A device for detecting a pressure test of a cable

Abstract

The application relates to the technical field of cable detection, in particular to a withstand voltage test device for detecting a cable, which comprises a pair of test pipes vertically arranged on an insulating support, the lower end of the test pipe is provided with a plugging ring, the plugging ring is provided with a jack for the cable to pass through, and the test pipe is further provided with a conductive rubber sleeve and an insulating sleeve tight ring; the conductive rubber sleeve comprises an upper sleeve and a lower sleeve, a pressing surface is formed between the inner wall of the upper sleeve and the inner wall of the lower sleeve, the inner diameter of the upper sleeve is matched with the outer diameter of an insulating layer, the inner diameter of the lower sleeve is matched with the outer diameter of a semi-conductive layer, and the insulating sleeve tight ring is arranged on the lower sleeve. After the pressing surface and the end surface of the semi-conductive layer are tightly pressed and combined, the lower sleeve is tightly sleeved by the insulating sleeve tight ring, the levelness at the boundary is guaranteed, the risk of electric field concentration points and breakdown caused by uneven ring cutting is avoided, and the cable terminal does not need to be processed into a conical surface, so that the manual work load is reduced.

Description

Technical Field

[0001] This invention relates to the field of cable testing technology, specifically to a device for testing the withstand voltage of cables. Background Technology

[0002] Cables may have some potential insulation defects during the manufacturing process, such as bubbles, impurities, and cracks in the insulation layer. Therefore, it is necessary to use a withstand voltage testing device to conduct a withstand voltage test on the cable. The principle is to test the insulation reliability and withstand capability of the cable under high voltage by applying a test voltage higher than its normal operating voltage to the cable.

[0003] To ensure uniform electric field distribution and prevent electric field concentration at cable terminations that could lead to insulation breakdown, the cable terminations must be treated before testing. This involves removing a certain length of the semi-conductive layer and grinding the edges of the terminations into a smooth, continuous conical surface. This treatment is mostly done manually, typically using simple tools such as electrician's knives and sandpaper to cut and grind the cable terminations. This not only results in inconsistent processing quality and low efficiency, but also makes it difficult to precisely control the angle, smoothness, and length of the conical surface. A conical surface that is too short, has an improper angle, or has scratches or steps on the surface can create fatal electric field concentration points during testing. This can not only cause innocent breakdowns of cables that should pass the test voltage, leading to misjudgments, but also potentially create hidden insulation faults during long-term operation of the cable. Summary of the Invention

[0004] The purpose of this invention is to provide a withstand voltage testing device for cables to address the problems raised in the background above.

[0005] This invention is achieved through the following technical solution: a withstand voltage test device for cables, comprising a pair of test tubes vertically mounted on an insulating support, a sealing ring at the lower end of each test tube, an insertion hole for the cable to pass through on the sealing ring, a conductive rubber sleeve and an insulating sleeve tightening ring inside each test tube, the conductive rubber sleeve comprising an upper sleeve and a lower sleeve distributed and connected vertically, a truncated ring-shaped pressure surface being formed between the inner walls of the upper sleeve and the lower sleeve, the inner diameter of the upper sleeve being adapted to the outer diameter of the cable's insulation layer, the inner diameter of the lower sleeve being adapted to the outer diameter of the cable's semi-conductive layer, and the insulating sleeve tightening ring being disposed on the lower sleeve;

[0006] The test method of the withstand voltage test device for the test cable includes the following steps:

[0007] Step 1: Strip the wires from both ends of the cable, exposing the insulation layer and the semi-conductive layer from top to bottom;

[0008] Step 2: Pass the cable end through the socket and the conductive rubber sleeve from bottom to top, and put the upper sleeve on the insulation layer and the lower sleeve on the semi-conductive layer.

[0009] Step 3: Pull the cable end and the conductive rubber sleeve in opposite directions to make the pressing surface and the end face of the semi-conductive layer press tightly together. Then use the insulating sleeve tightening ring to tighten the lower sleeve onto the semi-conductive layer so that the pressing surface and the end face of the semi-conductive layer are kept in a tight pressing state.

[0010] Step 4: Fill the two test tubes with water until the water just submerges the top surface of the conductive rubber sleeve, and then fill the two test tubes with silicone oil.

[0011] Step 5: Connect the conductor at one end of the cable to the power source and ground the shield at the other end of the cable to perform a test.

[0012] Optionally, the insulating sleeve tightening ring is slidably fitted onto the lower sleeve along the axial direction. The lower end of the lower sleeve is evenly provided with and connected to multiple clamping segments along the circumference. A slit is provided between two adjacent clamping segments. The inner walls of each clamping segment form a cylindrical surface, and the outer walls of each clamping segment form an outer conical surface. The inner wall of the lower end of the insulating sleeve tightening ring is an inner conical surface, and the inner conical surface matches the outer conical surface.

[0013] Optionally, it also includes an insulating positioning sleeve, which is confined inside the test tube by an insulating positioning frame, and the insulating positioning sleeve is movably fitted outside the insulating sleeve tight ring. An upper limit ring is connected to the top of the insulating positioning sleeve, and the upper limit ring has a first through hole for the cable to pass through. An overlapping ring is connected to the top of the outer wall of the upper sleeve, and the overlapping ring overlaps the top surface of the upper limit ring. An overflow pipe is connected to the side wall of the test tube, and the height of the overflow pipe is slightly higher than the top surface of the conductive rubber sleeve. A sealing plug is provided on the overflow pipe.

[0014] Optionally, an overlapping surface in the shape of a truncated ring is formed between the outer wall of the upper sleeve and the outer wall of the lower sleeve, and a first spring is pressed between the upper limit ring and the overlapping surface.

[0015] Optionally, a second spring is connected to the bottom surface of the upper limit ring. The stiffness coefficient of the second spring is greater than that of the first spring, and the second spring does not contact the insulating sleeve ring.

[0016] Optionally, the bottom of the insulating positioning sleeve is connected to a lower limiting ring, the lower limiting ring is provided with a second through hole for the cable to pass through, and the top surface of the lower limiting ring is connected to a third spring; in the natural state, when the third spring supports the insulating sleeve tight ring, there is no squeezing effect between the inner conical surface and the outer conical surface.

[0017] Optionally, the height of the insulating positioning frame is lower than the height of the insulating positioning sleeve, the outer end of the insulating positioning frame is fixedly connected to the inner wall of the test tube, and the outer wall of the insulating positioning sleeve and the inner end of the insulating positioning frame are axially fixed together.

[0018] Optionally, the outer wall of the insulating positioning sleeve and the inner end of the insulating positioning frame are circumferentially rotatable and axially fixed. The side wall of the insulating positioning sleeve is provided with an inverted triangular hole. The outer wall of the insulating sleeve tight ring is fixedly connected with a short shaft, which is disposed in the inverted triangular hole. When the insulating positioning sleeve is rotated, the hypotenuse of the inverted triangular hole can push the short shaft and the insulating sleeve tight ring to move upward.

[0019] Optionally, the outer wall of the clamping petal is formed with a T-shaped guide groove, and the inner wall of the inner conical surface is provided with a T-shaped guide strip, which is slidably disposed in the T-shaped guide groove.

[0020] Optionally, all edges of the outer wall of the conductive rubber sleeve are rounded, and the radius of the rounded corners is not less than 2mm.

[0021] Compared with the prior art, the present invention provides a withstand voltage testing device for cables, which has the following beneficial effects:

[0022] 1. The present invention provides a conductive rubber sleeve and an insulating sleeve tightening ring in the test tube. The conductive rubber sleeve includes an upper sleeve and a lower sleeve with a pressure surface. After the pressure surface is pressed tightly against the end face of the semiconductive layer, the insulating sleeve tightening ring is used to tighten the lower sleeve. This can transform the boundary between the semiconductor layer and the insulating layer, which may break down, into the boundary between the conductive rubber sleeve and the insulating layer, ensuring the levelness of the boundary and avoiding the risk of electric field concentration and breakdown caused by uneven ring cutting. At the same time, there is no need to process the conical surface of the cable end, reducing the amount of manual work.

[0023] 2. This invention designs an expansion sleeve structure between the bottom of the conductive rubber sleeve and the bottom of the insulating sleeve tight ring. An insulating positioning sleeve is set outside the insulating sleeve tight ring, and a first spring is set between the insulating positioning sleeve and the conductive rubber sleeve. Both are respectively equipped with an upper limit ring and an overlap ring. During the process of lifting the cable, the pressure surface can be tightly pressed against the end face of the semi-conductive layer and then clamp the lower sleeve by itself. After releasing, the conductive rubber sleeve automatically resets under the action of the first spring and keeps the top surface of the conductive rubber sleeve at a fixed height, slightly lower than the height of the overflow pipe. There is no need to observe and adjust the water level when filling water, and the overall operation is simple and efficient.

[0024] 3. In this invention, the insulating positioning sleeve is configured to rotate circumferentially and be fixed axially. An inverted triangular hole and a short shaft are respectively provided on the insulating positioning sleeve and the insulating sleeve tightening ring. After the test, manually rotating the insulating positioning sleeve can drive the insulating sleeve tightening ring to move upward and disengage from the clamping petal, which facilitates the release of the clamping state of the insulating sleeve tightening ring. A T-shaped guide groove and a T-shaped guide strip are respectively provided between the clamping petal and the inner conical surface. When the insulating sleeve tightening ring moves upward, it can pull the clamping petal to prevent the clamping petal from sticking to the cable, thereby facilitating the wire release. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall withstand voltage testing device for cables according to the present invention;

[0026] Figure 2 This is an assembly diagram of the conductive rubber sleeve, insulating sleeve tightening ring, and insulating positioning sleeve in the cable withstand voltage testing device of the present invention;

[0027] Figure 3 for Figure 2 A half-section perspective view along the axial direction;

[0028] Figure 4 This is a perspective view of the insulating sleeve tightening ring in the cable withstand voltage testing device of the present invention.

[0029] In the diagram: 1. Cable; 101. Shielding layer; 102. Semi-conductive layer; 103. Insulation layer; 104. Core wire; 2. Test tube; 201. Overflow pipe; 202. Water outlet pipe; 203. Sealing ring; 3. Insulating support; 4. Insulating positioning frame; 5. Conductive rubber sleeve; 501. Upper sleeve; 5011. First through hole; 5012. Overlap ring; 502. Lower sleeve; 5021. Clamping flap; 5022. 5023, outer conical surface; 5024, T-shaped guide groove; 503, pressing surface; 504, overlapping surface; 6, insulating sleeve tight ring; 601, inner conical surface; 602, T-shaped guide strip; 603, short shaft; 7, insulating positioning sleeve; 701, upper limit ring; 702, lower limit ring; 7021, second through hole; 703, inverted triangular hole; 8, first spring; 9, second spring; 10, third spring. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example: Please refer to Figures 1 to 4As shown, a withstand voltage testing device for cables includes a pair of test tubes 2 vertically mounted on an insulating support 3. The lower end of each test tube 2 has a sealing ring 203 with an insertion hole for the cable 1 to pass through. The test tubes 2 also contain a conductive rubber sleeve 5 and an insulating tightening ring 6. The conductive rubber sleeve 5 includes an upper sleeve 501 and a lower sleeve 502 that are vertically distributed and connected. A truncated ring-shaped pressure is formed between the inner walls of the upper sleeve 501 and the lower sleeve 502. The thickness of the pressure surface 503 is comparable to the thickness of the semi-conductive layer 102. The inner diameter of the upper sleeve 501 matches the outer diameter of the insulation layer 103 of the cable 1, and the inner diameter of the lower sleeve 502 matches the outer diameter of the semi-conductive layer 102 of the cable 1. An insulating tightening ring 6 is provided on the lower sleeve 502 to tighten and fix the lower sleeve 502 after the pressure surface 503 and the end face of the semi-conductive layer 102 are pressed together, thus avoiding gaps between the end face of the semi-conductive layer 102 and the pressure surface 503. The conductive rubber sleeve 5 can be designed and manufactured according to the standard outer diameter and semiconductor layer thickness of the cable for different specifications of cables, forming a series of standard components.

[0032] The test method for the above-mentioned withstand voltage test device for cables includes the following steps:

[0033] Step 1: Strip the wires from both ends of cable 1, exposing the insulation layer 103 and the semi-conductive layer 102 from top to bottom. At the same time, expose the wire core 104 at the left end of cable 1 and the shielding layer 101 at the right end of cable 1.

[0034] Step 2: Pass the end of cable 1 through the socket and the conductive rubber sleeve 5 from bottom to top, and put the upper sleeve 501 on the insulation layer 103 and the lower sleeve 502 on the semi-conductive layer 102.

[0035] Step 3: Pull the end of cable 1 and conductive rubber sleeve 5 in the opposite direction to make the pressure surface 503 and the end face of semi-conductive layer 102 tightly pressed together. Then use insulating sleeve tightening ring 6 to tighten the lower sleeve 502 onto semi-conductive layer 102 so that the pressure surface 503 and the end face of semi-conductive layer 102 are kept in a tight pressed state.

[0036] Step 4: Fill the two test tubes 2 with water until the water just submerges the top surface of the conductive rubber sleeve 5, and then fill the two test tubes 2 with silicone oil.

[0037] Step 5: Connect the conductor 104 at the left end of cable 1 to power, pull the shielding layer 101 at the right end of cable 1 to below the sealing ring 203 and ground it, and then conduct a withstand voltage test.

[0038] This embodiment eliminates the need to process a conical surface at the cable 1 terminal. After circumferentially cutting the semiconductive layer 102, the withstand voltage test device for the aforementioned test cable can be used directly. During circumferential cutting, the end face of the semiconductive layer 102 does not need to be precisely level. That is, differences in the quality of the circumferentially cut end face of the semiconductive layer 102 due to varying operator skill do not affect the withstand voltage test results. This embodiment transforms the boundary between the semiconductor layer and the insulating layer 103, which could potentially lead to breakdown, into the boundary between the conductive rubber sleeve 5 and the insulating layer 103. Since the top surface of the conductive rubber sleeve 5 is a fixed horizontal plane, it ensures that the interface between water and silicone oil precisely submerges the top surface of the conductive rubber sleeve 5. Therefore, this embodiment avoids the risk of electric field concentration and breakdown caused by uneven circumferential cutting, making the operation of the withstand voltage test device simpler and more efficient.

[0039] Based on the above embodiment, the insulating sleeve 6 is slidably sleeved on the lower sleeve 502 along the axial direction. The lower end of the lower sleeve 502 is evenly provided with and connected to multiple clamping segments 5021 along the circumference. A slit 5022 is provided between two adjacent clamping segments 5021. The inner wall of each clamping segment 5021 forms a cylindrical surface, and the outer wall of each clamping segment 5021 forms an outer conical surface 5023. The inner wall of the lower end of the insulating sleeve 6 is an inner conical surface 601, and the inner conical surface 601 cooperates with the outer conical surface 5023. An expansion sleeve structure is formed between the lower end of the insulating sleeve tightening ring 6 and the lower end of the lower sleeve 502. This expansion sleeve structure can clamp the cable 1. That is, when the lower sleeve 502 moves upward relative to the insulating sleeve tightening ring 6, the clamping petals 5021 are gathered and clamped on the outer wall of the cable 1 under the guidance of the inner conical surface 601. The cutting opening 5022 is also squeezed and sealed by the end faces between the two clamping petals 5021 that are gathered inward, thereby avoiding the possible generation of electric field concentration points at the edge of the cutting opening 5022.

[0040] Furthermore, the aforementioned withstand voltage test device for the test cable also includes an insulating positioning sleeve 7. The insulating positioning sleeve 7 is confined within the test tube 2 by the insulating positioning frame 4 to keep the height and radial direction of the insulating positioning sleeve 7 constant. The insulating positioning sleeve 7 is movably fitted outside the insulating sleeve tight ring 6. An upper limit ring 701 is connected to the top of the insulating positioning sleeve 7. The upper limit ring 701 is provided with a first through hole 5011 for the cable 1 to pass through. An overlapping ring 5012 is connected to the top of the outer wall of the upper sleeve 501. The overlapping ring 5012 overlaps the top surface of the upper limit ring 701. An overflow pipe 201 is connected to the side wall of the test tube 2. The height of the overflow pipe 201 is slightly higher than the top surface of the conductive rubber sleeve 5. A sealing plug is provided on the overflow pipe 201. Before water injection, the overlapping ring 5012 of the upper sleeve 501 is fixed at the height of the upper limit ring 701. After water is injected until it flows out from the overflow pipe 201, the water surface can be guaranteed to just submerge the top surface of the upper sleeve 501. After the sealing plug is plugged in, silicone oil is injected. Since the density of silicone oil is less than that of water and it is immiscible with water, the injected silicone oil will naturally float on the water surface, forming a stable oil-water separation interface.

[0041] To enable the overlapping ring 5012 to automatically conform to the upper end face of the upper limit ring 701, a frustum-shaped overlapping surface 504 is formed between the outer wall of the upper sleeve 501 and the outer wall of the lower sleeve 502. A first spring 8 is pressed between the upper limit ring 701 and the overlapping surface 504. This first spring 8 not only serves to reset the upper sleeve 501 to conform to the overlapping ring 5012 and the upper limit ring 701, but also provides a variable elastic preload for pulling the cable 1 upward to firmly press the pressure surface 503 and the end face of the semi-conductive layer 102 together. Compared to the upper limit ring 701 directly contacting the overlapping surface 504, this avoids the problem of excessive deformation of the semi-conductive layer 102 and its detachment from the pressure surface 503 due to excessive pulling.

[0042] Furthermore, a second spring 9 is connected to the bottom surface of the upper limit ring 701. The stiffness coefficient of the second spring 9 is greater than that of the first spring 8, and the second spring 9 does not contact the insulating sleeve tightening ring 6. A lower limit ring 702 is connected to the bottom of the insulating positioning sleeve 7. The lower limit ring 702 has a second through hole 7021 for the cable 1 to pass through. A third spring 10 is connected to the top surface of the lower limit ring 702. The stiffness coefficient of the third spring 10 is less than that of the first spring 8. In its natural state, when the third spring 10 supports the insulating sleeve tightening ring 6, there is no squeezing effect between the inner conical surface 601 and the outer conical surface 5023. By setting the second spring 9, which does not contact the insulating sleeve tightening ring 6, it can be ensured that when the cable 1 is pulled up, the pressure surface 503 is tightly pressed against the end face of the semi-conductive layer 102 and then clamps the lower sleeve 502 by itself. When the lower sleeve 502 is clamped, the lower sleeve 502 and the insulating clamping ring 6 move relative to each other in the axial direction. The third spring 10 supports the insulating clamping ring 6 to a certain height, so that after the first spring 8 returns to the position where the overlapping ring 5012 fits against the upper limit ring 701, the insulating clamping ring 6 can continue to move downward a certain distance to keep the insulating clamping ring 6 always tightly fitted to the lower sleeve 502. Based on the above embodiment, the height of the insulating positioning frame 4 is set lower than the height of the insulating positioning sleeve 7. The outer end of the insulating positioning frame 4 is fixedly connected to the inner wall of the test tube 2. The outer wall of the insulating positioning sleeve 7 and the inner end of the insulating positioning frame 4 are axially fixed, specifically circumferentially rotating and axially fixed. The side wall of the insulating positioning sleeve 7 is provided with an inverted triangular hole 703. The outer wall of the insulating clamping ring 6 is fixedly connected with a short shaft 603, which is set in the inverted triangular hole 703. When the insulating positioning sleeve 7 is rotated, the hypotenuse of the inverted triangular hole 703 can push the short shaft 603 and the insulating clamping ring 6 upward. After the withstand voltage test, manually rotating the insulating positioning sleeve 7 can move the insulating sleeve tightening ring 6 upward and disengage it from the clamping piece 5021, facilitating the release of the clamping state of the insulating sleeve tightening ring 6. The outer wall of the clamping piece 5021 is formed with a T-shaped guide groove 5024, and the inner wall of the inner conical surface 601 is provided with a T-shaped guide strip 602, which slides in the T-shaped guide groove 5024. This design allows the clamping piece 5021 to be pulled upward as the insulating sleeve tightening ring 6 moves upward, preventing the clamping piece 5021 from sticking to the cable 1, thus facilitating cable release. It should be noted that all edges of the outer wall of the conductive rubber sleeve 5 are rounded, with a radius of not less than 2mm. Rounding the edges of the conductive rubber sleeve 5 avoids the generation of electric field concentration points, improving the safety of the test. Furthermore, the insulating positioning sleeve 7 can be provided with several connecting holes that connect to its inner cavity, so that water can enter and completely fill the inner cavity of the insulating positioning sleeve 7, thereby using water to homogenize the charge on the conductive rubber sleeve 5 and the semi-conductive layer 102.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A withstand voltage testing device for cables, characterized in that: The test tube (2) is vertically mounted on an insulating support (3). The lower end of the test tube (2) is provided with a sealing ring (203). The sealing ring (203) is provided with a hole for the cable (1) to pass through. The test tube (2) is also provided with a conductive rubber sleeve (5) and an insulating sleeve tightening ring (6). The conductive rubber sleeve (5) includes an upper sleeve (501) and a lower sleeve (502) that are distributed and connected vertically. A truncated ring-shaped pressing surface (503) is formed between the inner wall of the upper sleeve (501) and the inner wall of the lower sleeve (502). The inner diameter of the upper sleeve (501) is adapted to the outer diameter of the insulation layer (103) of the cable (1). The inner diameter of the lower sleeve (502) is adapted to the outer diameter of the semi-conductive layer (102) of the cable (1). The insulating sleeve tightening ring (6) is located on the lower sleeve (502). The test method of the withstand voltage test device for the test cable includes the following steps: Step 1: Strip the wires from both ends of the cable (1) so that the insulation layer (103) and the semiconductive layer (102) are exposed from top to bottom; Step 2: Pass the end of the cable (1) through the socket and the conductive rubber sleeve (5) from bottom to top, and put the upper sleeve (501) on the insulating layer (103) and the lower sleeve (502) on the semi-conductive layer (102). Step 3: Pull the end of the cable (1) and the conductive rubber sleeve (5) in opposite directions to make the pressing surface (503) and the end face of the semi-conductive layer (102) press tightly together. Then use the insulating sleeve tightening ring (6) to tighten the lower sleeve (502) onto the semi-conductive layer (102) so that the pressing surface (503) and the end face of the semi-conductive layer (102) remain in a tight pressing state. Step 4: Fill the two test tubes (2) with water until the water just submerges the top surface of the conductive rubber sleeve (5), and then fill the two test tubes (2) with silicone oil. Step 5: Connect the conductor (104) at one end of the cable (1) to power, and ground the shield (101) at the other end of the cable (1) to perform a test.

2. The withstand voltage testing device for cables according to claim 1, characterized in that: The insulating sleeve (6) is slidably mounted on the lower sleeve (502) along the axial direction. The lower end of the lower sleeve (502) is uniformly provided with multiple clips (5021) along the circumferential direction. A slit (5022) is provided between two adjacent clips (5021). The inner walls of each clip (5021) form a cylindrical surface, and the outer walls of each clip (5021) form an outer conical surface (5023). The inner wall of the lower end of the insulating sleeve (6) is an inner conical surface (601), and the inner conical surface (601) and the outer conical surface (5023) cooperate with each other.

3. The withstand voltage testing device for cables according to claim 2, characterized in that: It also includes an insulating positioning sleeve (7), which is confined inside the test tube (2) by an insulating positioning frame (4), and the insulating positioning sleeve (7) is movably fitted outside the insulating sleeve tight ring (6). An upper limit ring (701) is connected to the top of the insulating positioning sleeve (7), and the upper limit ring (701) is provided with a first through hole (5011) for the cable (1) to pass through. An overlapping ring (5012) is connected to the top of the outer wall of the upper sleeve (501), and the overlapping ring (5012) overlaps the top surface of the upper limit ring (701). An overflow pipe (201) is connected to the side wall of the test tube (2), and the height of the overflow pipe (201) is slightly higher than the top surface of the conductive rubber sleeve (5). A sealing plug is provided on the overflow pipe (201).

4. The withstand voltage testing device for cables according to claim 3, characterized in that: An overlapping surface (504) in the shape of a truncated ring is formed between the outer wall of the upper sleeve (501) and the outer wall of the lower sleeve (502), and a first spring (8) is pressed between the upper limit ring (701) and the overlapping surface (504).

5. The withstand voltage testing device for cables according to claim 4, characterized in that: The bottom surface of the upper limit ring (701) is connected to a second spring (9), the spring constant of the second spring (9) is greater than that of the first spring (8), and the second spring (9) does not contact the insulating sleeve ring (6).

6. The withstand voltage testing device for cables according to claim 3, characterized in that: The bottom of the insulating positioning sleeve (7) is connected to a lower limiting ring (702), and the lower limiting ring (702) is provided with a second through hole (7021) for the cable (1) to pass through. The top surface of the lower limiting ring (702) is connected to a third spring (10). In the natural state, when the third spring (10) supports the insulating sleeve tight ring (6), there is no squeezing effect between the inner conical surface (601) and the outer conical surface (5023).

7. The withstand voltage testing device for cables according to claim 3, characterized in that: The height of the insulating positioning frame (4) is lower than the height of the insulating positioning sleeve (7). The outer end of the insulating positioning frame (4) is fixedly connected to the inner wall of the test tube (2). The outer wall of the insulating positioning sleeve (7) and the inner end of the insulating positioning frame (4) are axially fixed together.

8. The withstand voltage testing device for cables according to claim 7, characterized in that: The outer wall of the insulating positioning sleeve (7) and the inner end of the insulating positioning frame (4) are circumferentially rotatable and axially fixed. The side wall of the insulating positioning sleeve (7) is provided with an inverted triangular hole (703). The outer wall of the insulating sleeve tight ring (6) is fixedly connected with a short shaft (603). The short shaft (603) is disposed in the inverted triangular hole (703). When the insulating positioning sleeve (7) is rotated, the hypotenuse of the inverted triangular hole (703) can push the short shaft (603) and the insulating sleeve tight ring (6) to move upward.

9. The withstand voltage testing device for cables according to claim 2, characterized in that: The outer wall of the clamping petal (5021) is formed with a T-shaped guide groove (5024), and the inner wall of the inner conical surface (601) is provided with a T-shaped guide strip (602), which is slidably disposed in the T-shaped guide groove (5024).

10. A withstand voltage testing device for cables according to any one of claims 1-9, characterized in that: The outer wall of the conductive rubber sleeve (5) is rounded at all edges, and the radius of the rounded corner is not less than 2mm.

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