment, an additional step is performed. This additional step includes determining the location of the partial discharge event. Thus, the method according to the invention can be applied to locate the damaged portion of the power cable.

[0139] Figure 9AA clamp sensor 4 according to the present invention is shown. The clamp sensor 4 includes a main sensor component 34 and a plurality of auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37'. The main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' are mounted in a mounting structure 62. Therefore, the positions of the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' relative to each other are well defined and known. This information is applied when using mathematical statistical models to estimate the transfer functions from the conductor and screen to the main sensor component 34 and the sub-sensor components 35, 35', 35", 35"', 36, 36', 36", 36"', 37, 37' as linear projections and random noise components. The geometry of the mounting structure 62 can be arc-shaped, such as... Figure 9A As shown. However, the geometry of the mounting structure 62 can be different, as long as the positions of the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' relative to each other are well-defined and known. As an example, the geometry of the mounting structure 62 can be straight, such that the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' are arranged along a straight line.

[0140] Figure 9B The attached power cable 12 is shown. Figure 9A The clamp sensor 4 shown includes a power cable 12 comprising three single conductors 16, 18, and 20 and a conductive shield 22. The single conductors 16, 18, and 20 are electrically insulated from each other and surrounded by the conductive shield 22 spaced apart from the single conductors 16, 18, and 20. A shielding structure 60, forming an electromagnetic field shield, surrounds the power cable 12 and the clamp sensor 4.

[0141] Since the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37’ extend along the outer surface of the power cable 12, the distance from the center of the power cable 12 to the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37’ are known. To identify whether the current measurement is caused by a partial discharge event resulting from a leakage structure in the power cable 12 or the conductive shield 22, the present invention applies measurements performed by the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37', and known parameters (the positions of the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' relative to each other and the diameter of the power cable 12). By arranging the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' in the predetermined mounting structure 62, the positions of the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' relative to each other will be known.

[0142] By providing a sufficiently large number of additional sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37', sufficient measurement results can be provided and thus a sufficiently large number of equations can be provided to solve the system of equations and thus determine the current flowing in the single conductor and the current flowing in the conductive shield 22.

[0143] Figure 9C A clamp sensor 4 according to the invention is shown, which is clamped to the outside of a power cable comprising three single conductors 16, 18, 20 and a conductive shield 22. The single conductors 16, 18, 20 are electrically insulated from each other and are surrounded by the conductive shield 22 spaced apart from the single conductors 16, 18, 20.

[0144] The clamp sensor 4 includes a main sensor component 34 and several auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37', which are arranged relative to each other in a predefined manner and attached to a power cable. Therefore, the distance from the center of the power cable to the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37' is known. Therefore, by using a reference... Figure 9BThe same principle explained can be used to identify whether current measurements are caused by partial discharge events resulting from leaks in the power cable or conductive shielding.

[0145] Figure 9D Another clamp sensor 4 according to the invention is shown, which is clamped in a corresponding Figure 9C The power cable is shown outside. The clamp sensor 4 includes a main sensor component 34 and a plurality of auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37', 37”. Therefore, the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37’, 37” are arranged relative to each other in a predefined manner. Therefore, the distance from the center of the power cable to the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, 36”', 37, 37” are known. Therefore, by using a reference… Figure 9B and Figure 9C The same principle explained can be used to identify whether current measurements are caused by partial discharge events resulting from leaks in the power cable or conductive shielding.

[0146] Figure 10A A clamp sensor 4 according to the invention is shown, which is arranged on the outer surface of a power cable comprising three single conductors and a conductive shield. The single conductors are electrically insulated from each other and surrounded by a conductive shield spaced apart from the conductors.

[0147] The clamp sensor 4 includes a main sensor component 34 and several auxiliary sensor components 35, 35', 35”, 35”', 36, 36', and 36”, which are arranged and attached to the power cable in a predetermined manner (along the cylindrical surface of the power cable). The main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', and 36” are arranged along a plane extending perpendicular to the longitudinal axis X of the power cable. Therefore, the distance from the center of the power cable to the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', and 36” is known.

[0148] Therefore, by using reference Figure 9B and Figure 9D The same principle explains how to identify whether a current measurement is caused by a partial discharge event resulting from a leakage structure in the power cable or the conductive shielding.

[0149] Figure 10BAnother clamp-on sensor 4 according to the invention is shown, which is arranged on the outer surface of a power cable comprising three single conductors and a conductive shield. The power cable corresponds to... Figure 10A The power cable shown.

[0150] The clamp sensor 4 includes a main sensor component 34 and multiple auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36”, which are arranged along the surface of the power cable in a predetermined manner and attached to the power cable. The main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36” are arranged along a plane at an angle α (different from 90 degrees) relative to the longitudinal axis X of the power cable. If this angle α is unknown, the method according to the invention can still be used to identify whether the current measurement is caused by a partial discharge event caused by a leakage structure in the power cable or in the conductive shield. The distance from the center of the power cable to the main sensor component 34 and the auxiliary sensor components 35, 35', 35”, 35”', 36, 36', 36” is known. Therefore, by using a reference... Figure 9B and Figure 9D The same principle explained can be used to identify whether the current measurement is caused by a partial discharge event resulting from a leakage structure in the power cable or the conductive shielding.

[0151] Figure 10C A clamp sensor 4 according to the invention is shown, which is arranged in a position corresponding to Figure 9C and Figure 9D On the outer surface of the multi-conductor power cable shown. Clamp sensor 4 basically corresponds to Figure 9D The clamp sensor shown.

[0152] Figure 10D This illustrates how the method according to the invention can be used in a manner in which, as shown... Figure 10C The conductors of the multi-conductor cable shown can be considered as a single estimated conductor 21. This is possible because the current through the conductors of the multi-conductor cable is zero.

[0153] List of reference numerals in the attached diagram: 2: (Partial Discharge Analysis) System 4,4',4”,4”', 4””: Clamp-on sensor 6, 6', 6”, 6”', 6””: Sensor signals 8: Power station 10: Partial Discharge Events 12: Power cables (e.g., multi-conductor cables) 14: Lightning 16, 18, 20: Single conductor of power cable 21: Estimating the conductor 22: Conductive shielding components 24: Communication Unit 26: Cloud (servers accessed via the Internet) 28: Antenna 30: Wireless signal 32: Ground level 34: Main sensor component 35, 35', 35”, 35”': Additional sensor components 36, 36', 36”, 36”': Additional sensor components 37, 37', 37”: Additional sensor components 38: Electrical connector 40: Filler 42: Insulator 44: Insulation structure 46: Leaking Structure 48: Fusion region 50: Signal Processing Unit 52: Mathematical Statistical Model 54, 54': Curve 56, 58: Curves 60: Shielding structure 62: Installation Structure A1, A2: Amplitude α: Angle λ: wavelength B: Magnetic field lines X: Longitudinal axis.

Claims

1. A system for detecting insulation defects in underground power cables, said underground power cables comprising one or more single conductors surrounded by a conductive shield, wherein, The system includes two or more external clamp sensors clamped to or located near the power cable, wherein the clamp sensors are configured to provide one or more current measurements from outside the power cable without being electrically connected to any of the one or more single conductors of the power cable, wherein the system includes a signal processing unit, the clamp sensors being configured to detect partial discharge events, wherein the signal processing unit is adapted to process the measurements taken by the clamp sensors using a mathematical statistical model to identify whether the current measurements are caused by a partial discharge event resulting from a leakage structure in the power cable, characterized in that the mathematical statistical model is configured to linearly project the current in the single conductor and the conductive shield, wherein the mathematical statistical model is defined as: in It is a vector that determines the observation process at time t, including observation data from the clamp sensor; It is a vector that determines the potential process at time t, including the potential process data; that is, the currents originating from the single conductor and the conductive shield of the power cable, respectively. It is a regression matrix that determines the linear relationship between the potential process and the observed process at time t; It is an evolutionary matrix that determines the transition from time t-1 to time t in the potential process; and These are the random noise vectors of the observation process and the potential process, respectively; It is the observation variance-covariance matrix; It is the evolutionary variance-covariance matrix.

2. The system according to claim 1, characterized in that, The power cable comprises several single conductors.

3. The system according to claim 1, characterized in that, The system includes a plurality of spaced-apart clamp sensors arranged along the conductive shield of the power cable.

4. The system according to claim 1, characterized in that, The system includes a main sensor component and one or more additional sensor components arranged circumferentially along the conductive shield of the power cable, wherein the main sensor component and the additional sensor components are tangentially spaced apart.

5. The system according to claim 1, characterized in that, The system includes a calibration unit configured to perform calibration of one or more of the clamp sensors in order to calibrate the system to a physical location on the power cable and in the environment.

6. The system according to claim 5, characterized in that, The calibration unit is configured to calibrate the clamp sensor as the main sensor component and several additional sensor components of the clamp sensor move along the periphery of the power cable.

7. The system according to claim 1, characterized in that, The system includes: The communication unit extends from the clamp sensor toward the ground plane, and An antenna configured to transmit wireless signals. The system is configured to wirelessly transmit measurements taken by clamp sensors via an antenna.

8. The system according to claim 1, characterized in that, The shielding structure surrounds a portion of the entire circumference of the clamp sensor and the power cable, where the clamp sensor extends, and the shielding structure provides electromagnetic shielding.

9. The system according to claim 1, characterized in that, The signal processing unit includes a peak detector configured to analyze the current measurement and detect any current peaks.

10. The system according to claim 1, characterized in that, The signal processing unit includes an algorithm configured to automatically identify whether the current measurement is caused by a partial discharge event resulting from a leakage structure in the power cable.

11. A method for detecting insulation defects in an underground power cable, said underground power cable comprising one or more single conductors surrounded by a conductive shield, said method comprising the steps of: Two or more external clamp sensors are clamped to the outside of or arranged near the power cable, wherein the electrical conductors of the clamp sensors are configured to provide one or more current measurements from the outside of the power cable without being electrically connected to any one of the one or more single conductors of the power cable, wherein the method includes the step of applying a signal processing unit to process data, the clamp sensors being configured to detect partial discharge events, wherein the step of applying the signal processing unit to process data is performed using a mathematical statistical model, the mathematical statistical model processing the measurements made by the clamp sensors to identify whether the current measurements are caused by a partial discharge event caused by a leakage structure in the power cable, characterized in that the mathematical statistical model is used to linearly project the current in the single conductors and conductive shielding, wherein the mathematical statistical model is defined as: in It is a vector that determines the observation process at time t, including observation data from the clamp sensor; It is a vector that determines the potential process at time t, including the potential process data; that is, the currents originating from the single conductor and the conductive shield of the power cable, respectively. It is a regression matrix that determines the linear relationship between the potential process and the observed process at time t; It is an evolutionary matrix that determines the transition from time t-1 to time t in the potential process; and These are the random noise vectors of the observation process and the potential process, respectively; It is the observation variance-covariance matrix, and It is the evolutionary variance-covariance matrix.

12. The method according to claim 11, characterized in that, The power cable comprises several single conductors.

13. The method according to any one of claims 11-12, characterized in that, The method includes the following steps: exposing a portion of the power cable at one or more locations along the length of the power cable; At each location, one or more external clamp sensors are clamped to the outside of the power cable or placed near the power cable; Establish connections between each external clamp sensor and signal processing unit.

14. The method according to any one of claims 11-12, characterized in that, The method includes the step of calibrating the clamp sensor.

15. The method according to any one of claims 11-12, characterized in that, Each clamp sensor includes a main sensor component and one or more auxiliary sensor components, wherein the method includes the step of arranging the main sensor component and the auxiliary sensor components tangentially spaced apart along the circumference of the conductive shield of the power cable.

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