Underground Lines Research Articles

Key Factors in the Design of Urban Underground Metro Lines

Designing sustainable underground metro lines in dense urban environments is a highly challenging task that requires the collaboration of numerous stakeholders and consultants to make crucial decisions influenced by several factors. While it is impossible to address every issue influencing the decision-making process, identifying key factors and their interdependencies is essential for optimal design. This study focuses on six critical aspects of the reference design of metro systems: (1) track alignment, (2) tunneling strategy, (3) station typology, (4) operations and maintenance, (5) procurement strategy, and (6) environmental aspects. Amongst these aspects, we identify track alignment as the primary driving factor that influences the other factors. We analyze the decision between shallow and deep alignments as an engineering choice that necessitates balancing conflicting factors and constraints. Our contribution lies in mapping these factors and their dependencies, thus offering policymakers, project managers, and designers a framework to navigate the design process. Our discussion also provides guidance to public agencies in tendering for design teams more efficiently. Drawing from lessons learned by experienced design managers, this study aims to fill the gap in the literature by offering a generalist perspective on metro design.

Study on the effect of mitigation strategies for rail corrugation in metro lines

Rail corrugation appears as a periodic irregularity on the rail running surface that causes severe dynamic loads at the wheel-rail interface. These dynamic forces may generate ground-borne vibrations that propagate from the line to the surrounding buildings causing discomfort to residents. Rail grinding is the most used countermeasure for the mitigation of corrugation. However, this maintenance operation determines high operative costs if frequently performed and must be carefully scheduled. To this end, it is important to assess the effectiveness of other mitigation solutions that may prevent or slow down its growth. The main objective of this study is to investigate the formation of rail corrugation on a sharp curve of the Cityringen underground line in Copenhagen. A wheel-rail interaction model is developed in the frequency domain to identify the root causes of the problem on the specific curve and predict the corrugation wavelength. Once the accuracy of the model is tested against experimental observations on the reference curve, it is used to explore the effectiveness of different mitigation actions, such as the use of friction modifiers, the variation of the speed, track design and track gauge. The results indicate that friction modifiers and speed variation are the most effective measures.

Experimental determination of soil thermal conductivity for design of underground cables

The dimensioning of underground extra-high voltage direct current transmission lines (HVDC) requires detailed knowledge of soil properties, particularly thermal conductivity, to optimise cable spacing and minimise project costs and environmental impact. Given the absence of an internationally standardised procedure for testing soil thermal conductivity, a novel approach was developed as part of the SuedLink project - a 700 km long underground power line which will transmit renewable wind energy between northern and southern Germany. The unique aspect of this methodology lies in its ability to deliver reproducible results of the thermal conductivity of a soil across the entire water content spectrum. This allows the use of realistic thermal conductivity values, as opposed to the current use of overly conservative values in the design of underground power lines. Additionally, the highly efficient testing configuration enables the test to effectively be rolled out on a large scale as was shown with over 6000 tests done on the SuedLink project. This article explains the thermal conductivity test procedure and the evaluation of the raw-data obtained from these tests.

Revolutionizing energy infrastructure: Automated route planning for underground transmission lines in Phnom Penh

The capacity of conventional overhead transmission lines (OTL) has been exceeded by the energy consumption of Cambodia's flourishing cities. Underground transmission lines (UTL) provide a unique solution due to their technical and environmental advantages. However, engineers must contend with high UTL costs and the need for effective conduit cable installation. This study presents a solution that automates the shortest route method for determining the optimal path for routing UTL power supply cables between any two substations. Multiple algorithms are evaluated to identify the most effective solution to this design's inherent shortest-path problem. Using Geographic Information System (GIS) data, potential UTL network routes in Phnom Penh, Cambodia can be investigated. The ultimate product is an automated route planning support tool that has the potential to revolutionize energy project planning by generating optimal routes for UTL. This will increase efficiency and lower costs, making UTL a more viable option for meeting the energy demands of modern infrastructure. This study contributes significantly to the field of energy infrastructure planning and has the potential to be replicated in cities around the world.

Multicore underground power line health monitoring using optical fiber bragg grating

Multicore underground power line health monitoring using optical fiber bragg grating

Research on Tree Flash Fault Localization of Hybrid Overhead–Underground Lines Based on Improved Double-Ended Traveling Wave Method

Research on Tree Flash Fault Localization of Hybrid Overhead–Underground Lines Based on Improved Double-Ended Traveling Wave Method

Retraction Note: Applications of artificial intelligence and hybrid neural network methods with new bonding method to prevent electroshock risk and insulation faults in high-voltage underground cable lines

Retraction Note: Applications of artificial intelligence and hybrid neural network methods with new bonding method to prevent electroshock risk and insulation faults in high-voltage underground cable lines

Automated feeder routing for underground electricity distribution networks based on aerial images

The process towards a carbon-neutral society requires a substantial amount of investment into electricity distribution networks for integrating more sustainable technologies such as photovoltaic systems, electric vehicles, heat pumps, and others. In order to execute the large number of network expansion measures associated with this effort, strategic and operational planning of distribution networks benefit from higher degrees of automation. A key component in these planning processes is the routing of feeder segments, i.e., the task of finding feasible and cost-efficient paths for underground power lines between two geographic locations, such as residential buildings and transformer stations. In this paper, we present FEEDAIR, a novel and innovative approach to automate feeder routing based exclusively on aerial images. FEEDAIR integrates deep neural networks, which encode geoinformation from aerial images, and A* search, which identifies effective feeder routes based on this encoding. We train and evaluate FEEDAIR using a large data set of more than 7000 real-world electricity distribution network feeder segments. Thereby, we compare FEEDAIR to state-of-the-art approaches from related work and find that the feeder segments generated by FEEDAIR are on par or superior with regard to several characteristics and metrics. FEEDAIR achieves this performance by relying exclusively on aerial images, whereas competing approaches require data on geocoded land cover and estimated construction cost, which is not as widely available and is frequently based on potentially subjective expert opinion.

Field measurement of track vibration induced by full-load and empty-load condition in curve section of underground metro line

In order to compare the differences in vibration before and after wheel re-profiling and assess the vibration impact of train under full-load and empty-load condition, the field vibration measurement was conducted on an underground metro track components (including rail, sleeper, and track-bed) by using a specific testing car. The results indicate that wheel re-profiling is effective in reducing track vibration, within the frequency range of 31.5–1250 Hz, the vibration acceleration levels of the track after wheel re-profiling were notably lower than those prior to re-profiling and the vibration acceleration levels of the rail, sleeper, and track-bed decrease by 4.7 dB, 6.6 dB, and 6.7 dB, respectively. In the frequency domain, the characteristic peak frequencies of the three track components, whether under full load or empty load, align closely with the frequencies associated with track irregularities. Full-load condition primarily affects the vibration acceleration at lower frequencies, with minor influence on higher frequencies. The vibration acceleration levels of all three track components are higher under full load than empty load. Additionally, under full-load condition, the transmission loss from the rail to the sleeper increases, while the transmission loss from the sleeper to the ballast remains nearly constant. The results of vibration acceleration levels obtained from routine vehicle operations validate the limited impact of axle load on track components vibration.

UNDERGROUND POWER LINES: ANALYSIS OF ENVIRONMENTAL, VISUAL, ECONOMIC, AND SAFETY BENEFITS

This study investigates the transition from above-ground to underground power lines in Hawaii, focusing on the severe threats posed by downed lines during storms, particularly on roadways where escape routes are critical. The research uses a comprehensive approach to explore environmental, visual, economic, and safety aspects. The study employed a methodology that involved reviewing powerline undergrounding studies in New York City and Florida, chosen for their geographical resemblance to Hawaii. Legal submissions from activist groups and current event articles discussing safety concerns in comparable geographical scenarios were also analyzed. Findings indicate substantial benefits, including minimized environmental impact on landscapes and ecosystems, heightened visual aesthetics, and economic advantages through reduced maintenance costs. Crucially, the shift to underground power lines significantly enhances safety during storms, preventing life-threatening scenarios on vulnerable roadways. This research underscores the urgency and practicality of adopting underground power lines in storm-prone regions, providing a compelling case for policymakers and stakeholders to prioritize this transition for communities’ overall well-being and resilience.

UNDERGROUND POWER LINES: ANALYSIS OF ENVIRONMENTAL, VISUAL, ECONOMIC, AND SAFETY BENEFITS

This study investigates the transition from above-ground to underground power lines in Hawaii, focusing on the severe threats posed by downed lines during storms, particularly on roadways where escape routes are critical. The research uses a comprehensive approach to explore environmental, visual, economic, and safety aspects. The study employed a methodology that involved reviewing powerline undergrounding studies in New York City and Florida, chosen for their geographical resemblance to Hawaii. Legal submissions from activist groups and current event articles discussing safety concerns in comparable geographical scenarios were also analyzed. Findings indicate substantial benefits, including minimized environmental impact on landscapes and ecosystems, heightened visual aesthetics, and economic advantages through reduced maintenance costs. Crucially, the shift to underground power lines significantly enhances safety during storms, preventing life-threatening scenarios on vulnerable roadways. This research underscores the urgency and practicality of adopting underground power lines in storm-prone regions, providing a compelling case for policymakers and stakeholders to prioritize this transition for communities’ overall well-being and resilience.

Integrated Fault Detection System for Underground Lines Using ESP32 and LORA Communication Using IOT

Abstract: This paper introduces an advanced fault detection system tailored for underground line infrastructure, featuring the integration of ESP32 microcontroller technology and LORA communication protocols. The primary objective of this system is to enhance the reliability and efficiency of fault detection processes, crucial for maintaining the integrity of underground lines. At the core of this system lies the ESP32 microcontroller, serving as the central processing unit responsible for coordinating various functionalities. The detection mechanism incorporates six toggle switches strategically positioned along the underground lines, each assigned to monitor a specific location segment. In the event of a fault occurrence, the corresponding toggle switch is triggered, promptly initiating the fault detection process. Upon fault detection, the system seamlessly orchestrates the transmission of GPS location data to a LORA communication device. This data transmission mechanism ensures rapid dissemination of critical information regarding the fault's precise location. Additionally, an LED indicator is employed to provide immediate visual feedback, enabling quick identification of fault occurrences. Moreover, a LCD display unit offers realtime updates on the system's operational status, facilitating efficient monitoring and management. On the receiving end, the LORA communication device securely receives the transmitted data and forwards it to the cloud infrastructure using IOT technology. This cloud integration enables seamless data aggregation, storage, and analysis, empowering stakeholders with valuable insights into underground line health and performance.

Thermal Properties of Backfill Material for Underground Heat Exchange Applications

We are investigating the effect of the thermal properties of backfill material on the efficiency of underground thermal energy systems. We have used aluminum to increase the thermal properties of clay-bentonite and to investigate its potential as a backfill material in underground heat exchange applications. The measurements of thermal properties were made at room temperature using the Transient Plane Source (TPS) technique. The measurements were based on an infinite homogeneous medium using different composites of aluminum and clays in amounts of aluminum concentration ranging from 6 to 25 percent of the sample’s weight. The results confirmed an overall relative increase of 170% and 135% in the thermal conductivity and diffusivity, respectively as the Al content increased by 25%. The estimated average of the thermal transmittance (U-value ) of these samples was in the range from 0.40 to 1.1 W/m2K, which was directly proportional to the relative increase in the measured properties. Our findings can be applied to underground thermal energy systems, ground source heat pumps, and solid dielectric underground transmission lines.

Analysis the Impact of Distributed Generation Interconnection on the 20 kV Distribution Network: A Study Case of the Waste-to-Energy in Bantar Gebang and the Tambun Area Distribution Network

The need for electricity in Indonesia is increasing along with the growth of world industry in Indonesia. The use of power plants with fossil energy sources is decreasing with the aim of improving the environmental system. Electricity needs can be fulfilled by Distributed Generation (DG), namely generation that is connected to a distribution network in order to fulfill power needs and improve electricity quality. In Bekasi City, the Directorate General of the Bantar Gebang Waste-to-Energy Plant (WtE) is being built with a drained power of around 786 kW. In this research, an analysis will be carried out on the Bantar Gebang WtE, which is connected to the Tambun area distribution network. The simulation results show that the voltage drop at the transformer load is 0.3% to 3% in general. With PVUR values on sample transformers of 0.171%, 0.578%, and 0.187% and real and reactive power losses on Underground Lines, Overhead Lines, and transformers of 144 kW and 173 kvar leading before interconnection. After interconnection, there was an increase in real power loss to 147 kW and an improvement in PVUR values to 0.156%, 0.563%, and 0.183%, and reactive power to 164 kvar. The use of power at the Tambun feeder Dodge Substation has also decreased due to the interconnection of the Bantar Gebang WtE, which can generate around 786 kW of power to supply power to the distribution network connected to the Bantar Gebang WtE DG.

Analysis of Increased Induced Voltages on the Sheath of Double-Circuit Underground Transmission Lines Guaranteeing Ampacity

This paper quantifies and discusses the increase in induced voltage on a sheath due to changes in duct banks in terms of type and dimensions along an underground transmission line, guaranteeing the ampacity required for a project. The four most common duct banks in double-circuit underground transmission lines with phase transposition were considered in this study, along with two special cross-bonding techniques: continuous cross-bonding (CCB) and sectionalized cross-bonding (SCB). These techniques aim to reduce sheath currents and enhance the distribution of the induced voltage on the sheath. The analysis considers two distinct scenarios in which the profile of the induced voltage is calculated: the first one accounts for underground obstructions, intersections with important traffic avenues, and ground with high excavation costs that force changes in the duct bank dimensions and configuration, which is the most exact and realistic case. The second one solely considers one typical configuration of a duct bank along the route. This last scenario is normally applied to calculate the induced voltage when an underground transmission design is required. The results show that when installing cables at a greater depth, it is imperative to increase the distance between them to guarantee the ampacity. The induced voltage on the sheath will rise as the distance increases. Furthermore, the results reveal that instead of calculating the induced voltage by considering the scenario that is exact and most like a real case, it is enough to calculate following the second scenario and then add a scaling factor according to each duct bank configuration.

Protection of Mixed Overhead and Underground Cable Lines

Protection of Mixed Overhead and Underground Cable Lines

Optimization of Ampacity in High-Voltage Underground Cables with Thermal Backfill Using Dynamic PSO and Adaptive Strategies

This article addresses challenges in the design of underground high-voltage transmission lines, focusing on thermal management and cable ampacity determination. It introduces an innovative proposal that adjusts the dimensions of the backfill to enhance ampacity, contrasting with the conventional approach of increasing the core cable’s cross-sectional area. The methodology employs a particle swarm optimization (PSO) technique with adaptive penalization and restart strategies, implemented in MATLAB for parameter autoadaptation. The article emphasizes more efficient solutions than traditional PSO, showcasing improved convergence and precise results (success probability of 66.1%). While traditional PSO is 81% faster, the proposed PSO stands out for its accuracy. The inclusion of thermal backfill results in an 18.45% increase in cable ampacity, considering variations in soil thermal resistivity, backfill properties, and ambient temperature. Additionally, a sensitivity analysis was conducted, revealing conservative values that support the proposal’s robustness. This approach emerges as a crucial tool for underground installation, contributing to continuous ampacity improvement and highlighting its impact on decision making in energy systems.

Application of a Hot Melt Recoverable Anchor Cable in Foundation Pit Support

With the continuous development of the social economy, the depth of foundation pit excavation of proposed construction projects in various places gradually increases, which is closer to the building red line, and the surrounding environment is relatively complex; therefore, there are few supporting schemes for foundation pit selection. Based on the Vanke B-6 plot of a real estate development project, the project has close neighboring buildings. If we use a normal anchor cable, underground cut line problems are possible, and so we choose the hot melt-type recoverable anchor; with three element dispersion pressure, the anchor cable can minimize broken sections of brush slope excavation and has advantages of a simplified construction process and good seismic performance. Except for the cable barrel, the other parts and all steel strands can be recycled, and recycled parts can be reused. The recyclable bolt (cable) overcomes the disadvantages of the conventional bolt (cable) as a temporary support, such as pollution of the underground environment, encroachment on the underground space of adjacent buildings, and becoming an underground obstacle in follow-up projects. It accords with the characteristics of the times of environmental protection and sustainable development, and has achieved good economic and social benefits.

Circulating sheath currents in flat formation underground power lines

Three-phase underground power lines can induce voltages and currents in their recover sheaths. The sheath induced currents are undesirable and generate power losses and reduce the cable ampacity whereas the induced voltages can generate electric shocks to the workers that keep the power line. This means that when dealing with three-phase underground power lines, it is very important to know the sheath currents (called circulating currents) that can circulate throughout the sheath of the cables. It is very useful to know their values. The values of the circulating currents depend on different parameters, such as the sheath grounding system, the geometry of the cables, the gap between them, etc. In this work, different geometries of flat configuration underground three-phase power lines have been studied. For each geometry it has been computed the sheath circulating currents in each cable of the power line

Effects of the circulating sheath currents in the magnetic field generated by an underground power line.

In this paper the influence of the metallic sheath in the magnetic field generated by underground single core power cables is studied. When dealing with underground power cables, sheath circulating currents can be induced. These currents produce power losses in the sheaths and decrease the ampacity (capacity of carrying current) of the cables. The circulating sheath currents generate a magnetic field that adds to the cable magnetic field. In this paper the modification of the total magnetic field is studied.