High Temperature Low Sag Conductors Research Articles

Aluminum Conductor Steel-Supported Conductors for the Sustainable Growth of Power Line Capacity: A Review and Discussion.

Industrial development and population growth have increased the need for higher-capacity power transmission lines. Aluminum conductor steel-supported (ACSS) conductors, a type of high-temperature low-sag (HTLS) conductor, are now widely used in new designs and reconductoring applications. ACSS conductors are preferred over traditional aluminum conductor steel-reinforced (ACSR) conductors due to their high strength, low sag, and excellent thermal stability. These attributes have garnered significant interest from researchers, engineers, and manufacturers. This paper provides a comprehensive review of the structure, properties, testing methods, and environmental behavior of ACSS conductors.

An insight into the effect of carbon nanofillers in glass fibre epoxy nanocomposites through dielectric spectroscopy

Interfacial characteristics of nanocomposites are critical limiting factors in the design of polymer nanocomposites. The nanocomposites have complex structures and play a pivotal role in controlling functional properties. Analysis of interfacial layers in polymer nanocomposites, existing between the polymer matrix and the nanoparticles plays a major role in determining their characteristics. High-frequency analysis of electrical conductivity and dielectric properties of carbon nanofillers which are embedded in an epoxy matrix were analysed using alternating current dielectric spectra. This article provides a correlation between the electrical transport properties and dielectric behaviour of epoxy carbon nanocomposites at different temperatures are investigated with variations in frequency. Electrical transport properties of nanocomposites are primarily dictated by electron tunnelling and matrix, nanofillers conductivity. Dielectric spectroscopy in the frequency range 10 Hz–8 MHz has been performed on epoxy nanocomposites with and without hybrid carbon nanofillers at one weight percentage (2:3 ratio). Dominant dielectric relaxation mode is observed in the base composite at a low-frequency region (≥10 Hz), whereas nanocomposite with hybrid carbon nanofillers is observed to induce two dielectric relaxations in the kHz region. Increase in non-monotonic variations in dielectric spectra makes the nanocomposite suitable for high temperature low sag conductor core, aerospace and cryogenic engineering applications.

Advancing OHL Rating Calculations: Modeling Mixed-Convective Cooling and Conductor Geometry

The existing standard current-temperature calculations for overhead line (OHL) conductors have been adequate for conventional conductors and their operating temperatures. However, these calculations make assumptions and include simplifications about conductor geometry and aero-thermal-dynamics, introducing an error in the High-Temperature Low-Sag conductors operating temperatures. To quantify the error introduced by the shape of strands, the paper employs a Multi-Physics Finite Element Modeling approach that calculates the conjugate heat transfer for trapezoidal stranded OHL conductors. Furthermore, it proposes corrective equations to improve the accuracy of existing methods. The equations incorporate a new Nusselt number correlation for mixed convection and capture the surface area ignored by current calculations. The outer conductor geometry assumptions and the combined natural and forced convective cooling omission in the IEEE and CIGRE methods introduce an error at low (below 0.12 m/s) cross-flow wind speeds suggesting an underestimation of conductor temperature by up to 4%. In medium wind speeds, typically at 0.5 m/s–0.61 m/s, the standard methods overestimate the conductor temperature limiting its current-carrying capability. A 5% uprating for existing OHLs is potentially feasible, particularly for the trapezoidal stranded conductors, when removing the assumptions made in existing methods.

Advanced Composite Materials: A Panacea for Improved Electricity Transmission

The demand for electricity has increased drastically due to population explosion globally. Unfortunately, supply does not meet the demand. Consequently, the transmission grid becomes overloaded, culminating in frequent power outages. Worse still, the transmission grid lacks adequate maintenance, and this has led to energy crisis in Africa and some parts of Asia. In this review, studies on the strength and weaknesses of existing transmission conductors were conducted. Further studied were natural and artificial phenomena that attack the overhead transmission networks. It was observed that besides inherent conductor defects, overloading, bush fire, short-circuit, harsh weather, and lightning were the factors that ravage the transmission grid. Hence, there is the need to develop more robust conductor materials that can withstand these challenges. The conventional conductors such as all aluminum conductor (AAC) and aluminum conductor steel reinforced (ACSR) are challenged by low operating temperatures, among others. High-temperature low-sag (HTLS) conductors that were invented to tackle these shortcomings certainly have higher ampacity and better thermal rating than the conventional conductors. However, some challenges still devastate them. So, from the study conducted, it was discovered that developing advanced nano-based Al-composite conductor would help in ameliorating the challenges prevalent in the transmission grid. Such an Al-nanocomposite conductor would possess higher ampacity and better thermal stability and would be more durable and cost effective.

Evaluating Aeolian Vibration Performance of High-Temperature Low-Sag OHL Conductors

High-Temperature Low-Sag (HTLS) conductor technologies are often implemented, among many approaches, for optimizing the overhead lines utilization. The advancements of HTLS conductors are based on the differences in core and aluminum properties and installation procedures. This non-linear conductor behavior, although considered in the sag-tension calculations, by implementing the knee-point temperature, is often omitted from the aeolian vibration calculations. To understand the implications of the complex HTLS conductor structure on vibrations, a new calculation approach is proposed in this paper to quantify the effect of installation and operating conditions on the performance of any HTLS conductor. The proposed method conceives a prediction lay area that estimates where the actual field data are expected to lay, and is validated with good accuracy against the field data from ACSR, ACCC, and GZTACSR. The developed model enables the prediction of non-homogeneous (composite) conductors and should be implemented at above knee-point operating temperatures with zero aluminum tensions

Conductor sag comparison for 132 kV overhead transmission line improvement in Malaysia

This paper presents conductor sag comparison for 132 kV overhead transmission line improvement in Malaysia. Increasing industrialization and population growth around the world demands higher electricity supply. Power generation has yet to decline but transmitting sufficient electricity to consumers is worrisome due to scarce land space occupied by rapid urbanization. Hence reconductoring method was chosen to improve existing 132 kV overhead transmission line in Malaysia. A group of selected conductors were chosen for comparison where the high temperature low sag conductor stood out the most producing up to 40% sag reduction. This paper focuses on providing conductor alternatives to improve maximum sag of lowest conductor to ground for 132 kV transmission line in Malaysia in accordance to her climate and geographical factor.

Uncertainties in the Testing of the Coefficient of Thermal Expansion of Overhead Conductors

Overhead lines can be replaced by high temperature low sag (HTLS) conductors in order to increase their capacity. The coefficients of thermal expansion (CTE) of the HTLS conductors are lower than the CTE of conventional conductors. The utilities and conductor manufacturers usually carry out the verification of the CTE of the overhead conductors in an actual size span. The verification is based on the observation of the change of the conductor length as a result of the conductor temperature change. This process is influenced by the coefficient of thermal expansion to be verified. However, there are other factors that also affect it. This paper analyzes the effect of some of the uncertainty sources in the testing of the coefficient of thermal expansion of the overhead conductors. Firstly, the thermal expansion process is described and the uncertainty sources related to the conductor and the line section are identified. Then, the uncertainty sources and their effect on the CTE testing are quantified.

Investigations on High Temperature Low Sag (HTLS) Conductors

Electric power demand is growing at an exponential rate due to establishment of industries and economic growth in the country. Central electricity authority of India (CEA) has estimated per capita electricity consumption will increase at a rate of 6 percent per annum, this will increase the load on the transmission and distribution system. Limitations of Right of Way (ROW) has made it difficult to construct new lines, particularly in metropolitan and densely populated cities, hence high temperature low sag (HTLS) conductors are being used adopted, several projects in the country are being executed to overcome the problem of burdening of transmission/distribution system. HTLS conductors operate at 2–3 times higher ampacity and thermal rating, hence can be used for higher power transmission without upgrading the existing towers and infrastructure. The present investigation aims to understand and estimate the conductor temperature and ampacity dependent on different parameters like wind velocity, wind angle, emissivity and fault current level. The investigation highlights the dynamic thermal rating of HTLS conductor with change in wind velocity and angle, thermal performance of conductor during fault condition and thermal rating with emissivity, absorptivity and ambient temperature during flow of fault current is presented. A new experimental setup is established to investigate the performance of HTLS and Traction copper conductor in the laboratory, attempt has been made to study effect of magnetic fields and conduct EBSD analysis, some important conclusions drawn from the investigations are analyzed and presented.

Shape Sensing of Polymer Core Composite Electrical Transmission Lines Using FBG Sensors

Fiber Bragg grating (FBG) sensors are optical strain gauges embedded in an optical fiber. Using elementary beam theory and geometry, it is shown that 3-D shape sensing can be performed using parallel arrays of sensors on the surface of a cylindrical rod. The mathematics is explained in detail. Because FBG sensors are immune to electromagnetic interference, they can be used to perform shape sensing on cylindrical objects utilized in high-voltage transmission systems, such as the core support rods of high-temperature low-sag conductors.

Evaluation Study of Potential Use of Advanced Conductors in Transmission Line Projects

Transmission networks recently faced new technical and economic challenges. The direct use of advanced technologies and modern methods could solve these issues. This paper discusses the potential application of straightforward technology such as high-temperature low-sag conductors (HTLScs) as an additional measure for the protection and effective operation of overhead power lines. An evaluation was conducted to determine an approach for selecting the cross-sectional area and type of conductor with respect to a fault current limitation. It showed the potential benefits of using HTLScs based on an assessment of the throughput capacity and up-front capital costs. A case study considered two scenarios: the construction of a new power line and reconductoring of the existing one. The data for a real project with two overhead power lines were used. The obtained results are analyzed and discussed in detail in this paper.

A literature review on capacity uprate of transmission lines: 2008 to 2018

In this paper, the authors present the results of an in-depth review of available publications on capacity uprate of transmission lines produced during the period 2008–2018. It also provides statistics of publications going back to 1980, developed mainly to facilitate the analysis of trends. Before 2005, publications on this topic were scarce but grew in numbers exponentially thereafter. The largest share of publications found was in the category of the thermal uprate of lines, with its subcategory of the use of high temperature low sag (HTLS) conductors receiving most interest from researchers. This paper contributes to the discourse about the uprate of transmission lines. It provides an overview of the state-of-the-art of research on the capacity uprate of power lines, giving insight into trends on research on the capacity upgrade of lines and developing an in-depth repository of references which may be useful to engineers and scientists interested in the topic of the capacity uprate of lines.

HTLS Conductors: A Way to Optimize RES Generation and to Improve the Competitiveness of the Electrical Market—A Case Study in Sicily

Stringent environmental constraints make more difficult to identify new energy corridors and build new power lines. The increase in the generation of electricity from renewable energy sources (RESs) makes the operation of electrical systems increasingly difficult in some areas. The transmission system operators (TSOs), in Italy Terna, are forced to exploit the existing overhead transmission lines, increasing the possibility of dispatching energy, in particular RES, optimizing the transmission capacity. Therefore, after a brief presentation of the Sicilian electricity system and a brief description of high-temperature low-sag (HTLS) conductors, a case study is presented. It is shown how it is possible to optimize the dispatching from renewable sources and, finally, it is demonstrated how the use of HTLS conductor can contribute, together with other actions taken by the TSO, to the decrease of the zonal price of electricity, to the creation of a market with fewer constraints and to new operating conditions that increase the resilience of the electricity system in case of disturbances.

Investigations on the mechanical and electrical behaviour of HTLS conductors by accelerated ageing tests

To cope with future requirements, the transfer capacities of distribution systems as well as of transmission systems in Europe need to be increased. Therefore, repowering of existing overhead lines with high-temperature low-sag conductors (HTLS) can be one interesting possibility. Due to the limited experiences with that technology, current research of TU Dresden, the Federal Institute for Materials Research and Testing (BAM), and 50Hertz Transmission GmbH investigates the ageing behaviour of several different HTLS technologies in a consortium with other European partners. In this context, accelerated ageing tests of conductors and its corresponding fittings with combined mechanical and electrical loads are performed. To evaluate the changes due to ageing, several mechanical tests of the conductors are carried out and the contact behaviour of the fittings is analysed.

Evaluation of regulatory impacts on investments of distributed generation and upstream network under uncertainty: a new stochastic bi-level model

A new framework is proposed to study impacts of regulatory incentive policies on distributed generation (DG) investment, as well as upgrading of upstream transmission substations and sub-transmission lines. Investment incentives are fuel cost, firm contracts, capacity payments and investment subsidy. Conventional and wind generation technologies are considered as expansion candidates for investor which participate in wholesale and contractual markets. High Temperature Low Sag (HTLS) conductors are used as expansion candidates for lines. The problem is modelled as a stochastic bi-level optimization problem, where the upper-level consists of investor’s decisions maximizing its own profit, while both market clearing and decision on upgrading of substations and lines aimed at minimizing the total cost are considered in the lower-level. Due to non-convexity of lower level problem, an algorithm based on enumeration and mathematical optimization is used where for each expansion strategies of substations and lines, the bi-level problem is converted to a stochastic mathematical programming with equilibrium constraints and then converted to a mixed-integer linear program. The effectiveness of the proposed model is tested through on an actual 22-bus [The west of MAZANDARAN Regional Electric Company (MREC) sub-transmission network as an area of Iran interconnected power system.] network.

Finite element analysis to predict temperature rise tests in high‐capacity substation connectors

In the last years there has been a considerable increase in electricity consumption and generation from renewable sources, especially wind and solar photovoltaic. This phenomenon has increased the risk of line saturation with the consequent need of increasing the capacity of some power lines. Considering the high cost and the time involved in installing new power lines, the difficulty in acquiring tower sites and the related environmental impacts, some countries are considering to replace conventional conductors with high-temperature low-sag (HTLS) conductors. This is a feasible and economical solution. In this study a numerical-finite element method (FEM) approach to simulate the temperature rise test in both conventional and high-capacity substation connectors compatible with HTLS technology is presented. The proposed coupled electric-thermal 3D-FEM transient analysis allows calculating the temperature distribution in both the connector and the conductors for a given current profile. The temperature distribution in conductors and connectors for both transient and steady state conditions provided by the proposed simulation method shows good agreement with experimental data.

Techno Economic Analysis of the Use of High Temperature Low Sag (HTLS) Conductors in the Sri Lanka’s Transmission System

High Temperature Low Sag (HTLS) conductors are introduced with the intention of mitigating some of the disadvantages of the conventional overhead conductors. When compared to conventional conductors, HTLS conductors have better electrical and mechanical characteristics and by using these conductors in overhead transmission lines, some of the complex issues related to power transmissions could be resolved. However, most of the utilities are still in a quandary about using these conductors in place of conventional overhead conductors which have provided a commendable service to them over a period of a century or so. It is because of their lack of experience in using them in the field as well as because of the novel appearance of the conductors. Almost the entire transmission system in Sri Lanka comprises of overhead lines constructed using conventional conductors, especially ACSR conductors. Utility engineers therefore do not have much knowledge on HTLS conductors and also have very little experience in using them. This paper discusses the possibility of adopting the HTLS conductor technology in the Sri Lanka’s transmission system. The properties, behavior and special characteristics as well as the technoeconomic feasibility of using HTLS conductors instead of the conventional conductors are discussed in depth. Lastly, the issues and challenges related to the application of HTLS conductors are discussed. The results of this research will provide valuable information on the possibility of using HTLS conductors in the Sri Lanka’s transmission system.

Overhead line design considerations for conductor creep mitigation

Utilities are continuously investigating methods to economically reinforce their overhead line (OHL) networks by reconductoring with larger conductors or with novel high-temperature low-sag (HTLS) conductor technologies. To further optimise the OHL design, conductor creep ageing is calculated and mitigated at installation, which economically improves an OHLs’ performance. An already established methodology is used to investigate common and HTLS conductors ageing effect on sag and tension in order to highlight the benefits and risks that could result from existing creep mitigation methods particularly on HTLS conductors. The study aims to identify the impact of important design factors such as ice loading and emergency operation events and their frequency of occurrence on creep mitigation as well as to highlight the creep variation of the same materials used particularly on different HTLS conductors. The analysis presented here indicates that pre-tensioning could be more beneficial on soft aluminium HTLS conductors while over-tensioning can result in extensive durations of conductor over-stressing on steel supported and Gap-type conductors. Furthermore, the conductor technology majorly affects the creep of steel core which cannot be considered always as zero. The accuracy of the methodology is also re-validated using recent experimental data from Gap conductor.

Performance evaluation of high temperature high current conductors

A rapid increase in electric power consumption is witnessed, there is a demand for the uninterrupted power supply. Newer generation units are being built with the increased installed power. The available transmission lines are reaching critical limits of ampacity and sag; hence there exists an intricacy in finding corridors particularly in densely populated cities to construct new overhead lines in many industrialized countries including India. Most of the times, it becomes impossible to obtain a right of way for the new transmission lines; hence, present circumstances demand the use of available lines representing a cheaper solution than going in for an underground transmission. Increasing the transmission capacity of overhead lines using high temperature low sag (HTLS) conductors, replacing original ACSR conductors with approximately the same diameter is one of the techniques. HTLS conductors are capable of withstanding high-temperature, continuous operation above 200°C without loss of tensile strength or increase in sag. In the present work, a computer program is developed in accordance with IEEE Std.738 to estimate the current and temperature distribution for various HTLS conductors and a graphical user interface has been developed to optimize the selection of various hardware accessories used for HTLS conductors. A novel experimental facility has been built for the present study. Results obtained for both simulation and experimental investigations are analyzed and presented. An attempt has also been made to study the effect of magnetic fields due to higher currents in the conductors.

Power Network Reliability Evaluation Framework Considering OHL Electro-Thermal Design

Utilities continually investigate ways to optimize the utilization of their existing plant and improve their network's flexibility and resiliency to future uncertainties. With respect to overhead lines (OHL), smart grid solutions aim to increase adequacy through the implementation of probabilistic thermal rating (PTR), dynamic thermal rating (DTR) or novel high temperature low sag (HTLS) conductor technologies. At present, the risks related to these particular solutions, both for the OHL plant and the power network, are not quantified. This paper presents a novel methodology for power network reliability evaluation which integrates a network level sequential Monte Carlo algorithm with a detailed modeling of OHL. This integration facilitates a holistic evaluation of power network reliability as it considers the properties of OHL design technologies and their associated ageing risks. As a result, the network performance (adequacy) and plant risks (ageing) introduced by increased OHL capacities through PTR, DTR, and HTLS solutions can be objectively quantified. An application of the methodology is demonstrated using the IEEE-RTS 96 network which is assessed considering PTR-based OHL capacities.

Transmission expansion planning model considering conductor thermal dynamics and high temperature low sag conductors

The means for transporting more power through an existing transmission corridor have been given considerable attention in recent studies. Reconductoring a path with a conductor that has a higher thermal capacity, such as a high temperature low sag (HTLS) conductor, is one possible option with minimal structural modification and out-of-service time. Parallel line additions or HTLS parallel line additions are other options that can increase transfer capabilities and reduce operating costs. Thermal constraint relaxation is another option, which is an operational based method that allows the line flow to exceed the steady-state line rating for a certain penalty price. Since such operation may deteriorate the expected service time of the conductor, the penalty price should be determined properly. In this study, the above options are captured to create the proposed transmission expansion planning model. In addition, a conductor degradation model is introduced to capture the associated degradation costs due to operating conductors at elevated temperatures. Numerical simulations conducted on the IEEE-24 and IEEE-118 bus system indicate the effectiveness of the proposed approach to increase system capacity while preserving current right-of-ways (ROWs).