Cable Rating Research Articles

Thermal Analysis of Cable Routes with Joints or Other Discontinuities

The paper addresses rare issue in cable ampacity calculations, namely the presence of discontinuities along the routes. One which occurs in almost all cable installations is the presence of joints. In a standard cable rating analysis, the joints are ignored, mostly because of difficulties in building analytical models that represent the heat transfer phenomena within them. However, they can be a limiting part of the cable rating and, therefore, there is a need to model them correctly. This paper introduces an analytical algorithm for cable rating calculations in the presence of discontinuities with an emphasis on cable joints. New developments are illustrated by several numerical examples.

Active Distribution Network Expansion Planning With Dynamic Thermal Rating of Underground Cables and Transformers

The rapid development of renewable distributed generation in active distribution networks (ADNs) imposes an increasing burden on the transfer capability of the ADNs, bringing new challenges to the distribution network expansion planning (DNEP) problem. Dynamic thermal rating (DTR), which evaluates the equipment rating based on the actual weather conditions and equipment thermal states, can enhance the equipment transfer capability to support the integration of renewable distributed generation. In this paper, we propose a DNEP model of ADNs incorporating the DTR of cables and transformers, given that underground cable feeder is preferred in the rapid urbanization trends. Then, we derive a linear reformulation of the original DNEP model and propose a modified Benders decomposition (MBD) algorithm to solve the DNEP model. To select more effective representative day scenarios, we propose a cost-based clustering method for representative day selection applicable to solving the DNEP model. Case studies based on the IEEE 33-node system and the PG&E 69-node system show that the implementation of DTR saves 14.7% and 15.1% of the investment costs of the two systems respectively. The effectiveness of the MBD algorithm and the cost-based clustering method is also verified by the case studies.

Elastoplastic coupling analysis of surrounding rock-prestressed yielding anchor bolts/cables based on unified strength theory

A whole-process analytical theory for the coupled deformation of deep circular tunnel surrounding rock and prestressed yielding anchor bolt (cable) system is derived based on the unified strength theory and non-associated flow rule. This theory considers the strain softening characteristic of rock mass, the yielding reinforced characteristics of anchor bolt (cable), and the support timing. An analytical method is proposed to calculate the difference in displacement of anchor bolts (cables). This study highlights the importance of monitoring anchor bolts (cables) elongation rate in high-stress tunnels by integrating theoretical analysis with engineering practice. The displacement difference that occurs during the coordinated deformation of the bolts (cables) and the surrounding rock provides the support resistance. Therefore, the safety margin standard of elongation rate can be used to assess the integrity and effectiveness of the support structure during the real-time bolts (cables) action. The present study aims to validate the rationality of the analytical theory by conducting numerical simulations using ABAQUS software. Specifically, we focus on analyzing the ground response curves (GRC) underthe bolt (cable) support and the elongation rate of the bolt (cable). Various factors such as prestress, yielding amount, support timing, intermediate principal stress coefficient, radial/longitudinal spacing, and length are considered tocompare and analyze their effects on the GRC. The results showed that anchor bolts (cables) can significantly reduce the surrounding rock convergence. With prestressed bolt (cable) support, the GRC exhibits a stepwise drop, significantly and timely reducing the support force required for the surrounding rock equilibrium. After setting the yielding structure, the increase in anchor cable stress was limited, thereby slightly increasing the surrounding rock displacement. However, the anchor cable elongation rate significantly decreased, thereby greatly enhancing the support structure safety. The support timing affects the starting point of bolts (cables) function. The displacement control effect is more pronounced when support is provided earlier. However, this also leads to an increase in the elongation rate of the bolt (cable). The intermediate principal stress coefficient reflects the self-bearing capacity of the surrounding rock, and increasing this value can improve the deformation control performance of the surrounding rock under anchor bolt (cable) support as a whole and reduce the elongation rate through the coupled function of the surrounding rock–anchor bolt (cable) system. The spacing between anchor cables significantly impacts the convergence control of surrounding rock. Smaller spacing leads to better control of the surrounding rock deformation and lower stress of the anchor cables. As the length of the anchor cables increases, the elongation rate and stress of the anchor cables continuously decrease. However, the surrounding rock deformation exhibits an initially decreasing and increasing pattern. This paper presents a theoretical and computational approach to analyze the effect of prestressed yielding anchor bolt (cable) support and the safety of support structures in tunnel engineering. The findings of this study can serve as a valuable reference for the convergence analysis of circular tunnels in underground engineering.

An Improved Method for Swing State Estimation in Multirotor Slung Load Applications

A method is proposed to estimate the swing state of a suspended payload in multirotor drone delivery scenarios. Starting from the equations of motion of the coupled slung load system, defined by two point masses interconnected by a rigid link, a recursive algorithm is developed to estimate cable swing angle and rate from acceleration measurements available from an onboard Inertial Measurement Unit, without the need for extra sensors. The estimation problem is addressed according to the Extended Kalman Filter structure. With respect to the classical linear formulation, the proposed approach allows for improved estimation accuracy in both stationary and maneuvering flight. As an additional contribution, filter performance is enhanced by accounting for aerodynamic disturbance force, which largely affects the estimation accuracy in windy flight conditions. The validity of the proposed methodology is demonstrated as follows. First, it is applied to an octarotor platform where propellers are modeled according to blade element theory and the load is suspended by an elastic cable. Numerical simulations show that estimated swing angle and rate represent suitable feedback variables for payload stabilization, with benefits on flying qualities and energy demand. The algorithm is finally implemented on a small-scale quadrotor and is investigated through an outdoor experimental campaign, thus proving the effectiveness of the approach in a real application scenario.

K-mer Frequency Encoding Model for Cable Defect Identification: A Combination of Non-Destructive Testing Approach with Artificial Intelligence

This paper describes a non-destructive detection method for identifying cable defects using K-mer frequency encoding. The detection methodology combines magnetic leakage detection equipment with artificial intelligence for precise identification. The cable defect identification process includes cable signal acquisition, K-mer frequency encoding, and artificial intelligence-based identification. A magnetic leakage detection device detects signals via sensors and records their corresponding positions to obtain cable signals. The K-mer frequency encoding method consists of several steps, including cable signal normalization, the establishment of K-mer frequency encoding, repeated sampling of cable signals, and conversion for comparison to derive the K-mer frequency. The K-mer frequency coding method has advantages in data processing and repeated sampling. In the identification step of the artificial intelligence identification model, an autoencoder model is used as the algorithm, and the K-mer frequency coding method is used to introduce artificial parameters. Proper adjustments of these parameters are required for optimal cable defect identification performance in various applications and usage scenarios. Experiment results show that the proposed K-mer frequency encoding method is effective, with a cable identification accuracy rate of 91% achieved through repeated sampling.

Experimental study on fire spread behavior of single 110 kV cable under different layout conditions

High-voltage cable fire accidents can cause large-scale power outages. In particular, the 110 kV large-section (diameter 10 cm) cable has complex cable structures. Therefore, based on the actual cable laying scenarios, three cable layout conditions are set, including the horizontal cable above horizontal floor structure (HCAHFS), the inclined cable above horizontal floor structure (ICAHFS), and the inclined cable above inclined floor structure (ICAIFS). The combustion behaviors and flame spread characteristics of 110 kV large-section cable are experimentally studied. It is found that the flame cannot spread on the surface of the flame-retardant outer sheath of the cable. However, when the cable-floor distance (lcf) is between 0.75 d and 2 d (d is the cable diameter) in HCAHFS, i.e. there is a floor under the cable that can catch cable melt, and the flame spread characteristics is different. After the cable is ignited, the cable fire can be divided into two parts, outer sheath flame and melt flame, and the cable fire can spread under the joint action of two flames. When lcf ≤ 0.75 d, the space under the cable is narrow. With the accumulation of melt on the floor, air entrainment is limited during cable combustion, resulting in the cable flame unsustainable. When lcf ≥ 2 d, the thermal radiation and convection from the melt and outer sheath flame to the cable preheat zone are weakened, resulting in cable flame extinction as well. In ICAHFS, the cable flame spread rate is first increased and then decreased with the increasing lcf at the fixed inclination angle; In ICAIFS, the upward spread rate of cable flame is faster than the downward spread rate at the fixed inclined angle. Moreover, the cable flame spread rate (FSR) in HCAHFS is the slowest compared to that in ICAIFS with different inclined angles. The preheating length for ICAIFS increases under both upper and lower ignition modes, while it is obviously at upper ignition, due to the melt flow. Finally, a correlation of FSR was proposed for various ignition positions and inclined angles. This study provides a reference for fire protection design and numerical simulation parameter setting of 110 kV cable fire.

Opportunities to Improve Marine Power Cable Ratings with Ocean Bottom Temperature Models

Determining reliable cable ampacities for marine High Voltage Cables is currently the subject of significant industry and academic reassessment in order to optimize (maximizing load while maintaining safe operating temperatures) design and reduce costs. Ampacity models can be elaborate, and inaccuracies are increasingly predicated on the uncertainty in environmental inputs. A stark example is the role of ambient temperature at cable depth, which, due to the scale of cables and the inaccessibility of the seafloor, is commonly estimated at 15 °C. Oceanographic models incorporating ocean bottom temperature are increasingly available, and they achieve coverage and spatiotemporal resolutions for cable applications without the requirement for project specific measurements. Here, a rudimental validation of the AMM15 and AMM7 mean monthly ocean bottom temperature models for the NW European Shelf indicates encouraging accuracies (MBE ≤ 1.48 °C; RMSE ≤ 2.2 °C). A series of cable case studies are used to demonstrate that cable ratings can change between −4.1% and +7.8% relative to ratings based on a common static (15 °C) ambient temperature value. Consideration of such variations can result in both significant ratings (and hence capital expenditure and operating costs) gains and/or the avoidance of cable overheating. Consequently, validated modelled ocean bottom temperatures are deemed sufficiently accurate, providing incomparable coverage and spatiotemporal resolutions of the whole annual temperature signal, thereby facilitating much more robust ambient temperatures and drastically improving ampacity estimates.

A novel grounding mode for enhancing current rating of AC submarine cables

Due to the deficiency in using the cross-bonded grounding mode, a large circulating current is usually induced in the metal sheaths and armors, reducing the permissible current rating of submarine cables. To address this issue, this paper proposes a novel grounding mode to suppress these circulating currents and enhance the permissible current rating within the voltage limits of metal sheaths and armors. To achieve the best performance of the novel grounding mode, the optimal grounding impedances are given. Theoretical analyses indicate that for general submarine cables, the novel grounding mode can suppress the circulating currents within the voltage limits compared with the two-ends grounding mode, and can reduce the short-circuit terminal voltage of metal sheaths and armors compared with the non-interlinked version of the proposed mode. The numerical results further validate the better comprehensive performances of the novel grounding mode in reducing the power loss and short-circuit overvoltage.

Soil Dryout in the Vicinity of Cables With Cyclic Load Installed in a Backfill

The IEC Standard 60287-1-1 provides the procedure for modelling of soil dryout in the vicinity of current currying power cables. Two important assumptions limit the application of the formula to the cases with uniform burial conditions and a uniform current with 100% load factor. Another standard in this series, 60287-2-1, contains the formula for the calculations of the external thermal resistance of cables laid in thermal backfills. It is based on the pioneering work of Neher and McGrath published in 1957. The Neher/McGrath paper provides also a modification of the external thermal resistance of buried power cables with a non-unity load factor with an assumption of the uniform burial conditions. This paper develops new formulae for the calculation of cable current ratings taking into account all three factors; that is, consideration of the soil dryout for cables laid in a thermal backfill and loaded with a variable current with known load factor. The results obtained with the proposed approach are compared with detailed finite element studies.

Analytical Approach to Current Rating of Three-Phase Power Cable with Round Conductors

The continuous increase in the demand for electricity makes it necessary to modernize or build new transmission lines. This, in turn, results in research that is still being carried out on the optimal use of power cables. In the paper, an improved analytical method for the determination of the current rating of power cables was proposed. The method for determining the ampacity of the power cable presented in the IEC standard assumes that power losses in the phase conductors and screens are determined by taking into account skin and the proximity effects on the basis of tabulated coefficients. The methodology proposed in the paper is based on the method presented in the IEC standard, but the power losses in the conductive elements of the cable are determined analytically, which offers higher accuracy. In order to validate the analytical method proposed in this paper, numerical calculations based on the finite element method with very fine mesh were also performed. Exemplary calculations carried out for three types of cables with use of the proposed method, IEC standard and finite elements showed very good agreement in the results. The proposed method requires more computational effort, but it offers more accurate results than the IEC standard and can be used when higher accuracy is required. It can also serve as a reference point for simplified calculations.

Condition Assessment of Grouped Cable Forces of Cable-Stayed Bridge Using Deflection Data

The stress state of the cable group in a cable-stayed bridge directly affects the overall performance. A novel method for assessing grouped cable forces using deflection data is proposed in this article. Firstly, a simplified equation between the variation in cable forces and the girder deflection was built according to the geometric relationship of the deformation. Secondly, the threshold value of cable force change rate for a single cable can be determined by the proposed theoretical equation and the deflection limit in the specification. On this basis, the evaluation standard of single cable force of piecewise linear mode was established. Thirdly, considering the uniform and non-uniform changes in the cable forces, the condition assessment method of grouped cable forces was established based on the variable weight synthesis method and the gray correlation degree theory. Finally, a case study of a real bridge was undertaken. The results show that the case data validate the correctness of the proposed theoretical equation. The threshold of change rate for long cable is 30%. Six-year assessment scores of grouped cables are generally decreasing, which also reflects the development of other component defects from the side.

Extended Thermal Probe Method for Measuring Thermal Stability of Soils Surrounding Buried Power Cables

The single most influential factor in determining the rating of underground cables is the thermal resistivity of the soil that surrounds the cables. An accurate measurement of soil thermal resistivity is therefore critical to the determination of cable ratings. Ratings are also strongly influenced by the thermal stability of the soil, because heat generated by the cables can often drive soil moisture away from the cables resulting in an unexpected steep rise in the soil resistivity and a corresponding sharp reduction in cable ratings. Soil thermal stability can be determined by a simple, short-duration test that involves a thermal probe that has traditionally been used to measure thermal resistivity if the duration of the test is extended. Therefore a single test with a thermal probe can be employed to provide a measure of the soil's thermal stability as well as its thermal resistivity. Armed with knowledge of both resistivity and stability of the soil, a utility engineer can confidently calculate cable ratings that will result in safe cable operating temperatures even under the most adverse unstable soil conditions. Measurements of soil stability are shown to be influenced by the soil's properties, the heat generated in the cables, the diameter of the cable/soil interface and the duration that the soil experiences heating by the cables. Experimental measurements of soil stability using the extended probe method are demonstrated for four different soils, and measurements of stability are shown to influence the rating of several different cable installations.

Implementation of Unbalanced Thermoelectric Equivalent Circuit for Power Flow and Thermal Rating of Underground LV and MV Cables

This manuscript proposes a time-series temperature-dependent power flow method for unbalanced distribution networks consisting of underground cables. A thermal circuit model for unbalanced three-phase multi-core cables is developed to estimate the conductor temperature and resistance of Medium (MV) and Low Voltage (LV) distribution networks. More specifically, a novel approach is proposed to model and estimate the parameters of the three-phase thermal circuit of 3- or 4-core cables, using the results of Finite Element Method and Particle Swarm Optimization. The proposed approach is generic and can be accurately applied to any kind of 3- or 4-core cables buried in homogeneous or non-homogeneous soil. Furthermore, it is applicable in cases where one or more adjacent cables exist. Using the proposed approach, the conductor temperature of each core can be individually and precisely calculated even under unbalanced loading conditions. The proposed approach is expected to be an important tool for simulating unbalanced distribution networks and estimating the conductor temperatures. The proposed thermal circuit is validated using two 4-core LV and one 3-core MV cables buried in different depths in homogeneous or non-homogeneous soil. Time-series power flow for a whole year is performed in a 25-bus unbalanced LV network consisting of multicore underground cables.

Detecting Cable Force Anomalies on Cable-Stayed Bridges Using the STA/LTA Method

The cable force of cable-stayed bridges may become abnormal during operation, so cable force anomaly detection is essential for evaluating the health of cables. The current methods for detecting cable force anomalies have poor resistance to temperature disturbances and are insensitive to abnormal cable force, making it challenging to detect minor cable force anomalies. Therefore, this work employs the short-time-average over long-time-average (STA/LTA) method to detect cable force anomalies. The characteristic function and key parameters of the STA/LTA method are optimized and tested by combining measured cable force data with cable force anomaly simulation. The results show that the STA/LTA method can effectively mitigate the interference of temperature in the detection of cable force anomalies and that it has good sensitivity to minor cable force anomalies. By examining detecting the measured cable force data of the Xiangjiang Bridge in Dongzhou, Hengyang, China, it is further verified that the STA/LTA method could effectively detect a cable force anomaly with a cable force deviation rate of higher than 1%.

A Diaphanous and Enabled-dependent asymmetric actin cable array repositions nuclei during Drosophila oogenesis.

Cells reposition their nuclei for diverse specialized functions through a wide variety of cytoskeletal mechanisms. During Drosophila oogenesis, 15 nurse cells connected by ring canals to each other and the oocyte contract, 'dumping' their cytoplasm into the oocyte. Prior to dumping, actin cables initiate from the nurse cell cortex and elongate toward their nuclei, pushing them away from ring canals to prevent obstruction. How the cable arrays reposition nuclei is unknown. We found that these arrays are asymmetric, with regional differences in actin cable growth rate dependent on the differential localization of the actin assembly factors Enabled and Diaphanous. Enabled mislocalization produces a uniform growth rate. In oocyte-contacting nurse cells with asymmetric cable arrays, nuclei move away from ring canals. With uniform arrays, these nuclei move toward the adjacent ring canal instead. This correlated with ring canal nuclear blockage and incomplete dumping. Our data suggest that nuclear repositioning relies on the regulated cortical localization of Diaphanous and Enabled to produce actin cable arrays with asymmetric growth that push nuclei away from ring canals, enabling successful oogenesis.

Optimal Number and Locations of Smart RMUs for Self-Healing Distribution Networks

Smart grids with self-healing (SH) capability provide an important intelligent feature to help in fast correction actions in case of network faults. SH architecture consists of modern communication systems, smart equipment, and intelligent sensors. With the high cost of SH components (especially smart ring main unit (SRMU)), optimization is required to achieve optimum performance with minimum cost. This study presents a proposed methodology to determine the optimum number and locations of SRMUs in electricity distribution networks considering various cost issues. The disconnection cost of on-grid photovoltaic (PV) plants is taken into consideration as an important factor in determining the locations of the SRMUs. The nonlinear programming (NLP) optimization technique is used to determine the required number of SRMUs, considering the cost/benefit analysis (cost of upgrading MRMUs to SRMUs/benefit due to interruption time reduction), which is the most important factor from DISCOs’ perspective. The mixed integer linear programming (MILP) optimization technique is employed for selecting the optimal locations of the SRMUs considering the cost of losses, energy not supplied (ENS), and PV disconnection, which improves network operation cost. The methodology takes into consideration the cable failure rate and the interest rate. Moreover, the study introduces the Egyptian electrical distribution network and a pilot project for control centre development using SRMUs. The methodology is applied to a modified IEEE 37-node test feeder and a part of a specific district network in South Cairo consisting of 158 nodes; both systems include a number of PV distributed generation plants. Simulation results are presented to show the effectiveness of the proposed method.

Offshore Windfarm Design Optimization Using Dynamic Rating for Transmission Components

The foreseen development of large-scale Offshore Windfarms (OWFs) further from the shore dictates that the OWF transmission system must be optimally designed based on Dynamic Thermal Rating (DTR) in order to fully utilize the intermittent nature of the wind and to keep the offshore wind cost-competitive. In this paper, a comprehensive, DTR-based, two-stage stochastic model is presented, which has been developed for investment decision support for OWF size and HVAC transmission systems. Complex DTR models for all the critical HV components are made fit for the mixed-integer linear programming problem, while accounting for the stochasticity in wind generation and component availability. The main decisions incorporate the discrete size of OWFs, HV subsea export cable cross-sections and ratings for transformers and shunt reactors. For validation, an actual testcase OWF off the east coast of U.K. has been used. Results indicate that DTR-based iterative design of OWF and its transmission components can significantly improve the business case, even though transmission efficiency and energy delivered are not maximum for the optimal design

Study of the Fire Behavior of Multilayer Cables in a Mine Tunnel

Fires caused by cables occur frequently in mines, which endanger the safety of workers. To explore the characteristics of a multilayer cable fire in a mine tunnel, multilayer cable fire simulations were carried out using the Fire Dynamics Simulator (FDS). The influence of cable tray spacing, ignition position, and tunnel ventilation speed on the characteristics of the fire were studied. The results showed that these factors change the amount of contact between the cable and air, the heat accumulation, and the heat transfer by the flame interaction between the cables. It was also noted that increasing the spacing or wind speed both made the peak of heat release rate (PHRR) initially increase and then decrease. The influence of wind speed on the cable burnout rate in the upstream and downstream sides of the fire source was not consistent, and the wind speed had a sensitive effect on the cable burn out rate in the upstream side of the fire source. The higher the ignition position was, the longer the arrival time of PHRR was and the slower the fire developed. There was a higher burn velocity close to the ceiling. The cable hooks obstructed the cable fire. This study provides a theoretical basis for cable fire prevention and control in mine tunnels.

DC Fault Study of a Point-to-Point HVDC System Integrating Offshore Wind Farm Using High-Temperature Superconductor DC Cables

This paper presents a feasibility study of an offshore wind farm (OWF) HVDC integration system using high-temperature superconductor (HTS) DC cables. A representative ±100 kV/2 GW point-to-point OWF HVDC system is proposed including HTS DC cables and two converter stations using modular multilevel converters (MMCs). To be compatible with the high current rating of the HTS cables, each of the offshore and onshore converter stations consists of three MMCs in parallel. To study the interaction between HTS DC cables and MMCs, a multiple lumped π-section model of a HTS DC cable considering electrical and thermal functionality is developed. This paper provides a critical assessment of the proposed HVDC-HTS system, with emphasis on the performance under fast DC fault transients. Detailed simulations presented in this paper reveal that the HVDC-HTS system provides effective current limiting against DC cable short circuit faults.

Research on High Voltage Cable Condition Detection Technology based on Wireless Sensor Network

The development and progress of modern society cannot be achieved without the support of electric power resources, and at present, electric power is the most important energy source to promote social development and maintain human life. As a key unit under the power distribution and transmission system, the high-voltage cable of the power grid will undertake the task of supplying power resources to the whole power grid. Therefore, based on the transmission line fault diagnosis framework of Wireless Sensor Networks (WSN), a high-voltage cable path condition monitoring scheme using LoRa technology is proposed. Three high-voltage cable condition monitoring periods are proposed according to the difference of high-voltage cable fault rate, and the delay and energy consumption of the high-voltage cable monitoring system are optimized by multi-objective particle swarm algorithm reality. The experimental results show that the proposed high-voltage cable detection technology can switch the working mode according to different environments, and the data communication packet loss rate is less than 5%, while the detection platform has excellent delay performance and energy saving effect. The high-voltage cable status detection solution can effectively solve the problem of blind high-voltage cable channels in high mountain areas of China. The research content has important reference value for the detection of China’s power grid circuit system.