A device and method for monitoring dielectric loss and leakage current of a direct current cable simultaneously

Abstract

The application relates to the technical field of high-voltage direct-current cable insulation state monitoring, and discloses a device and a method for synchronously monitoring the dielectric loss and the leakage current of a direct-current cable, wherein the device comprises a harmonic direct-current source, a monitoring filter module, a measured cable and a grounding end; the harmonic direct-current source is used for outputting a direct-current high-voltage excitation containing a power frequency fundamental wave and harmonic components; the monitoring filter module is connected in series with the measured cable, the monitoring filter 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 ammeter and a second ammeter; a first end portion of the measured cable is connected with the monitoring filter module, and a second end portion is respectively connected with the harmonic direct-current source and the grounding end. The method can simultaneously monitor the leakage current and the dielectric loss of the direct-current cable, and through simplifying the system configuration, real-time online monitoring is realized, and the monitoring precision and reliability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct-current cable insulation state monitoring, and in particular to a direct-current cable dielectric loss and leakage current synchronous monitoring device and method. BACKGROUND

[0002] In modern high-voltage direct-current power transmission systems, the insulation performance of direct-current cables, as the core carrier of electric energy transmission, directly determines the safety and reliability of the power system. With the rapid development of new energy power generation, cross-regional power grid interconnection and other technologies, the application scenarios of high-voltage direct-current cables are increasing, the voltage level is continuously increasing, and the operating environment is also more complex. Under this background, accurate detection of leakage current has become a key means to evaluate the insulation state of the cable and predict potential faults.

[0003] The leakage current of a direct-current cable is often composed of a direct-current component and an alternating-current component. The main direct-current component is determined by the insulation conductance characteristic, which reflects the aging degree or moisture condition of the insulation medium. The alternating-current component includes power frequency harmonics, impulse overvoltage transient currents, and high-frequency pulse signals generated by partial discharge, with a frequency band distribution range from 50Hz to MHz. The detection of different components has complementary value for insulation state diagnosis. For example, an abnormal direct-current component may indicate overall insulation deterioration, while a high-frequency alternating-current component is closely related to partial discharge and other local defects.

[0004] However, the current traditional measurement method mostly uses a microammeter in series with the circuit to measure the leakage current of the direct-current cable, which not only makes it difficult to detect the high-frequency component of the leakage current, but also introduces additional grounding impedance, affecting the grounding structure of the direct-current cable. The industry urgently needs a detection method that can realize leakage current measurement, ensuring measurement accuracy while solving the problem of affecting the grounding system and being difficult to measure in full frequency band, to meet the needs of intelligent operation and maintenance of high-voltage direct-current cables. SUMMARY

[0005] The purpose of the present application is to provide a direct-current cable dielectric loss and leakage current synchronous monitoring device and method, which can simultaneously monitor the leakage current and dielectric loss of a direct-current cable, simplify system configuration, realize real-time online monitoring, and improve monitoring accuracy and reliability, thereby helping to better perform online monitoring and evaluation of high-voltage direct-current equipment.

[0006] To achieve the above purpose, the technical solution adopted is as follows:

[0007] In a first aspect, the application provides a device for monitoring dielectric loss and leakage current of a DC cable simultaneously, comprising a harmonic DC source, a monitoring filter module, a measured cable and a grounding terminal; the harmonic DC source is used to output a DC high voltage excitation containing a fundamental wave and harmonic components; the monitoring filter module is connected in series with the measured cable, and the monitoring filter module comprises a measurement resistor and a measurement capacitor connected in parallel, and the measurement resistor and the measurement capacitor are respectively connected in series with a first ammeter and a second ammeter; a first end of the measured cable is connected with the monitoring filter module, and a second end is respectively connected with the harmonic DC source and the grounding terminal.

[0008] Further, the DC high voltage amplitude output by the harmonic DC source is greater than the rated voltage of the measured cable, the harmonic component is a 2-5th harmonic of the fundamental frequency, and the harmonic amplitude is 1%-5% of the DC high voltage amplitude.

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

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

[0011] Connecting the harmonic DC source, the monitoring filter module, the measured cable and the grounding terminal in order;

[0012] Outputting a DC high voltage excitation containing a fundamental wave and harmonic components by the harmonic DC source;

[0013] Obtaining a leakage current response by the first ammeter connected in series with the measurement resistor, and obtaining an alternating current response by the second ammeter connected in series with the measurement capacitor;

[0014] Calculating the insulation resistance and the dielectric loss tangent value based on the leakage current response and the alternating current response.

[0015] Further, the frequency of the harmonic component is a 2-5th harmonic frequency of the fundamental frequency.

[0016] Further, the insulation resistance is calculated by the following formula:

[0017] R X = U X / I X

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

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

[0020] Based on the AC current response, the equivalent capacitance of the cable is calculated;

[0021] Based on the equivalent capacitance of the cable and the insulation resistance, the dielectric loss tangent is calculated.

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

[0023]

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

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

[0026]

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

[0028] The present application realizes high-precision synchronous measurement of DC cable leakage current and dielectric loss tangent tanδ through an innovative harmonic excitation and cooperative monitoring architecture, and has 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 through a single test of two current values, and the leakage current and tanδ can be directly outputted by combining the calculation model, which is simple and easy to operate.

[0030] (2) Simplification of hardware architecture: the inherent harmonic component of the DC high-voltage source is used as an AC excitation signal, which eliminates the additional AC power supply and switching circuit in the traditional scheme, reducing the installation cost.

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

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

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

[0034] Figure label:

[0035] 10. Harmonic DC source; 20. Monitoring and filtering module; 21. Resistor measurement; 22. Capacitor measurement; 23. First ammeter; 24. Second ammeter; 30. Cable under test; 31. First end; 32. Second end; 40. Grounding terminal; 50. Calculation module. Detailed Implementation

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

[0037] The specific implementation methods of this application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0038] Example 1:

[0039] This application provides a device for synchronously monitoring the 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 power frequency fundamental wave and harmonic components. The monitoring and filtering module 20 is connected in series with the cable under test 30. The monitoring and filtering module 20 includes a measuring resistor 21 and a measuring capacitor 22 connected in parallel. 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 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 state parameters of cables under the same excitation source (harmonic DC source): dielectric loss (tanδ) and insulation resistance. This avoids the inconvenience and time consumption of traditional methods that may require applying AC and DC voltages separately. By superimposing a small power frequency harmonic component onto the DC high voltage, it cleverly achieves the evaluation of the dielectric loss characteristics of insulation materials near the power frequency under near-actual DC operating conditions, solving the problem of being unable to measure phase difference under pure DC voltage. The parallel RC branch design, by selecting appropriate R and C values, can effectively separate DC leakage current, AC resistive loss current, and AC capacitive current. The capacitor branch has a certain filtering effect on high-frequency interference, improving the accuracy of AC component measurement. The resistor branch directly measures the current containing the DC component, accurately obtaining the leakage current value of the cable under high-voltage DC, which is a direct indicator for assessing overall insulation degradation. The overall structure of the device is relatively simple and easy to implement. It mainly includes a standard high-voltage source, resistor, capacitor, and ammeter. The structure is clear, the implementation cost is relatively low, and it is easy to apply in engineering and integrate into online monitoring systems.

[0041] In some embodiments, the harmonic DC source 10 can output a power frequency fundamental wave and harmonic components (with an amplitude of U). s Ideally, a DC high voltage (amplitude U) with 2nd-5th harmonics is required. 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 selection of the values ​​of the resistor and capacitor conforms to the parameter matching criteria. Where f h Rm is the selected harmonic frequency, Cm is the resistance value of the measuring resistor, and Cm is the capacitance value of the measuring capacitor.

[0043] In some embodiments, such 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 data processing module, such as a computer. The calculation module 50 is connected to the first ammeter 23 and the second ammeter 24, and is configured to calculate insulation resistance and dielectric loss tangent.

[0044] The insulation resistance calculation process includes: under DC high-voltage excitation containing power frequency fundamental and harmonic components, measuring the current across resistor 21 using 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 U X This represents the amplitude of a DC high voltage.

[0045] The calculation process for the dielectric loss tangent includes: under DC high-voltage excitation containing power frequency fundamental and harmonic components, measuring the current on the measuring capacitor 22 through 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 X The equivalent capacitance C of the cable X Thus through Calculate the tangent of its dielectric loss angle, tanδ.

[0046] Example 2:

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

[0048] Step 1, Circuit connection preparation.

[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) → Cable under test 30 → Grounding terminal 40.

[0050] Step 2: Apply high-pressure excitation.

[0051] The output of the harmonic DC high voltage source includes the fundamental frequency and harmonic components (amplitude U). S Ideally, a DC high voltage (amplitude U) with 2nd-5th harmonics is required. X )excitation.

[0052] Step 3, leakage current test.

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

[0054] Step 4, calculate dielectric loss.

[0055] The current measured at this time on the second ammeter 24 connected in series with the measuring capacitor 22 is the alternating current response I. S The dielectric loss is calculated using the following formula:

[0056]

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

[0058] The above embodiments are only used to illustrate this application and are not intended to limit this application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this application. Therefore, all equivalent technical solutions also fall within the scope of this application, and the patent protection scope of this application should be defined by the claims.

Claims

1. A device for simultaneous monitoring of dielectric loss and leakage current of a DC cable, characterized in that The harmonic DC source is used for outputting DC high voltage excitation containing fundamental wave and harmonic component of power frequency; the monitoring filter module is connected in series with the measured cable, and the monitoring filter 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 ammeter and a second ammeter; the first end of the measured cable is connected with the monitoring filter module, and the second end is respectively connected with the harmonic DC source and the grounding end.

2. The apparatus for monitoring the dielectric loss and the leakage current of a DC cable in synchronization according to claim 1, characterized by, The DC high voltage amplitude output by the harmonic DC source is greater than the rated voltage of the measured cable, the harmonic component is 2-5 times of the fundamental wave of power frequency, and the harmonic amplitude is 1%-5% of the DC high voltage amplitude.

3. The apparatus for monitoring the dielectric loss and the leakage current of a DC cable in synchronization according to claim 1, characterized by, The measurement resistance and the measurement capacitance satisfy a parameter matching criterion: where f h is the selected harmonic frequency, Rm is the resistance value of the measurement resistance, and Cm is the capacitance value of the measurement capacitance.

4. A method for simultaneous monitoring of dielectric loss and leakage current of a DC cable, characterized by The device based on any one of claims 1 to 3, comprising the following steps: sequentially connecting the harmonic DC source, the monitoring filter module, the measured cable and the grounding end; outputting, by the harmonic DC source, DC high voltage excitation containing fundamental wave and harmonic component of power frequency; obtaining, by the first ammeter connected in series with the measuring resistor, a leakage current response, and obtaining, by the second ammeter connected in series with the measuring capacitor, an alternating current response; calculating, based on the leakage current response and the alternating current response, insulation resistance and dielectric loss tangent value.

5. The method for monitoring the dielectric loss and the leakage current of a DC cable in synchronization according to claim 4, characterized in that, The frequency of the harmonic component is 2-5 times of the fundamental wave frequency of power frequency.

6. The method for monitoring the dielectric loss and the leakage current of a DC cable in synchronization according to claim 4, characterized in that, The insulation resistance is calculated by the following formula: R X =U X / I X wherein 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 monitoring the dielectric loss and the leakage current of a DC cable in synchronization according to claim 4 or 6, characterized in that, The dielectric loss tangent value is calculated by the following method: calculating, based on the alternating current response, the equivalent capacitance of the cable; calculating, based on the equivalent capacitance of the cable and the insulation resistance, the dielectric loss tangent value.

8. The method for monitoring the dielectric loss and the leakage current of a DC cable in synchronization according to claim 7, characterized in that, The equivalent capacitance of the cable is calculated by the following formula based on the alternating current response: where 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.

9. The method for monitoring the dielectric loss and the leakage current of a DC cable in synchronization according to claim 7, characterized in that, The dielectric loss tangent value is calculated by the following formula based on the equivalent capacitance of the cable and the insulation resistance: where tan δ is the dielectric loss tangent, C X is the equivalent capacitance of the cable, f h is the selected harmonic frequency, R X is the insulation resistance.

Images