Advancements and Challenges in Power Cable Laying

Abstract

The laying of power cables is a crucial aspect of developing and maintaining modern electrical infrastructure, which is vital for transmitting electricity reliably and efficiently. This review discusses the challenges and advancements in cable laying technologies, emphasizing the critical role of these techniques in meeting the increasing demands for power transmission in the backdrop of the global shift to renewable energy. Three main traditional cable laying methods are explored, including underground, overhead, and submarine, each suited to specific environmental and operational conditions. Then, the cable faults due to the impropriate laying process are discussed. Subsequently, the challenges and advancements encountered in cable laying processes are investigated, especially the difficulties of the cable laying of underground cable, submarine cable, and high-temperature superconductivity cable. This review also considers the impact of technological innovations on improving efficiency in cable laying processes, highlighting the advances driven by digitalization and automation.

1. Introduction

Electric energy constitutes the fundamental driving force of contemporary society, with power cables serving as essential channels for its transmission [1]. These cables facilitate the flow of electrical energy among power stations, substations, converter stations, and end users, thereby enabling the transportation and distribution of electrical power. As a vital element of the electrical power system, ensuring the safe and stable operation of these transmission lines is crucial. In addition to the cable structures and materials, the reliable transmission of electricity significantly relies on adept cable laying techniques. In studies of cable faults, the data show that mechanical stresses during laying contribute significantly to cable failures [2]. The techniques involve the cable laying in settings that may be underground, underwater, or overhead [3].

The choice of cable laying method is closely related to the laying length and environment, as well as the cable material and structure. Figure 1a depicts a typical single-core cable, characterized by its simple structure, ease of maintenance, and efficient heat dissipation. They are commonly used in high-voltage applications exceeding 110 kV, as they can effectively withstand high voltages without generating excessive electromagnetic interference. Additionally, there are also multi-core cables, such as triple-core cables, as illustrated in Figure 1b, particularly in three-phase electrical systems. Each core in these cables independently conducts one phase of current, enhancing spatial efficiency and potentially reducing costs. Triple-core cables, often shielded with armored steel strips, exhibit a degree of leniency in their laying environments and provide a protective barrier against general external forces [4]. However, they are susceptible to inter-phase short circuits if the insulating materials become damp or deteriorate. Conversely, single-core cables, typically spaced farther apart, predominantly experience grounding short circuits under similar conditions of insulation degradation, with inter-phase short circuits being a rare occurrence. Additionally, single-core cables require a more stringent laying environment due to the absence of magnetic steel strips.

From the innermost to the outermost components of the coaxial cable, they are the conductor, inner semiconductive layer, insulation layer, outer semiconductive layer, water-blocking tape, metallic sheath, armoring, and other serving layers. Among them, the conductor, insulation layer, metallic sheath, and armoring are the most closely related to the laying environment and process. The core conductor, which carries the current, is commonly made from copper or aluminum [5]. Copper-core cables are preferred for their higher current-carrying capacity, lower voltage loss, and resistance to oxidation and corrosion. The metallic sheath layer can prevent the insulation from coming into contact with moisture, which can lead to the formation of water trees [6], and it also acts as a pathway for zero-sequence fault currents in the event of a fault. The sheath grounding methods mainly include single-ended earthing, neutral point earthing, double-ended earthing, and cross-bonded earthing [7]. The choice of grounding method depends on factors such as voltage level, cable length, and environmental conditions. Single-ended earthing is suitable for shorter, single-core underground cables and can reduce circulating currents. Double-ended earthing is used for three-core cables or long-distance submarine cables, where direct grounding should be performed at both ends of the line. If there are intermediate joints, these should also be directly grounded, which is known as neutral point earthing. The cross-bonding grounding method is used for long-distance cables, where insulated joints should be used to divide the metal sheath and insulation shield into three segments or multiples of three to reduce induced voltage and circulating currents. Cross-linked polyethylene (XLPE) is widely employed as an insulation layer due to its excellent current-carrying capacity, mechanical strength, corrosion resistance, thermal aging resistance, and ease of laying [8]. Furthermore, thermoplastic materials such as polypropylene (PP) [9] are anticipated to facilitate the self-healing of defects and self-restoration of insulation properties while maintaining superior electrical insulation and thermal resistance, marking a significant direction for the future development of insulation materials. Improper cable installation can cause various faults and safety hazards, leading to failures in the insulating and mechanical properties of the cable, as well as short circuits and even electrical breakdown.

Therefore, it is essential to select laying methods and techniques that are tailored to the diverse characteristics of various environments, cable types, and operational requirements. In recent years, the demands for power transmission capacity and distance have increased all over the world [1]. The rapid pace of urbanization and the expansion of underground utility tunnels have complicated the environment for cable laying and operation [10]. Additionally, the development of offshore energy has also heightened the demands for submarine cables laying over long distances, which face a more complex laying environment compared to underground cables, such as the impact of sea waves, the tensile forces during laying, and the traction forces from ships [11]. Moreover, the increasing demand for electrical infrastructure coupled with the urgent necessity for low-carbon and sustainable energy solutions has spurred the development of novel cable types, such as superconducting cables [12]. The installation practices for these advanced cable types are still being refined and represent a critical area of ongoing research and development.

This paper explores the evolution of cable laying techniques, discussing the challenges and adaptions of traditional methods when meeting the demands of increasingly complex and varied installation environments. The discussion will provide insights into how these developments contribute not only to cable laying but also to the broader goals of energy efficiency, sustainability, and infrastructure resilience.

2. Traditional Cable Laying Methods

According to the laying environment, traditional laying methods include underground cables, overhead lines, and submarine cables. Overhead lines are generally bare conductors, and some are wrapped with insulation layers. However, since overhead lines are also one of the most important power transmission approaches, they are also discussed in this section. Each laying method has its own set of advantages, depending on geographical, economic, and environmental factors.

Table 1. Comparison of the three main laying methods.

	Underground Cable	Overhead Line	Submarine Cable
Era of the started application	1850s [13]	1880s [14]	1850s [15]
Current voltage level	400 kV (AC); ±800 kV (DC)	1200 kV (AC); ±1100 kV (DC)	525 kV (AC); ±600 kV (DC)
Cost of cable laying	USD 125–USD 200 per meter [16]	USD 6–USD 156 per meter [17]	USD 500–USD 1500 per meter [18]
Advantages	Safety, reliability, and aesthetical	Lower cost, adaptable to various terrains	Connecting the regions separated by water
Disadvantages	Higher costs; difficult to repair and maintain	Susceptible to weather; inaesthetic	Very high cost; susceptible to sea wave motion and marine activities
Typical Application	Cities and areas with harsh weather conditions where overhead lines might be vulnerable	Rural and suburban areas with lower population density and greater distances	Used for crossing rivers, lakes, and seas

highlights the differences between the various methods for comparison purposes. In addition, the choice of laying method is closely related to the voltage level: the higher the voltage level, the more stringent the laying requirements to ensure the safety and reliability of the cable operation. The underground and submarine cables laid at different voltage levels are listed in

Table 2. The laying method of underground and submarine cables at different voltage levels.

	Underground Cable			Submarine Cable
	Direct Burial and Trenching	Ducting and Conduits	Tunnel	Surface Laying	Buried Laying	CLV
<1 kV (LV)	√			√
1~35 kV (MV)	√	√		√	In shallow areas or rocky areas of the seabed	√
35~220 kV (HV)		√	√	√	√	√
220~800 kV (EHV)		√	√		√	√
>800 kV (UHV)		√	√		√	√

. In this section, we will discuss the characteristics of each laying method in detail.

2.1. Underground Cable

The first underground cables were laid in the latter part of the 19th century [13]. Installing underground cables is a complex and time-consuming process with specialized equipment, including trenching, laying the cables, and backfilling the trenches. According to different environmental conditions, ampacity requirements, and maintenance needs, the following are the main laying methods, which are also presented in Figure 2:

• Direct burial and trenching: The most common method used in rural or less congested urban areas where disturbance is minimal. Initially, a trench is excavated, into which the cable is placed, followed by a layer of protective sand, and finally, the trench is backfilled with soil. This approach is cost-effective and straightforward, making it suitable for a variety of environments. Typically, direct burial is used when ampacity demands are relatively low and only a few cable circuits are required. In contrast, trenches are commonly utilized within industrial sites or buildings where a larger number of cables are required. These trenches allow for the addition of multiple cable circuits based on the electrical load demands, accommodating numerous cables and facilitating easy and quick maintenance.
• Ducting and conduits: Often employed in urban areas to allow easier cable maintenance and future upgrades. This method involves placing cables inside regularly spaced protective conduits made of plastic or cement and pouring concrete around them to provide additional protection. The piped laying approach offers strong resistance to external forces, effectively safeguarding the cables. It also has advantages such as ease of construction and minimal excavation. When crossing roads and rivers or tunneling beneath structures, where large-scale excavation is impractical, the use of small-diameter pipe-jacking tunnels is considered.
• Tunnel installation: More costly and complex than other methods, while offering long-term benefits in terms of durability, ease of access, and minimal environmental impact. The construction of tunnels is accessible by digging a large bore using tunneling machines such as a Tunnel Boring Machine. Then workers or machinery enter the tunnel and install cable racks or trays along the walls or ceiling of the tunnel. Tunnels can accommodate multiple high-capacity cables, making them ideal for central business districts or industrial zones where large amounts of power transmission are necessary. Cables in tunnels are well-protected from environmental hazards such as flooding, chemical corrosion, and physical impacts from above-ground activities. In addition, maintenance and replacement of cables are significantly easier in tunnel installations compared to other methods.

The direct and trenching methods are usually used for cables with low-voltage (LV) and medium-voltage (MV) levels. On the other hand, ducting, conduits, and tunnel installation are typically employed for cables with higher voltage levels, such as high voltage (HV), extra-high voltage (EHV), and ultra-high voltage (UHV). Additionally, with the development of technology, laying techniques range from traditional trenching and plowing to horizontal directional drilling (HDD) [19]. HDD is playing an increasingly important role in power engineering applications because of its low social and environmental impact and high construction speed. According to different operating scenarios and needs, the appropriate laying method is selected based on operational reliability and economy. When the laying method is determined, the key parameters that affect the quality of laying include the laying depth [20,21,22], thermal envelope [20,22], cable arrangement [23,24,25,26], cable spacing [22,24,25], and so on.

(1) Thermal envelope and laying depth: The ampacity of a cable very much depends on the thermal resistance of the surrounding medium [27]. To facilitate heat dissipation, a backfill with lower thermal resistivity is used around the cable, as illustrated in Figure 2. Francisco et al. [20] found that a small quantity of backfill can produce sizable ampacity gains. In addition, the thermal envelope or the laying depth would also affect the thermal resistance and heat path [21,22].

(2) Cable arrangement and spacing: To meet ampacity requirements and improve space effectiveness, a multi-circuit laying environment is usually employed. However, the mutual inductance and mutual heating effect between cables will limit the maximum ampacity of the cable [24]. The interaction between cables would be affected by the quantity [23,25], spacing [21,25], and arrangement [21,25] of the cables. Therefore, it is necessary to select appropriate cable spacing to ensure that the cable can operate safely and effectively while increasing capacity.

The complexity of the laying process leads to longer project durations and higher labor costs. Additionally, coordination with other infrastructure projects, such as road construction or urban development, becomes essential to avoid conflicts and ensure proper cable protection. Therefore, there is an urgent need to develop new underground cable laying technologies.

2.2. Overhead Lines

Due to the imbalance of energy resources across different regions, long-distance transmission of electrical power is essential. The interconnection of electrical systems via transmission overhead lines enables the efficient utilization of electricity from regions with abundant energy resources. Additionally, overhead lines are highly adaptable to complex terrains, allowing them to span mountains, lakes, and railways.

The installation of overhead lines involves erecting support structures, stringing power conductors, and connecting necessary accessories [14], which is less complex compared to underground cable laying. In the installation process of high-voltage and ultra-high-voltage cables, tension stringing and tensioning are the most common methods. The diagram of the tension-stringing method is demonstrated in Figure 3. Tension stringing machines, which are highly automated, enhance construction efficiency and conserve labor and resources. The process of tension stringing involves the use of unmanned aerial vehicles or manual methods to thread a pulling rope through transmission towers and grounding pulleys. Subsequently, a tensioning device retracts the pulling rope, which in turn pulls the cable to complete its installation. During the installation process, the cable does not come into contact with the ground, preventing abrasion and damage to the outer sheath of the cable.

During the installation of overhead lines, an unintended nonlinear coupling of movements is observed between the transmission towers and the power lines. The pulling force exerted by tensioning machines can cause significant deformation at the hinged and sliding connections between the tower and the power lines. This deformation impacts the movement of the power lines and induces loads on the transmission towers. Additionally, the power lines can sometimes break during installation. In such instances, the power lines impose shock loads on the transmission towers, leading to vibrations or even resonance, which, in severe cases, can cause the towers to collapse or topple. Moreover, the load on the tower and power lines would also be affected by weather conditions, especially wind, rain, and snow. IEC 60286-2017 provides a calculation method for load for overhead line systems affected by wind and ice coverage [28] and grades the reliability levels. Many studies have researched the static and dynamic aspects of transmission tower line systems using both linear and nonlinear finite element methods [29]. Since this review mainly focuses on the laying methods involving underground cables and submarine cables, the current research status of overhead lines will not be discussed further.

2.3. Submarine Cable

Cross-sea power transmission is a crucial method for interconnecting power grids across seas, developing offshore energy resources, and facilitating long-distance energy transfer. The primary modalities for achieving cross-sea transmission include submarine cables, cross-sea bridges, undersea tunnels, and overhead lines spanning the sea, with submarine cables being the most commonly used [11]. The first successful laying of a submarine cable was completed in the 1850s across the English Channel. Today, these cables are critical for global internet connectivity and offshore energy utilization. Given the unique environmental challenges [30], submarine cable laying demands more rigorous conditions and more complex laying methods compared to underground cables and overhead lines. The submarine cable laying necessitates careful consideration of specific marine environments, the physical characteristics of the cables, cost factors, and future maintenance needs. Effective laying methods can maximize the lifespan of the cables and minimize maintenance costs. The laying method can be classified according to the laying position or the laying steps.

The laying methods categorized by the cable location include surface laying, buried laying, and suspended laying:

• Surface laying: The cable is directly placed on the surface of the seabed, as shown in Figure 4a [31]. It is suitable for areas with gentle currents and flat seabed conditions. It is generally the most widespread due to its advantages of cost-effectiveness, simplicity, and flexibility. However, the cable is vulnerable to damage from external factors such as anchors.
• Buried laying: The cable is buried at a certain depth beneath the seabed by using underwater trenching machines or water jet trenching technology, as shown in Figure 4b [32]. This method effectively protects the cable from physical damage and external disturbances (such as tides and ocean currents), making it suitable for areas with heavy traffic or frequent seabed activity. However, this method brings great difficulties to the maintenance, fault finding, and accurate positioning of cables.
• Suspended laying: Suitable for regions with complex underwater topographies and significant seabed undulations, such as seamounts or rift valleys. In these areas, the cable needs to be suspended above seabed obstacles, typically requiring special support structures to maintain the stability and integrity of the cable.

In addition to LV cables being generally laid directly, the choice of submarine cables with higher voltage levels is mainly determined by the environment, as demonstrated above. When classified by laying steps, the laying methods mainly include the following:

• Simultaneous laying and burying: Higher requirements for the cable laying vessel (CLV) and equipment. The underwater machine is used to trench while simultaneously releasing the cable into the pre-excavated deep trench on the seabed, as shown in Figure 4c [32]. When the second segment of the cable is in position, a hard joint is used to connect the first segment, enabling the simultaneous completion of laying and burying in one operation. This method is suitable for short routes with minimal shipping traffic and favorable sea and geological conditions.
• Pre-laying and burying: The CLV deploys the cable onto the seabed according to the pre-designed route. Subsequently, divers or Remote Operated Vehicle (ROV) utilize underwater equipment to bury the cable on the seabed. Figure 4d presents a photograph of ROV [11]. This method is generally applicable in areas with poor geological conditions or shallow waters inaccessible to large laying vessels.
• Free-fall technique: The cable is sunk onto the seabed under its weight and directly placed on the surface of the seabed, making the installation the simplest. However, it is less secure compared to deep burial, particularly in shallow waters where it is susceptible to damage from fishing activities and ship anchors. Therefore, it is primarily used in deep sea areas with water depths exceeding 500 m.

CLV [33] is a specialized vessel designed for submarine laying routing, installation, and layout, as presented in Figure 4e. There are usually the cable laying machine (CLM) and ROV [34] mounted on the CLV. The CLM refers to the equipment used for deploying cables during installation, while the ROV mainly works for submarine cable burial and maintenance. A typical ROV is shown in Figure 4d. In addition, an accurate positioning system [11] is essential for CLV to effectively control the water entry angle and tension of the cable, ensuring that the submarine cable is laid according to the designed coordinates while avoiding poor local terrain. The submarine cable laying includes tension laying and slack laying. The former is a technique where the tension of the cable is controlled, the speed of the cable released matches the vessel speed, and no additional slack is provided. In shallow waters, where the seabed is relatively flat, the preset tension values on the deployment equipment do not require frequent adjustments, making this method suitable for shallow water laying. In contrast, deep sea installations often face complex and variable terrain, making slack laying the preferable method. The focus is on controlling the cable release speed so that it slightly exceeds the vessel speed. Since the vessel speed remains relatively constant, adapting to various seabed terrains is achieved by timely adjustments to the release speed to maintain the necessary slack.

Similar to underground cables, the influence of the thermal resistance of the surrounding environment needs to be considered during the submarine cable operation [11,35]. Additionally, the wind [36,37], and the sea waves [35,38,39] also have effects on the conductor temperature of submarine cables.

3. Cable Faults Due to Impropriate Laying Process

Various types of cable faults can arise due to impropriety in the laying process. The three main faults include mechanical damage attributable to inappropriate stress, joint failures resulting from incorrect installation techniques or connections, and insulation defects. This section introduces several cable faults caused by inappropriate laying processes. Except for joint failure, the cable fault categories due to the impropriate laying process are illustrated in Figure 5. The analysis of the typical faults provides scientific guidance for operating specifications and future cable laying technology improvements.

3.1. Mechanical Damage

Mechanical damage during the cable laying process mainly covers problems such as armor flattening, cable twisting, and sheath fracture, among which sheath fracture is particularly common [40]. The core function of the cable outer sheath is to provide mechanical protection and electrical insulation. Therefore, the insulation properties and mechanical properties of the sheath material are the keys to determining the overall performance of the sheath. The mechanical properties include tensile strength, elongation at break, and elastic modulus. Tensile strength represents the performance of a material when it withstands tensile and bending forces. High tensile strength means stronger tensile and bending resistance. Elastic modulus reflects the material’s ability to resist deformation. A lower elastic modulus indicates that the material is resistant to deformation. The deformation is small after bearing force, and the elongation at break is an important indicator for evaluating the impact resistance of the material. A higher elongation at break can enhance the impact absorption capacity of the material. Taking XLPE insulation power cable as an example, the tensile strength value is in the range of 20 to 30 MPa [41], with a requirement of no less than 300% of the elongation at break and an elastic modulus in the range of 400 to 800 MPa [42].

The laying of cables is usually carried out by manual traction, tractors, or conveyors, involving a variety of laying tools, such as traction heads, wire protectors, anti-twist devices, linear pulleys, corner pulleys, and conveyors [43]. During the traction process, the cable is subjected to various mechanical forces, such as traction force, bending force, lateral pressure, and friction. Most of these forces act directly on the outer sheath of the cable. When the mechanical force on the outer sheath exceeds its withstand capacity, it may cause the sheath to crack, as shown in Figure 5. The friction of the cable on the ground, pipe wall, or bracket during the laying out process also increases the risk of cracking the cable sheath. IEEE 1185-2019 has demonstrated that the maximum stress that the sheath can withstand during cable laying is 20–40 MPa [44]. The abusive stress may cause the cable sheath to be damaged. When a cable sheath breaks, several extreme situations can occur, such as conductor deformation or breakage, water or chemical exposure, overheating, short circuits, and insulation aging and breakdown [45]. For instance, a short circuit can cause currents exceeding 20 kA [46], leading to power system failure and potential fire hazards.

In addition, during the pulling and pay-off process, the tension may not be constantly controlled or braked, and the pay-off speed may be uneven. These factors will cause the cable to have a too-small bending radius and excessive stress, thus affecting the mechanical properties and span of the cable. IEC 60840 (2020) recommends a minimum bending radius of 15 times the cable’s outer diameter during cable laying [47].

In summary, appropriate material selection, precise use of laying equipment, and strict operating procedures are key factors in protecting cables from mechanical damage during laying. By improving material performance and optimizing construction equipment and technology, mechanical damage during cable laying can be significantly reduced, and the stability and safety of the cable system can be guaranteed.

3.2. Insulation Failure

Inappropriate mechanical stress during the cable laying process can significantly damage the insulation layer of cables, leading to a degradation in both mechanical and insulating properties. Commonly identified insulation defects include water trees and electrical trees, which are often initiated by protrusions, conductive impurities, or air gaps resulting from cracks. Water trees [6], in particular, are critical due to the electric field concentration at the tips of their branches, which can stimulate the formation of electrical trees [8,48]. These defects may cause partial discharge, potentially leading to complete insulation breakdown, phase-to-phase short circuits, or ground faults, thereby compromising the reliability and stability of the power system.

The structure of water trees or electrical trees typically exhibits a tree- or bush-like pattern within the XLPE insulation, as illustrated in Figure 6, impacting the long-term insulating properties of the cable. Identification and location can often be addressed through effective monitoring methods [6] due to their lengthy incubation periods. Nonetheless, current online detection and fault location techniques require further enhancement to address these faults, particularly in complex laying environments where the fault process is both difficult and costly.

To mitigate these risks, it is crucial to adhere to proper installation practices. Potential causes of insulation failure during cable laying include the following:

• Utilizing a cable bending radius smaller than the minimum allowable value, which can damage the internal insulation layer;
• Laying practices that result in scratches, crushing, or punctures, compromising the integrity of the insulation layer;
• Extended exposure of the cable to high temperatures, leading to aging, deformation, or melting of the insulation material;
• Contact with harmful chemical substances such as oils, acids, and alkalis, which can corrode the insulation material and diminish its performance.

Furthermore, during operation, power cables experience thermal expansion and contraction in response to variations in load current and ambient temperature. This dynamic can generate significant mechanical forces, particularly in cables with larger core cross-sections, and lead to insulation damage. Repeated cycles of thermal expansion and contraction can also induce creep deterioration in both the core and metal sheath. Additionally, mismatches in the physical properties among the different cable layers may lead to delamination during thermal cycling or create interface air gaps, further leading to discharge and insulation degradation.

3.3. Joint Failure

Joint failure during the cable laying process is a prevalent issue that arises due to several factors, including improper installation techniques, environmental influences, and mechanical stresses. Cable joints are crucial components within cable systems, serving to connect cable segments, facilitate repairs, or reroute cables. They also provide essential electrical insulation and protection against short circuits and ground faults, thereby safeguarding the system from environmental hazards. Failure of these joints can impede current transmission, potentially leading to arcing, short circuits, and abnormal fluctuations in voltage or current. Such disturbances can introduce instability, overload, and breakdown risks to the power system. The main reasons that may cause joint failure due to improper laying process include the following:

• Improper connection: Joint failures can occur if the connections are not executed in strict compliance with specifications. Common issues include unclean contact surfaces, loose conductor connections, and the incorrect selection or application of insulating materials.
• Poor sealing: Inadequate sealing of joints can allow moisture and other corrosive substances to penetrate, damaging the insulation layer and heightening the risk of joint failure. In corrosive environments, such as those characterized by acidic or salt spray conditions, the metallic components of the joints are particularly susceptible to accelerated corrosion, leading to premature failure.
• Environmental factors: Extreme temperature fluctuations can induce thermal expansion or contraction of the joint materials, leading to physical and structural deformations that compromise both sealing and electrical performance.
• Mechanical stress: Excessive mechanical stress imposed during cable laying, such as overstretching, undue pressure, or improper bending, can physically damage or structurally deform the joint, further elevating the risk of failure.

It was found that the failure rate of accessories far exceeds that of submarine cable bodies, with intermediate joints accounting for about 70% of accessory failures [49]. Joint design and installation remain crucial bottlenecks that researchers and manufacturing enterprises need to improve in the development of cable technologies. Although the insulation materials of accessories themselves possess good insulation properties, the interface formed with the cable body often becomes a weak point in insulation. Prefabricated joints and terminals often need to be installed outdoors under relatively harsh conditions, making it difficult to ensure the installation process [50]. Therefore, the key to improving the reliability of accessories lies in strengthening the control of the on-site installation process to ensure coordination between the accessories and the cable body materials at the interface.

4. Laying Methods and Challenges in a Complex Environment

As the electricity demand continues to grow around the world, the construction of power transmission is also facing unprecedented challenges. On the one hand, due to a reduction in available land, new power cables need to be laid in more complex and varied terrain, including mountainous areas with high heights and steep terrain. On the other hand, with the development of emerging energy technologies such as offshore wind power generation, the construction of transmission lines must also be expanded to undeveloped areas such as the deep sea. The cable laid in these complex environments not only faces the severe stresses of natural conditions such as hurricanes, storms, blizzards, typhoons, and other extreme weather [51], but also environmental protection requirements that need to be taken into account to ensure that the impact on the ecosystem is minimized [11]. Moreover, with the continuous advancement of high-temperature superconducting (HTS) technology [12], the application of HTS cables has become possible. HTS cables have great advantages in energy loss reduction, power transmission efficiency, and environmental advantages. However, although the laying method of HTS cables is similar to that of traditional cables, additional equipment and technology are required to maintain their superconducting state. Therefore, practical applications also face many technical and economic challenges.

The laying challenges in several typical complex laying environments are introduced in this section.

4.1. The Underground Cable Laying in Complex Environment

The discussion of fault types in high-voltage cables reveals that exceeding rated values of traction and friction forces during cable laying, or uneven distribution of mechanical stress, are key factors leading to failures in both the cable body and accessories. Presently, there exists a contradiction between the increasing demand for power transmission lines and the decreasing available space for power cable laying. With the rapid expansion of infrastructure projects such as urban elevated highways and high-speed railways and the proliferation of high-rise buildings and densely populated urban areas, cables are increasingly being installed in complex environments, exacerbating the challenges of cable laying [10]. In addition, factors such as the presence of other utility lines and the need to comply with stringent safety regulations further complicate the laying process. Consequently, cables laying in increasingly complex terrain have been a focal point for electric construction. However, the study of cable laying theory has received comparatively less attention, with research efforts often concentrated on aspects such as ampacity and thermal properties across diverse laying environments. Nevertheless, the intricacies of cable laying mechanics, encompassing factors like traction dynamics and friction management, need deeper investigation to enhance operational efficiency and mitigate potential damage risks.

A cable laying under a complex environment [52] is illustrated in Figure 7. The whole laying path includes cable interlayers, cable trenches, row tubers, stay tube sections, and high-drop sections. Among them, the main difficulties in laying are stay tube sections and high-drop sections. The simplified ideal model for traction force calculation in stay tube section and high-drop section is demonstrated in Figure 7, where L is the horizontal distance of the cable laying in stay tube section; θ₁ and θ₂ are the incident angle and the exit angle of the cable laying in stay tube section, respectively; h₁ and h₂ are the depth of the incident end and the depth of the exit end of the cable laying in stay tube section; R₁, R₂, and R are the radius corresponding to the arc. The cable has different bending states along the entire path, causing differences in the traction force on the cable. The traction calculation model during cable laying is given in

Table 3. The calculation model of traction force during the cable laying process [53].

Bend Type	Schematic Diagram	Traction Calculation Model
Horizontal linear reaction		$F=\mu WL$ 1
Inclined linear reaction		$\begin{array}{l}{F}_1=WL(\mu \cos {\theta }_1-\sin {\theta }_1)\\ F_2=WL(\mu \cos {\theta }_1+\sin {\theta }_1)\end{array}$
Inclined surface traction (concave surface)		$\begin{array}{ll}{F}_2=& F_1{e}^{\mu \theta }+\frac{WR\sin \alpha }{1+{\mu }^2}[-(1-{\mu }^2)\sin \theta +\\ & 2\mu (\cos \theta -e^{\mu \theta })\end{array}$
		$\begin{array}{ll}{F}_2=& F_1{e}^{\mu \theta }+\frac{WR\sin \alpha }{1+{\mu }^2}[2\mu \sin \theta +\\ & (1-{\mu }^2)(\cos \theta -e^{\mu \theta })\end{array}$

¹ L is the laying horizontal distance; W is the weight of the unit length of the cable; and μ represents the coefficient of friction.

[53], where L is the laying horizontal distance, W is the weight of the unit length of the cable, and μ is the coefficient of friction.

According to Table 3, the traction force during cable laying is influenced primarily by factors such as the self-gravity of the cable, the friction between the cable and the laying surface, the angle of inclination along the path, and the bending radius of the cable. A large flexural deformation of the cable would occur under the action of a large traction force. Effective control of traction can significantly mitigate the risk of cable damage. Minimizing friction is essential to reducing cable wear, and this can be achieved through the strategic placement of rollers and the application of lubricants at points of contact friction, such as between cables and pipe walls or shaft supports. Current methods often employ roller brackets constructed by inserting a steel pipe through perforated plastic rollers to facilitate cable introduction into the working well. However, the sliding friction between the plastic rollers and steel pipe results in significant resistance and inconvenient movement along the pipe. In tunnel construction, triangular steel tube erecting methods with pulleys installed on the horizontal side are commonly used. Despite providing stable support, this method occupies walking space, leading to reduced work efficiency and challenges in emergency rescue operations.

The traditional cable laying transmission and traction equipment is poorly portable, not highly intelligent, and its installation, layout, and use are limited by the environment of the site power channel. The authors built distributed, integrated and miniaturized cable-laying equipment for complex working conditions. The authors designed a new type of cable conveyor structure, cancel the original cable conveyor gear box. The power system is changed to the “motor + gearbox” form of the structure, the transmission is changed to the “track + sprocket + spindle” form. The authors designed an intelligent cable traction device to realize automated traction of cable with constant tension, based on closed-loop control, real-time monitoring and feedback control of key parameters such as traction force, tension, rotation speed and position deviation as shown in Figure 7. Compared to the traditional cable laying system, the size and weight of the new system are half.

In addition, trenchless HDD technology can be used in areas that are not suitable for development, such as high speeds, electrified railways, and navigable rivers [19,54,55]. HDD is used in the laying of underground cables and submarine cables, and its impact on the environment is relatively small. However, the trade-off between friction resistance and allowable traction force remains a key constraint in long-distance laying. While robotic construction offers advantages, improvements are needed in power supply methods, self-rescue capabilities during emergencies, and navigation and communication within complex structural pipelines. Furthermore, abnormal phenomena such as blockages and pipeline displacements due to geological subsidence or laying quality issues can result in cable damage, reducing its service life. Traditional manual methods for duct dredging and cleaning provide limited insight into pipeline defects, highlighting the need for cable laying condition monitoring systems to ensure safe laying practices [56].

4.2. Deep Sea and Long-Distance Laying

There is a need to utilize 70% of undiscovered land under the seas and oceans to connect continents through power cables, establish renewable energy farms in the open seas [39], or even excavate for offshore sources of hydrocarbon fossil fuels. As the demand for sustainable energy sources such as wind power increases, the expansion of offshore wind farms is expanding across the world, and so is the need for cables laid under the sea. These put extremely high requirements on cable materials, cable structures, laying equipment, and laying methods.

4.2.1. The Thermal and Mechanical Stress in the Deep Sea

The thermal resistance and ampacity changes to the cable need to be considered during laying. The thermal conductivities and diffusivities of the seabed and its ambient temperature, as well as the laying depths, may vary along the route [57]. This may be a result of natural route conditions or a possible settlement of the cable into soft sediment, as well as silting and sediment deposition. Both may result in much greater soil coverage than the design value, thus leading to unacceptable rises in cable temperatures. In addition, the ocean current will also affect the temperature distribution and current carrying capacity of the cable in the form of convection heat transfer [35,38,58]. A calculation model combining heat transfer with thermo-electric effects and ocean current is illustrated in Figure 8 [35]. Therefore, when calculating heat flux and current carrying capacity, the influence of heat convection and heat transfer must be considered.

Cao et al. [32] investigated the cable conductor and its surrounding temperature in multi-layered sediment, where the burial depth and soil permeability have a significant impact on the temperature distribution. Li et al. [59] proposed a method to predict the change in submarine cable burial depth based on convolutional neural networks and long short-term memory units. As shown in Figure 9, the change in submarine cable burial depth is predicted based on the thermal path model. The experimental verification was further conducted for the proposed algorithm. Accurate prediction of the burial depth is helpful for later calculations of thermal resistance and ampacity. These studies provide crucial insights into the physical factors influencing cable performance and offer practical tools for predicting changes that affect cable reliability and efficiency. However, the universality of the models remains to be validated, as does the potential impact of geological variations on temperature across different regions. Furthermore, advanced machine learning methods rely heavily on large volumes of data and high-quality data inputs, where data acquisition and processing can pose challenges.

The deep sea environment is extremely harsh, including conditions such as high pressure, low temperature, and strong currents. In addition to the frictional resistance and traction force encountered by underground cables, submarine cables also need to withstand more complex mechanical environments, such as seawater pressure and fluid dynamics. Bayoumi et al. [39] analyzed the fluid forces experienced by cables laid directly on the seabed surface in a static state and thus studied the ability of the cable to maintain stability using its weight on the seabed, as shown in Figure 10. The results show that the force on the cable fluctuates greatly due to seawater fluctuations. Therefore, the complexity of the subsea cable laying environment demands careful consideration of the variations in stress caused by wave motion, ensuring cable integrity and functionality under such dynamic conditions.

4.2.2. The Cable Material and Structure

As ocean depths increase, submarine cables face increasing requirements for radial and longitudinal water resistance to withstand hydrostatic pressure. Consequently, designs are increasingly oriented towards solidification [11], enhancing water-blocking capabilities but also augmenting the weight of the cable. This increased weight, as indicated by the analysis in Table 2, requires greater traction force during deployment, imposing higher demands on the laying equipment. Moreover, with the extension of cross-sea power transmission distances, the operational reliability of submarine cable projects becomes crucial, particularly at vulnerable points such as joints and terminals. A current solution is to extend the length of individual submarine cables, minimizing the need for intermediate joints. However, the production of these extended, jointless cables largely depends on the feasibility of maintaining a continuous cross-linking process without interruptions. Despite these advancements, the long distances covered still require numerous joints, underscoring the need for ongoing improvements in joint installation techniques and quality. Therefore, to meet the requirements of laying submarine cables deeper and over longer distances, there is still much to be achieved in terms of cable structure and insulation design.

4.2.3. The Laying Method

The method of laying cables needs to adjust to the increasing depth and distance. In deep sea laying, there are often complex and varied terrains; hence, slack laying is preferred. The focus is on controlling the speed at which the cable is released so that it is slightly faster than the vessel speed. Since the vessel speed remains relatively constant, adapting to different seabed terrains is achieved by timely adjustments to the release speed to maintain the necessary slack. However, slack laying is a complex process that needs to be managed carefully. Having too much slack can cause cable wastage and twisting damage, while having too little slack can lead to excessive tension and cable suspension issues.

The dynamics of submarine cables laid by a cable laying vessel can be described through two-dimensional or three-dimensional stationary models. In a two-dimensional stationary model, it is assumed that the vessel travels at a constant speed and the seafloor is flat, with a constant cable laying or hauling rate. As shown in Figure 11, the mechanical behavior of the submarine cable can be described by the following simplified formula [60]:

$$T(s)=T_0+w{\displaystyle {\int }_0^s\sin (\theta (u))du}$$

(1)

where T(s) is the tension at position s, T₀ is the initial tension, w is the weight per unit length of the cable, and θ(u) is the angle between the cable and the horizontal direction, with its rate of change given by the following:

$$\frac{d\theta }{ds}=\frac{wcon\sin (\theta (u))-D}{T(s)}$$

(2)

where D is the drag coefficient.

A two-dimensional model is relatively simple. However, for environments with complex terrain or strong lateral ocean currents, a two-dimensional model may not provide sufficient analysis. If the irregularities of the seafloor and the effects of ocean currents are considered, a more complex three-dimensional stationary model is used:

$$T=T_0+\Delta T\cos (\omega t+\phi )$$

(3)

where T is the tension at any point, T₀ is the tension when undisturbed, and ΔT, ω, and φ represent the amplitude, frequency, and phase of the disturbance, respectively. The three-dimensional motion equations of the cable can be described as follows:

$$\left\{\begin{array}{c}\frac{{\partial }^{2}X}{\partial t^2}=-g\sin (\theta )+R_x\\ \frac{{\partial }^{2}Y}{\partial t^2}=R_y\\ \frac{{\partial }^{2}Z}{\partial t^2}=-g\cos (\theta )+R_z\end{array}\right.$$

(4)

where X, Y, and Z represent the positions of the cable in three-dimensional space, g is the acceleration due to gravity, R_x, R_y, and R_z are the drag components in the respective directions, and θ is the angle between the cable and the horizontal direction.

Based on the dynamic models, some studies have investigated the dynamics of cable laying, from basic analytical models to complex numerical simulations and software applications [43,61,62]. It was found that the key factors affecting the dynamics of cable laying include velocity and acceleration of vessels [43], elastic stretch and bending radius of the cable [61], the interaction between ship and cable, velocity and fluctuation of current, and so on. Moreover, there is a coupling relationship between different factors. Bi et al. [63] employed the rigid finite element method to discretize the system and transform it into a rigid–flexible coupled multibody system composed of rigid elements and spring damper units. This model simulates the umbilical cable laying system used for underwater robots connected to a ship-mounted deployment winch, which provides power and communication to the robot and withstands the tension during robot operations. They established a mathematical model of the motion chain for the seabed umbilical cable laying system and conducted dynamic analyses under three conditions: ideal laying, actual laying with wave disturbances, and actual laying with tension compensation. It was found that the motion disturbances of the laying platform, particularly heaving and pitching, caused significant fluctuations in cable tension and laying speed under the influence of ocean waves.

In addition, since the actual situation is simplified in the model to facilitate calculation, there are still deviations between the results of the simulation or numerical calculation and the value of the actual situation. As mentioned in [43], the analytical model should be reconsidered if the constant speed of the construction vessel is very high and if the mass difference between the construction vessel and the submarine cable is not large. Therefore, experimental tests based on actual conditions are still necessary, such as the compression tests adopted in [62]. However, considering the complexity and high cost of experimental simulation, simulation is still the main method at present.

4.2.4. The Laying Equipment

Since the laying of deep sea cables requires extremely high precision and technical levels, cables need to be laid in complex seafloor terrains, such as seamounts, trenches, and other geological structures, which requires advanced navigation technology and sophisticated operating equipment, such as submarine cable ships, positioning systems, CLM, submarine cable trenchers, seabed exploration equipment, and so on. These laying types of equipment must reach the corresponding cable-carrying capacity and working water depth. For example, the carrying capacity of submarine cable ships is required to reach more than 1000 tons [33]. Currently, the capabilities of CLVs remain relatively limited, failing to meet the complex demands of cable deployment.

Additionally, the essential features and characteristics of modern CLVs comprise advanced dynamic positioning (DP) systems, automated CLM, ROV, Internet of Things-based (IoT) residual material control systems, and other automated control and measurement systems. DP systems adjust various thrusters, such as propellers, side thrusters, and rudders, based on accurate data on positioning, weather, and tidal currents. This ensures precise dynamic positioning, and they are categorized into three levels, namely DP-1, DP-2, and DP-3, depending on the quantity of autonomous DP systems that can maintain the position of the vessel and heading.

However, maintaining the exact position of a cable laying vessel in deeper and turbulent waters is still a challenge. This can lead to inaccuracies in cable laying, which can result in faults or inefficient cable paths. There are two types of CLM—linear and drum. Each type has its own advantages. Drum-type CLMs occupy less deck space, offer high tension, and operate stably, while linear CLMs are suitable for long-distance operations, utilizing larger spaces with lower tension. Moreover, the deeper and more complex the cable route, the greater the need for advanced ROVs equipped with high-definition cameras and precision tools for installation and repair. However, the development of autonomous or semi-autonomous ROVs that can operate in challenging conditions is still an area where more advancement is needed. Lastly, with the increasing use of IoT technologies and sophisticated onboard systems, managing vast amounts of data for real-time decision-making becomes a challenge.

4.3. The Laying of High-Temperature Superconducting Cables

The global transition towards achieving zero carbon emissions has significantly heightened electricity demand, primarily driven by the widespread electrification of heating systems and transportation networks [64]. This surge in electricity demand requires innovative solutions to accommodate increased power loads without extensive physical infrastructure expansion. High-temperature superconductor (HTS) cables are emerging as a highly effective solution [65,66]. Unlike traditional power cables, HTS cables can transmit electricity at much higher capacities and are considerably more efficient over long distances, all while occupying a smaller physical space. This compact size is crucial in urban areas where space is limited and building new electrical infrastructure is impractical. Recent studies show that despite higher initial investment, HTS cables offer long-term benefits such as reduced transmission losses and a less frequent need for infrastructure upgrades, making them a cost-effective option [12,67]. These studies suggest that HTS cables, together with the latest advancements in cooling technology, offer a sustainable and economically feasible solution to meet the growing electricity demand, supporting the overall goal of achieving carbon neutrality.

4.3.1. Typical Structure of HTS Cables

The basic structure of superconducting cables is illustrated in Figure 12 [68]. Compared to traditional extruded cables, the key differences include the addition of the HTS material, a liquid nitrogen (LN₂) vessel, a cryostat layer, and thermal insulation layers. The conductor layer of cable is generally wound with multiple layers of HTS material. The HTS material mainly includes MgB₂, BSCCO (Bismuth Strontium Calcium Copper Oxide, such as Bi-2212 and Bi-2223), REBCO (Rare Earth Barium Copper Oxide), and so on. The critical temperature of MgB₂ is around 39 K [69], which is a little lower than other HTS materials. Bi-2212 (Bi₂Sr₂CaCu₂O₈) [70] is an isotropic HTS material of circular structures, with a critical temperature of around 85 K and a high critical magnetic field. Bi-2223 (Bi₂Sr₂Ca₂Cu₃O₁₀) and REBCO are usually flat band structures, which are called first-generation and second-generation HTS materials, respectively. Bi-2223 has a higher critical temperature than Bi-2212 (around 110 K), making it suitable for high-current density applications. However, it has disadvantages such as poor mechanical properties, high production costs, and high AC losses. Compared with other HTS materials, REBCO has many advantages, such as high critical current density, good mechanical properties, and high critical magnetic fields [71]. The most common REBCO is YBCO (YBa₂Cu₃O_7−x), with a critical temperature of around 92 K.

Depending on the location of the electrical insulation layer, the structure of HTS cables can be divided into warm dielectric (WD) and cold dielectric (CD) [72]. The electrical insulation layer of the WD cable is located in the ambient temperature region outside the thermal insulation layer. In this case, conventional insulation materials and technologies can be used. However, it will cause greater transmission loss because of its larger inductance and magnetic leakage. On the contrary, the electrical insulation layer is located in the low-temperature region of CD cables. A shielding layer made of superconducting materials can be arranged from the outside of the electrical insulation layer, which can reduce the inductance and leakage of the cable. The thermal insulation layer generally adopts a double stainless steel ripple structure with high vacuum and thermal insulation capacity. This structure not only ensures the flexibility of the cable, but also maintains the high real vacuum of the mezzanine, reducing the heat exchange between the cable and the external environment.

4.3.2. Laying Method for HTS Cables

The laying methods for superconducting cables largely depend on the application scenario and design requirements, generally including the following:

• Underground laying: The most common method, as it minimizes physical damage and environmental impact. It requires consideration of the soil type, moisture content, and other geological factors. Additionally, an appropriate cooling system must be designed to maintain the low temperatures required for HTS cables.
• Pipeline laying: HTS cables can be laid through prefabricated pipelines, which helps protect the cables from external disturbances and facilitates maintenance and replacement. The interior of the pipeline is usually filled with LN₂ or another cooling medium to maintain the low-temperature environment required for the cables.
• Overhead laying: HTS cables may need to be suspended in applications involving crossing specific areas. This method has obvious advantages in improving power transmission efficiency and reducing energy loss, but it also faces the challenges of complex cooling systems and high environmental adaptability requirements.
• Submarine laying: This method can be used for cross-sea power transmission, such as connecting islands and the mainland, across the strait of power transmission projects. Subsea laying needs to consider special requirements such as water resistance and pressure resistance, as well as the corresponding cooling systems to maintain the superconducting state.

Each laying method must consider multiple factors, including cooling needs, mechanical strength, ease of maintenance, and cost-effectiveness. Choosing the appropriate installation method is crucial for the efficient operation of superconducting cables.

Table 4. Typical applications of HTS cables.

Laying Method	Project	Year	Material	Transmission Length	Capacity and Voltage Level
Underground	LIPA, USA	2008	Bi-2223	600 m	138 kV, 574 MW
	Yokohama, Japan	2012	REBCO	250 m	66 kV, 200 MW
	AmpaCity, Germany	2014	REBCO	1 km	10 kV, 40 MW
	Jeju Island, Republic of Korea	2019	Bi-2223	1 km	23 kV, 22.9 MW
Pipeline	BEST PATHS, European	2014–2018	MgB2	30 m	320 kV, 3.2 GW
	Shanghai, China	2019	Bi-2223	1.2 km	35 kV, 2.2 GW
	Shingal, Republic of Korea	2019	REBCO	1 km	23 kV, 60 MW

gives some typical applications of HTS cables with different laying methods all over the world [65,66,67,73,74,75]. Among them, the overhead and submarine laying methods are still in the experimental stage and have little substantive application. Therefore, only the underground and pipeline laying are introduced in this review.

4.3.3. Thermal and Mechanical Control

The design and laying of HTS cables are significantly more complex than traditional cables, with one of the major bottlenecks being the cooling system. Since HTS cables require a low-temperature environment to maintain their superconducting properties, any failure in the cooling system could cause the superconducting material to lose its superconducting characteristics, thereby affecting the stability and safety of the entire power grid. Therefore, the cooling system must be highly reliable. An efficient cooling system can ensure that the HTS cable is uniformly cooled along its entire length, preventing the formation of any hot spots.

The operating temperature is a fundamental parameter of the cooling system, primarily determined by the cooling medium. Liquid nitrogen (LN₂) is commonly used as the cooling medium due to its boiling point of approximately 77 K, which is suitable for the operating temperatures of most HTS materials. In some high-demand applications, more expensive liquid helium (LHe) [76], with a boiling point of around 4.2 K, may be used, as well as liquid hydrogen (LH₂) with a boiling point of 20 K [77]. The coefficient of performance (COP) is a typical parameter to characterize the system’s performance and efficiency. COP is defined as the ratio of the heat removed by the system to the electrical energy consumed by the system, and a higher COP indicates higher efficiency. Factors affecting COP include the temperature difference between the operation and the environment, the cooling medium and its flow and pressure, heat exchanger efficiency, the insulation effect, cooling head efficiency, and load matching. For instance, the COP of a typical LN₂ cooling system falls within the range of 0.1–0.3, while the COP of an LHe cooling system usually ranges between 0.01 and 0.1. The exploration of COP improvements to reduce energy consumption is one of the key challenges for the current HTS cable transmission systems.

The cooling system can be divided into an open system and a closed system, as illustrated in Figure 13 [78]. In an open system, the cooling energy is provided by evaporating the cooling medium under vacuum conditions in a sub-cooler. Conversely, a closed cooling system uses a cryocooler to re-cool the cooling medium electrically. The former is medium consumption, while the latter is electric consumption. The closed cooling system can more precisely control the temperature, which is critical for maintaining the superconducting state of the cable. A typical closed cooling system comprises several key components, including the thermosyphon, cooling medium storage tank, circulation pump, vacuum pump, and cryocooler. The innovations in these component technologies such as the cryocooler are urgent to reduce energy consumption and increase cooling capacity.

In addition to temperature control, the superconducting tape, due to its relatively low mechanical strength and sensitivity to stress, may suffer structural damage from excessive stretching, twisting, or bending during installation, which impacts its superconducting performance [79]. Additionally, it has been observed that after cable laying, the inner insulation tube contacts the outer insulation tube at the offset points, leading to increased heat ingress into the cable. As a result, the thermal ingress could increase by 1.2 times [64]. Therefore, precise control of the mechanical stress applied to the tape is essential during the HTS cable design and laying processes.

In summary, the deployment of HTS cables presents a series of complex challenges and difficulties, mainly associated with the construction and maintenance of effective cooling systems crucial for maintaining superconductivity. Furthermore, the mechanical sensitivity of the superconducting tapes requires meticulous handling during laying to prevent structural damage. These complexities highlight the intricate balance required between technological innovation and practical implementation in the advancement of HTS cable systems.

5. Future Trends of Cable Laying

With the increasing focus on reducing carbon emissions worldwide, there is a growing need for electricity capacity. This has resulted in unique challenges and opportunities for cable laying technologies. In the future, advancements in cable installation will be driven by technological innovations, particularly in monitoring and automatic adjustment of laying parameters, as well as robotic laying technologies.

5.1. Laying Parameter Monitoring

The use of monitoring and automatic adjustment technologies can significantly improve the efficiency and reliability of cable systems. Currently, cable laying is performed mechanically with limited intelligence. Therefore, there is a need to focus on the research and development of real-time monitoring technologies that can monitor cable laying parameters. By incorporating advanced sensors and IoT technologies, cable laying systems can monitor crucial operational parameters such as cable tension, temperature, pressure, bending radius, and environmental conditions in real time.

Qi et al. used a tension sensor mounted on the tow to measure the tension force in the towing cable [80]. Shen et al. also employed the tension sensor to monitor the cable laying process, with a measuring range of 0–10 T and an accuracy of 0.01 T [56]. Zhai et al. investigated the monitoring of seawater temperature using bow tie fiber and found that the temperature sensitivity increases with the wavelength or the length of the fiber, with a highest value of around −1.27 nm/°C [81]. Additionally, the application of fiber Bragg grating (FBG) allows for the simultaneous measurement of temperature and vibration signals [82]. As technology advances, the new generation of sensors is expected to be more compact, cost-effective, accurate, and cover a broader range of monitoring. Furthermore, enhancing the environmental adaptability and durability of sensors will be crucial in overcoming harsh underground or submarine conditions.

5.2. Automatic Adjustment

The use of IoT technology enables the collection and analysis of real-time data streams [83]. By integrating advanced sensor technology, communication technology (such as Zigbee, LoRa, NB-IoT, PLC, etc.), network protocols (such as IPv6, MQTT, etc.), and cloud computing and machine learning algorithms, IoT technology realizes the intelligence and digitalization of cable laying. Through IoT, the data collected during the cable laying process can be transmitted to cloud platforms or data centers, allowing operators to instantly understand the status of the cable laying process. Simultaneously, control systems can quickly respond to potential issues, automatically adjusting parameters to optimize performance and extend cable life.

For instance, if a cable experiences excessive tension, the system can automatically adjust mechanical components to reduce tension and prevent cable damage. With ongoing technological advancements, IoT is expected to deepen further, particularly in conjunction with real-time data-driven artificial intelligence and machine learning. These advancements will not only enable devices to collect data but also learn from that data, resulting in self-optimization, significantly improving the precision and response speed of cable laying, and reducing the risks associated with parameter deviations. This means that future cable laying and maintenance operations will be more automated and intelligent, enhancing construction precision and efficiency and thereby achieving higher reliability and lower operational costs. The further development of IoT technology could benefit the maintenance of cable systems more proactive and preventive.

5.3. Robotics Application

The application of robotics in cable laying processes, particularly in the field of submarine cable laying, represents a significant advancement. The introduction of automated submarine cable laying robots enhances the precision and efficiency of the installation process, while also reducing human errors and labor costs. These robots are equipped with advanced sensors and navigation systems, such as Global Positioning System (GPS), laser scanning, and visual recognition systems, enabling them to operate independently without direct human control [84]. Additionally, artificial intelligence learning algorithms can be introduced during the cable laying process to adapt to complex underground or submarine terrains and environments [85], integrating multiple functions such as detection, cleaning, and maintenance to ensure optimal performance of the cable systems over the long term.

Unmanned aerial vehicles (UAVs) can also be utilized in cable laying, particularly in situations involving crossing rivers, canyons, or other complex terrains. UAVs can carry lightweight cables for quick installation or act as a pilot line for subsequent heavier cable installations, further reducing laying and maintenance costs while enhancing project efficiency.

Further developments include the use of advanced remote control and autonomous technologies, allowing robots to operate independently in environments difficult for humans to access directly, thereby improving the quality and efficiency of cable laying in submarines and other hard-to-reach areas.

6. Conclusions

This review starts by discussing traditional cable laying techniques. It then explores the challenges encountered in complex installation environments due to the growing energy demands and examines future trends in cable laying. The main conclusions are as follows:

(1) There are three main traditional cable laying methods: underground, overhead, and submarine. Each method is suitable for specific environmental and operational conditions and has its advantages and limitations. Underground laying is generally considered the safest and most reliable option, despite being more expensive. Overhead laying is less expensive and adaptable to various terrains, but it can be aesthetically unappealing. Submarine laying, although the most expensive, provides connectivity across bodies of water and makes marine resources accessible.

(2) Improper practices during the laying process can result in various cable faults, such as mechanical damage, joint failures, and insulation defects. These faults can impact the long-term performance and safety of the cables, potentially leading to short circuits or complete cable failure in severe cases.

(3) As urbanization speeds up and the need for renewable energy grows, the environment for laying cables is becoming more complex. This review discusses new challenges in expanding cities and developing offshore energy, such as complex terrain, high environmental protection requirements, and extreme weather conditions. All of these factors place higher demands on cable laying technology. Additionally, the review discusses the challenges related to the application of HTS cables.

As technology continues to advance, cable laying techniques will increasingly depend on technological innovations such as digitalization and automation to improve efficiency and accuracy. Additionally, the use of HTS cables is considered a crucial step in reducing energy loss and enhancing transmission efficiency in the future. Future research will focus on exploring more economical and environmentally friendly laying methods and materials to meet the growing global demand for electricity.