Device and method for measuring friction coefficient of oil flow inside submarine oil-filled cable

Abstract

The present application provides a device and method for measuring the friction coefficient of the oil flow in the internal oil channel of a submarine oil-filled cable. Due to the special structure of the oil channel inside the oil-filled cable, it is impossible to estimate the friction coefficient of the insulating oil flowing therein. Therefore, the present application proposes an insulating oil circulation structure, which includes a circulation pipeline arranged between the output end of a centrifugal pump at the outlet of the insulating oil tank and the inlet of the oil-filled cable, and between the outlet of the oil-filled cable and the inlet of the insulating oil tank; the circulation pipeline is respectively provided with seamless steel pipes with the same diameter as the oil channel of the oil-filled cable at the inlet and outlet of the oil-filled cable; the seamless steel pipes are respectively connected to the inlet and outlet of the insulating oil tank through oil-filled pipes with the same diameter as the oil channel; a measuring unit is provided on the insulating oil circulation structure, and the measuring unit is communicatively connected to a calculation unit; in this way, the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable can be calculated by the measuring unit and the calculation unit.

Description

Technical Field

[0001] The present application relates to the field of power engineering technology, and in particular to a device and method for measuring the friction coefficient of oil flow inside a submarine oil-filled cable. Background Art

[0002] Submarine oil-filled cables are oil-filled cables used for high-voltage submarine power transmission. They utilize oil-immersed insulation technology, which improves the insulation performance of submarine cables by filling them with insulating oil to eliminate air gaps between cable layers. A typical oil-filled cable consists of an insulating oil channel, copper conductors, insulating oil paper, a lead sheath, and an outer jacket.

[0003] Oil-filled cables have excellent insulation properties and can withstand very high working electric field strengths. They have very low dielectric loss, good heat dissipation and reliable sheath protection. Oil-filled cables are generally used for cross-sea high-voltage power transmission. Due to the unique oil channel design of oil-filled cables, it is necessary to measure their friction coefficient to facilitate the digital twin of the insulating oil flow inside the oil channel of the oil-filled cable, thereby monitoring the operating status of the cable and promptly detecting possible leaks.

[0004] At present, for an ordinary horizontal pipe, if the flow inside it is laminar, its friction coefficient is Where Re is the Reynolds number (which depends on the flow rate, fluid density, viscosity, and pipe diameter). If the internal flow is turbulent, a Moody diagram can be used to interpolate the Reynolds number. However, since the conductor inside the submarine oil-filled cable is made of spirally wound copper tape, forming a hollow pipe, namely the oil channel, this creates gaps on the surface of the oil channel caused by the spiral winding of the copper tape. The friction coefficient of the fluid flowing in the oil channel may not conform to the existing friction coefficient model. Therefore, using the existing friction coefficient model to calculate the friction coefficient of the insulating oil flowing inside the oil channel of the submarine oil-filled cable cannot obtain accurate calculation results. Summary of the Invention

[0005] The purpose of the present application is to solve at least one of the above-mentioned technical defects, especially the technical defect that in the prior art, there are gaps on the surface of the oil channel of the submarine oil-filled cable caused by the spiral winding of copper tape, and the friction coefficient of the fluid flowing in the oil channel may not comply with the existing friction coefficient model. Therefore, the use of the existing friction coefficient model to calculate the friction coefficient of the insulating oil flow inside the oil channel of the submarine oil-filled cable cannot obtain accurate calculation results.

[0006] The present application provides an insulating oil circulation structure, which comprises: a circulation pipeline provided between an output end of a centrifugal pump at an insulating oil tank outlet and an inlet of an oil-filled cable, and between the outlet of the oil-filled cable and the inlet of the insulating oil tank;

[0007] The circulation pipeline is provided with seamless steel pipes having the same diameter as the oil channel of the oil-filled cable at the inlet and outlet of the oil-filled cable respectively;

[0008] The seamless steel pipe is connected to the inlet and outlet of the insulating oil tank respectively through oil-filled pipes with the same diameter as the seamless steel pipe.

[0009] Optionally, the length of the seamless steel pipe is at least one hundred times the diameter of the oil channel of the oil-filled cable.

[0010] Optionally, the length of the oil-filled pipe is at least two hundred times the diameter of the oil channel of the oil-filled cable.

[0011] Optionally, the radius of the elbow of the oil-filled pipe is at least 15 times the diameter of the oil channel of the oil-filled cable.

[0012] The present application also provides a device for measuring the friction coefficient of oil flow in an internal oil-filled submarine cable, the device comprising the insulating oil circulation structure as described in any one of the above embodiments, a measuring unit provided on the insulating oil circulation structure, and a computing unit in communication with the measuring unit;

[0013] The measuring unit is configured to measure the flow rate of the insulating oil output by the centrifugal pump in the insulating oil circulation structure at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, the temperature of the insulating oil in the insulating oil tank, and the oil channel pressure of the oil-filled cable, and send the measurement results to the calculation unit;

[0014] The calculation unit is used to calculate the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable according to the measurement result sent by the measuring unit.

[0015] Optionally, the measuring unit includes a flow meter, a differential pressure gauge, a pressure gauge and a thermometer;

[0016] The flow meter is arranged on the oil-filled pipeline;

[0017] The differential pressure gauge is arranged at the inlet and outlet of the oil-filled cable;

[0018] The pressure gauge is arranged at the outlet of the oil-filled cable;

[0019] The temperature sensing element of the thermometer is inserted into the insulating oil tank.

[0020] The present application also provides a method for measuring the friction coefficient of the oil flow in the internal oil path of a submarine oil-filled cable, which is applied to a calculation unit of the device for measuring the friction coefficient of the oil flow in the internal oil path of a submarine oil-filled cable in any one of the above embodiments. The method comprises:

[0021] When calculating the friction coefficient of insulating oil flowing in the oil channel of the oil-filled cable, the flow rate of the insulating oil output by the centrifugal pump at different speeds and the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, sent by the measuring unit, are obtained, and the oil channel diameter and oil channel length of the oil-filled cable are determined;

[0022] The friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable is calculated based on the flow rate of the insulating oil output by the centrifugal pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable.

[0023] Optionally, before obtaining the flow rate of the insulating oil output by the centrifugal pump at different speeds and the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates sent by the measuring unit, the method further includes:

[0024] obtaining the temperature of the insulating oil in the insulating oil tank sent by the measuring unit, and determining the oil channel diameter of the oil-filled cable;

[0025] Calculating the density and viscosity of the insulating oil according to the temperature of the insulating oil, and determining, based on the density and viscosity of the insulating oil and the diameter of the oil passage of the oil-filled cable, a flow rate of the insulating oil such that the Reynolds number of the oil passage of the oil-filled cable covers a laminar flow, a transitional flow, and a turbulent flow range;

[0026] The rotation speed of the centrifugal pump is adjusted according to the flow rate of the insulating oil so that the Reynolds number range of the oil channel of the oil-filled cable covers the laminar flow, transitional flow and turbulent flow ranges.

[0027] Optionally, calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable based on the flow rates of the insulating oil output by the centrifugal pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and length of the oil-filled cable includes:

[0028] acquiring a current oil channel pressure of the oil-filled cable sent by the measuring unit;

[0029] If the current oil channel pressure is different from the last obtained oil channel pressure, the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable is calculated multiple times based on the flow rate of the insulating oil output by the centrifugal pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable;

[0030] determining an average value of the friction coefficients obtained from multiple calculations, and using the average value as a final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable at the current oil channel pressure;

[0031] If the current oil channel pressure is the same as the oil channel pressure obtained last time, the friction coefficient calculated last time is used as the final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable under the current oil channel pressure.

[0032] Optionally, the calculation formula for calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable based on the flow rate of the insulating oil output by the centrifugal pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable is:

[0033]

[0034] Among them, H f is the head loss, U is the average flow velocity in the oil channel of the oil-filled cable, D is the oil channel diameter of the charging cable, L is the oil channel length, and g is the acceleration due to gravity.

[0035] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0036] The present application provides a device and method for measuring the friction coefficient of the oil flow in the internal oil channel of a submarine oil-filled cable. Due to the special structure of the oil channel inside the oil-filled cable, it is impossible to estimate the friction coefficient of the insulating oil flow therein. Therefore, the present application proposes an insulating oil circulation structure, which includes a circulation pipeline between the output end of a centrifugal pump arranged at the outlet of the insulating oil tank and the inlet of the oil-filled cable, and between the outlet of the oil-filled cable and the inlet of the insulating oil tank; the circulation pipeline is respectively provided with seamless steel pipes with the same diameter as the oil channel of the oil-filled cable at the inlet and outlet of the oil-filled cable; the seamless steel pipes are respectively connected to the inlet and outlet of the insulating oil tank through oil-filled pipes with the same diameter as the oil channel; and the device for measuring the friction coefficient of the oil flow in the internal oil channel of the submarine oil-filled cable includes an insulating oil circulation structure, a measuring unit arranged on the insulating oil circulation structure, and a computing unit communicated with the measuring unit; the measuring unit is used to measure the oil in the insulating oil circulation structure. The flow rate of the insulating oil output by the heart pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, the temperature of the insulating oil in the insulating oil tank and the oil channel pressure of the oil-filled cable are measured, and the measurement results are sent to the calculation unit; the calculation unit is used to calculate the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable according to the measurement results sent by the measuring unit. The friction coefficient thus calculated takes into account the flow rate of the insulating oil, the pressure difference of the insulating oil, the temperature of the insulating oil and the oil channel pressure of the oil-filled cable, thereby effectively improving the calculation accuracy of the friction coefficient while reducing the measurement cost; in addition, the present application can also use this friction coefficient to perform digital twinning of the insulating oil flow inside the oil-filled cable. When the actually measured insulating oil flow data deviates greatly from the digital twin result, it indicates that the oil-filled cable may be leaking, so that the leakage of the oil-filled cable can be effectively monitored. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0038] Figure 1 A schematic structural diagram of an insulating oil circulation structure provided in an embodiment of the present application;

[0039] Figure 2 A schematic diagram of the specific structure of the insulating oil circulation structure provided in an embodiment of the present application;

[0040] Figure 3 A schematic flow chart of a method for measuring the friction coefficient of oil flow in an internal oil-filled submarine cable provided in an embodiment of the present application;

[0041] Figure 4 Schematic diagram of the relationship between different pipeline surface roughness and flow friction coefficient provided in the embodiments of the present application. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0043] At present, for an ordinary horizontal pipe, if the flow inside it is laminar, its friction coefficient is Where Re is the Reynolds number (which depends on the flow rate, fluid density, viscosity, and pipe diameter). If the internal flow is turbulent, a Moody diagram can be used to interpolate the Reynolds number. However, since the conductor inside the submarine oil-filled cable is made of spirally wound copper tape, forming a hollow pipe, namely the oil channel, this creates gaps on the surface of the oil channel caused by the spiral winding of the copper tape. The friction coefficient of the fluid flowing in the oil channel may not conform to the existing friction coefficient model. Therefore, using the existing friction coefficient model to calculate the friction coefficient of the insulating oil flowing inside the oil channel of the submarine oil-filled cable cannot obtain accurate calculation results.

[0044] Based on this, this application proposes the following technical solutions, please refer to the following for details:

[0045] In one embodiment, Figure 1 As shown, Figure 1 This is a structural schematic diagram of an insulating oil circulation structure provided in an embodiment of the present application; the present application provides an insulating oil circulation structure, which includes: a circulation pipeline between the output end of a centrifugal pump 3 arranged at the outlet of the insulating oil tank 2 and the inlet of the oil-filled cable 1, and between the outlet of the oil-filled cable 1 and the inlet of the insulating oil tank 2.

[0046] The circulation pipeline is provided with seamless steel pipes 4 having the same diameter as the oil channel of the oil-filled cable 1 at the inlet and outlet of the oil-filled cable 1 respectively.

[0047] The seamless steel pipe 4 is connected to the inlet and outlet of the insulating oil tank 2 respectively through an oil-filled pipe 5 having the same diameter as the seamless steel pipe 4 .

[0048] In this embodiment, Figure 1 As shown, due to the special structure of the oil passage inside the oil-filled cable 1, it is impossible to estimate the friction coefficient of the insulating oil flowing therein. Therefore, the present application provides a circulation pipeline between the output end of the centrifugal pump 3 at the outlet of the insulating oil tank 2 and the inlet of the oil-filled cable 1, and between the outlet of the oil-filled cable 1 and the inlet of the insulating oil tank 2. The circulation pipeline includes a seamless steel pipe 4 and an oil-filled pipe 5. The seamless steel pipe 4 is arranged at the inlet and outlet of the oil-filled cable 1, and the diameter of the seamless steel pipe 4 is the same as the diameter of the oil passage inside the oil-filled cable 1. The oil-filled pipe 5 is arranged between the seamless steel pipe 4 and the output end of the centrifugal pump 3 and the insulating oil inlet, and the diameter is the same as the diameter of the seamless steel pipe 4. In this way, relevant parameters can be measured by designing relevant measuring instruments on the above-mentioned circulation pipeline, and the relevant parameters can be used to calculate the friction coefficient of the oil passage flowing inside the oil-filled cable 1.

[0049] It can be understood that the present application uses a pipeline design that combines a seamless steel pipe 4 with an oil-filled cable 1, and a seamless steel pipe 4 with the same diameter as the internal oil channel of the oil-filled cable 1 is arranged near the inlet and outlet of the oil-filled cable 1. The seamless steel pipe 4 is a straight pipe, which can ensure the stability of the flow of insulating oil; at the same time, the present application uses a certain length of oil-filled pipeline 5 to connect with the seamless steel pipe 4 and the inlet and outlet of the insulating oil pipe, so that the flow of insulating oil in the pipeline can be fully developed, and the flow rate of the insulating oil can be collected conveniently.

[0050] In one embodiment, Figure 2 As shown, Figure 2 This is a schematic diagram of the specific structure of the insulating oil circulation structure provided in the embodiment of the present application; the length of the seamless steel pipe 4 is at least one hundred times the diameter of the oil channel of the oil-filled cable 1, so that the flow of the insulating oil in the pipe can be fully developed. In addition, Figure 2 DP is a differential pressure gauge, F is a flow meter, T is a thermometer, and P is a pressure gauge.

[0051] In one embodiment, Figure 2As shown, the length of the oil-filled pipe 5 is at least two hundred times the diameter of the oil channel of the oil-filled cable 1, so that the flow of the insulating oil in the pipe can be fully developed.

[0052] In one embodiment, Figure 2 As shown, the radius of the elbow of the oil-filled pipe 5 is at least 15 times the diameter of the oil channel of the oil-filled cable 1, so that the flow of the insulating oil in the pipe can be fully developed and the measurement error caused by flow disturbance can be eliminated.

[0053] In one embodiment, the present application also provides a device for measuring the friction coefficient of the internal oil flow of a submarine oil-filled cable 1, the device comprising an insulating oil circulation structure as described in any one of the above embodiments, a measuring unit arranged on the insulating oil circulation structure, and a computing unit communicatively connected to the measuring unit.

[0054] The measuring unit is used to measure the flow rate of the insulating oil output by the centrifugal pump 3 in the insulating oil circulation structure at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, the temperature of the insulating oil in the insulating oil tank 2, and the oil channel pressure of the oil-filled cable 1, and send the measurement results to the calculation unit.

[0055] The calculation unit is used to calculate the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 according to the measurement result sent by the measurement unit.

[0056] In this embodiment, due to the special structure of the oil channel inside the oil-filled cable 1, it is impossible to estimate the friction coefficient of the insulating oil flowing therein. Therefore, the present application designs the above-mentioned insulating oil circulation structure, and on this basis proposes a device for measuring the friction coefficient of the oil channel flow inside the submarine oil-filled cable 1, the device comprising an insulating oil circulation structure, a measuring unit arranged on the insulating oil circulation structure, and a computing unit communicatively connected to the measuring unit; wherein the measuring unit can measure the flow rate of the insulating oil output by the centrifugal pump 3 in the insulating oil circulation structure at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, the temperature of the insulating oil in the insulating oil tank 2, and the oil channel pressure of the oil-filled cable 1, and send the measurement results to the computing unit, so as to enable The calculation unit can calculate the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 based on the measurement results sent by the measuring unit. This process estimates the friction coefficient of the oil flow in the internal oil channel of the oil-filled cable 1 through a simple measuring device, taking into account the flow rate of the insulating oil, the pressure difference of the insulating oil, the temperature of the insulating oil and the oil channel pressure of the oil-filled cable 1, thereby effectively improving the calculation accuracy of the friction coefficient while reducing the measurement cost; and, the present application can also use this friction coefficient to perform digital twinning of the insulating oil flow inside the oil-filled cable 1. When the actual measured insulating oil flow data deviates greatly from the digital twin result, it indicates that the oil-filled cable 1 may be leaking, so that the leakage of the oil-filled cable 1 can be effectively monitored.

[0057] In one embodiment, the measuring unit includes a flow meter, a differential pressure gauge, a pressure gauge, and a thermometer.

[0058] The flow meter is arranged on the oil-filled pipeline 5 .

[0059] The differential pressure gauge is arranged at the inlet and outlet of the oil-filled cable 1 .

[0060] The pressure gauge is arranged at the outlet of the oil-filled cable 1 .

[0061] The temperature sensing element of the thermometer is inserted into the insulating oil tank 2 .

[0062] In this embodiment, Figure 2As shown, the present application sets a measuring unit in the insulating oil circulation structure, which includes but is not limited to a flow meter, a differential pressure gauge, a pressure gauge, and a thermometer. Among them, the flow meter of the present application is set on the oil-filled pipe 5, and is used to measure the flow rate of the insulating oil output by the centrifugal pump 3 in the insulating oil circulation structure at different speeds. The flow measurement of the present application uses a Coriolis flow meter that ensures measurement accuracy under low flow rates, or other flow meters with higher accuracy, which are not limited here; the differential pressure gauge of the present application is set at the inlet and outlet of the oil-filled cable 1, so that the oil channel pressure difference of the oil-filled cable 1 can be detected; the pressure gauge of the present application is set at the outlet of the oil-filled cable 1 to measure the oil channel pressure of the oil-filled cable 1; and the temperature sensing element of the thermometer of the present application is inserted into the interior of the insulating oil tank 2 to measure the temperature of the insulating oil in the insulating oil tank 2.

[0063] In one embodiment, Figure 3 As shown, Figure 3 A flow chart of a method for measuring the friction coefficient of the oil flow in the internal oil path of a submarine oil-filled cable 1 provided in an embodiment of the present application is provided. The present application also provides a method for measuring the friction coefficient of the oil flow in the internal oil path of a submarine oil-filled cable 1, which is applied to the calculation unit of the device for measuring the friction coefficient of the oil flow in the internal oil path of a submarine oil-filled cable 1 in any of the above embodiments. The method may include:

[0064] S110: When calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1, the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds and the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates sent by the measuring unit are obtained, and the oil channel diameter and oil channel length of the oil-filled cable 1 are determined.

[0065] S120: Calculate the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 based on the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable 1.

[0066] In this embodiment, when calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1, the calculation unit in the device for measuring the friction coefficient of the oil flow in the oil channel of the oil-filled cable 1 can obtain the flow rate of the insulating oil output by the centrifugal pump 3 at different rotational speeds and the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, which are sent by the measurement unit, and determine the oil channel diameter and oil channel length of the oil-filled cable 1. In this way, the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 can be calculated based on the flow rate of the insulating oil output by the centrifugal pump 3 at different rotational speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable 1.

[0067] In a specific implementation, after the present application obtains the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds through a flow meter, the flow rate of the insulating oil output at different speeds can be calculated based on the diameter and flow rate of the oil-filled pipe 5; and after the present application obtains the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, as well as the oil channel diameter and oil channel length of the oil-filled cable 1, the flow rate of the insulating oil flowing through the oil-filled cable 1 at different flow rates can be calculated in combination with the effective head difference at both ends of the oil channel of the oil-filled cable 1. By using the flow rate of the insulating oil output at different speeds and the flow rate of the insulating oil flowing through the oil-filled cable 1 at different flow rates, a more accurate flow rate of the insulating oil at different flow rates can be obtained.

[0068] Furthermore, since the Reynolds number is related to the flow rate, density, viscosity of the fluid, and the diameter of the pipe, when calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1, the present application can calculate the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 output by the centrifugal pump 3 at different speeds, thereby obtaining the friction coefficient corresponding to different Reynolds numbers.

[0069] In one embodiment, before obtaining the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds and the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates sent by the measuring unit in S110, the following steps may also be included:

[0070] S101: Acquire the temperature of the insulating oil in the insulating oil tank 2 sent by the measuring unit, and determine the oil channel diameter of the oil-filled cable 1.

[0071] S102: Calculate the density and viscosity of the insulating oil according to the temperature of the insulating oil, and determine the flow rate of the insulating oil so that the Reynolds number range of the oil channel of the oil-filled cable 1 covers the laminar flow, transitional flow, and turbulent flow ranges based on the density and viscosity of the insulating oil and the oil channel diameter of the oil-filled cable 1.

[0072] S103: adjusting the rotation speed of the centrifugal pump 3 according to the flow rate of the insulating oil so that the Reynolds number range of the oil channel of the oil-filled cable 1 covers the laminar flow, transitional flow and turbulent flow ranges.

[0073] In this embodiment, since the Reynolds number is related to the friction coefficient, which in turn is related to the flow rate, density, viscosity, and pipe diameter of the fluid, when calculating the friction coefficient of insulating oil flowing in the oil channel of the oil-filled cable 1, the temperature of the insulating oil in the insulating oil tank 2, as transmitted by the measuring unit, can be first obtained, and the diameter of the oil channel of the oil-filled cable 1 can be determined. The density and viscosity of the insulating oil can then be calculated based on the temperature of the insulating oil. Based on the density and viscosity of the insulating oil and the diameter of the oil channel of the oil-filled cable 1, the flow rate of the insulating oil can be determined so that the Reynolds number range of the oil channel of the oil-filled cable 1 covers laminar flow, transitional flow, and turbulent flow (Re = 1e2 to 1e6). In this way, the rotation speed of the centrifugal pump 3 can be adjusted according to different Reynolds number ranges, and different insulating oil flow rates can be set at regular intervals. The pressure differential of the insulating oil flowing through the cable at different flow rates can then be measured. Combined with the insulating oil flow rate, the friction coefficient can be calculated using a relevant algorithm to obtain the friction coefficient of the oil channel flow within the oil-filled cable 1 at different Reynolds numbers.

[0074] Schematically, as Figure 4 As shown, Figure 4 Schematic diagram of the relationship between different pipeline surface roughness and flow friction coefficient provided in the embodiment of this application; Figure 4 It can be seen that the flow friction coefficient corresponding to the different surface roughness of the pipeline (∈ is the average surface roughness height, D is the pipeline diameter) is also different, that is, the rougher the pipeline surface, the greater the flow friction coefficient, and the corresponding flow friction coefficient under different Reynolds numbers is also different. This application can draw the Reynolds number-friction coefficient curve corresponding to different Reynolds numbers based on the measured data, which is convenient for subsequent digital twin model interpolation.

[0075] In one embodiment, calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 in S120 based on the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, and the oil channel diameter and length of the oil-filled cable 1 may include:

[0076] S121: Acquire the current oil channel pressure of the oil-filled cable 1 sent by the measuring unit.

[0077] S122: If the current oil channel pressure is different from the oil channel pressure obtained last time, the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 is calculated multiple times based on the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable 1.

[0078] S123: Determine an average value of the friction coefficients obtained through multiple calculations, and use the average value as a final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 under the current oil channel pressure.

[0079] S124: If the current oil channel pressure is the same as the oil channel pressure obtained last time, the friction coefficient calculated last time is used as the final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 under the current oil channel pressure.

[0080] In this embodiment, since pressure variations may cause the insulating oil to leak into other cable layers to varying degrees as it flows within the oil channel, separate friction coefficient measurements are performed for different pipe pressure conditions. Furthermore, due to flow and pressure fluctuations caused by centrifugal pump 3 during the measurement process, multiple measurements are performed for each operating condition, and the calculated friction coefficients are averaged to eliminate measurement errors caused by pump pressure fluctuations.

[0081] In a specific implementation method, the present application can first obtain the current oil channel pressure of the oil-filled cable 1 sent by the measuring unit, and compare it with the oil channel pressure obtained last time. If the current oil channel pressure is different from the oil channel pressure obtained last time, the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 is calculated multiple times according to the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable 1. Then, the average value of the multiple friction coefficients is taken as the final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 under the current oil channel pressure, and the Reynolds number-friction coefficient curve corresponding to different Reynolds numbers under different pipe pressure conditions is drawn based on the measured data to facilitate the subsequent digital twin model interpolation. If the current oil channel pressure is the same as the oil channel pressure obtained last time, the friction coefficient calculated last time is used as the final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 under the current oil channel pressure, thereby reducing the calculation time and improving the measurement efficiency.

[0082] In one embodiment, the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable 1 is calculated according to the flow rate of the insulating oil output by the centrifugal pump 3 at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable 1 at different flow rates, and the oil channel diameter and length of the oil-filled cable 1. The calculation formula is:

[0083]

[0084] Among them, H f is the head loss, U is the average flow velocity in the oil channel of the oil-filled cable 1, D is the oil channel diameter of the charging cable, L is the oil channel length, and g is the acceleration due to gravity.

[0085] It is understood that after obtaining the flow rate of insulating oil output by the centrifugal pump 3 at different speeds through a flow meter, the present application can calculate the flow rate of the insulating oil output at different speeds based on the diameter and flow rate of the oil-filled pipe 5. Furthermore, after obtaining the pressure differential of the insulating oil flowing through the oil-filled cable 1 at different flow rates, as well as the oil channel diameter and length of the oil-filled cable 1, the present application can combine the effective head difference at both ends of the oil channel of the oil-filled cable 1 to calculate the flow rate of the insulating oil flowing through the oil-filled cable 1 at different flow rates. By using the flow rate of the insulating oil output at different speeds and the flow rate of the insulating oil flowing through the oil-filled cable 1 at different flow rates, a more accurate flow rate of the insulating oil at different flow rates can be obtained. Furthermore, because the present application incorporates the effective head difference at both ends of the oil channel of the oil-filled cable 1 to calculate the flow rate of the insulating oil flowing through the oil-filled cable 1 at different flow rates, the present application can further calculate the head loss when calculating the friction coefficient using the Darcy-Weisbach formula, thereby improving the accuracy of the friction coefficient calculation.

[0086] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0087] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referenced to each other.

[0088] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for measuring the friction coefficient of oil flow inside a submarine oil-filled cable, characterized in that: The device includes an insulating oil circulation structure, a measuring unit provided on the insulating oil circulation structure, and a computing unit communicatively connected to the measuring unit; The circulation structure includes a circulation pipeline provided between the output end of the centrifugal pump at the outlet of the insulating oil tank and the inlet of the oil-filled cable, and between the outlet of the oil-filled cable and the inlet of the insulating oil tank; The circulation pipeline is provided with seamless steel pipes having the same diameter as the oil channel of the oil-filled cable at the inlet and outlet of the oil-filled cable respectively; The seamless steel pipe is connected to the inlet and outlet of the insulating oil tank respectively through an oil-filled pipe with the same diameter as the seamless steel pipe; The length of the seamless steel pipe is at least one hundred times the diameter of the oil channel of the oil-filled cable; The length of the oil-filled pipe is at least two hundred times the diameter of the oil channel of the oil-filled cable; The radius of the elbow of the oil-filled pipe is at least 15 times the diameter of the oil channel of the oil-filled cable; The measuring unit is configured to measure the flow rate of the insulating oil output by the centrifugal pump in the insulating oil circulation structure at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, the temperature of the insulating oil in the insulating oil tank, and the oil channel pressure of the oil-filled cable, and send the measurement results to the calculation unit; The calculation unit is configured to obtain the flow rates of the insulating oil output by the centrifugal pump at different rotational speeds and the pressure differential of the insulating oil flowing through the oil-filled cable at different flow rates, which are sent by the measuring unit, and determine the oil channel diameter and oil channel length of the oil-filled cable. A calculation formula for calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable is as follows based on the flow rates of the insulating oil output by the centrifugal pump at different rotational speeds, the pressure differential of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable: ； in, is the head loss, is the average flow velocity in the oil channel of the oil-filled cable, is the oil channel diameter of the charging cable, is the oil channel length, is the acceleration due to gravity.

2. The device for measuring the friction coefficient of the oil flow inside the submarine oil-filled cable according to claim 1 is characterized in that: The measuring unit includes a flow meter, a differential pressure gauge, a pressure gauge and a thermometer; The flow meter is arranged on the oil-filled pipeline; The differential pressure gauge is arranged at the inlet and outlet of the oil-filled cable; The pressure gauge is arranged at the outlet of the oil-filled cable; The temperature sensing element of the thermometer is inserted into the insulating oil tank.

3. A method for measuring the friction coefficient of the oil flow in the internal oil path of a submarine oil-filled cable, applied to a calculation unit of a device for measuring the friction coefficient of the oil flow in the internal oil path of a submarine oil-filled cable according to any one of claims 1 to 2, characterized in that: The method comprises: When calculating the friction coefficient of insulating oil flowing in the oil channel of the oil-filled cable, the flow rate of the insulating oil output by the centrifugal pump at different speeds and the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, sent by the measuring unit, are obtained, and the oil channel diameter and oil channel length of the oil-filled cable are determined; Based on the flow rate of the insulating oil output by the centrifugal pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable, the calculation formula for calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable is: ； in, is the head loss, is the average flow velocity in the oil channel of the oil-filled cable, is the oil channel diameter of the charging cable, is the oil channel length, is the acceleration due to gravity.

4. The method for measuring the friction coefficient of the oil flow inside the submarine oil-filled cable according to claim 3 is characterized in that: Before obtaining the flow rate of the insulating oil output by the centrifugal pump at different speeds and the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates sent by the measuring unit, the method further includes: obtaining the temperature of the insulating oil in the insulating oil tank sent by the measuring unit, and determining the oil channel diameter of the oil-filled cable; Calculating the density and viscosity of the insulating oil according to the temperature of the insulating oil, and determining, based on the density and viscosity of the insulating oil and the diameter of the oil passage of the oil-filled cable, a flow rate of the insulating oil such that the Reynolds number of the oil passage of the oil-filled cable covers a laminar flow, a transitional flow, and a turbulent flow range; The rotation speed of the centrifugal pump is adjusted according to the flow rate of the insulating oil so that the Reynolds number range of the oil channel of the oil-filled cable covers the laminar flow, transitional flow and turbulent flow ranges.

5. The method for measuring the friction coefficient of the oil flow inside the submarine oil-filled cable according to claim 3 is characterized in that: Calculating the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable based on the flow rate of the insulating oil output by the centrifugal pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable includes: acquiring a current oil channel pressure of the oil-filled cable sent by the measuring unit; If the current oil channel pressure is different from the last obtained oil channel pressure, the friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable is calculated multiple times based on the flow rate of the insulating oil output by the centrifugal pump at different speeds, the pressure difference of the insulating oil flowing through the oil-filled cable at different flow rates, and the oil channel diameter and oil channel length of the oil-filled cable; determining an average value of the friction coefficients obtained from multiple calculations, and using the average value as a final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable at the current oil channel pressure; If the current oil channel pressure is the same as the oil channel pressure obtained last time, the friction coefficient calculated last time is used as the final friction coefficient of the insulating oil flowing in the oil channel of the oil-filled cable under the current oil channel pressure.

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