Submarine cables in underwater environments

With the rapid development of deep-sea resource development and marine engineering, submarine cables, as an important transmission medium connecting submarine facilities, their performance and reliability are increasingly valued. The deep-sea environment is complex and changeable, and extreme conditions such as high voltage, high salt, and low temperature have put higher requirements on cable materials and structure. The article focuses on the HYJQF41-F model submarine cable, and systematically studies its material performance and structural design under the voltage levels of 35KV, 66KV and 220KV. Through material performance testing, structural reliability analysis and practical application case studies, effective ways to improve the performance and reliability of submarine cables are explored, and technical support is provided for deep-sea energy development and marine engineering.

Research and analysis of material properties of submarine cables

 1.Overview of cable materials

The deep-sea transmission cable of model HYJQF41-F is used as a reference for the heart of the cable. The cathode copper material with a purity of up to 99.95% is made of low impedance characteristics and excellent conduction efficiency, ensuring high efficiency transmission of power energy. The isolation layer uses crosslinked polyolefin (XLPE) as the manufacturing material, and its voltage withstandability can reach an astonishing 40 kV/mm, which greatly exceeds the nominal operating voltage of 35 kV, 66 kV and 220 kV power cables, thus ensuring excellent electrical isolation characteristics [1]. The protective layer uses high-strength polyethylene (HDPE) to show excellent resistance to marine corrosion and physical protection. Its tensile strength is as high as 24 MPa, which is sufficient to cope with the changing terrain and mechanical pressures of the seabed. For a schematic diagram of the deep-sea wire structure, please refer to Figure .

2.Material performance test in deep-sea environment

 In order to comprehensively evaluate the material properties of HYJQF41-F model submarine cables in deep-sea environments, the following test methods were adopted in this study:

 (1) High voltage tolerance test: The cable sample simulates a deep-sea high-voltage environment in the laboratory, and continuously applies a 35KV voltage for 100 hours to detect the stability and breakdown voltage of the insulating layer.

 (2) Corrosion resistance test: The HDPE protective layer of the cable was soaked in 3.5% NaCl solution for 96 hours, and the corrosion resistance of the material was evaluated by measuring the weight loss rate.

 (3) Mechanical performance test: Perform a bending test of 1000 cYcles on the cable sample, and the bending radius is set to 10 times the cable diameter to evaluate the flexibility and durability of the material.

 (4) Microstructure analysis: Microstructure analysis of the conductive core, isolation layer and protective layer of the cable is performed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The specific results of the HYJQF41-F model submarine cable material performance test are shown in the table below.

Subsea cable structure design principles The design plan of the subsea transmission line is crucial, which ensures the continuous and stable operation of the cable in a deep-sea environment. The cable design should comply with a number of standards, including mechanical strength, electrical isolation, chemical stability and environmental adaptability. In terms of mechanical stability, the cable must be able to withstand tension, pressure and loads during operation during submarine laying. The electrical isolation design must ensure that the conductors are transmitted stably in high-voltage environments and avoid energy losses and electrical failures. Chemical stability requires that the material is able to withstand corrosive substances in seawater to keep its long-term function unaffected.

3.Data analysis and discussion

According to the evaluation of experimental data, the components used in the HYJQF41-F type marine cable showed extreme instability in deep ocean conditions. It was verified by high-voltage experiment that the crosslinked polyethylene insulating part maintained stability while continuously withstanding high voltages, and no performance reduction occurred. The results of corrosion resistance assessment have once again verified the performance of high-density polyethylene protective layer material in continuous marine immersion environment. Its slim weight reduction ratio shows the material's excellent anticorrosion ability. The inspection data of mechanical properties demonstrates the ability of this substance to adapt to variable conditions in the deep sea. The excellent elasticity and durability of the wires ensure the stability of the laying and operation stages. This information provides a solid backing for the structure and material selection of wires, and also provides a theoretical basis for the future development and improvement of deep-sea transmission line materials.

Structural design and reliability evaluation of submarine cables

1.Submarine cable structure design principles

 The concept of transmission lines in the deep ocean is extremely critical. It ensures the long-lasting and stable operation of wires in deep-sea conditions. The line structure must meet a series of criteria covering mechanical strength, electrical insulation, chemical stability and environmental suitability. In the field of mechanical reliability, wires need to be able to withstand tension, compression and loads during marine paving. When designing electrical insulation, it is necessary to ensure that the cable can reliably transmit signal under strong voltage conditions, reduce power consumption and prevent failure of electrical equipment. Chemical durability requires substances to withstand erosion factors in the ocean to ensure that their lasting effects are not damaged.

2.Structural reliability analysis method

 The structural stability assessment is a key method to determine whether marine cables can maintain normal functioning during their expected service life. Failure mode and effect analysis (FMEA) methods can be used to detect potential defect types in wire structures and measure the potential impact of these defects on overall system functions. Numerical modeling technology (FEM) is used to simulate the structural characteristics of wires under the conditions of the ocean bottom to estimate the pressure map and durability period of components. Probability analysis and statistical techniques are also commonly used in wire stability identification. They are estimated by establishing durability distribution models to estimate the fault probability and expected life of wires. The comprehensive application of these evaluation techniques can thoroughly examine the stability of wire structure and provide solid theoretical support for design improvement and hazard control.

3.Structural improvement plan

 In view of the results of the tectonic stability assessment, a targeted tectonic optimization plan can be planned. For example, for high-risk failure types detected during the Failure Mode and Impact Analysis (FMEA), it can be enhanced by thickening the wire protective layer or adjusting the material composition to enhance its resistance to corrosion and physical toughness. The data obtained by the FEA study helps to improve the details of the wire design, such as changing the size of the isolation layer and the protective layer, in order to coordinate the electrical characteristics of the wire with the physical load potential.

Study on the comprehensive performance of submarine cable materials and structures

1.Microstructure analysis of submarine cable materials

The microscopic characteristics of marine optical cables play a key role in their overall function. The microstructure of the conductive core, isolation layer and protective shell of HYJQF41-F marine wires is deeply explored using cutting-edge characterization methods such as scanning electron microscope (SEM) and transmission electron microscope (TEM). The observation of microscale structures of conductive substances revealed that the copper obtained by electrolysis had a uniform crystal particle size, a distinct demarcation line, and no significant defects [3]. This characteristic is beneficial to improve current transfer efficiency and reduce resistance value. The microstructure investigation results revealed that high-density polyethylene, a material for protective layer, exhibited a relatively regular chain-like arrangement on the molecular level and had a significant crystallization level. This characteristic is extremely beneficial for enhancing the protective layer's resistance to chemical erosion and environmental stress cracking. The microstructure of submarine cable materials, see the figure.

2.Research on the dynamic performance of submarine cable structure

 In actual operation, transmission lines in the deep ocean will inevitably be disturbed by dynamic elements such as tides and ocean currents, and the dynamic characteristics of their structure are particularly critical. The deep sea conditions were reproduced in the laboratory to test the wires for cyclic bending, traction and vibration. Periodic tortuous experiments in an environment that mimics the terrain fluctuations at the bottom of the ocean revealed that under the continuous tortuous action, the cable still maintains its structural integrity without damage, and its minimum allowable radius of twists is six times the diameter of the cable. Data from the stretch experiment revealed that the wires kept the structure intact and showed excellent tensile strength under 120% of the design maximum tension. In the vibration experiment, no damage to the insulation or protective layer was observed under the oscillating loads of the frequency range from 1 Hz to 10 Hz, which verified its excellent vibration resistance.

3.Long-term reliability assessment of submarine cables

 Assessing the durable robustness of marine cables is critical Given that it is related to its stable performance over all expected service life, a scheme was created to speculate on the service life of the wire and analyzed based on actual marine situational data. Experimental data show that when the predetermined service life is set to twenty years, the isolation resistance value of the wire is stable at more than 500 megaohms, significantly exceeding the level specified in the specification. The integrity of the wire can be determined instantly by continuously tracking and accumulating operational data. The durable stability analysis points out that after careful structure and material selection, the HYJQF41-F type marine wire has the ability to continuously operate in deep-sea conditions to ensure uninterrupted operation for at least 30 years.

Through in-depth exploration of the internal structure of the material, real-time monitoring of performance changes and continuous identification of stability, the compatibility and endurance of wires under harsh sea areas are demonstrated. Looking forward to the future, the continuous improvement of the material and structure of submarine transmission lines will inevitably lay a more solid foundation for the mining and application of marine resources.       Shanghai Lansheng Cable can meet your various cable needs.