Submarine cable electrical insulation performance test method based on frequency conversion series resonance circuit

Abstract

The invention discloses a submarine cable electrical insulation performance test method based on a frequency conversion series resonance circuit. The method comprises the following steps: S1, cleaning and protecting a test site; s2, equipment and instruments enter the field; s3, connecting equipment and instruments; s4, checking phases at two ends of the three-phase cable line; s5, measuring the insulation resistance of the main insulation before voltage withstanding; s6, performing a main insulation AC voltage withstand test; s7, measuring the insulation resistance of the main insulation after voltage withstanding; s8, power frequency parameter detection of the line: using a high-voltage line parameter frequency conversion test system to test positive sequence impedance, zero sequence impedance, positive sequence capacitance and zero sequence electricity of the cable in sequence; and S9, the equipment instrument leaves the site and the site is cleaned. According to the submarine cable electrical insulation performance testing method, submarine cable electrical insulation performance testing is carried out according to the sequence, the testing efficiency is high, the testing is safer, the testing site is cleaned and protected before the voltage withstanding test, dust in air in the testing site is removed, the humidity in the air is regulated and controlled, and the testing efficiency is improved. Therefore, potential safety hazards in the test can be eliminated.

Description

Technical Field

[0001] The invention relates to the technical field of submarine cable installation and construction, in particular to a method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit. Background Art

[0002] Submarine cables are cables wrapped in insulating materials, laid on the seabed, and used for telecommunication transmission. Submarine cables are divided into submarine communication cables and submarine power cables. Modern submarine cables use optical fiber as material to transmit telephone and Internet signals. Submarine cables are divided into submarine communication cables and submarine power cables. Submarine communication cables are mainly used for communication services. They are expensive but highly confidential. Submarine power cables are mainly used to transmit high-power electrical energy underwater. They have the same function as underground power cables, but they are used in different occasions and laid in different ways. Since submarine cable projects are recognized by countries around the world as complex and difficult large-scale projects, complex technologies are used in environmental detection, marine physical surveys, and cable design, manufacturing, and installation.

[0003] The withstand voltage test of long-length submarine cables is a very important link. Due to their thick diameter and long length, the high voltage and long-distance submarine cables have a large capacitance to the ground, so the withstand voltage test power supply equipment is very demanding, and the on-site test is difficult. At present, the series-parallel resonance test method is usually used to conduct AC withstand voltage tests on submarine cables. The series-parallel resonance test method uses the resonance principle to compensate the capacitive current of the submarine cable to the ground through series and parallel reactor groups, and adjusts the frequency through the frequency conversion device to achieve resonance, so as to achieve the purpose of making the submarine cable reach the test voltage when the test power supply is minimum. However, in the test of the electrical insulation performance of the submarine cable, the submarine cable will experience an operational overvoltage, forming a destructive discharge; in addition, in the test of the electrical insulation performance of the submarine cable, due to insufficient attention to the test environment, there are potential safety hazards. Summary of the invention

[0004] The object of the present invention is to provide a safe and reliable method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit comprises the following steps: S1. Cleaning and protection of the test site: select a relatively open area as the test operation area. Before the operation, the test operation area must be cleaned and the equipment must be protected from moisture and rain. The test operation area must be dust-free to ensure that no dust and metal particles are generated in the test operation area; S2. Equipment and instruments entering the site: Unload and load the test equipment, instruments and materials, and place them in the test operation area according to the equipment usage status and arrange the test instruments reasonably. Prepare the equipment according to the test requirements and check and maintain its performance and status. The test equipment and instruments include insulation resistance tester, variable frequency series resonant AC withstand voltage test device and high voltage line parameter variable frequency test system; S3. Equipment and instrument connection: After the equipment is in place, first connect the ground wire, then the connection wires and power lines between the equipment, and finally connect the test high-voltage lead. The support insulators are arranged along the test high-voltage lead. S4. Check the phases at both ends of the three-phase cable line: ground the metal sheath of the three-phase cable line, and use an insulation resistance tester to apply 5kV voltage to the three phases of the 220kV submarine cable respectively; measure the main insulation resistance of the cable between the cable core and the metal sheath. If the main insulation resistance of the three-phase cable is normal, short-circuit the cable core of one phase at the other end of the submarine cable line and ground it, and use an insulation resistance tester to apply 5kV voltage to measure the main insulation resistance of the cable between the cable core and the metal sheath. If the main insulation resistance of one phase cannot be measured normally due to short-circuiting to the ground, determine the phase sequence of the phase of the cable line, and confirm the three phases of the cable line in turn; S5. Measurement of main insulation resistance before withstand voltage: Use an insulation resistance tester to apply 5kV voltage between the cable core and the metal sheath for 1 minute and record the value; S6. Main insulation AC withstand voltage test: Use variable frequency series resonant withstand voltage test device to conduct withstand voltage test; the test is conducted in phases. When one phase is subjected to withstand voltage, the cable cores and cable technical sheaths of the other two phases should be directly grounded; S7. Measurement of main insulation resistance after withstand voltage: After each phase of the cable withstand voltage is completed, the phase is fully discharged, and then a 5kV voltage is applied with an insulation resistance tester to record the resistance value of the main insulation between the cable core and the metal sheath. There should be no obvious change compared with before withstand voltage; S8. Power frequency parameter detection of the line: Use the high-voltage line parameter frequency conversion test system to test the positive-sequence impedance, zero-sequence impedance, positive-sequence capacitance, and zero-sequence impedance of the cable in sequence; during the test, the high-voltage end of the cable needs to be suspended, and when testing the positive-sequence impedance and zero-sequence impedance, the high-voltage side of the other end of the line is short-circuited and grounded; when testing the positive-sequence capacitance and zero-sequence capacitance, the three phases of the high-voltage side of the other end of the line are disconnected; measure and record the following data parameter values: positive-sequence resistance, positive-sequence reactance, positive-sequence capacitance to ground, zero-sequence resistance, zero-sequence reactance, zero-sequence capacitance to ground, and zero-sequence mutual inductance; S9. Equipment and instruments are removed from the test operation area and the site is cleaned up: After the equipment and instruments have left the test operation area, the test operation area is cleaned up, safety protection measures are removed, and the test operation area is restored to its pre-test state.

[0006] Furthermore, in step S1, the humidity in the test operation area is controlled below 60%.

[0007] Furthermore, in step S2, the insulation resistance tester used is a FLUKE-1555 insulation resistance tester.

[0008] Furthermore, in step S2, the high-voltage line parameter frequency conversion test system adopts a DC-208 high-voltage line parameter frequency conversion test system.

[0009] Further, in step S2, the variable frequency series resonant AC withstand voltage test device includes a system operation box, a variable frequency power supply cabinet, an excitation transformer, a reactor, a high-voltage capacitive voltage divider, two detection leads and two detection fixtures. The system operation box is used to control the variable frequency power supply cabinet, the variable frequency power supply cabinet is electrically connected to the excitation transformer, the excitation transformer, the reactor and the high-voltage capacitive voltage divider are connected in series in sequence, the electrical input end and the electrical output end of the high-voltage capacitive voltage divider are respectively electrically connected to one end of the two detection leads, and the other ends of the two detection leads are respectively connected to two detection fixtures, and the two detection fixtures are used to clamp the detection points of the cable under test.

[0010] Furthermore, in step S2, the reactor in the variable frequency series resonant AC withstand voltage test device is provided with four reactors, and the four reactors are connected in parallel.

[0011] Furthermore, in step S3, supporting insulators of 220 kV or above are arranged along the high voltage lead line for testing.

[0012] Further, in step S6, the method of the main insulation AC withstand voltage test is as follows: S6.1. Turn off the main power switch of the frequency conversion power supply cabinet; S6.2. Carry out the test wiring according to the diagram and after checking that it is correct, first select the voltage level with the smallest transformation ratio for the excitation transformer. After determining the resonant frequency, determine the voltage level of the excitation transformer by calculating the quality factor Q value of the resonant circuit; S6.3. Connect the test power supply to the frequency conversion power supply cabinet and set the parameters on the system operation box: test voltage, pressurization time, boost speed and limit voltage; S6.4. Press the start button on the system operation box to start the test. The initial test frequency is 20Hz. After the low-voltage side is boosted to 20V, the frequency is adjusted. During the test, check and monitor the power supply and test circuit. If any abnormality is found, stop the test immediately. Before the AC withstand voltage test of the cable main insulation, all grounding boxes with cable sheath protectors in the line should be short-circuited and grounded to prevent damage to the cable sheath protectors in the grounding boxes during the withstand voltage test. S6.5. After the test time is over, record the withstand voltage test data, the voltage automatically returns to zero, disconnect the power switch in the test control panel, and disconnect the main power switch.

[0013] Furthermore, in step S6.3, when the cable under test is a 127 / 220KV cable, the test voltage is 1.7U0, U0 is a phase voltage of 127KV, and the pressurization time is 60min; when the cable under test is a 18 / 30KV cable, the test voltage is 2.0U0, U0 is a phase voltage of 18KV, and the pressurization time is 5min.

[0014] Further, in step S7, the insulation resistance tester applies a 5 kV voltage for a duration of 1 min.

[0015] The beneficial effects of the present invention are: The electrical insulation performance test of a submarine cable is carried out in the sequence of the method for testing the electrical insulation performance of a submarine cable of the present invention, which not only has high test efficiency but also is safer. Before the withstand voltage test, the present invention cleans and protects the test site, removes dust in the air in the test site, and regulates the humidity in the air to eliminate potential safety hazards in the test.

[0016] The present invention adds a high-voltage capacitive voltage divider in parallel with the submarine cable under test in the variable frequency series resonant AC withstand voltage test device. When the submarine cable under test is discharged, the loop capacitance formed by the high-voltage capacitive voltage divider is discharged instantaneously, so the current output by the power supply is small, thereby limiting the serious damage to the insulation of the submarine cable under test. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of a method for testing the electrical insulation performance of a submarine cable according to the present invention; Figure 2 This is the electrical schematic diagram of the variable frequency series resonant AC withstand voltage test device. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features therein can be combined with each other without conflict.

[0019] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper surface", "lower surface", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "forward", "reverse", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0020] like Figure 1 As shown, a method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit comprises the following steps: S1. Cleaning and protection of the test site: Select a relatively open area as the test operation area. Before the operation, the test operation area must be cleaned and the equipment must be protected from moisture and rain. The test operation area must be dust-free to ensure that no dust and metal particles are generated in the test operation area; the humidity of the test operation area is controlled below 60%. Before the pressure test, the present invention cleans and protects the test site, removes dust in the air in the test site, and controls the humidity in the air to eliminate potential safety hazards in the test.

[0021] S2. Equipment and instruments entering the site: Unload and load the test equipment, instruments and materials, and place them in the test operation area according to the equipment usage status and arrange the test instruments reasonably. Prepare the equipment according to the test requirements and check and maintain its performance and status. The test equipment and instruments include insulation resistance tester, variable frequency series resonant AC withstand voltage test device and high voltage line parameter variable frequency test system.

[0022] The insulation resistance tester used is FLUKE-1555 insulation resistance tester; the high-voltage line parameter frequency conversion test system uses DC-208 high-voltage line parameter frequency conversion test system.

[0023] like Figure 2As shown, the variable frequency series resonant AC withstand voltage test device includes a system operation box 7, a variable frequency power supply cabinet 1, an excitation transformer 2, a reactor 3, a high-voltage capacitive voltage divider 4, two detection leads 5 and two detection fixtures 6. The system operation box 7 is used to control the variable frequency power supply cabinet 1. The variable frequency power supply cabinet 1 is electrically connected to the excitation transformer 2. The excitation transformer 2, the reactor 3 and the high-voltage capacitive voltage divider 4 are connected in series in sequence. The electrical input end and the electrical output end of the high-voltage capacitive voltage divider 4 are respectively electrically connected to one end of the two detection leads 5, and the other ends of the two detection leads 5 are respectively connected to two detection fixtures 6. The two detection fixtures 6 are used to clamp the detection points of the tested cable 8; the reactor 3 in the variable frequency series resonant AC withstand voltage test device is provided with 4 sections, and the 4 sections of the reactor 3 are connected in parallel.

[0024] S3. Equipment and instrument connection: After the equipment is in place, first connect the ground wire, then connect the connection wires and power lines between the equipment, and finally connect the test high-voltage lead. The test high-voltage lead is extended along the line with supporting insulators of more than 220kV.

[0025] S4. Check the phases at both ends of the three-phase cable line: ground the metal sheath of the three-phase cable line, and use an insulation resistance tester to apply 5kV voltage to the three phases of the 220kV submarine cable respectively; measure the main insulation resistance of the cable between the cable core and the metal sheath. If the main insulation resistance of the three-phase cable is normal, short-circuit the cable core of one phase at the other end of the submarine cable line and ground it, and use an insulation resistance tester to apply 5kV voltage to measure the main insulation resistance of the cable between the cable core and the metal sheath. If the main insulation resistance of one phase cannot be measured normally due to short-circuiting to the ground, determine the phase sequence of the phase of the cable line, and confirm the three phases of the cable line in turn; S5. Measurement of main insulation resistance before withstand voltage: Use an insulation resistance tester to apply 5kV voltage between the cable core and the metal sheath for 1 minute and record the value.

[0026] S6. Main insulation AC withstand voltage test: Use variable frequency series resonant withstand voltage test equipment for withstand voltage test; the test is carried out in phases, when one phase is subjected to withstand voltage test, the cable cores and cable technical sheaths of the other two phases should be directly grounded.

[0027] The method for main insulation AC withstand voltage test is as follows: S6.1. Turn off the main power switch of the frequency conversion power supply cabinet; S6.2. Carry out the test wiring according to the diagram and after checking that it is correct, first select the voltage level with the smallest transformation ratio for the excitation transformer. After determining the resonant frequency, determine the voltage level of the excitation transformer by calculating the quality factor Q value of the resonant circuit; S6.3. Connect the test power supply to the frequency conversion power supply cabinet and set the parameters on the system operation box: test voltage, pressurization time, boost speed and limit voltage; S6.4. Press the start button on the system operation box to start the test. The initial test frequency is 20Hz. After the low-voltage side is boosted to 20V, the frequency is adjusted. During the test, check and monitor the power supply and test circuit. If any abnormality is found, stop the test immediately. Before the AC withstand voltage test of the cable main insulation, all grounding boxes with cable sheath protectors in the line should be short-circuited and grounded to prevent damage to the cable sheath protectors in the grounding boxes during the withstand voltage test. S6.5. After the test time is over, record the withstand voltage test data, the voltage automatically returns to zero, disconnect the power switch in the test control panel, and disconnect the main power switch.

[0028] Furthermore, in step S6.3, when the cable under test is a 127 / 220KV cable, the test voltage is 1.7U0, U0 is a phase voltage of 127KV, and the pressurization time is 60min; when the cable under test is a 18 / 30KV cable, the test voltage is 2.0U0, U0 is a phase voltage of 18KV, and the pressurization time is 5min.

[0029] S7. Measurement of main insulation resistance after withstand voltage: After each phase of the cable withstand voltage is over, fully discharge the phase, and then use an insulation resistance tester to apply a 5kV voltage to record the resistance value of the main insulation between the cable core and the metal sheath. There should be no obvious change compared with before the withstand voltage; the insulation resistance tester applies a 5kV voltage for 1 minute.

[0030] S8. Detection of power frequency parameters of the line: Use the high-voltage line parameter frequency conversion test system to test the positive-sequence impedance, zero-sequence impedance, positive-sequence capacitance, and zero-sequence capacitance of the cable in sequence; during the test, the high-voltage end of the cable needs to be suspended, and when testing the positive-sequence impedance and zero-sequence impedance, the high-voltage side of the other end of the line should be short-circuited and grounded; when testing the positive-sequence capacitance and zero-sequence capacitance, the three-phase high-voltage side of the other end of the line should be disconnected; measure and record the following data parameter values: positive-sequence resistance, positive-sequence reactance, positive-sequence capacitance to ground, zero-sequence resistance, zero-sequence reactance, zero-sequence capacitance to ground, and zero-sequence mutual inductance.

[0031] S9. Equipment and instruments are removed from the test operation area and the site is cleaned up: After the equipment and instruments have left the test operation area, the test operation area is cleaned up, safety protection measures are removed, and the test operation area is restored to its pre-test state.

[0032] Working principle: The electrical insulation performance test of the submarine cable is carried out in the sequence of the method for testing the electrical insulation performance of the submarine cable of the present invention. Not only is the test efficiency high, but it is also safer. Before the voltage test, the present invention cleans and protects the test site, removes the dust in the air in the test site, and regulates the humidity in the air to eliminate potential safety hazards in the test.

[0033] In addition, the present invention adds a high-voltage capacitive voltage divider connected in parallel with the submarine cable under test in the variable frequency series resonant AC withstand voltage test device. When the submarine cable under test is discharged, the loop capacitance formed by the high-voltage capacitive voltage divider is discharged instantaneously, so the current output by the power supply is small, thereby limiting the serious damage to the insulation of the submarine cable under test.

[0034] In addition, those skilled in the art may combine and combine the different embodiments or examples and the features of the different embodiments or examples described in this specification without contradiction. Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for testing the electrical insulation performance of submarine cables based on a variable frequency series resonant circuit. It is characterized in that The following steps are involved: S1. Cleaning and protection of the test site: select a relatively open area as the test operation area. Before the operation, the test operation area must be cleaned and the equipment must be protected from moisture and rain. The test operation area must be dust-free to ensure that no dust and metal particles are generated in the test operation area; S2. Equipment and instruments entering the site: Unload and load the test equipment, instruments and materials, and place them in the test operation area according to the equipment usage status and arrange the test instruments reasonably. Prepare the equipment according to the test requirements and check and maintain its performance and status. The test equipment and instruments include insulation resistance tester, variable frequency series resonant AC withstand voltage test device and high voltage line parameter variable frequency test system; S3. Equipment and instrument connection: After the equipment is in place, first connect the ground wire, then the connection wires and power lines between the equipment, and finally connect the test high-voltage lead. The support insulators are arranged along the test high-voltage lead. S4. Check the phases at both ends of the three-phase cable line: ground the metal sheath of the three-phase cable line, and use an insulation resistance tester to apply 5kV voltage to the three phases of the 220kV submarine cable respectively; measure the main insulation resistance of the cable between the cable core and the metal sheath. If the main insulation resistance of the three-phase cable is normal, short-circuit the cable core of one phase at the other end of the submarine cable line and ground it, and use an insulation resistance tester to apply 5kV voltage to measure the main insulation resistance of the cable between the cable core and the metal sheath. If the main insulation resistance of one phase cannot be measured normally due to short-circuiting to the ground, determine the phase sequence of the phase of the cable line, and confirm the three phases of the cable line in turn; S5. Measurement of main insulation resistance before withstand voltage: Use an insulation resistance tester to apply 5kV voltage between the cable core and the metal sheath for 1 minute and record the value; S6. Main insulation AC withstand voltage test: Use variable frequency series resonant withstand voltage test device to conduct withstand voltage test; the test is conducted in phases. When one phase is subjected to withstand voltage, the cable cores and cable technical sheaths of the other two phases should be directly grounded; S7. Measurement of main insulation resistance after withstand voltage: After each phase of the cable withstand voltage is completed, the phase is fully discharged, and then a 5kV voltage is applied with an insulation resistance tester to record the resistance value of the main insulation between the cable core and the metal sheath. There should be no obvious change compared with before withstand voltage; S8. Power frequency parameter detection of the line: Use the high-voltage line parameter frequency conversion test system to test the positive-sequence impedance, zero-sequence impedance, positive-sequence capacitance, and zero-sequence impedance of the cable in sequence; during the test, the high-voltage end of the cable needs to be suspended, and when testing the positive-sequence impedance and zero-sequence impedance, the high-voltage side of the other end of the line is short-circuited and grounded; when testing the positive-sequence capacitance and zero-sequence capacitance, the three phases of the high-voltage side of the other end of the line are disconnected; measure and record the following data parameter values: positive-sequence resistance, positive-sequence reactance, positive-sequence capacitance to ground, zero-sequence resistance, zero-sequence reactance, zero-sequence capacitance to ground, and zero-sequence mutual inductance; S9. Equipment and instruments are removed from the test operation area and the site is cleaned up: After the equipment and instruments have left the test operation area, the test operation area is cleaned up, safety protection measures are removed, and the test operation area is restored to its pre-test state.

2. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 1, Features: In step S1, the humidity in the test operation area is controlled below 60%.

3. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 1, Features: In step S2, the insulation resistance tester used is a FLUKE-1555 insulation resistance tester.

4. According to the method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit as described in claim 1, Features: In step S2, the high-voltage line parameter frequency conversion test system adopts the DC-208 high-voltage line parameter frequency conversion test system.

5. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 1, Features: In step S2, the variable frequency series resonant AC withstand voltage test device includes a system operation box, a variable frequency power supply cabinet, an excitation transformer, a reactor, a high-voltage capacitive voltage divider, two detection leads and two detection fixtures. The system operation box is used to control the variable frequency power supply cabinet, the variable frequency power supply cabinet is electrically connected to the excitation transformer, the excitation transformer, the reactor and the high-voltage capacitive voltage divider are connected in series in sequence, the electrical input end and the electrical output end of the high-voltage capacitive voltage divider are respectively electrically connected to one end of the two detection leads, and the other ends of the two detection leads are respectively connected to two detection fixtures, and the two detection fixtures are used to clamp the detection points of the cable under test.

6. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 5, Features: In step S2, the reactor in the variable frequency series resonant AC withstand voltage test device is provided with four reactors, and the four reactors are connected in parallel.

7. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 1, It is characterized in that In step S3, supporting insulators of 220 kV or above are arranged along the high voltage lead line for testing.

8. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 1, It is characterized in that In step S6, the method of the main insulation AC withstand voltage test is as follows: S6.

1. Turn off the main power switch of the frequency conversion power supply cabinet; S6.

2. Carry out the test wiring according to the diagram and after checking that it is correct, first select the voltage level with the smallest transformation ratio for the excitation transformer. After determining the resonant frequency, determine the voltage level of the excitation transformer by calculating the quality factor Q value of the resonant circuit; S6.

3. Connect the test power supply to the frequency conversion power supply cabinet and set the parameters on the system operation box: test voltage, pressurization time, boost speed and limit voltage; S6.

4. Press the start button on the system operation box to start the test. The initial test frequency is 20Hz. After the low-voltage side is boosted to 20V, the frequency is adjusted. During the test, check and monitor the power supply and test circuit. If any abnormality is found, stop the test immediately. Before the AC withstand voltage test of the cable main insulation, all grounding boxes with cable sheath protectors in the line should be short-circuited and grounded to prevent damage to the cable sheath protectors in the grounding boxes during the withstand voltage test. S6.

5. After the test time is over, record the withstand voltage test data, the voltage automatically returns to zero, disconnect the power switch in the test control panel, and disconnect the main power switch.

9. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 8, Features: In step S6.3, when the cable under test is a 127 / 220KV cable, the test voltage is 1.7U0, U0 is the phase voltage of 127KV, and the pressurization time is 60min; when the cable under test is a 18 / 30KV cable, the test voltage is 2.0U0, U0 is the phase voltage of 18KV, and the pressurization time is 5min.

10. The method for testing the electrical insulation performance of a submarine cable based on a variable frequency series resonant circuit according to claim 1, Features: In step S7, the insulation resistance tester applies a 5 kV voltage for a duration of 1 minute.

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