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JP-7857293-B2 - System and method for detecting insulation defects in underground power cables

JP7857293B2JP 7857293 B2JP7857293 B2JP 7857293B2JP-7857293-B2

Inventors

  • エスコロド マドセン，ボー

Assignees

  • レモニ エー／エス

Dates

Publication Date
20260512
Application Date
20211123
Priority Date
20201124

Claims (20)

  1. A system (2) for detecting insulation defects in an underground power cable (12) comprising one or more single conductors (16, 18, 20) surrounded by a conductive shield (22), wherein the system (2) comprises two or more external clamp-on sensors (subsensors) (4, 4', 4'', 4''') that are attached to or positioned close to the underground power cable (12), and the external clamp-on sensors (4, 4', 4'', 4''') are not electrically connected to any of the one or more single conductors (16, 18, 20) of the underground power cable (12) and can be detected from outside the underground power cable (12) or configured to provide multiple current measurements, the system (2) comprises a signal processing unit (50), the external 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), the mathematical statistical model (52) processes the measurements obtained by the external clamp-on sensors (4, 4', 4'', 4'''') to identify whether the current measurements were caused by partial discharge events (6, 6', 6'', 6'''', 6'''') triggered in the leakage structure (46) in the underground power cable (12), Here, the system (2) is configured such that the mathematical statistical model (52) produces a linear projection of the current in the single conductors (16, 18, 20) and the conductive shield (22), and the mathematical statistical model (52) Yt=Ft(θt)+εt εt～δ1(Vt) θt=gt(θt-1)+Θt Θt~δ2(Wt) It is characterized by being defined as follows: Here, Yt is a vector that determines the observed processing at time t, comprising data observed from the external clamp-on sensors (S1, S2, ..., Sn). θt is a vector for determining the latent probabilistic processing at time t, comprising latent processing data, i.e., currents generated from the single conductors (16, 18, 20) and the conductive shield (22) of the underground power cable (12). Ft is a regression matrix that determines the linear relationship between the latent probabilistic processing and the processing observed at time t. gt is an evolutionary matrix used in the aforementioned latent probability processing to determine the transition from time t-1 to time t. δ1 and δ2 are the stochastic noise vectors for the observed and latent processes, respectively. Vt is the observational variance-covariance matrix , Wt is the evolutionary variance-covariance matrix . System (2).
  2. The system (2) according to claim 1, characterized in that the underground power cable (12) comprises several single conductors (16, 18, 20).
  3. The system (2) according to claim 1 or 2, characterized by comprising several spaced sensors (4, 4', 4'', 4'''') arranged along the conductive shield (22) of the underground power cable (12).
  4. The system (2) according to any one of claims 1 to 3, comprising one main sensor member (34) and one or more additional sensor members (36, 36', 36'', 36''') arranged along the outer circumference of the conductive shield (22) of the underground power cable (12), wherein the main sensor member and the additional sensor members (34, 36, 36', 36'', 36''') are spaced apart in the tangential direction.
  5. The system (2) according to any one of claims 1 to 4, further comprising a calibration unit (54) configured to perform calibration of one or more of the external clamp-on sensors (4, 4', 4'', 4'''') in order to calibrate the system (2) with respect to the physical arrangement of cables and the environment.
  6. The system (2) according to claim 5, characterized in that the calibration unit (54) is separated from the external clamp-on sensors (4, 4', 4'', 4'''').
  7. The system (2) according to claim 5, characterized in that the calibration unit (54) is integrated with each of the external clamp-on sensors (4, 4', 4'', 4'''').
  8. The system (2) according to claim 5, characterized in that the calibration unit (54) is configured to calibrate the external clamp-on sensors (4, 4', 4'', 4''') as the main sensor member (34) and several additional sensor members (36, 36', 36'', 36''') of the external clamp-on sensors (4, 4', 4'', 4''') move along the perimeter of the underground power cable (12).
  9. The system (2) according to any one of claims 1 to 8, characterized in that one or more of the external clamp-on sensors (4, 4', 4'', 4'''') are equipped with an energy harvester.
  10. The system (2) according to claim 9, characterized in that the energy harvester comprises a thermoelectric generator or an electric field environment harvesting device.
  11. A communication unit (24) extends from the sensor (4) toward the ground surface, The system (2) according to any one of claims 1 to 10, comprising an antenna (28) configured to transmit a wireless signal (30), wherein the measurement values obtained by the sensor (4) are wirelessly transmitted by the antenna (30).
  12. The system (2) according to any one of claims 1 to 11, characterized in that the shield structure (60) surrounds the sensors (4, 4', 4'', 4''') and the entire outer circumference of the portion of the underground power cable (12) to which the sensors (4, 4', 4'', 4'''') extend, and the shield structure (60) is an electromagnetic field shield (60).
  13. The system (2) according to any one of claims 1 to 12, wherein the signal processing unit (50) is equipped with a peak detector, and the peak detector is configured to analyze the current measurement value and detect an arbitrary current peak.
  14. The system (2) according to any one of claims 1 to 13, characterized in that the signal processing unit (50) is equipped with a high-pass filter and is configured to apply the current measurement value to the high-pass filter.
  15. The system (2) according to any one of claims 1 to 14, characterized in that the signal processing unit (50) comprises an algorithm configured to automatically identify whether the current measurement was caused by a partial discharge event (6, 6', 6'', 6'''', 6'''') triggered in the leakage structure (46) of the power cable (12).
  16. A method for detecting an insulation defect in an underground power cable (12) having one or more single conductors (16, 18, 20) surrounded by a conductive shield (22), the method comprising the steps of securing two or more external clamp-on sensors (4, 4', 4'', 4'''') outside the underground power cable (12) or positioning them close to the underground power cable (12), wherein the power conductors of the external clamp-on sensors are configured to provide one or more current measurements from outside the underground power cable (12) without being electrically connected to any of the one or more conductors (16, 18, 20) in the underground power cable (12), and the method is The step of providing a signal processing unit (50) for processing the data is performed using a mathematical statistical model (52), which processes the measurements obtained from the external clamp-on sensors (4, 4', 4'', 4''') to identify whether the current measurements were caused by partial discharge events (6, 6', 6'', 6'''', 6'''') triggered in the leakage structure (46) of the underground power cable (12), Here, the method is configured such that the mathematical statistical model (52) produces a linear projection of the current in the conductors (16, 18, 20) and the conductive shield (22), and the mathematical statistical model (52) is Yt=Ft(θt)+εt εt～δ1(Vt) θt=gt(θt-1)+Θt Θt~δ2(Wt) It is characterized by being defined as follows: Here, Yt is a vector that determines the observed processing at time t, comprising data observed from the external clamp-on sensors (S1, S2, ..., Sn). θt is a vector that determines the latent probabilistic processing at time t, which includes latent processing data, i.e., currents generated from the conductor and shield (22) of the cable (12), respectively. Ft is a regression matrix that determines the linear relationship between the latent probabilistic processing and the processing observed at time t. gt is an evolutionary matrix used in the aforementioned latent probability processing to determine the transition from time t-1 to time t. δ1 and δ2 are the stochastic noise vectors for the observed and latent processes, respectively. Vt is the observational variance-covariance matrix , and Wt is the evolutionary variance-covariance matrix . method.
  17. The method according to claim 16, characterized in that the underground power cable (12) comprises several single conductors (16, 18, 20).
  18. The steps include exposing a portion of the underground power cable (12) at one or more locations along the extension of the underground power cable (12), The steps include: securing one or more external clamp-on sensors (4, 4', 4'', 4''') at each location outside the underground power cable (12) or positioning them close to the underground power cable (12); The steps include establishing a connection between each of the external clamp-on sensors (4, 4', 4'', 4'''') and the signal processing unit (50), The method according to claim 16 or 17, characterized by including the following:
  19. The method according to any one of claims 16 to 18, characterized by including the step of calibrating the external clamp-on sensors (4, 4', 4'', 4'''').
  20. The method according to any one of claims 16 to 19, wherein each sensor (4, 4', 4'', 4'''') comprises a main sensor member (34) and one or more additional sensor members (36, 36', 36'', 36''''), and the method includes the step of arranging the main sensor member (34) and the additional sensor members (36, 36', 36'', 36'''') tangentially separated along the outer circumference of the shield (22) of the underground power cable (12).

Description

This invention relates to a system for analyzing partial discharge and a method for performing partial discharge analysis. More specifically, this invention relates to a system and method for detecting insulation defects in underground power cables. According to the International Electrotechnical Commission (IEC), an international standard, partial discharge is defined as follows: "A localized electrical discharge that partially bridges the insulation between conductors, which may or may not occur adjacent to the conductors." Partial discharge occurs when impurities or cavities inside the conductor's insulation, or protrusions outside the conductor's insulation, create a stressed area. This stressed area may be formed by sharp edges or protrusions around the conductor. 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. The detection and measurement of electrical discharge are based on the energy exchange that occurs during the discharge. These exchanges are represented as electrical pulse currents. However, existing solutions are difficult and costly to set up because they require electrical connection to power cables. Therefore, applying these solutions necessitates inserting them into the power cable network. This has been a major unresolved issue for decades. Prior art partial discharge analysis tools are expensive because they require costly sensors, and these sensors must be configured by being electrically connected around a conductor or single conductor. Therefore, these analysis tools are not suitable for use. Technical staff in underground power distribution systems more frequently face the decision of whether to replace older sections of cable. Measurements of partial discharge are used to determine whether the cable should be replaced with new cable or repaired as needed. However, studies have shown that using partial discharge measurements in power cables to reliably determine whether they should be replaced is difficult. Removing these cables based solely on partial discharge measurements is not a valid reason, because external events (e.g., lightning or network switching), as well as leakage structures in the power cable insulation, can cause partial discharge events. A challenge with prior art solutions is the inability to distinguish whether a discharge event was caused by an external event (e.g., lightning) or by a leakage structure in the power cable. U.S. Patent Application Publication No. 20090177420 discloses a device for identifying, locating, and identifying partial discharges occurring at partial discharge sites along electrical equipment. However, this device is not suitable for determining partial discharges with sufficient accuracy. Therefore, it is desirable to have systems and methods that mitigate, or even eliminate, the disadvantages of prior art solutions. It is also desirable to have improved apparatus and methods for detecting, locating, and elucidating partial discharges. U.S. Patent Application Publication No. 20090177420 This is a schematic diagram of the system according to the present invention, which includes several external clamp-on sensors attached to the outside of an underground power cable.This figure shows a curve representing the current as a function of time, indicating a partial discharge signal.This figure shows a curve representing the current as a function of time, where no partial discharge signal is present.This is a schematic diagram of the system according to the present invention, including an external clamp-on sensor that is attached to the outside of an underground power cable.This figure shows the sensor according to the present invention.This is a diagram showing power cables.This figure shows the sensor shown in Figure 4A attached to the power cable shown in Figure 4B.This diagram shows a power cable that includes a leakage current structure.This figure shows a power cable, as indicated in Figure 5A, where the leakage current structure has been replaced by a melted area.This figure shows the sensor according to the present invention.This is a diagram showing power cables.This figure shows the sensor shown in Figure 6A, which is attached to a power cable.This diagram shows the partial discharge currents flowing through the conductor and shield, respectively.This figure shows the sensor according to the present invention.This figure shows another sensor according to the present invention.This is a flowchart illustrating the method according to the present invention.This figure shows the sensor according to the present invention.This figure shows the sensor shown in Figure 9A, which is attached to a power cable having three conductors and a conductive shield.This figure shows a sensor according to the present invention, attached to the outside