A high-voltage cable built-in partial discharge on-line monitoring device and application method

Abstract

The application discloses a high-voltage cable built-in partial discharge on-line monitoring device and an application method. The high-voltage cable built-in partial discharge on-line monitoring device comprises a device body, a partial discharge detection antenna and a circuit board. The device body is used for being mounted on a cable accessory protection shell of a high-voltage cable. The partial discharge detection antenna is arranged inside the cable accessory protection shell and is used for detecting an electric field distribution formed after a partial discharge signal transmitted by a cable core of the high-voltage cable passes through an inner semi-conductive layer, main cable insulation and an outer semi-conductive layer. The circuit board is arranged in the device body. A signal transmission circuit is arranged on the circuit board. The partial discharge detection antenna is connected with the signal transmission circuit on the circuit board. The application aims to realize accurate and effective monitoring of a partial discharge signal and evaluate an insulation state of the high-voltage cable and accessories in operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of built-in partial discharge signal detection of high-voltage cable, in particular to a built-in partial discharge on-line monitoring device of high-voltage cable and application method. BACKGROUND

[0002] In recent years, with the continuous acceleration of urbanization process, the cableization rate of power grid is rising, and cross-linked polyethylene power cable (XLPE cable for short) is widely used in cable lines due to its superior electrical performance, good heat resistance and mechanical properties. The production quality of the cable body and accessories (insulation resistance, breakdown strength, dielectric constant, dielectric loss, thermal performance, etc. of the insulation material), laying and installation technology level, installation and operation environment (humidity, dust, temperature change, etc.) will all affect the insulation condition of the cable, especially the cable accessories have become the weak link of the insulation of high-voltage cable lines and the typical part of operation failure. Partial discharge is one of the main causes of insulation deterioration and is the main characteristic quantity representing the insulation condition. When partial discharge occurs in the cable body, the signal will be coupled to the cable grounding loop. The traditional high-frequency partial discharge detection collects the pulse current signal generated by partial discharge on the cable grounding loop through a through-current sensor. The sensor of the partial discharge monitoring device is a certain distance away from the cable body, and the existence of the cable grounding metal sheath shields part of the partial discharge signal. The coupled partial discharge signal is weak, and there is electromagnetic interference in the field. A large number of operation experiences of partial discharge monitoring devices show that the partial discharge detection effect is not ideal. SUMMARY

[0003] The technical problem to be solved by the present application: in view of the above problems of the prior art, a built-in partial discharge on-line monitoring device of high-voltage cable and application method are provided, and the present application aims to realize accurate and effective monitoring of partial discharge signals and evaluate the operation insulation state of high-voltage cables and accessories.

[0004] In order to solve the above technical problems, the technical scheme adopted by the present application is:

[0005] A built-in partial discharge on-line monitoring device of high-voltage cable, comprising a device body, a partial discharge detection antenna and a circuit board, the device body is used for being installed on a cable accessory protection shell of a high-voltage cable, the connection part of the high-voltage cable in the middle of the cable accessory protection shell removes the buffer layer, corrugated aluminum sheath and outer insulation of the high-voltage cable and retains the cable core, inner semi-conductive layer, cable main insulation and outer semi-conductive layer, the partial discharge detection antenna is arranged inside the cable accessory protection shell for detecting the electric field distribution formed by the partial discharge signal transmitted by the cable core of the high-voltage cable after passing through the inner semi-conductive layer, cable main insulation and outer semi-conductive layer, the circuit board is arranged in the device body, a signal transmitting circuit is arranged on the circuit board, and the partial discharge detection antenna and the signal transmitting circuit on the circuit board are connected.

[0006] Optionally, the signal transmission circuit on the circuit board is a wireless signal transmission circuit, and a communication antenna is installed on the device body, which is connected to the wireless signal transmission circuit.

[0007] Optionally, the device body includes an upper shell and a connector. The cable accessory protective shell is provided with a mounting flange. The upper shell is mounted on the mounting flange through the connector. The partial discharge detection antenna passes through the mounting flange and is installed inside the cable accessory protective shell.

[0008] Optionally, the cable accessory protective shell includes a middle section shell and end shells located on both sides of the middle section shell. An accessory partition is provided between the middle section shell and the end shells, and a lead seal is provided at the outer end of the end shells to keep the interior of the middle section shell and the end shells sealed. The device body is used to be installed on the end shells of the cable accessory protective shell.

[0009] Optionally, the partial discharge detection antenna is a double-sided helical antenna.

[0010] Optionally, the double-sided helical antenna includes a substrate and helical antennas with the same shape and overlapping on the front and back sides of the substrate, respectively. The terminals on the inner side of the helical antennas on both sides are connected through vias on the substrate, and the terminals on the outer side are connected to the circuit board.

[0011] Furthermore, the present invention also provides an application method for the aforementioned high-voltage cable built-in partial discharge online monitoring device, comprising the following steps in designing a partial discharge detection antenna:

[0012] S1, extract the electrical parameters of the high-voltage cable per unit length, including resistance R, inductance L and capacitance C;

[0013] S2, based on the electrical parameters of a high-voltage cable per unit length, establishes a length of... l The distributed cable model of high-voltage cables, and based on the length of... l The transfer function of the high-voltage cable is calculated using a distributed cable model.

[0014] S3, the length is calculated based on the transfer function of the high-voltage cable. l The 3dB bandwidth of the high-voltage cable, where 3dB bandwidth refers to the output signal amplitude attenuated to the input signal amplitude. The frequency width corresponding to a multiple;

[0015] S4, with length as lThe 3dB bandwidth of the high-voltage cable is used as the upper limit of the center frequency of the partial discharge detection antenna. The structural parameters of the partial discharge detection antenna are simulated and adjusted in combination with the installation position and installation distance of the partial discharge detection antenna, so as to obtain the structural parameters of the partial discharge detection antenna that meet the center frequency requirements, including the material, radius and thickness of the substrate, the inner circle radius, outer circle radius, number of spirals, line width and line spacing of the spiral antenna.

[0016] Optionally, in step S2, a length of [length missing] is established. l The distributed cable model of high-voltage cables includes resistance R. m,1 ~resistance R m,N and capacitor C m,1 ~Capacitor C m,N resistance R m,1 ~resistance R m,N The capacitance C represents the resistance of the first to Nth unit lengths of cable. m,1 ~Capacitor C m,N The capacitance and resistance R of the first to Nth unit lengths of cable are represented. m,1 ~resistance R m,N Connected in series, any capacitor C m,1 One end is connected to resistor R m,1 One end is grounded and the other end is grounded.

[0017] Optionally, in step S2, based on the length as l The transfer function of the high-voltage cable, calculated using a distributed cable model, is expressed as follows:

[0018] ,

[0019] In the above formula, For transfer functions, The resistance per unit length of cable. The capacitance per unit length of cable. For length is l The number of high-voltage cables per unit length. The unit length sequence number For the Laplace operator.

[0020] Optionally, in step S3, the length of the high-voltage cable is calculated based on its transfer function. l The functional expression for the 3dB bandwidth of a high-voltage cable is:

[0021] ,

[0022] In the above formula, For length is l The 3dB bandwidth of the high-voltage cable The resistance per unit length of cable. Capacitance per unit length of cable, Capacitance per unit length of high-voltage cable, l Number per unit length of high-voltage cable, Serial number per unit length.

[0023] Optionally, after step S4, further comprising selecting a matching circuit from the plurality of preset matching circuits, so that the input reflection coefficient of the partial discharge detection antenna is minimized, so that the center frequency of the partial discharge detection antenna can be adjusted within the 3dB bandwidth range of the high-voltage cable and the input reflection coefficient is minimized.

[0024] Compared with the prior art, the present application mainly has the following advantages:

[0025] 1. The partial discharge detection antenna of the present application is arranged inside the cable accessory protection shell for detecting the electric field distribution formed by the partial discharge signal transmitted by the cable core of the high-voltage cable after passing through the inner semi-conductive layer and the cable main insulation. The partial discharge signal is directly received by the built-in partial discharge detection antenna, so that the detection sensitivity and accuracy are high. The pulse current method, high-frequency current method and other methods are affected by the propagation channel of the partial discharge signal, and cannot realize direct detection of the partial discharge signal.

[0026] 2. Since the accessory is the part of the cable that is most prone to insulation defects, the present application reserves a flange interface for installing the partial discharge detection antenna at the lead sealing position of the cable terminal and intermediate joint (cable accessory protection shell), which is beneficial for sensitive acquisition of the cable partial discharge signal, and at the same time avoids damaging the structure of the cable body. DETAILED DESCRIPTION

[0027] Figure 1 The figure is a structural schematic diagram of the device in the embodiment of the present application.

[0028] Figure 2 The figure is a partial sectional structural schematic diagram of the device in the embodiment of the present application.

[0029] Figure 3 The figure is a structural schematic diagram of the partial discharge detection antenna in the embodiment of the present application.

[0030] Figure 4 The figure is a flowchart of the application method of the partial discharge detection antenna in the embodiment of the present application.

[0031] Figure 5 The figure is an electric field distribution diagram of the cable in the embodiment of the present application.

[0032] Figure 6 The figure is an electric field distribution diagram of the cable main insulation layer and the outer semi-conductive layer in the embodiment of the present application.

[0033] Figure 7 The figure is a schematic diagram of the distributed model of the cable in the embodiment of the present application.

[0034] Legend: 1, device body; 10, communication antenna; 11, upper shell; 12, connecting piece; 2, partial discharge detection antenna; 21, base plate; 22, spiral antenna; 3, circuit board; 4, high-voltage cable; 41, cable core wire; 42, inner semi-conductive layer; 43, cable main insulation; 44, outer semi-conductive layer; 45, buffer layer; 46, corrugated aluminum sheath; 47, outer insulation; 5, cable accessory protection shell; 51, mounting flange. DETAILED DESCRIPTION

[0035] The embodiments of the present application will be described in detail below with reference to the accompanying drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are for the purpose of explaining the present application only, and should not be understood as limiting the present application. In the description of the present application, if there is a description to first, second, etc., it is only for the purpose of distinguishing technical features and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features. If there is a description of orientation, such as upper, lower, etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, the above orientation description is only for the purpose of facilitating the description of the present application and simplifying the description, and should not be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be understood as limiting the present application. Unless otherwise explicitly defined, the terms disposed, mounted, connected, etc. in the description of the present application should be broadly interpreted, and the skilled person in the art can reasonably determine the specific meaning of the above terms in the present application in combination with the specific content of the technical solution.

[0036] As shown in Figure 1 and Figure 2 , the high-voltage cable built-in partial discharge on-line monitoring device of the present embodiment includes a device body 1, a partial discharge detection antenna 2 and a circuit board 3, the device body 1 is used to be mounted on the cable accessory protection shell 5 of the high-voltage cable 4, the connecting part of the high-voltage cable 4 in the middle of the cable accessory protection shell 5 removes the buffer layer 45, the corrugated aluminum sheath 46 and the outer insulation 47 of the high-voltage cable 4 and retains the cable core wire 41, the inner semi-conductive layer 42, the cable main insulation 43 and the outer semi-conductive layer 44, the partial discharge detection antenna 2 is arranged inside the cable accessory protection shell 5 for detecting the electric field distribution formed after the partial discharge signal transmitted by the cable core wire 41 of the high-voltage cable 4 passes through the inner semi-conductive layer 42, the cable main insulation 43 and the outer semi-conductive layer 44, the circuit board 3 is provided in the device body 1, the circuit board 3 is provided with a signal transmitting circuit, and the partial discharge detection antenna 2 and the signal transmitting circuit on the circuit board 3 are connected. Outside the cable main insulation 43 and the outer semi-conductive layer 44 of the high-voltage cable 4, there is electromagnetic radiation of the partial discharge signal, and this signal radiation can effectively detect the internal partial discharge signal of the cable.

[0037] like Figure 1 As shown, in this embodiment, the signal transmission circuit on the circuit board 3 is a wireless signal transmission circuit, and the device body 1 is equipped with a communication antenna 10, which is connected to the wireless signal transmission circuit.

[0038] like Figure 1 As shown, in this embodiment, the device body 1 includes an upper shell 11 and a connector 12. The cable accessory protective shell 5 is provided with a mounting flange 51. The upper shell 11 is mounted on the mounting flange 51 via the connector 12. The partial discharge detection antenna 2 passes through the mounting flange 51 and is installed inside the cable accessory protective shell 5. The cable accessory protective shell 5 has a pre-installed mounting flange 51, allowing for convenient installation of the partial discharge detection antenna 2. In this embodiment, the mounting flange 51 for installing the partial discharge detection antenna 2 is made of copper rod, machined into an integral flange shape and welded. After machining, the wall thickness is 20mm, capable of withstanding external forces during normal use. The connector 12 between the upper shell 11 and the cable accessory protective shell 5 is made of POM (polypropylene) steel with excellent insulation properties. The interface is filled and covered with high-performance insulating material to ensure that the insulation performance is not affected. A double-layer sealing ring structure is designed on the flange to prevent impurities from entering.

[0039] like Figure 3 As shown, in this embodiment, the partial discharge detection antenna 2 is a double-sided spiral antenna. The double-sided spiral antenna includes a substrate 21 and spiral antennas 22 with the same shape and overlapping on the front and back sides of the substrate 21, respectively. The terminals on the inner side of the spiral antennas 22 on both sides are connected through the vias on the substrate 21, and the terminals on the outer side are connected to the circuit board 3.

[0040] In addition, such as Figure 4 As shown, this embodiment also provides an application method for a high-voltage cable-embedded partial discharge online monitoring device, including the following steps in designing the partial discharge detection antenna 2:

[0041] S1, extract the electrical parameters of the high-voltage cable 4 per unit length, including resistance R, inductance L and capacitance C;

[0042] S2, based on the electrical parameters of the high-voltage cable 4 per unit length, establishes a length of... l The distributed cable model of high-voltage cable 4, and based on the length of... l The transfer function of high-voltage cable 4 was calculated using a cable distributed model.

[0043] S3, the length is calculated based on the transfer function of high-voltage cable 4. l The 3dB bandwidth of the high-voltage cable 4, wherein the 3dB bandwidth refers to the output signal amplitude attenuated to the input signal amplitude. The frequency width corresponding to a multiple;

[0044] S4, the 3dB bandwidth of the high-voltage cable 4 with a length of l as the upper limit of the center frequency of the partial discharge detection antenna 2, and the installation position and distance of the partial discharge detection antenna 2 are simulated and adjusted to obtain the structural parameters of the partial discharge detection antenna 2 with a center frequency meeting the requirements, including the material, radius and thickness of the substrate, the inner radius, outer radius, number of spirals, wire width and wire spacing of the spiral antenna.

[0045] In step S1 of the embodiment, the electrical parameters of the unit length of the high-voltage cable 4 are extracted by simulation, and in addition, they can also be obtained by measurement or by consulting the factory data as needed. In this embodiment, according to the structural characteristic parameters of the XLPE high-voltage cable (the sizes of the copper conductor, the inner shielding layer of the main insulation, the main insulation, the outer semiconductive layer of the main insulation, the water-blocking belt, etc.), the dielectric constant ɛ r , the thermal conductivity λ, the thermal expansion coefficient α, the elastic modulus E, and the Poisson's ratio), the cable partial discharge signal transmission characteristics are obtained by modeling and simulation, and the resistance R, the inductance L, and the capacitance C of the unit length of the XLPE high-voltage cable are extracted. The obtained cable cross-section electric field distribution is shown in Figure 5 , and the electric field distribution of the outer semiconductive layer of the cable main insulation is shown in Figure 6 . As can be seen from Figure 5 and Figure 6 , the electric field strength gradually weakens from the cable core wire 41 to the outer semiconductive layer 44, and after passing through the cable main insulation 43, there is still an electric field, which means that it is feasible to design the partial discharge detection antenna 2 to receive the partial discharge signal transmitted by the cable outside the cable main insulation 43, and the partial discharge signal can be effectively detected outside the cable main insulation 43 of the high-voltage cable.

[0046] In step S2 of the embodiment, a cable distributed model of the high-voltage cable 4 with a length of l is established based on the electrical parameters of the unit length of the high-voltage cable 4, as shown in Figure 7 . In step S2 of the embodiment, the cable distributed model of the high-voltage cable 4 with a length of l includes resistances R m,1 ~ R m,N and capacitances C m,1 ~ C m,N , the resistances R m,1 ~ R m,N represent the resistances of the 1st~Nth unit length of the cable, the capacitances C m,1 ~ C m,N represent the capacitances of the 1st~Nth unit length of the cable, and the resistances R m,1 ~ R m,N are connected in series, and any capacitance C m,1 is connected at one endm,1 One end is grounded and the other end is grounded. Figure 7 The transfer function of the cable distributed model shown It can be represented as:

[0047] ,

[0048] In the above formula, ~ The coefficients of the denominator polynomial in the transfer function. For length is l The number of high-voltage cables per unit length 4 This is the Laplace operator. For a given capacitance C... m,i and resistance R m,i ,have:

[0049] ,

[0050] That is, transfer function In addition to the Laplace operator One item In addition, the Laplace operator The higher-order terms are all much smaller than 1e when N (cable length) is greater than 100. -6 , can be ignored, and have:

[0051] .

[0052] Therefore, in step S2 of this embodiment, the length is... l The transfer function of high-voltage cable 4, calculated using the cable distribution model, can be approximated as follows:

[0053] ,

[0054] In the above formula, For transfer functions, The resistance per unit length of cable. The capacitance per unit length of cable. For length is l The number of high-voltage cables per unit length 4 The unit length sequence number For the Laplace operator.

[0055] In step S3 of this embodiment, the length is calculated based on the transfer function of the high-voltage cable 4. l The functional expression for the 3dB bandwidth of the high-voltage cable 4 is:

[0056] ,

[0057] In the above formula, the 3dB bandwidth of the high-voltage cable 4 of length l , the resistance per unit length of the cable, the capacitance per unit length of the cable, the number of units of length of the high-voltage cable 4 of length l , the serial number per unit length.

[0058] The structure parameters (cable length > 100 meters) of the cable partial discharge detection antenna 2 of the center frequency meeting the requirements and the model ZC-YJLW03-Z 64 / 110 1*800 obtained by the embodiment step S4 include the material, radius and thickness of the substrate 21, the inner circle radius, outer circle radius, spiral number, wire width and wire spacing of the spiral antenna 22. Specifically, the finally optimized inner circle radius is 9mm, the outer circle radius is 24mm, the radius of the substrate is 26mm, and FR4 material is used. There are 19 turns of spiral on each side of the substrate 21 (the spiral number is 19), the wire width is 0.3947mm, the wire spacing is 0.35mm, and the substrate thickness is 1.6mm. In the case of top view, the shapes of the spiral antennas 22 on both sides are completely coincident. The inner circle starting point is connected to the inner circle end point of the spiral on the other side by a via hole. At the outer circle end point, the back trace is slightly longer, and about 2mm lead is connected to the terminal on the front and back respectively. The PCB board material with good conductivity and convenient processing is selected to manufacture the substrate 21 of the partial discharge detection antenna 2, so as to ensure that the antenna can efficiently receive the partial discharge signal and has the convenience of installation.

[0059] As shown in Figure 4 , as an optional implementation, after step S4, it further includes selecting a matching circuit in a plurality of preset matching circuits, so that the input reflection coefficient of the partial discharge detection antenna 2 is the smallest, so that the center frequency of the partial discharge detection antenna 2 can be adjusted within the 3dB bandwidth of the high-voltage cable 4 and the input reflection coefficient is the smallest. The matching circuit here refers to the detection circuit of the partial discharge detection antenna 2.

[0060] The high-voltage cable built-in partial discharge on-line monitoring device of the embodiment can accurately monitor the partial discharge signal inside the cable body. As an optional implementation, the application method of the high-voltage cable built-in partial discharge on-line monitoring device of the embodiment further includes: acquiring the waveform features of the partial discharge signal, and inputting the waveform features of the partial discharge signal into a pre-trained machine learning model to obtain the type of the partial discharge signal. The machine learning model is pre-trained to establish a mapping relationship between the waveform features of the partial discharge signal and the type of the partial discharge signal. The waveform features of the partial discharge signal include part or all of the following features: pulse peak value, which is the maximum amplitude of the pulse signal and can be measured by an oscilloscope; peak time, which is the phase when the pulse occurs and can be measured by an oscilloscope; pulse rise time, which is the time required for the pulse to rise from 10% to 90% of the maximum amplitude; fall time, which is the time required for the pulse to fall from 90% to 10% of the maximum amplitude; pulse width, which is the duration of the pulse, usually starting from 10% of the maximum amplitude of the rising edge to ending at 10% of the maximum amplitude of the falling edge; 50% maximum pulse duration, which is a measure of pulse width, starting from 50% of the maximum amplitude of the rising edge to ending at 50% of the maximum amplitude of the falling edge; phase resolution partial discharge spectrum, which can reflect the relationship between the number of discharges, discharge amount, etc. and the phase in multiple cycles; pulse amplitude distribution, which is the amplitude distribution feature of the pulse signal and can be used to identify the type of multi-discharge source. The machine learning model can use a support vector machine or a deep learning neural network model.

[0061] As an optional implementation, the high-voltage cable built-in partial discharge on-line monitoring device of the embodiment is installed at the line terminal and the intermediate joint of the high-voltage cable 4. The application method of the high-voltage cable built-in partial discharge on-line monitoring device of the embodiment further includes positioning the cable insulation defect position according to the partial discharge waveform time and amplitude size collected by the high-voltage cable built-in partial discharge on-line monitoring devices at the two line terminals of the high-voltage cable 4.

[0062] The above is only a preferred embodiment of the present application, and the protection scope of the present application is not limited to the above embodiment. Any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled persons in the technical field, some improvements and refinements without departing from the principles of the present application shall also be considered as the protection scope of the present application.

Claims

1. A method of using a built-in partial discharge on-line monitoring device for high voltage cables, characterized in that, The high-voltage cable built-in partial discharge on-line monitoring device comprises a device body (1), a partial discharge detection antenna (2) and a circuit board (3), the device body (1) is used for being installed on a cable accessory protection shell (5) of a high-voltage cable (4), the connection part of the high-voltage cable (4) at the middle part of the cable accessory protection shell (5) removes a buffer layer (45), a corrugated aluminum sheath (46) and an outer layer insulation (47) and retains a cable core wire (41), an inner semi-conductive layer (42), a cable main insulation (43) and an outer semi-conductive layer (44), the partial discharge detection antenna (2) is arranged inside the cable accessory protection shell (5) and is used for detecting an electric field distribution formed by a partial discharge signal transmitted by the cable core wire (41) of the high-voltage cable (4) after passing through the inner semi-conductive layer (42), the cable main insulation (43) and the outer semi-conductive layer (44), the circuit board (3) is arranged in the device body (1), a signal transmission circuit is arranged on the circuit board (3), and the partial discharge detection antenna (2) and the signal transmission circuit on the circuit board (3) are connected; the partial discharge detection antenna (2) is a double-sided spiral antenna; the double-sided spiral antenna comprises a substrate (21) and spiral antennas (22) arranged on the front and back surfaces of the substrate (21) and having the same shape and being overlapped with each other, and the terminals inside the spiral antennas (22) on the two surfaces are connected through a via hole on the substrate (21), and the terminals outside the spiral antennas (22) are connected with the circuit board (3); the application method comprises the following steps of designing the partial discharge detection antenna (2): S1, extracting the electrical parameters of the high-voltage cable (4) per unit length, including resistance R, inductance L and capacitance C; S2, establishing a cable distributed model of the high-voltage cable (4) with a length of l based on the electrical parameters of the high-voltage cable (4) per unit length, and calculating a transfer function of the high-voltage cable (4) according to the cable distributed model of the high-voltage cable (4) with a length of l ​ S3, a 3dB bandwidth of the high-voltage cable (4) having a length of l is calculated from a transfer function of the high-voltage cable (4), the 3dB bandwidth referring to a frequency width at which an output signal amplitude is attenuated to times an input signal. S4, the 3dB bandwidth of the high-voltage cable (4) with a length of l The 3dB bandwidth of the high-voltage cable (4) with a length of 100km is taken as the upper limit of the center frequency of the partial discharge detection antenna (2), and the structure parameters of the partial discharge detection antenna (2) are simulated and adjusted in combination with the installation position and installation distance of the partial discharge detection antenna (2), so as to obtain the structure parameters of the partial discharge detection antenna (2) with a center frequency meeting the requirements, including the material, radius and thickness of the substrate (21), the inner circle radius, outer circle radius, spiral number, line width and line spacing of the spiral antenna (22).

2. The method of using the built-in partial discharge on-line monitoring device of high voltage cable according to claim 1, characterized in that, The signal transmission circuit on the circuit board (3) is a wireless signal transmission circuit, a communication antenna (10) is arranged on the device body (1), and the communication antenna (10) is connected with the wireless signal transmission circuit.

3. The method of using the built-in partial discharge on-line monitoring device for high voltage cable according to claim 1, characterized in that, The device body (1) comprises an upper shell (11) and a connecting piece (12), the cable accessory protection shell (5) is provided with a mounting flange (51), the upper shell (11) is mounted on the mounting flange (51) through the connecting piece (12), and the partial discharge detection antenna (2) is mounted inside the cable accessory protection shell (5) after penetrating through the mounting flange (51).

4. The method of using the built-in partial discharge on-line monitoring device for high voltage cable according to claim 1, characterized in that, The cable distributed model of the high voltage cable (4) of the length of l established in step S2 includes resistors R m,1 ~ R m,N and capacitors C m,1 ~ C m,N , the resistors R m,1 ~ R m,N represent the resistances of the 1st~Nth unit length cable, the capacitors C m,1 ~ C m,N represent the capacitances of the 1st~Nth unit length cable, the resistors R m,1 ~ R m,N are connected in series in turn, and any capacitor C m,1 has one end connected to one end of the resistor R m,1 and the other end grounded.

5. The method of using a high voltage cable built-in partial discharge on-line monitoring device according to claim 4, characterized in that, The function expression of the transfer function of the high-voltage cable (4) calculated in step S2 according to the cable distributed model of the high-voltage cable (4) with the length of l is: ， In the above formulae, is the transfer function, is the resistance per unit length of the cable, is the capacitance per unit length of the cable, is the number of units of length of the high-voltage cable (4) of length l is the unit length number, is the unit length number, is the Laplace operator.

6. The method of using the built-in partial discharge on-line monitoring device of high voltage cable according to claim 4, characterized in that, The function expression of the 3dB bandwidth of the high-voltage cable (4) with the length of l is calculated in step S3 according to the transfer function of the high-voltage cable (4) ， In the above formula, For length is l The 3dB bandwidth of the high-voltage cable (4), The resistance per unit length of cable. The capacitance per unit length of cable. For length is l The number of high-voltage cables (4) per unit length, The unit length number.

7. The method of using the apparatus for on-line partial discharge monitoring of high voltage cables according to claim 1, characterized in that, After step S4, the following step is further included: selecting a matching circuit that makes the input reflection coefficient of the partial discharge detection antenna (2) minimum from a plurality of preset matching circuits, so that the center frequency of the partial discharge detection antenna (2) can be adjusted within the 3dB bandwidth range of the high-voltage cable (4) and the input reflection coefficient is minimum.

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