Direct-current cable dielectric loss and leakage current synchronous monitoring device and method

Abstract

The invention relates to the technical field of high-voltage direct-current cable insulation state monitoring, and discloses a direct-current cable dielectric loss and leakage current synchronous monitoring device and method, and the device comprises a harmonic direct-current source, a monitoring filtering module, a detected cable and a grounding end. The harmonic direct-current source is used for outputting direct-current high-voltage excitation containing power frequency fundamental waves and harmonic components; the monitoring filtering module is connected in series with a measured cable, the monitoring filtering module comprises a measuring resistor and a measuring capacitor which are arranged in parallel, and the measuring resistor and the measuring capacitor are respectively connected in series with a first ampere meter and a second ampere meter; the first end part of the detected cable is connected with the monitoring filtering module, and the second end part is connected with the harmonic DC source and the grounding end. According to the method, the leakage current and the dielectric loss of the direct current cable can be monitored at the same time, real-time online monitoring is achieved by simplifying system configuration, and the monitoring precision and reliability are improved.

Description

Technical Field

[0001] The present application relates to the technical field of high-voltage DC cable insulation status monitoring, and in particular to a device and method for synchronously monitoring DC cable dielectric loss and leakage current. Background Art

[0002] In modern HVDC transmission systems, DC cables serve as the core carrier for power transmission, and their insulation performance directly determines the safety and reliability of the power system. With the rapid development of technologies such as renewable energy generation and cross-regional grid interconnection, the application scenarios of HVDC cables are expanding, voltage levels are constantly increasing, and operating environments are becoming more complex. In this context, accurate leakage current detection has become a key method for assessing cable insulation status and predicting potential faults.

[0003] The leakage current of a DC cable is often composed of both DC and AC components. The primary DC component is determined by the insulation's conductivity and reflects the insulation's aging or moisture content. The AC component, on the other hand, consists of high-frequency pulse signals generated by power frequency harmonics, surge overvoltage transients, and partial discharges, with frequencies ranging from 50 Hz to the MHz level. Detecting these different components offers complementary benefits for insulation condition diagnosis. For example, an abnormal DC component may indicate overall insulation degradation, while a high-frequency AC component is closely associated with localized defects such as partial discharges.

[0004] However, traditional methods often use a microammeter connected in series with the circuit to measure DC cable leakage current. This not only makes it difficult to detect the high-frequency components of the leakage current, but also introduces additional ground impedance, affecting the DC cable's grounding structure. The industry urgently needs a leakage current measurement method that can achieve accurate measurement while addressing issues affecting the grounding system and making full-band measurement difficult, thus meeting the needs of intelligent operation and maintenance of high-voltage DC cables. Summary of the Invention

[0005] The purpose of this application is to provide a device and method for synchronously monitoring the dielectric loss and leakage current of a DC cable, which can simultaneously monitor the leakage current and dielectric loss of a DC cable. By simplifying the system configuration, real-time online monitoring is achieved, and the monitoring accuracy and reliability are improved, thereby facilitating better online monitoring and evaluation of high-voltage DC equipment.

[0006] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0007] In a first aspect, the present application provides a device for synchronously monitoring dielectric loss and leakage current of a DC cable, comprising a harmonic DC source, a monitoring filter module, a cable under test, and a ground terminal; the harmonic DC source is used to output a DC high-voltage excitation containing an industrial frequency fundamental wave and harmonic components; the monitoring filter module is connected in series with the cable under test, and the monitoring filter module includes a measuring resistor and a measuring capacitor arranged in parallel, and the measuring resistor and the measuring capacitor are respectively connected in series with a first ammeter and a second ammeter; the first end of the cable under test is connected to the monitoring filter module, and the second end is respectively connected to the harmonic DC source and the ground terminal.

[0008] Furthermore, the DC high voltage amplitude output by the harmonic DC source is greater than the rated voltage of the tested cable, the harmonic components are 2nd to 5th power frequency harmonics, and the harmonic amplitude is 1% to 5% of the DC high voltage amplitude.

[0009] Furthermore, the measuring resistance and the measuring capacitance satisfy the parameter matching criterion: where f h is the selected harmonic frequency, Rm is the resistance of the measured resistor, and Cm is the capacitance of the measured capacitor.

[0010] In a second aspect, the present application provides a method for synchronously monitoring dielectric loss and leakage current of a DC cable, based on the apparatus described above, comprising the following steps:

[0011] Connect the harmonic DC source, monitoring filter module, tested cable and ground terminal in sequence;

[0012] Outputting a DC high-voltage excitation including the power frequency fundamental wave and harmonic components through the harmonic DC source;

[0013] Acquire leakage current response through a first ammeter connected in series with a measuring resistor, and acquire AC current response through a second ammeter connected in series with a measuring capacitor;

[0014] Insulation resistance and dielectric loss tangent are calculated based on the leakage current response and the AC current response.

[0015] Furthermore, the frequency of the harmonic component is the 2nd to 5th power frequency harmonic frequency.

[0016] Furthermore, the insulation resistance is calculated using the following formula:

[0017] R X =U X / I X

[0018] Among them, R X is the insulation resistance, U X is the DC high voltage amplitude, I X is the leakage current response.

[0019] Furthermore, the dielectric loss tangent is calculated by the following method:

[0020] calculating an equivalent capacitance of the cable based on the AC current response;

[0021] The dielectric loss tangent value is calculated based on the equivalent capacitance and insulation resistance of the cable.

[0022] Furthermore, based on the AC current response, the equivalent capacitance of the cable is calculated using the following formula:

[0023]

[0024] Among them, C X is the equivalent capacitance of the cable, I S is the AC current response, f h is the selected harmonic frequency, U S is the amplitude of the harmonic component.

[0025] Furthermore, based on the equivalent capacitance and insulation resistance of the cable, the dielectric loss tangent is calculated using the following formula:

[0026]

[0027] Among them, tanδ is the dielectric loss tangent value, C X is the equivalent capacitance of the cable, f h is the selected harmonic frequency, R X is the insulation resistance.

[0028] This application uses an innovative harmonic excitation collaborative monitoring architecture to achieve high-precision synchronous measurement of DC cable leakage current and dielectric loss tangent tanδ, with the following significant technical effects:

[0029] (1) Dual-parameter synchronous measurement: Based on the composite excitation characteristics of the harmonic DC source, the insulation resistance and equivalent capacitance can be directly and synchronously obtained by testing two current values ​​in a single test. The leakage current and tanδ can be directly output in combination with the calculation model. The method is simple and easy to operate.

[0030] (2) Simplified hardware architecture: The inherent harmonic components of the DC high-voltage source are used as the AC excitation signal, eliminating the additional AC power supply and switching circuit in the traditional solution, reducing installation costs.

[0031] (3) Error reduction: Through filtering design and synchronous measurement, the influence of harmonics on leakage current measurement is suppressed, and data asynchrony and error accumulation caused by time-sharing measurement are avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1A schematic structural diagram of a DC cable leakage current full-band detection device based on multi-sensor fusion according to an embodiment of the present application is shown;

[0033] Figure 2 A flowchart of a full-band detection method for DC cable leakage current based on multi-sensor fusion according to an embodiment of the present application is shown.

[0034] Reference numerals:

[0035] 10. Harmonic DC source; 20. Monitoring filter module; 21. Measuring resistance; 22. Measuring capacitance; 23. First ammeter; 24. Second ammeter; 30. Cable under test; 31. First end; 32. Second end; 40. Grounding terminal; 50. Calculation module. DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present application through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0037] The specific implementation of the present application is further described in detail below with reference to the accompanying drawings and examples.

[0038] Example 1:

[0039] The embodiment of the present application provides a device for synchronously monitoring dielectric loss and leakage current of a DC cable, such as Figure 1 As shown, the device includes a harmonic DC source 10, a monitoring and filtering module 20, a cable under test 30 and a grounding terminal 40; the harmonic DC source 10 is used to output a DC high-voltage excitation containing the power frequency fundamental wave and harmonic components; the monitoring and filtering module 20 is connected in series with the cable under test 30, and the monitoring and filtering module 20 includes a measuring resistor 21 and a measuring capacitor 22 arranged in parallel, and the measuring resistor 21 and the measuring capacitor 22 are respectively connected in series with a first ammeter 23 and a second ammeter 24; the first end 31 of the cable under test 30 is connected to the monitoring and filtering module 20, and the second end 32 is respectively connected to the harmonic DC source 10 and the grounding terminal 40.

[0040] The core advantage of this device lies in its ability to simultaneously and synchronously measure two key insulation parameters: dielectric loss (tanδ) and insulation resistance, under the same excitation source (harmonic DC source). This eliminates the cumbersome and time-consuming requirements of traditional methods, which require separate application of AC and DC voltages. By superimposing a small power-frequency harmonic component on the DC high voltage, it cleverly enables the evaluation of the dielectric loss characteristics of insulation materials near the power frequency under conditions close to actual DC operating conditions, resolving the difficulty of measuring phase difference under pure DC voltage. The parallel RC branch design effectively separates DC leakage current, AC resistive loss current, and AC capacitive current by selecting appropriate R and C values. The capacitor branch provides a filtering effect on high-frequency interference, improving the accuracy of measuring the AC component. The resistor branch directly measures the current containing the DC component, accurately obtaining the cable's leakage current under high-voltage DC conditions—a direct indicator of overall insulation degradation. The device's overall structure is relatively simple and easy to implement. Consisting primarily of a standard high-voltage source, resistors, capacitors, and an ammeter, it boasts a clear structure and relatively low implementation cost, facilitating engineering applications and integration into online monitoring systems.

[0041] In some embodiments, the harmonic DC source 10 can output a power frequency fundamental wave and harmonic components (amplitude is U s , preferably 2-5th harmonic) DC high voltage (amplitude is U X )excitation.

[0042] In some embodiments, the monitoring filter module 20 includes a measuring resistor and a measuring capacitor connected in parallel, and a first ammeter 23 and a second ammeter 24 connected in series, respectively. The values ​​of the resistor and the capacitor are selected in accordance with the parameter matching criteria: where f h is the selected harmonic frequency, Rm is the resistance of the measured resistor, and Cm is the capacitance of the measured capacitor.

[0043] In some embodiments, as Figure 1 As shown, the DC cable dielectric loss and leakage current synchronous monitoring device also includes a calculation module 50. This calculation module 50 can be implemented as an existing module with data processing capabilities, such as a computer. The calculation module 50 is signal-connected to the first ammeter 23 and the second ammeter 24. The calculation module 50 is configured to calculate insulation resistance and dielectric loss tangent.

[0044] The insulation resistance calculation process includes: under the DC high voltage excitation containing the power frequency fundamental wave and harmonic components, the current on the measuring resistor 21 is measured by the first ammeter 23 to obtain the leakage current response I X and through r X =U X / I X Calculate the insulation resistance RX , where U X is the DC high voltage amplitude.

[0045] The dielectric loss tangent calculation process includes: under the DC high voltage excitation containing the power frequency fundamental wave and harmonic components, the current on the measuring capacitor 22 is measured by the second power meter 24 to obtain the AC current response I S ,use Estimate the equivalent capacitance C of the cable X The insulation resistance R obtained by the above method is X and the equivalent capacitance C of the cable X , thus through Calculate its dielectric loss tangent tanδ.

[0046] Example 2:

[0047] The embodiment of the present application provides a method for synchronously monitoring dielectric loss and leakage current of a DC cable, based on the device described in any embodiment of embodiment 1, such as Figure 2 As shown, the method includes the following steps:

[0048] Step 1: Prepare circuit connections.

[0049] according to Figure 1 Select appropriate parameters and connect the system: harmonic DC high-voltage source 10 → monitoring filter module 20 (measuring resistor 21 and measuring capacitor 22 are connected in parallel, and each is connected in series with a first ammeter 23 and a second ammeter 24) → measured cable 30 → ground terminal 40.

[0050] Step 2: Apply high voltage excitation.

[0051] Use harmonic DC high voltage source to output the power frequency fundamental wave and harmonic components (amplitude is U S , preferably 2-5th harmonic) DC high voltage (amplitude is U X )excitation.

[0052] Step 3: Leakage current test.

[0053] The current measured on the first ammeter 23 connected in series with the measuring resistor 21 is the leakage current response I X , which is the DC leakage current.

[0054] Step 4: Calculate dielectric loss.

[0055] The current measured on the second ammeter 24 connected in series with the measuring capacitor 22 is the AC current response I S , the dielectric loss is calculated by the following formula:

[0056]

[0057] Among them, C X is the equivalent capacitance of the cable, I S is the AC current response, f h is the selected harmonic frequency, U S is the harmonic component amplitude, tanv is the dielectric loss tangent, C X is the equivalent capacitance of the cable, R X is the insulation resistance.

[0058] The above implementation modes are only used to illustrate the present application and are not intended to limit the present application. Ordinary technicians in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, all equivalent technical solutions also fall within the scope of the present application, and the scope of patent protection of the present application shall be defined by the claims.

Claims

1. A device for synchronously monitoring dielectric loss and leakage current of a DC cable, characterized in that: It includes a harmonic DC source, a monitoring and filtering module, a cable under test and a ground terminal; the harmonic DC source is used to output a DC high-voltage excitation containing the power frequency fundamental wave and harmonic components; the monitoring and filtering module is connected in series with the cable under test, and the monitoring and filtering module includes a measuring resistor and a measuring capacitor arranged in parallel, and the measuring resistor and the measuring capacitor are respectively connected in series with a first ammeter and a second ammeter; the first end of the cable under test is connected to the monitoring and filtering module, and the second end is respectively connected to the harmonic DC source and the ground terminal.

2. The device for synchronously monitoring DC cable dielectric loss and leakage current according to claim 1, characterized in that: The DC high voltage amplitude output by the harmonic DC source is greater than the rated voltage of the tested cable, the harmonic components are 2nd to 5th power frequency harmonics, and the harmonic amplitude is 1% to 5% of the DC high voltage amplitude.

3. The device for synchronously monitoring dielectric loss and leakage current of a DC cable according to claim 1, characterized in that: The measuring resistance and measuring capacitance meet the parameter matching criteria: where f h is the selected harmonic frequency, Rm is the resistance of the measured resistor, and Cm is the capacitance of the measured capacitor.

4. A method for synchronously monitoring dielectric loss and leakage current of a DC cable, characterized in that: The device according to any one of claims 1 to 3 comprises the following steps: Connect the harmonic DC source, monitoring filter module, tested cable and ground terminal in sequence; Outputting a DC high-voltage excitation including the power frequency fundamental wave and harmonic components through the harmonic DC source; Acquire leakage current response through a first ammeter connected in series with a measuring resistor, and acquire AC current response through a second ammeter connected in series with a measuring capacitor; Insulation resistance and dielectric loss tangent are calculated based on the leakage current response and the AC current response.

5. The method for synchronously monitoring DC cable dielectric loss and leakage current according to claim 4, characterized in that: The frequency of the harmonic component is the 2nd to 5th power frequency harmonic frequency.

6. The method for synchronously monitoring DC cable dielectric loss and leakage current according to claim 4, characterized in that: The insulation resistance is calculated using the following formula: R X =U X / I X Among them, R X is the insulation resistance, U X is the DC high voltage amplitude, I X is the leakage current response.

7. The method for synchronously monitoring DC cable dielectric loss and leakage current according to claim 4 or 6, characterized in that: The dielectric loss tangent is calculated as follows: calculating an equivalent capacitance of the cable based on the AC current response; The dielectric loss tangent value is calculated based on the equivalent capacitance and insulation resistance of the cable.

8. The method for synchronously monitoring DC cable dielectric loss and leakage current according to claim 7, characterized in that: Based on the AC current response, the equivalent capacitance of the cable is calculated using the following formula: Among them, C X is the equivalent capacitance of the cable, I S is the AC current response, f h is the selected harmonic frequency, U S is the amplitude of the harmonic component.

9. The method for synchronously monitoring DC cable dielectric loss and leakage current according to claim 7, characterized in that: Based on the equivalent capacitance and insulation resistance of the cable, the dielectric loss tangent is calculated using the following formula: Among them, tanδ is the dielectric loss tangent value, C X is the equivalent capacitance of the cable, f h is the selected harmonic frequency, R X is the insulation resistance.

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