Cable Ducts Research Articles

Distributed fiber optic sensing (DFOS) as a part of diagnostics and monitoring of prestressed structures

Distributed Fiber Optic Sensing (DFOS) is a measurement technology that has experienced dynamic development in recent years and is increasingly used in various industries, including construction. By embedding sensors during the manufacturing stage of prestressed concrete elements, significant insights can be gained into their behavior during concrete pouring, prestressing, curing, and under rheological influences. DFOS sensors allow for the analysis of structural behavior under load and changes occurring over time with a level of accuracy previously unattainable with conventional methods. The paper presents research results on the implementation of this technology in pre-tensioned and post-tensioned elements. The main objective of the research was to verify the feasibility of using DFOS sensors to identify damages (e.g., cracks and simulated voids in cable ducts) and monitor the state of deformations and displacements in prestressed concrete elements.

Diagnostics of Post-Tensioned Bridge Girders Using Distributed Fiber Optic Sensors

In contemporary bridge construction, post-tensioned concrete technology stands as one of the prevailing methods. Over the past several decades, it has been extensively employed in constructing medium-span bridges worldwide. As time has elapsed, many of these structures now demand diagnostic assessments due to deteriorating technical conditions. A promising approach for diagnosing such bridges involves utilizing distributed fiber optic sensing (DFOS) technology. DFOS enables continuous measurements to be acquired along the entire structural length, which is particularly crucial for these bridge types. Its advantages have already been demonstrated in civil engineering applications, notably in contexts related to concrete structures. The paper presents research conducted on post-tensioned beams with curvilinear multiwire prestressing strands. Optical sensors were installed before and after concreting the beams. The main aims were to measure strains, crack widths and beams’ displacements. It also compared results from DFOS-based sensors embedded in concrete during execution (for new structures) to sensors in pre-made near-surface grooves (for existing structures) and to detect defects within one beam using sensors inside the cable duct, analyzing strain data. DFOS measurements were compared with conventional spot techniques, achieving very good compliance. This investigation establishes that a well-structured DFOS-based system, encompassing suitable measurement methodologies, optical sensor configurations, installation techniques, and post-processing algorithms, emerges as a relevant tool for the comprehensive diagnostics of post-tensioned concrete bridges, both the new and existing ones.

Terahertz gas sensor and its application in gas detection of power pipe gallery

During the operation of a power cable duct, the content of flammable gas is an important element in the safety of the cable duct. The accurate detection and location of gas in the pipeline corridor are important to improve the safety and stability of the power system. In view of the change of the refractive index of the gas in the power cable tube gallery, this paper presents the important application of terahertz one-dimensional photonic crystals with high-quality factors in gas sensing, change of the gas refractive index in the tube gallery simulated, and the gas refractive index change in the tube gallery can be obtained accurately by analyzing the change of transmission peak at terahertz range, the potential of terahertz sensor in gas detection in power tube gallery is verified.

Analysis on the Improved Calculation Method of Cable Duct Inclination Angle for Cable-stayed Bridges

Analysis on the Improved Calculation Method of Cable Duct Inclination Angle for Cable-stayed Bridges

Dosimetry of a self-shielded gamma irradiator small animal whole-body irradiations: comparisons between ionisation chamber and alanine.

Because of reproducibility and repeatability problems with reference measurements made with an ionisation chamber in a self-protected GSRD1 irradiator, a comparison was made with alanine dosimetry for a whole-body mouse irradiation setup in a sterile box. The twisting of the cables in the cable duct and in the irradiator cell and the irradiation of the ionisation chamber connector are likely to have caused the problems encountered. These problems are not observed on other types of irradiators with more suitable cable passages. A difference up to 8.4% was observed between the alanine dosimetry and ionisation chamber. The influence of the number of animals in the sterile box on the whole-body dose of the animals was also evaluated with alanine and found to be <2%.

Strain, crack, stress and shape diagnostics of new and existing post-tensioned structures through distributed fibre optic sensors

Prestressed concrete is commonly used in the construction of safety–critical structures such as large-span girders or slabs. The article focuses on post-tensioned elements, in which curvilinear multiwire strands are tensioned after concrete’s hardening to transfer the compressive force to the concrete. The overall idea is to confront external forces and achieve extended benefits, e.g. longer spans or reduced cracking. However, the design, construction and maintenance of such elements are particularly challenging because of their complexity, including spatial stress state in the anchorage zones and also the standard features of concrete structures like heterogeneity, material imperfections and, most importantly, local discontinuities (cracks). Reliable diagnostic solutions are therefore essential for both new and existing components. Distributed fibre optic sensing (DFOS) allows the measurements to be taken continuously over the entire structural length and its advantages have already been proven in civil engineering applications, especially those related to concrete structures. However, the novelty of the presented research lies in 1) simultaneous analysis of strains, stresses, cracks and displacements (shape changes); 2) direct comparison of results from monolithic sensors embedded in the concrete (for new structures) and those installed in pre-made near-to-surface grooves (for existing structures); 3)the application of the embedded composite strain sensor to the bi-directional analysis of the stress field within the anchorage zones; 4) possibility of strain transfer analysis between the cracked concrete, cable duct, injection and prestressing tendon during mechanical bending tests. The DFOS-based strain, crack and displacement results were also compared with reference measurements made with conventional spot techniques, achieving very good compliance. The research proved that a well-designed DFOS-based system, including appropriate measurement techniques, optical sensors, installation methods and post-processing algorithms, is the relevant tool for the diagnostics of post-tensioned concrete structures.

Traffic Vibration Signal Analysis of DAS Fiber Optic Cables with Different Coupling Based on an Improved Wavelet Thresholding Method.

Distributed Acoustic Sensing (DAS) is a novel technology that uses fiber optics to sense and monitor vibrations. It has demonstrated immense potential for various applications, including seismology research, traffic vibration detection, structural health inspection, and lifeline engineering. DAS technology transforms long sections of fiber optic cables into a high-density array of vibration sensors, providing exceptional spatial and temporal resolution for real-time monitoring of vibrations. Obtaining high-quality vibration data using DAS requires a robust coupling between the fiber optic cable and the ground layer. The study utilized the DAS system to detect vibration signals generated by vehicles operating on the campus road of Beijing Jiaotong University. Three distinct deployment methods were employed: the uncoupled fiber on the road, the underground communication fiber optic cable ducts, and the cement-bonded fixed fiber optic cable on the road shoulder, and compared for their outcomes. Vehicle vibration signals under the three deployment methods were analyzed using an improved wavelet threshold algorithm, which was verified to be effective. The results indicate that for practical applications, the most effective deployment method is the cement-bonded fixed fiber optic cable on the road shoulder, followed by the uncoupled fiber on the road, and the underground communication fiber optic cable ducts are the least effective. This has important implications for the future development of DAS as a tool for various fields.

Research on the rapid calculation method of temperature rise of cable core of duct cable under emergency load

In order to facilitate engineers to manage dynamic loads in real time and improve the utilization of power cables, it is necessary to accurately calculate the temperature rise of cable cores under duct laying conditions. The transient thermal circuit model involved in this paper helps to improve the speed of dynamic response and the accuracy of transient temperature rise calculation for power cable cores under duct laying conditions. Since the impact of the environmental conditions, exploring the computational relationships of the thermal circuit model parameters helps to improve the engineering applicability of the model. The duct cable can be broken down into three parts: the cable body, the air inside the pipe and the external environment. In engineering, the thermal circuit model parameters of the cable body can be made into a table and applied by looking up the table. The thermal circuit model parameters of air in duct are related to the cable outside diameter and duct inside diameter, and can also be engineered using tables for application. The fit gives the third part of the equation with respect to the thermal resistance coefficient of the duct and soil and the burial depth. The error in applying the decentralized thermal circuit model and parametric expressions is less than 1 °C compared to the results of finite element calculations. This proves that the decomposition of the duct power cable model improves the accuracy of the transient temperature rise calculation. The relationship equation between the parameters of the thermal circuit model and the laying conditions helps to improve the engineering adaptability of the method.

Field implementation of enzyme-induced carbonate precipitation technology for reinforcing a bedding layer beneath an underground cable duct

A suitable bearing capacity of foundation is critical for the safety of civil structures. Sometimes foundation reinforcement is necessary and an effective and environmentally friendly method would be the preferred choice. In this study, the potential application of enzyme-induced carbonate precipitation (EICP) was investigated for reinforcing a 0.6 m bedding layer on top of clay to improve the bearing capacity of the foundation underneath an underground cable duct. Laboratory experiments were conducted to determine the optimal operational parameters for the extraction of crude urease liquid and optimal grain size range of sea sands to be used to construct the bedding layer. Field tests were planned based on orthogonal experimental design to study the factors that would significantly affect the bio-cementation effect on site. The dynamic deformation modulus, calcium carbonate content and long-term ground stress variations were used to evaluate the bio-cementation effect and the long-term performance of the EICP-treated bedding layer. The laboratory test results showed that the optimal duration for the extraction of crude urease liquid is 1 h and the optimal usage of soybean husk powder in urease extraction solution is 100 g/L. The calcium carbonate production rate decreases significantly when the concentration of cementation solution exceeds 0.5 mol/L. The results of site trial showed that the number of EICP treatments has the most significant impact on the effectiveness of EICP treatment and the highest dynamic deformation modulus ( E vd ) of EICP-treated bedding layer reached 50.55 MPa. The area with better bio-cementation effect was found to take higher ground stress which validates that the EICP treatment could improve the bearing capacity of foundation by reinforcing the bedding layer. The field trial described and the analysis introduced in this paper can provide a practical basis for applying EICP technology to the reinforcement of bedding layer in poor ground conditions.

Low-Cost Online Partial Discharge Monitoring System for Power Transformers

The article presents in detail the construction of a low-cost, portable online PD monitoring system based on the acoustic emission (AE) technique. A highly sensitive piezoelectric transducer was used as the PD detector, whose frequency response characteristics were optimized to the frequency of AE waves generated by discharges in oil-paper insulation. The popular and inexpensive Teensy 3.2 development board featuring a 32-bit MK20DX256 microcontroller with the ARM Cortex-M4 core was used to count the AE pulses. The advantage of the system is its small dimensions and weight, easy and quick installation on the transformer tank, storage of measurement data on a memory card, battery power supply, and immediate readiness for operation without the need to configure. This system may contribute to promoting the idea of short-term (several days or weeks) PD monitoring, especially in developing countries where, with the dynamically growing demand for electricity, the need for inexpensive transformer diagnostics systems is also increasing. Another area of application is medium-power transformers (up to 100 MVA), where temporary PD monitoring using complex measurement systems requiring additional infrastructure (e.g., control cabinet, cable ducts for power supply, and data transmission) and qualified staff is economically unjustified.

An approach to thermal modeling of power cables installed in ducts

The power cables laying in the urban areas require utilization of the protective ducts, mainly to facilitate the faulty section replacement. However, the use of cable ducts results in reduced capacity to dissipate generated heat to the surroundings. Thus, the thermal analysis of cables placed in ducts is very important for proper power cable operation. The thermal response of cables laid in mutual and in separate ducts, respectively, is considered at two values of current load. The full-scale field measurement setup is utilized to carry out the analysis of both steady-state and dynamic power cable heating under actual field conditions for the two backfill configurations. The measurement results provide the insight into the power cable heating dynamics related to the situations of a short-term over-loads and fault drive-through responses and also the opportunity to verify the proposed numerical approach based on the use of finite element method and the boundary conditions on the interior duct surface. The approach could be considered as a compromise between the standardized procedure and the tedious procedure involving the computational fluid dynamics simulations due to straightforward implementation and very good accuracy. The results obtained suggest that cables laid in mutual duct lead to a less favorable thermal situation when compared to cables laid in separate ducts. Also, the numerical results suggest that the use of non-uniform heat flux around the inner duct surface results in a significantly better agreement with measurements, compared to the purely numerical approach utilizing the concept of the effective thermal conductivity to model heat transfer in the air gap between cable and duct. Finally, the sensitivity analysis has been carried out to assess the effects of various backfill thermal conductivities and the ground surface temperature on the resulting thermal field. • Full scale field measurements. • Simplified approach for thermal field estimation when cabled are placed in ducts. • Nonuniform heat flux distribution along the cable duct is implemented. • Better agreement with measurements when non-uniform heat flux distribution is used. • Use of effective thermal conductivity results in notable temperature underestimation.

Reliability of the grouting of tendons under consideration of uncertainties under on-site conditions

This paper contributes to the body of knowledge from German research work Deutscher Ausschuss für Stahlbeton and from author’s experiences, to improve the reliability of cable ducts grouting. The complete and reliable filling of post-tensioned tendons with grout is necessary to protect the prestressing steel against corrosion and for bond between prestressing steel and the concrete structure, which is in both limit states applied. Diagnostics of bridges built in the last century showed the cases of faulty grouting of cable ducts. These faults are cause of corrosion prestressing steel often. Based on these diagnostics, bridges are after 35 to 70 years of service life demolished, although service life of these bridges was to 100 years declared. In the studied research work were investigated the effects of individual components, procedures and conditions of the grout and results of grouting investigated. Tests have been performed both on the experiment cable ducts and the real structures. Based on this paper, certain principles have been recommended that aim to prevent grouting faults and to improve the reliability of the grouting. In these recommendations are suggestions of controls of grouting included.

Величина тока утечки при тушении электрооборудования под напряжением автоматическими установками газового и водяного пожаротушения

PURPOSE. The article studies the issue of extinguishing live electrical equipment by means of automatic fire suppression systems (AFSS). The purpose of the work is to assess the possibility of personnel’s safe use of various types of automatic fire suppression systems when extinguishing live electrical equipment at power facilities. The authors analyze the statistics of transformer substation and cable duct fires in the Russian Federation within the period from 2018 to 2021 and regulations in the field of application of automatic fire suppression systems for extinguishing fires of live electrical equipment. A series of experiments was carried out to determine the leakage current when a fire extinguishing agent is supplied from AFSS to energized equipment. METHODS. To study the possibility of using AFSS in case of fires of live electrical equipment at power facilities, methods of analysis and experiment are used. FINDINGS. The first series of experiments was carried out on an automatic gas fire suppression system using halon 125 as a fire extinguishing agent. Extinction of B1 simulated fire sources filled with n-heptane was carried out. Over the whole experiment on the hand-operated starting device of the automatic system leakage current did not exceed the threshold non-perceptible value of 0.5 mA. The second series of experiments was carried out on a water spray automatic fire suppression system. The large spray angle of the nozzles prevented the entire amount of fire extinguishing agent from reaching the standard target; therefore, in order to obtain more accurate data, a new target sized 3 000×3,000 mm was manufactured. Spray nozzles with different k-factor values were investigated. The experiment made it possible to determine the values of leakage current on a pump unit body and spray nozzle. RESEARCH APPLICATION FIELD. The obtained experimental data indicate the possibility of safe use of water spray and gas automatic fire suppression systems to extinguish live electrical equipment. CONCLUSIONS. The results of the study can provide a substantiation for measures that exclude electric shock to facility personnel in case of using automatic fire suppression systems when extinguishing live electrical equipment.

Dimensioning of the Clearance as a Means of Avoiding Burr and Film Formation during the Punching of PC/ABS Cable Ducts

The production of staple articles such as cable ducts offers reductions in resource and production energy consumption if the process is optimized. Side recesses made of polyvinyl chloride (PVC) have already been punched successfully as one of the process steps during the production of cable ducts. However, punching cable ducts made of flame-retardant polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) is challenging because increased burr and film formation occurs. This study introduces the correct dimensioning of the clearance as a means of reducing the burr and film formation and presents the ideal clearance dimensions. This new process design approach comprises the dimensioning of the clearance and its subsequent successful application. Tools with clearances in the relevant size range were purchased and examined by means of punching tests. The punch-outs were evaluated regarding the quality characteristics, such as the burr, film, cut surface quality, shear droop, and plastic flow characteristics. Excerpts from high-speed recordings were used to assess the punch-outs qualitatively. The burr formation is significantly decreased by the use of a correctly dimensioned clearance, allowing for the crack initiated at the punch side and the crack initiated at the die side to meet perfectly. It is assumed that film formation can be avoided via a significant reduction in the friction or heat input during the punching process.

The Effect of Cable Duct Diameter on the Ampacity of High-Voltage Power Cables

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Design of cable laying condition monitoring system

This paper designs a cable laying condition monitoring system. The system uses endoscope to monitor the defects in the pipeline, and uses tension sensor to monitor the traction in the process of cable laying. Through the test and test data analysis, the tension measurement range of the system is 0-10T and the measurement accuracy is 0.01T. The video system can clearly observe the defects in the cable duct. Therefore, the monitoring system designed in this paper can monitor the cable laying state and avoid the damage to the cable caused by pipeline defects and excessive tension.

Using Digital Twins for the Optimization of Control Cabinet Engineering

The digital twin adds a great value to the interlinking of work steps in control cabinet construction. The model is created in electrical design and during assembly planning. The twin then accompanies the entire production process and provides the individual departments with their information. The unique feature: customer, switchgear manufacturers, and their suppliers work with the same model. The device manufacturers supply macros in which all the properties of their products are mapped. The electrical designers insert these devices into their schematic and thus generate a logical version of the model. The layout planner then puts the model into physical form by arranging the devices in the virtual switchgear cabinet. The finished model includes all dimensions and shows the individual devices inside the realistic 3D digital layout. Also included is the entire wiring with all wire paths, cable ducts, top-hat rails (position and length), and all drill holes and cutouts. The haptic representation simplifies many activities, as individual positions in the cabinet are more easily recognized. As a result, production is less time-consuming, and the susceptibility to errors is significantly reduced. Such a solution is presented using the EPLAN platform and the products Data Portal, Electric P8, Pro Panel, including the connection of the software to the actual machines, which have the task of creating a real construction out of the simulation of a digital twin.

Improvement of test methods and criteria for evaluation of resistance to flame propagation of long elements of the wiring system

The test methods for flame propagation of long elements of the electrical wiring system, in particular, cables, cable conduits and ducts, are analyzed, and differences in them are found in the test conditions and criteria for evaluating the resistance to flame propagation. Using a substrate of a wooden board covered with a layer of tissue paper with an areal density of (21±9) g/m2, adopted for testing other elements of the electrical wiring system, a cable was identified that is not resistant to flame propagation. It is proposed to use this substrate for testing the flame propagation of cables instead of a substrate made of a double layer of filter paper with a surface density of (80±15) g/m2. In one of three experiments, a cable that was not resistant to flame propagation was found based on the criterion of the presence of ignition of the substrate located under it. To reduce the risk of making an incorrect decision on compliance, it is proposed that the assessment of long elements of the wiring system be carried out according to the rules established for cable ducts, trays and ladders in EN 50085-1 and IEC 61537. For the AVVG cable with an outer diameter of 10 mm to 60 mm, when it touches the blue flame cone of 1 kW, the correlation coefficient of the dependence of the length of the charred part on the diameter was 0.969. For a distance of 100 mm between the sample and the burner along its axis, a correlation coefficient of 0.985 was obtained. It is proposed to test cables under the second condition recommended in IEC 60695-11-2. For two conduits, flame propagation was revealed when exposed to a 1 kW flame for 120 s and 240 s. However, for these pipelines, flame propagation did not occur under standard conditions of exposure to such a flame for 20 s and 25 s. To identify long elements of the wiring system that are not resistant to flame propagation, it is proposed to test them at a duration of exposure to a flame of 1 kW, established for cables in IEC 60332-1-2

Effect of Water Condensate on Corrosion of Wires in Ungrouted Ducts.

In the case of existing prestressed concrete structures, information about the actual state of prestressing is an important basis for determining their load-carrying capacity, as well as remaining service lifetime. This is even more important in the case of existing prestressed concrete bridges, which are exposed to a more aggressive environment than the other prestressed concrete structures. The level of prestressing is affected and reduced by prestress losses at a given time. In calculating the internal forces and stresses, required for the assessment of the Ultimate Limit State and the Serviceability Limit State, it is necessary to know not only the prestressing level but also the cross-sectional area of the prestressing steel (wire, strand or cable), which can change in time due to corrosion. In practice, in the case of the pre-tensioned concrete members, it has often happened in the past that cable ducts have been grouted only partially, or not at all, due to poor grouting technology. Experts did not realize what this could cause in the future—the penetration of water with aggressive agents directly into the cable duct and consequently corrosion of the prestressing steel, which means not increased protection of the steel, but rather acceleration of degradation. On the other hand, in many cases, corrosion also occurs in ducts that are not grouted and no water has entered them. This paper deals with this phenomenon—the formation of corrosion of prestressing steel in cable ducts in ungrouted ducts due to moisture. This problem was investigated experimentally and numerically in the simulation program ESP-r. Experimental measurements and numerical simulations have shown that the water vapor condenses in the cable ducts, which can subsequently cause corrosion of the prestressing steel.

Developments in fibre reinforced concrete in tunnelling

AbstractThis paper will provide an overview of the state of the art of the use of fibre reinforced concrete in tunnelling. The major applications for fibres are for the reinforcement of sprayed concrete and pre‐cast concrete segmental linings, but fibre reinforcement is also increasingly used for other applications such as trackbed/trackslab and minor precast concrete elements such as cable ducts, drip shields, and drainage elements. As the technology has matured, a wide variety of fibre types, made from different materials, has emerged. Standards have been developed for the manufacture, testing and application of all these fibre types. Moreover, design guidelines and codes have been published and new design methods are still being developed. The International Tunnelling Association has published several guidance documents in this field. Last but not least, FRC has an important role to play in reducing the carbon footprint of tunnelling projects.