CN114325106A

CN114325106A - Low-frequency cylinder testing tool of three-coaxial-method cable shielding effectiveness testing system

Info

Publication number: CN114325106A
Application number: CN202210023581.5A
Authority: CN
Inventors: 赵大勇; 杨润泽
Original assignee: SHANGHAI LINGSHI ELECTROMAGNETIC TECHNOLOGY CO LTD
Current assignee: SHANGHAI LINGSHI ELECTROMAGNETIC TECHNOLOGY CO LTD
Priority date: 2021-11-15
Filing date: 2022-01-10
Publication date: 2022-04-12
Also published as: CN217820596U; CN217820584U; CN114325132A

Abstract

The invention provides a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system. The low-frequency cylinder testing tool comprises an outer loop near-end short circuit structure, a shielding cap structure and a metal cylinder structure, wherein the outer loop near-end short circuit structure comprises an end cover, a short circuit clamping piece, a second chuck seat, a second elastic chuck and a second chuck nut; the shield cap structure includes an inner loop distal shield box, an outer loop distal assembly, a support assembly, and a connector.

Description

Low-frequency cylinder testing tool of three-coaxial-method cable shielding effectiveness testing system

Technical Field

The invention belongs to the field of electrical measurement technology and instruments, and particularly relates to a low-frequency cylinder test tool of a cable shielding effectiveness test system based on a three-coaxial method.

Background

The research patents distributed in the fields of electric automobiles, aerospace, ships and the like, relating to cable shielding effectiveness evaluation exist in China, a high-frequency band test system aiming at the shielding effectiveness of radio frequency coaxial cables based on a triple-axis method is provided, and the system is also in blank areas in the field of high-voltage shielding cables of rail transit.

In practice, users often need to know the shielding effectiveness of the cable in order to use and design. Since the shielding layer structure of the shielded cable is various, and the shielding effectiveness of the cable can only be ideally analyzed. If the cable shielding effectiveness can be directly obtained through testing aiming at the shielding cables with different specifications, accurate investigation basis can be provided when the shielding cables are evaluated, compared, designed and used in engineering.

The cable shielding effectiveness testing method and system are basically implemented by slightly changing or even not changing based on an IEC standard method, the changing positions are mostly concentrated on input and output interfaces, the improvement schemes of the characteristics of the input and output interfaces of the testing equipment are more, but the prior art scheme with flexible operation and simple structure is less.

Related research of a cable shielding effectiveness analysis algorithm is only related to Hunan university at present, adjustment is carried out on a surface transfer impedance model of a foreign keyli scholars, and related published technical schemes are still rare.

The control software of the cable shielding effectiveness test system only has winCOMET software of Rosenberger in the industry at present, but has no published prior art data.

Disclosure of Invention

In order to overcome the technical defects in the prior art and improve the scientificity and accuracy of measurement, the design of the short-circuit structure at the near end of the outer loop, the shielding cap structure at the far end of the outer loop and the insulating support structure is simplified, and the flexibility and convenience of use are improved, so that the low-frequency cylinder testing tool of the low-frequency three-coaxial-method cable shielding effectiveness testing system is provided.

The invention provides a low-frequency cylinder testing tool which is a component of a three-coaxial cable shielding effectiveness testing system. The low-frequency cylinder test tool is mainly applied to testing the transfer impedance of a tested cable (high-voltage cable) when the frequency is less than 30 MHz.

The testing principle of the low-frequency cylinder testing tool is a short-circuit-matching three-coaxial method, namely, the near end of an outer loop is short-circuited, and the terminal of an inner loop is connected with a matching resistor.

The low-frequency test system comprises a vector network analyzer, a tested cable, an inner loop injection structure (tool), a low-frequency cylinder test tool, an outer loop far-end matching resistance structure (tool) and a metal cylinder supporting structure.

On the one hand, provide this test system's low frequency drum test fixture. The low-frequency cylinder testing tool consists of an outer loop near-end short circuit structure, a metal cylinder and a shielding cap structure, wherein the outer loop near-end short circuit structure comprises an end cover, a short circuit clamping piece, a second chuck seat, a second elastic chuck and a second chuck nut; the shielding cap structure comprises an inner loop far-end shielding box, an outer loop far-end assembly, a supporting assembly and a connector;

the end cover is arranged on one side of the metal cylinder, preferably a threaded end cover, and is matched with threads arranged on one side of the metal cylinder; the short circuit clamping piece is arranged on the inner side of the end cover and is used for fixedly clamping one end of a tested cable and is in contact with the cable shielding layer; the second chuck seat is coaxially arranged on the short circuit clip; the second chuck nut is arranged on the second chuck seat, and an elastic second chuck is arranged between the second chuck seat and the second chuck nut; the outer loop far-end assembly is arranged on the other side of the metal cylinder, and the inner loop far-end shielding box and the supporting assembly are arranged in the outer loop far-end assembly; the far-end shielding box of the inner loop fixedly clamps the other end of the tested cable; the supporting component is used for fixing the inner loop far-end shielding box in the outer loop far-end component;

preferably, the short circuit clamping piece is used for clamping and fixing one end of the tested cable and is in contact with the shielding layer of the tested cable; the far-end shielding box of the inner loop clamps and fixes the other end of the tested cable;

preferably, the inner loop far-end shielding box comprises a first chuck screw cap, a first elastic chuck, a first chuck seat, a connecting plate and an electrical appliance connector pin; the first chuck seat is connected with the connecting plate; the elastic chuck I is arranged in the chuck I and used for clamping the shielding layer at the other end of the tested cable; the first chuck nut and the first chuck seat are connected with a first compression elastic chuck; the connecting plate is connected with one end of the electric appliance connector contact pin.

Preferably, the matching resistor is a metal film resistor, which is welded between the inner conductor and the shielding layer of the cable to be tested, and the resistance value of the metal film resistor is the same as the characteristic impedance of the cable to be tested.

Preferably, the first elastic chuck is a metal hollow cylinder, a plurality of grooves are uniformly distributed on the upper end surface and the lower end surface of the metal hollow cylinder along the axial direction of the metal hollow cylinder, the number of the grooves is preferably 4, 6 or 8, the grooves are parallel to each other, and the number of the grooves on the upper end surface is equal to that of the grooves on the lower end surface; the scheme is suitable for the tested high-voltage shielded cable with larger wire diameter; the elastic chuck of this scheme is putting into the in-process of chuck seat, along with screwing up gradually of chuck nut (convex chuck cap promptly), the elastic chuck is whole to the axis direction tighten up to comparatively closely contact with the cable shielding layer that is surveyed, when reducing contact resistance, improve the convenience of assembly.

Preferably, the metal hollow cylinder has a taper, and the chuck nut has a larger diameter.

Preferably, the number of the grooves uniformly distributed on the upper end surface and the lower end surface of the metal hollow cylinder along the axial direction of the metal hollow cylinder is preferably 4-8.

Preferably, the number of the grooves of the upper end surface and the number of the grooves of the lower end surface are both 6, and the distance between the adjacent grooves of the upper end surface and the adjacent grooves of the lower end surface is equal.

Preferably, the first chuck seat and the connecting plate are designed integrally.

Preferably, the first chuck seat and the connecting plate are designed in a split mode, and the split design of the first chuck seat and the connecting plate is beneficial to convenience of equipment, and particularly beneficial to installation of connecting pins of the electric appliance connector.

Preferably, the near-end short circuit material is non-ferromagnetic copper, zinc, magnesium or aluminum, and the content of iron element is lower than 0.15%; after the mechanical strength, the processing performance and the conductivity are comprehensively considered, the following materials are preferably selected: cu60.5-63.5%, Fe less than 0.15%, and zn for the rest.

Preferably, the outer loop distal end assembly comprises a hoop end cover, and the hoop end cover is arranged outside the other side of the metal cylinder;

preferably, the supporting component comprises an insulating connecting plate and an electric appliance connector pin insulating sleeve; one end of the insulating connecting plate is connected with the connecting plate, and the other end of the insulating connecting plate is connected with the clamp end cover; the electrical connector contact pin insulation sleeve is arranged at the top of the clamp end cover and penetrates through the clamp end cover; the electric appliance connector contact pin penetrates through the electric appliance connector contact pin insulating sleeve;

preferably, the connector is pressed on the outer side of the hoop end cover through screws; the connector is electrically connected with the head of the electric appliance connector contact pin.

Wherein, metal cylinder bearing structure includes, left bearing structure and right bearing structure. The right supporting structure comprises a hoop, a hoop connecting block, a hoop fixing block, a metal hand wheel and a metal thread plate; the clamp is arranged on the clamp end cover in a surrounding mode and is provided with two parallel extending parts; the metal thread plate is fixed on the parallel projecting piece; a shaft lever of the metal hand wheel penetrates through the extension piece and is placed in the metal thread plate to clamp the clamp; the clamp bracket is used for fixing and supporting a clamp. The left supporting structure comprises a supporting plate and a supporting plate base, wherein the supporting plate supports one end of the metal barrel, and the supporting plate is arranged on the supporting plate base.

The inner loop injection tool realizes the functions of fixing the tested cable and connecting the tested cable with the vector network analyzer. The fixed recess on the left side of the inner loop tool can be adjusted according to different sizes of the cable to be measured. The cable to be tested is placed into the inner loop injection tool, the left side fixing groove compresses the cable to be tested shielding layer, and the right side welds the cable to be tested inner conductor to the joint of the connector.

The outer loop matching resistance tool is adopted when the characteristic impedance of the tested cable is not equal to 50 omega, and the outer loop matching resistance tool has the function of matching the outer loop and reducing the influence of the unmatched outer loop on the test result. The inner resistance of the tool is connected by a metal film resistor in a welding mode, and the purpose is that the inner resistance of the tool can be flexibly adjusted when the inner resistance of the tool is used for dealing with tested cables with different sizes and different characteristic impedances so as to ensure the accuracy of a test result.

The implementation of the low-frequency cylinder testing tool shielding sleeve assembly and the overall testing tool connection is described above, the overall design considers the characteristics and requirements of the three coaxial devices, a modularized design idea is embodied, and the assembly and the testing of the whole set of device are facilitated while the connection reliability and the good electrical continuity of the device are ensured.

The invention has the beneficial effects that: the test system can be applied to the fields of rail transit, new energy automobiles, photovoltaic, aerospace and the like, and the surface transfer impedance of the tested cable is measured by a three-coaxial method so as to evaluate the shielding effectiveness of the cable. The test system has the characteristics of basically no requirement on the test environment, high precision of test results, wide application range and the like. The device design of the whole set of test system not only ensures the scientificity and accuracy of measurement, but also highlights the simplicity and the innovation of the device design on the design of the short circuit structure, the shielding cap structure and the insulating support structure at the near end of the outer loop. Based on the characteristic of simple design of the test system, the process of using the test system and butting the input and output interfaces is flexible and convenient.

Drawings

The advantages and spirit of the present invention can be further understood by the following detailed description of the invention and the accompanying drawings.

FIG. 1 is a schematic view of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

FIG. 2 is a cross-sectional view of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 3 is a schematic diagram of one or two chuck nuts in a near-end short circuit structure and a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 4 is a schematic diagram of one or two of a near-end short circuit structure and a chuck base in a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 5a is a schematic diagram of one embodiment of one or two elastic clamps in a near-end short-circuit structure and a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 5b is a schematic diagram of another embodiment of a first or second elastic clamp in a near-end short-circuit structure and a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

FIG. 6 is a schematic diagram of a short circuit clip in a near end short circuit structure of a low frequency cylinder test fixture of a three coaxial cable shielding effectiveness test system according to the present invention;

FIG. 7 is a schematic view of a threaded end cap in a near-end short-circuit structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

FIG. 8 is a schematic diagram of an electrical connector pin in a shield cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 9 is a schematic diagram of an N-KF50 connector in a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 10 is a schematic diagram of a connecting plate in a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 11 is a schematic diagram of a first insulating connecting plate in a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 12 is a schematic diagram of a second insulating connecting plate in the shielding cap structure of the low-frequency cylinder testing tool of the three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 13 is a schematic view of a hoop end cap in a shield cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 14 is a schematic diagram of an insulating sleeve of an electrical connector pin in a shielding cap structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 15 is a schematic view of a support plate in a left support structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 16a to 16c are schematic diagrams of a hoop and a hoop bracket in a right support structure of a low-frequency cylinder test fixture of a three-coaxial cable shielding effectiveness test system according to the present invention, including fig. 16a being a schematic diagram of a hoop connection block, fig. 16b being a schematic diagram of a hoop fixing plate, and fig. 16c being a schematic diagram of a hoop;

fig. 17 is a schematic view of a stainless steel hand wheel in a right support structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

fig. 18 is a schematic view of a metal thread plate in a right support structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention;

FIG. 19 is a schematic view of a support plate base in a left support structure of a low-frequency cylinder testing tool of a three-coaxial cable shielding effectiveness testing system according to the present invention

Reference numerals:

1. a hoop end cover; 2. a connecting plate; 3. a first chuck seat; 4. a first elastic chuck; 5. a first chuck nut; 6. a second chuck nut; 7. a threaded end cap; 8. a second chuck seat; 9. a second elastic chuck; 10. a short circuit clip; 11. a support plate; 12. a support plate base; 13. the plate is fixed by a clamp; 14. a clamp connecting block; 15. clamping a hoop; 16. an insulating connecting plate; 17. a connector; 18. an electrical appliance connector pin; 19. an electric appliance connector contact pin insulating sleeve; 20. a shield cap structure; 21. a proximal short circuit structure; 22. metal cylinder

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order to overcome the technical defects in the prior art and improve the scientificity and accuracy of measurement, and meanwhile, the design simplicity and the flexibility and convenience of use of the device are improved in the design of the short-circuit structure, the shielding cap structure 20 and the insulating support structure at the near end of the outer loop, and a three-coaxial cable shielding effectiveness testing system is provided.

The invention provides a three-coaxial cable shielding effectiveness testing system which is composed of a vector network analyzer and a low-frequency cylinder testing tool. The low-frequency cylinder test tool is mainly applied to testing the transfer impedance of a tested cable (high-voltage cable) when the frequency is less than 30 MHz.

The low-frequency test system comprises a vector network analyzer, a tested cable, an inner loop injection structure (tool), a low-frequency cylinder test tool, an outer loop far-end matching resistance structure (tool) and a metal cylinder 22 supporting structure.

On the one hand, provide this test system's low frequency drum test fixture.

The low-frequency cylinder testing tool consists of an outer loop near-end short-circuit structure 21, a metal cylinder 22 and a shielding cap structure 20, wherein the outer loop near-end short-circuit structure 21 comprises a threaded end cover 7, a short-circuit clamping piece 10, a second chuck seat 8, a second elastic chuck 9 and a second chuck nut 6; the shielding cap structure 20 includes an inner loop distal shielding box, an outer loop distal assembly, a support assembly, and a connector;

wherein, the threaded end cap 7 is arranged at one side of the metal cylinder 22; the short circuit clamping piece 10 is arranged on the inner side of the threaded end cover 7 and is used for fixedly clamping one end of a tested cable and is in contact with the cable shielding layer; the second chuck seat 8 is coaxially arranged on the short circuit clamping piece 10; the second chuck nut 6 is arranged on the second chuck seat 8, and an elastic second chuck 9 is arranged between the second chuck seat 8 and the second chuck nut 6; the outer loop distal end assembly is arranged on the other side of the metal cylinder 22, and the inner loop distal end assembly and the support assembly are arranged in the outer loop distal end assembly; the far-end shielding box of the inner loop fixedly clamps the other end of the tested cable; the supporting component is used for fixing the inner loop far-end shielding box in the outer loop far-end component;

preferably, the implementation of the near-end short circuit is as follows: first, one end of the tested cable (defined as end 1, and the other end of the tested cable as end 2) passes through the short circuit clip 10 (fixing plate) shown in fig. 6, the second chuck base 8 (note that the thread at the B end faces the short circuit clip 10) shown in fig. 4, the second elastic chuck 9 shown in fig. 5a or 5B, the second chuck nut 6 shown in fig. 3, and the threaded end cap 7 shown in fig. 7 in sequence. The second elastic chuck 9 shown in fig. 5B (the top end of the second elastic chuck 9 is provided with an elastic collar) is used for clamping the shielding layer at the tested cable end 1 in a 360-degree surrounding manner and then inserting the shielding layer into the a end of the second chuck seat 8, after the B end of the second chuck seat 8 shown in fig. 4 is connected with the short circuit clamping piece 10 shown in fig. 6 through threads, the a end threads of the second chuck seat 8 shown in fig. 4 are connected with the second chuck nut shown in fig. 3, then the threaded end cover 7 shown in fig. 7 is integrally penetrated, and finally the threaded end cover 7 shown in fig. 7 is connected with the metal cylinder 22, so that the electrical short circuit between the tested cable shielding layer and the metal cylinder 22 is effectively realized.

In the design process of the near-end short-circuit structure 21, the short-circuit material needs to have the following characteristics: the short circuit material has no ferromagnetism, good mechanical strength, excellent processing performance and high conductivity. In view of the above characteristics, the materials are finally looked at copper materials and aluminum materials. H62 brass is selected for processing the short circuit clamping piece 10, the second chuck seat 8, the second elastic chuck 9 and the second chuck nut 6, and the short circuit clamping piece has good cutting performance and mechanical strength, and excellent corrosion resistance and electric conductivity which meet the design requirements; the threaded end cover 7 is made of 6063-T5 aluminum, and the material has the characteristics of easiness in plasticity and high mechanical strength, and meets the design requirements of reliable short circuit and small contact resistance.

Another preferable structure of the collet (as shown in fig. 5 a) is a metal hollow cylinder, the upper end surface and the lower end surface of the metal hollow cylinder are respectively and uniformly distributed with 6 grooves along the axial direction of the metal hollow cylinder, the grooves are parallel to each other, the number of the grooves of the upper end surface is equal to that of the grooves of the lower end surface, and the distance between the grooves of the adjacent upper end surface and the distance between the grooves of the lower end surface are equal.

Wherein, the elastic chuck (as shown in fig. 5 b) is another preferable structure, and the structure is a chuck composed of 2 mutually symmetrical semicircles, which is advantageous in that the elastic chuck is suitable for the situation that the cable diameter is small.

The connection mode of the preferable structure of the two elastic structures is the same, the elastic chuck which is matched with the diameter of the tested cable is selected, the tested cable is placed in the elastic chuck, the shielding layer is fully contacted with the elastic chuck, and the chuck nut shown in figure 3 is screwed to realize good electrical connection.

In one aspect, the entire assembly of the shield cap structure 20 of the test system is provided, including the shield clip header, the first insulating web shown in fig. 11, the second insulating web shown in fig. 12, the clip end cap 1 shown in fig. 13, and the like. Preferably, one implementation of inner loop far end matching is as follows: firstly, a coaxial line (hereinafter called coaxial line 1) with a single-end SMA male head is selected to strip a sheath layer and an outer shielding layer, and after an insulating medium layer and an inner conductor are reserved, the coaxial line is connected with an SMA female head terminal arranged at the center of the inner side of a hoop end cover 1 shown in figure 13; then, the first insulation connecting plate shown in the figure 11 is connected with the inner side of the hoop end cover 1 shown in the figure 13 through four hexagonal screws arranged on the periphery of the first insulation connecting plate, and the coaxial line 1 is led out from the side surface through a groove arranged on the lower part of the first insulation connecting plate; then, connecting a second insulating connecting plate shown in the figure 12 with the first insulating connecting plate through four hexagonal screws arranged on the periphery; then, the inner conductor part of the coaxial line 1 is tightly wound at the nearby 3 hexagonal screws for fixing the shielding chuck seat, and the shielding chuck seat is fixed on a second insulating connecting plate shown in fig. 12 through four hexagonal screws; thus, the shield case is integrally assembled. Then, the step of placing the inner loop resistor is as follows: firstly, sequentially passing the end 2 of the tested cable through a clamping head nut I5 shown in figure 3 and an elastic clamping head I4 shown in figure 5; after the shielding layer at the tested cable end 2 is clamped in a 360-degree surrounding manner through the elastic clamp I4 shown in FIG. 5, the N-type inner loop resistor is connected with the N-end connector at the end 2; finally, the whole is placed in a shielding chuck seat, and a good shielding cap structure 20 is formed by screwing a first chuck nut 5 shown in figure 3.

Preferably, the shield clip mount, the clip end cap 1 shown in fig. 13, and the first and second insulating webs shown in fig. 11 and 12 are modified as follows:

1. the bottom end of the shielding clip base is added with an M6 threaded hole, and simultaneously, an electrical connector pin 18 design which is matched with the threaded hole is added, and the electrical connector pin 18 design is shown in figure 8. The clamp head seat and the connecting plate part contained in the shielding clamp head seat are integrally designed; in another preferred embodiment, the split design is a first chuck seat 3 as shown in fig. 4 and a connecting plate 2 as shown in fig. 10, which facilitate the connection of the electrical connector pin 18 as shown in fig. 8.

2. The outside connector of the hoop end cover 1 shown in fig. 13 is designed to be a matching model N-50KF radio frequency connector.

3. The insulating connecting plate shown in fig. 11 and 12 is optimized from the former two blocks into one block, and the groove design on the lower side of the connecting plate 2 is omitted.

After the change is introduced, the effective electrical connection between the radio frequency connector and the shielding chuck seat can be easily realized (the electrical appliance connector contact pin 18 is directly inserted into the end face of the inner conductor of the radio frequency connector of a specific model), and the integral assembly of the shielding cap is simplified. The reduction of the number of the insulating connecting plates and the omission of the design of the grooves on the lower sides of the insulating connecting plates enable the assembly and the processing of the shielding caps to be more convenient.

For the description of the inner loop matching resistance placement, the above described situation is ideal (N-terminal connector at end 2 of the cable under test). In the actual test process, the situation that the port of the tested cable is not provided with the corresponding joint is common. Aiming at the situation, the inner loop resistance is matched by welding, namely, the metal film resistance is welded between the inner conductor and the shielding layer of the tested cable in preparation for testing. The resistance value of the selected metal film resistor is the same as the characteristic impedance of the tested cable, and the power of the metal film resistor is selected as small as possible for welding after the resistance value is determined. Then the tested cable welded with the matching resistor is placed into the elastic clamp head I4 shown in the figure 5a of the attached drawing, so that the shielding layer of the tested cable is fully contacted with the elastic clamp head I4, and then good electrical connection is realized by screwing the clamp head nut I5 shown in the figure 3.

On one hand, the selected metal film resistor has the characteristics of high precision, stable performance, wide resistance range and the like. The adaptation to the measured cable characteristic impedance can be satisfied, and the metal film resistance welding is convenient simultaneously, easily changes.

On the one hand, the above modifications are made for the shielding clip head seat, the clip end cover 1 shown in fig. 15, and the first and second insulating connecting plates shown in fig. 11 and 12 to provide an inner loop distal end matching mode as follows:

the clip end cover 1 shown in fig. 13 is fixedly arranged at one end of a metal cylinder 22, the insulating connecting plate is arranged on the metal cylinder, the clip head seat one 3 shown in fig. 4 is arranged on the connecting plate 2 shown in fig. 10, the elastic clip head one 4 shown in fig. 5a is coaxially arranged at the inner side of the end a of the clip head seat one shown in fig. 4, and the clip head nut one 5 shown in fig. 3 is coaxially arranged at the outer side of the end a of the clip head seat one 3 shown in fig. 4; the electrical connector pins 18 shown in fig. 8 are arranged on the upper head of the connecting plate 2 shown in fig. 10 along the central axis of the metal cylinder 22 and point to the clamp end cap 1 shown in fig. 13, and the N-KF50 connector 17 shown in fig. 9 is arranged outside the clamp end cap 1 as a radio frequency connector and is connected with the electrical connector pins 18 shown in fig. 8.

On the one hand, for the support of the other end of the metal cylinder 22 (the right end in fig. 2, namely at the shield cap structure 20), a clip 15 shown in fig. 16c, a clip connecting block 14 shown in fig. 16a, a clip fixing plate 13 shown in fig. 16b (a clip support includes the clip connecting block 14 and the clip fixing plate 13), a metal hand wheel shown in fig. 17 and a metal thread plate shown in fig. 18 of the test system are provided to support the shield cap structure 20 connected to the other end of the metal cylinder 22. The metal hand wheel acts as a clamping band 15, so that the band 15 can fix the band end cover 1 well. At the left end of the metal cylinder 22, i.e., the shield cap structure 20, as shown in fig. 1, the shield cap structure 20 and the metal cylinder 22 are connected using a clip 15 as shown in fig. 15, a metal handwheel as shown in fig. 17, a metal thread plate as shown in fig. 18, and a clip bracket. The clamp 15 has two parallel protruding members to which the metal thread plate is fixed; the shaft lever of the metal hand wheel penetrates through the extension piece and is placed in the metal thread plate to clamp the clamp, and the clamp support is used for fixing and supporting the clamp.

Preferably, copper, aluminum and teflon are selected as processing materials for the components of the shield cap structure 20. Wherein the chuck nut one 5 shown in fig. 3, the elastic chuck one 4 shown in fig. 5, the chuck base one 3 shown in fig. 4 and the connecting plate 2 shown in fig. 10 are processed by brass, the band end cover 1 shown in fig. 13, the band 15 and the band bracket shown in fig. 16 and the insulating connecting plates one and two shown in fig. 11 and 12 are processed by polyethylene, polytetrafluoroethylene and polystyrene, preferably polytetrafluoroethylene, as processing materials of the insulating connecting plates, the materials have smaller relative dielectric constants of three pre-selected materials on the basis of meeting the requirements of high strength, easy processing, good high-frequency response and the like, and the relative dielectric constant is epsilon _ r 2.1, which means that the dielectric loss of the materials is lower and meets the design requirements. In the design process, the following consideration is made on the selection of the material of the insulating connecting plate, and the selected homogeneous material needs to have the characteristics of good insulating property, good high-frequency response, low dielectric loss, higher strength, easiness in processing and the like.

The butt joint relation of the parts of the metal cylinder 22 of the main body part of the three-coaxial cable shielding effectiveness testing system is described in detail, and material characteristics are comprehensively considered and selected in the design process; short-circuiting structure 21 at the near end

And the shield cap structure 20, in combination with the reliability of the connection and the simplicity and ease of connection of the various components.

On one hand, the metal cylinder 22 of the main testing structure of the low-frequency cylinder testing tool of the cable shielding effectiveness testing system with the triple-coaxial method shown in fig. 1 needs to introduce two components to realize connection with a vector network analyzer, namely an inner loop injection tool (not shown in the figure) and an outer loop matching resistance tool (not shown in the figure).

The resistance values of the inner loop matching resistor and the outer loop matching resistor mentioned above are explained.

The resistance value of the inner loop matching resistor (not shown in the figure) is determined by the characteristic impedance of the tested cable, and the resistance value is equal to the characteristic impedance of the tested cable (the low-frequency testing tool is a testing object for the high-voltage cable, and the characteristic impedance needs to be measured and obtained by a vector network analyzer before testing). The resistance value of the internal welding resistor of the external loop matching resistor tool can be estimated according to a formula in standard EN 50289-1-62002 test method standard electrical test method-electromagnetic performance.

An estimation formula of the matching resistance of the outer loop is as follows:

wherein d is₀Denotes the inner diameter (unit mm), d, of the metal cylinder 22_cAnd represents the outer diameter (unit mm) of the shielding layer of the tested cable.

The butt joint relation of the low-frequency cylinder testing tool parts of the main body part of the three-coaxial cable shielding effectiveness testing system is described in detail above.

The embodiments described in the specification are only preferred embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the present invention. Those skilled in the art can obtain technical solutions through logical analysis, reasoning or limited experiments according to the concepts of the present invention, and all such technical solutions are within the scope of the present invention.

Claims

1. The low-frequency cylinder testing tool of the cable shielding effectiveness testing system adopting the three-coaxial method is characterized by comprising an outer loop near-end short-circuit structure, a shielding cap structure and a metal cylinder structure, wherein the outer loop near-end short-circuit structure comprises an end cover, a short-circuit clamping piece, a second chuck seat, a second elastic chuck and a second chuck nut; the shielding cap structure comprises an inner loop far-end shielding box, an outer loop far-end assembly, a supporting assembly and a connector;

the end cover is arranged on one side of the metal cylinder, the short circuit clamping piece is arranged on the inner side of the end cover, the second chuck seat is coaxially arranged on the short circuit clamping piece, the second chuck nut is arranged on the second chuck seat, and an elastic second chuck is arranged between the second chuck seat and the second chuck nut; the outer loop far-end assembly is arranged on the other side of the metal cylinder, the inner loop far-end shielding box and the supporting assembly are arranged in the outer loop far-end assembly, and the supporting assembly is used for fixing the inner loop far-end shielding box in the outer loop far-end assembly;

the short circuit clamping piece is used for clamping and fixing one end of a tested cable and is in contact with a shielding layer of the tested cable; and the shielding box at the far end of the inner loop clamps and fixes the other end of the tested cable.

2. The low-frequency cylinder test tool of the three-coaxial cable shielding effectiveness test system according to claim 1, wherein the inner loop far-end shielding box comprises a first chuck screw cap, a first elastic chuck, a first chuck seat, a connecting plate and an electrical connector pin; the first chuck seat is connected with the connecting plate; the elastic chuck I is arranged in the chuck seat and is used for clamping the other end of the tested cable; the first chuck nut is connected with the first chuck seat and tightly presses the first elastic chuck; the connecting plate is connected with one end of the electric appliance connector contact pin.

3. The low frequency cylinder test fixture of a three-coaxial cable shielding effectiveness test system according to claim 1, wherein the outer loop distal end assembly comprises a clamp end cap, and the clamp end cap is disposed outside the metal cylinder.

4. The low-frequency cylinder test tool of the three-coaxial cable shielding effectiveness test system according to claim 3, wherein the support assembly comprises an insulation connecting plate and an electrical connector pin insulation sleeve; one end of the insulating connecting plate is connected with the connecting plate, and the other end of the insulating connecting plate is connected with the clamp end cover; the electrical appliance connector contact pin insulating sleeve is arranged at the top of the clamp end cover; the electric appliance connector contact pin penetrates through the electric appliance connector contact pin insulating sleeve.

5. The low-frequency cylinder testing tool of the three-coaxial cable shielding effectiveness testing system according to claim 2, wherein the first elastic chuck is a chuck composed of 2 mutually symmetrical semicircles, and the first elastic chuck clamps the shielding layer at one end of the tested cable in a 360-degree surrounding manner.

6. The low-frequency cylinder testing tool of the three-coaxial cable shielding effectiveness testing system according to claim 4, wherein the first elastic clamp is a metal hollow cylinder, a plurality of grooves are uniformly distributed on the upper end surface and the lower end surface of the metal hollow cylinder along the axial direction of the metal hollow cylinder, the grooves are parallel to each other, and the number of the grooves on the upper end surface is equal to that of the grooves on the lower end surface.

7. The low-frequency cylinder testing tool of the three-coaxial cable shielding effectiveness testing system according to claim 6, wherein the number of the grooves on the upper end surface and the number of the grooves on the lower end surface are both 6, and the adjacent grooves on the upper end surface and the adjacent grooves on the lower end surface have the same distance.

8. The low-frequency cylinder testing tool of the three-coaxial cable shielding effectiveness testing system according to claim 2, wherein the first chuck seat and the connecting plate are designed separately.

9. The low-frequency cylinder test fixture of the three-coaxial cable shielding effectiveness test system according to claim 2, wherein the first chuck seat and the connecting plate are integrally designed.

10. The low-frequency cylinder test fixture of the three-coaxial cable shielding effectiveness test system according to claim 3, wherein the near-end short-circuit material is free of ferromagnetism, and the content of iron element is lower than 0.15%.

11. The low-frequency cylinder test fixture of the three-coaxial cable shielding effectiveness test system according to claim 3, further comprising a left support structure and a right support structure for supporting the metal cylinder.

12. The low-frequency cylinder test fixture of a three-coaxial cable shielding effectiveness test system according to claim 11, wherein the right support structure comprises a clamp, a clamp connection block, a clamp fixing block, a metal hand wheel, and a metal thread plate; the clamp is arranged on the clamp end cover in a surrounding mode and is provided with two parallel extending parts; the metal thread plate is fixed on the parallel projecting piece; a shaft lever of the metal hand wheel penetrates through the extension piece and is arranged in the metal thread plate to clamp the clamp; the clamp bracket is used for fixing and supporting the clamp.

13. The low-frequency cylinder testing tool of the three-coaxial cable shielding effectiveness testing system according to claim 11, wherein the left supporting structure comprises a supporting plate and a supporting plate base, the supporting plate supports one end of the metal cylinder, and the supporting plate is arranged on the supporting plate base.