This is the accepted manuscript, which has been accepted by IEEE for publication. © 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The full reference is: ‘A Holistic Method for Conductor Ampacity and Sag Computation on an OHL Structure’ K. Kopsidas, S. M. Rowland, B. Boumecid, IEEE Trans Power Delivery, Volume: 27, pp. 1047-1054 (2012) DOI: 10.1109/TPWRD.2012.2187464 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012 1047 A Holistic Method for Conductor Ampacity and Sag Computation on an OHL Structure Konstantinos Kopsidas, Member, IEEE, Simon M. Rowland, Senior Member, IEEE, and Boud Boumecid Abstract—The rating current (ampacity) of a conductor erected on a particular overhead line (OHL) structure installed at a specified location is influenced by the conductor, the OHL structure, as well as weather and operational parameters. Many studies have been carried out regarding calculating an aerial bare conductor’s ampacity at a steady-state conductor temperature, but without considering the OHL structure as part of the system. In this paper, a holistic methodology for calculating the conductor’s ampacity and sag at any temperature and power frequency, erected onto a prespecified OHL structure is developed, considering together the mechanical and electrical parameters of the overall system. This methodology incorporates the conductor’s basic material properties allowing the calculations to be applied to newly developed high-temperature low-sag composite conductors. In this way, it becomes possible to identify, at the system level, the potential benefits that may result from the improved performance of these conductors as well as to indicate new sizes that may better fit a prespecified system, optimizing its performance. The methodology is also validated with a real system application, resulting in correct predictions of the performance of a four-span double-line system. Index Terms—Aging, ampacity, bare conductors, conductor creep, high temperature, low sag, overhead line, reconductoring, re-tensioning, sag, tension, thermal rating, upgrating, uprating. I. INTRODUCTION T HE NEED TO increase the power transfer capacity of existing distribution and transmission lines has resulted from the growth in demand for, and generation patterns of, electrical power. However, this is not always easy to achieve in a deregulated environment where competition forces utilities to operate existing lines at maximum rated capacities due to environmental and cost barriers. As a result, utilities may attempt to extract the most out of the installed lines by operating them closer to the thermal limit, and even temporarily exceeding it, causing a loss of strength in the conductor and increased sags, leading to higher risk operation and occasional blackouts [1]. Manuscript received June 15, 2009; revised April 18, 2011; accepted November 09, 2011. Date of publication June 14, 2012; date of current version June 20, 2012. This work was supported by the EPSRC Supergen V, U.K. Energy Infrastructure (AMPerES) Grant in collaboration with the U.K. electricity network operators working under Ofgem’s Innovation Funding Incentive scheme. Paper no. TPWRD-00449-2009. K. Kopsidas and S. M. Rowland are with the School of Electrical and Electronic Engineering, The University of Manchester, Manchester M13 9PL, U.K. (e-mail: k.kopsidas@manchester.ac.uk; s.rowland@manchester.ac.uk). B. Boumecid is with the National Grid Electricity Network Investment Department-Asset Policy, Warwick CV34 6DA, U.K. (e-mail: boud.boumecid@uk.ngrid.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPWRD.2012.2187464 An economical method to increase the capacity of an existing system can be achieved by enabling existing lines to operate at higher temperatures. This may infringe ground-clearance requirements, but can be accomplished by re-tensioning the conductor, a technique mainly based on the increase of the conductor’s clearance to the ground by increasing its tension on the power line. This, therefore, will increase the thermal limit of the line since more thermal expansion can be allowed, permitting more current to flow through it. Another way to achieve power capacity increase is to replace conductors (reconductoring) with larger all aluminum alloy conductors (AAAC) or aluminum conductor steel reinforced (ACSR) wire or conductors with new materials which permit higher temperature operation and developing lower sags. The latter are usually referred to as high-temperature low-sag (HTLS) conductors. Either way, the computations for the new maximum current capacity and conductor sag have to be performed for the new conductor which will become part of the existing OHL system. This paper presents a holistic methodology that enables evaluation of the maximum sag and ampacity of a conductor considering its structure and the electromechanical properties of its basic materials as well as OHL structure constraints. This methodology provides the flexibility to evaluate the performance of nonstandard conductors on a prespecified OHL system. The validation of this methodology with a real system application is also presented. II. OVERVIEW OF EXISTING LITERATURE ON SAG-TENSION METHODS Many studies have dealt with calculating an aerial bare conductor’s sag and ampacity at a steady-state conductor temperature. Most of this paper makes use of the widely accepted “ruling span” method of sag-tension calculation for multiple suspension spans. The method provides solutions to the parabolic and hyperbolic equations which define the relationship between span, sag, and tension. Considerable work on the topic took place during the 1950s and 1960s, mainly focusing on graphical and analytical methods for sag-tension calculations [2]–[4] and methods for the estimation of the current-carrying capacity of ACSR conductors [5], [6]. A method for sag-tension calculation based on stress-strain and temperature elongation data obtained on ACSR conductors was presented in [7] and had been further extended and developed to a computer program (STESS) for use in transmission line and operation [8]. A similar stress-strain approach is also followed by [9] in an attempt to deal with the limitations of existing methods and software concerning gap-type conductors. Other recent modifications to the methods include a hy- 0885-8977/$31.00 © 2012 IEEE 1048 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012 brid numerical method to calculate the sag of composite conductors [10] and an “aluminum stress method” which allows vibration constraints to be based on specified values of static tensile aluminum stress [11]. There are also commercially available sag-tension programs which give good results for most practical applications [12], [13]. These methods were initially developed to evaluate the performance of conventional (AAAC and ACSR) conductors by also incorporating experimental measurements of existing conductors. Recent research in this area has been extended to include novel (HTLS) conductors in these evaluations [14]–[17]. A comparison of the performance of ACSS with ACSR and aluminum conductors aluminum reinforced (ACAR) is presented in [15] assuming the system is under specific extreme heavy loading conditions. With this specific comparison, the ACSS conductor appears to perform better because of the different maximum tension at the heavy load condition [15]. In [16], ACSS, ZTACIR, and CTACSR conductors are also compared with ACSRs due to their bimetallic similarities. Most of the sag-tension methods and packages, even though producing acceptable predictions, are limited to estimating conductors’ performance based on data provided by conductors’ manufacturers. Hence, they are not flexible to investigate how nonstandard conductors will perform. Furthermore, limited work has been done to examine conductor performance incorporating the properties of the structure (wood pole or lattice towers) to evaluate the real benefit of different HTLS conductors when compared with ACSRs and AAACs. In order to progress efficiently to these investigations, a more holistic approach should incorporate, along with the weather loading and conductor properties, the system limitations to allow nonconventional conductors (in size and materials) to be evaluated on prespecified systems. These considerations are taken into account in the methodology introduced in this paper. This allows the overall performance evaluation of lighter conductor technologies with different sag performance, instead of limiting the comparisons only to conductors’ sag performance. Furthermore, reconductoring scenarios can be investigated considering new technologies and conductors of composite materials and nonstandard sizes. III. COMPUTATIONAL FRAMEWORK A. Outline of the Computations The current rating of a conductor erected on a particular OHL structure at a specified location is controlled by the weather, the conductor, the OHL structure, and operational conditions. This current rating specifies the maximum power transfer capability of the OHL system. The overall performance of the system is affected by properties that can be divided into three distinct groups: 1) mechanical; 2) electrical; and 3) aging. Consequently, the computations are performed in three levels: 1) mechanical; 2) electrical; and 3) aging. Every level is influenced by the weather, conductor structure, and operational conditions. These three distinct computational levels are linked together as shown in Fig. 1 in order to compute the conductor maximum current capacity and maximum sag. The input data are divided into four groups: 1) the OHL support structure Fig. 1. Flowchart of the computations. data; 2) the weather data; 3) the conductor data; and 4) the operational data. OHL data describe the structure at the time of installation of the wires. These include the design installation tensile stress of the electrically unloaded conductor, the ambient temperature during the installation, the span length, the type of insulation sets, and the difference between the insulation set attachment levels as well as their heights from the ground. The last three are determined by the support structure (i.e., the lattice tower or wood pole) of the OHL system. The weather data include the ice thickness, ice density, and the wind speed at a given ambient temperature which define the designed maximum weather loading. These data are usually described by weather maps [18]–[20] or can be derived from historical data. These determine the absolute maximum working tension (AMWT) that the conductors may experience and, therefore, the maximum sag value developed at low temperatures. This group also includes weather data that are used for the current-temperature calculations as described in [21]. The conductor data involve a conductor’s electrical and mechanical properties as well as its physical design. The most basic properties are the density, modulus of elasticity, coefficient of thermal expansion, tensile strength, conductivity, stranding pattern, grease pattern and density, and type of strands (trapezoidal or cylindrical), as well as their diameter. These are usually provided by conductor manufacturers and are included in relevant standards [22]–[29] for the most standard conductor types. The last group, operational data, includes the maximum operating temperature of the conductor, system frequency, methodology used for mitigation of the conductor creep (if any), predicted duration of the maximum conductor operating temperature, designed emergency loading, and duration of operation at the elevated temperature. KOPSIDAS et al.: HOLISTIC METHOD FOR CONDUCTOR AMPACITY AND SAG COMPUTATION Some of the variables that describe the overall structure have to be predefined in order to initiate the computations. These variables are the ones that define the weather loading, the maximum operating loading, and the OHL structure. The methodology summarized in Fig. 1 and detailed in subsequent sections can then be used to calculate and compare the electrical and mechanical performance of different conductors for the same OHL structure and identify the most suitable for the particular structure. Changes in the OHL structure cause changes in the performance of the same conductor, as do weather changes (e.g., maximum ambient temperature, maximum wind speed, ice loading, etc.). Fig. 1 also shows that the computations at the aging level are performed at the end in order to calculate the final conductor sag. This computation level can also be used to evaluate the increase of initial conductor tension that is needed to balance the plastic strain of the conductor. Furthermore, if pretensioning of the conductor is considered in the initial input data (affecting the OHL and conductor data groups), this part may be omitted, for simplification, and the final system condition would be the conductor sag calculated at the mechanical level with the same conductor ampacity. However, conductor pre-tensioning may not be permitted by the strength of the support structure. B. Mechanical Computations The mechanical part of the computations is performed to calculate the conductor sag and tension at the designed maximum operating temperature of the conductor . In order to achieve this, the maximum conductor tension (MCT) of the specified OHL system is required. The MCT (i.e., the maximum working tension of the conductor on a particular OHL system) is controlled by the following limitations that are generally applied in any structure: • the maximum permitted tension allowed by the weakest system component which may be the insulator pin, the insulator, or the tower/pole structure; this tension limit is defined in the calculations as the structure maximum working tension (SMWT); • the self-damping vibration limit tension of the conductor effectively defines the everyday tension (EDT) at a specified conductor temperature; this limit is usually employed to reduce the aeolian vibrations to an acceptable level [20] and determines the conductor’s vibration limited maximum working tension (VLMWT); • the absolute conductor working tension (ACWT) for the specified weather loading, for example, 50% of the conductor rated breaking strength (RBS) at 5.6 C with combined wind and ice [20], [29]; the weather (ice and wind) loading and the minimum temperature of the conductor influence the MCT since they affect the elastic (weight) and thermal (temperature) elongation of the cable. The procedure to determine the MCT of the power-line design is illustrated in Fig. 2. Initially, the weather-loading conditions of a power line (for example, load cases 1 to 6 in [29] and [30]) are identified by its location and the help of weather maps [20], [29] or historical data. The weather-loading conditions also define the corresponding safety factors (SF) [29]–[31]. These safety factors are applied to the conductor 1049 Fig. 2. Flowchart of the procedure for MCT calculation of an OHL system. and the structure (insulator/insulator pin), and the smallest maximum allowable tension of these is set as the absolute maximum working tension (AMWT) of the conductor applied on the specified system (Fig. 2). The Newton–Raphson iteration method is employed on the change of state (1), derived from the catenary curve. In (1), the elastic and thermal elongations of the conductor are included with the plastic elongation computed separately since the latter is affected by the operating conditions [32] (1) with Thermal elongation Elastic elongation where subscripts respectively, and and define the final and initial conditions, horizontal conductor tensile force; resulting conductor weight per-unit length; span length; conductor temperature; conductor’s coefficient of thermal expansion; conductors modulus of elasticity; conductor cross-sectional area. The everyday tension (i.e., the design stress in the unloaded conductor that is applied to minimize the aeolian vibrations of the conductor at a designed temperature) and the conductor weight are set as initial conditions while the final conditions are the conductor resulting weight (i.e., the vectorian sum of the 1050 conductor, wind, and ice weight) and the VLMWT at the maximum-designed weather loading. The output VLMWT of this iteration is then compared with the AMWT and the smallest one defines the MCT of the OHL system at the specified weather loading. Once the MCT is known, then a second Newton–Raphson iteration of (1) takes place having as initial conditions the MCT of the OHL system and the conductor resulting weight (i.e., the sum of the conductor, wind, and ice weight) at the maximum designed weather loading temperature, in order to identify the conductor tension at any operating temperature (Fig. 1). Once the conductor tension at the operating temperature is calculated, the sag is computed by using the catenary curve. The output is then linked with the other two computational parts. The MCT computation (described in Fig. 2) is performed based on the conductor design and material properties as illustrated in Fig. 3. This condition is set as a reference point and then using (1), the final tension and sag can be evaluated at different temperatures with an iteration process using small (1 C) temperature steps. The aluminum and steel tensions are computed from the conductor tension incorporating the conductor creep. The iteration continues up to the knee point, which defines the temperature at which the aluminum contributes zero force to the conductor. The tension and sag at this point are then set as initial conditions to perform calculations for temperatures above the knee point. A new iteration takes place to evaluate the final tension and sag conditions above this point. This is performed using a modified version of (1), where the that affect the thermal and conductor properties elastic elongations are replaced with the values that correspond , since the core deto the conductor’s core fines the elastic and thermal elongations of the equation above the knee-point temperatures. C. Electrical Computations The electrical part of the computation is used to calculate the of any conductor at any temperature deac resistance fined in the previous part of the computations instead of using the linear interpolation and the tabulated data of [33] for the standard conductor sizes described in [21]. This increases the flexibility in the type and size of conductors that can be examined, since this method is not limited to the conductors included in [33]. It also improves accuracy. The detailed computations within this step of the process are illustrated in the flowchart of Fig. 4. The basic electrical and physical properties of the materials used for the conductor, as well as the conductor itself are used to calculate the dc resistance at 20 C based on the conductivity, thermal coefficients, diameter and number of strands, and spiraling factors specified by ASTM for cylindrical and trapezoidal strands [22]–[29]. For wires of distinct strength (core) and conductive (aluminum) is calculated separately and every part is members, the then corrected to the operational temperature by using the apof the propriate temperature coefficients [22]. The overall conductor is then computed by considering core and outer conductive member resistances in parallel configuration. When the IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012 Fig. 3. Flowchart of mechanical computations for the conductor tension and sag at final system conditions. conductor’s core is of the same material and shape of strands, then the is calculated by omitting the core’s calculations. , the skin factor is calculated To compute conductor based on the physical structure of the conductor. The skin factor calculation is based on the work of Dwight [34]–[36] and Lewis and Tuttle [37] which is further simplified with the use of [38] in the code presented in this paper. The skin factor calculation is performed on cylindrical and tubular conductor shapes, in order to evaluate the effect of non-conductive core materials on conductors. calculations is then A second correction factor for the applied for cases when steel material is used for the core design of the conductor, in order to address the magnetization effect . This effect is negligible of the core on the conductor’s on ACSR conductors with even numbers of aluminum layers [21], [33], [37], [39] and so, it is not considered in these cases. For the ACSR conductors with an odd number of aluminum layers, however, the magnetization factor is used to accurately (Fig. 4). In the case of single-layer ACSR, calculate the the correction method described in [21] is used, while for the three-layer conductors, the approach of [39] is employed. Since the magnetization factor is influenced by current flow through the conductor, an iteration with the use of [21] takes place to correct the calculation as illustrated in Fig. 4. This makes the resistance of steel core conductor technologies dependent on conductor temperature and current flow, unlike other conductor technologies whose resistance is dependent on the conductor temperature. KOPSIDAS et al.: HOLISTIC METHOD FOR CONDUCTOR AMPACITY AND SAG COMPUTATION 1051 TABLE I CREEP PREDICTOR EQUATIONS FOR DIFFERENT CONDUCTOR TYPES AT NORMAL AND ELEVATED TEMPERATURES Fig. 4. Synopsis of the ac resistance calculation methodology used. The method described here is employed for calculating of any aluminum alloy conductors (AAC), ACAR, the AAAC, and ACSR or any other bimetallic and “bimaterial” conductor technology, type, and size. It can, furthermore, be used for “tubular stranded” conductors or more practically for non-conductive composite core stranded conductors. The computation between difference in the final result of the of the different types of conductors is determined by the overall cross-section area of the conductor, the skin factor, and the magnetization factor differences. D. Aging Computations Within this part of the computation, the nonelastic elongation (i.e., conductor creep) of the conductors under the permanent tensile load is calculated for the operating conditions and conductor temperature defined during the mechanical computation part. Aging computations are divided into two clusters depending on the type of conductor. The first one regards the well-established conductor types AAC, AAAC, ACAR, and ACSR and the second is in reference to the recently developed aluminum conductor composite reinforced (ACCR) and aluminum conductor composite core (ACCC) composite conductors [14], [40]. In the first cluster of computations, the predictor equations of Table I are used under the prespecified designed operating conditions of the system [41]–[43]. These conditions are defined as follows. • EDT and the ambient temperature at which this tension occurs as well as its predicted duration. • Maximum operating conductor temperature, conductor tension at that temperature, and its predicted duration. • Conductor’s MCT at the designed ambient temperature at which this tension occurs and its predicted duration. The computations include the prediction of elevated temperature creep (Table I) which occurs above 75 C for aluminum conductors and 100 C for the steel-reinforced conductors [42]. The second cluster of the aging computation is very similar to the first one but instead of using the well-established predictor equations (Table I) adapted from [41], the stress-strain curves produced by testing the conductors are used in the absence of standard data. It should also be noted that the aging computations use an iteration process, since the stress is reduced with time as the creep strain gradually increases. IV. IMPLEMENTATION OF THE METHODOLOGY ON A REAL OHL SYSTEM The methodology described in this paper is used to predict the sag and identify the ampacity of a 400-kV L2-type lattice tower OHL system after 29 years from the initial installation of the conductor. The system was strung with a twin-bundle Rubus AL5 aluminum alloy conductor. The conductor’s electrical and mechanical properties are computed using the described methodology. Table II shows the conditions relevant to the conductor’s installation along with the surveyed and predicted sag values after 29 years of the OHL’s operation. As can be observed, the sag prediction is very good and the calculated creep for the 29 years . The differences in span lengths beis 597.2 microstrains tween the left and right circuits in the first and fourth spans are due to the use of angle towers at the tension points. This difference in tower type results in nonparallelism of the contiguous tower cross-arms and, therefore, in different conductor span lengths for the right and left circuits. 1052 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012 TABLE II SURVEYED DATA VALUES OF THE 400-kV OHL SYSTEM AND PREDICTED SAG Fig. 5. Surveyed profile of the critical span complemented with calculated catenary curves at surveyed and maximum electrical loading temperatures. 3 Difference between the measured sag and the calculated predicted values. TABLE III INPUT SURVEYED DATA FOR THE CURRENT FLOW CALCULATIONS The ampacity calculations at the surveyed operating conductor temperatures resulted in similar values as those given by the survey data for both circuits as illustrated in Table III. The sag at 75 C (maximum electrical loading) is also calculated (Table II) and the catenary curve of the most critical span of this OHL system is fitted on the conductor (surveyed) sag profile. This is illustrated in Fig. 5 and as can be seen, the conductor preserves the 7.6 m of phase-to-ground required clearance [30], [44]. This, therefore, allows for higher operating conductor temperatures without the requirement of re-tensioning the conductor. Consequently, it enables increasing the line’s thermal rating, but with an increase in conductor creep that will be caused by the elevated operating temperature according to [41]. In order to compute the new maximum operating temperature (and, therefore, the system’s ampacity), the calculations should be performed again from the beginning and the estimated amount of hours that the line would operate above 75 C should also be specified. This step is important since the elevated conductor temperature could affect the conductor aging and, thus, the ground clearance after a long period of the conductor in service. V. GENERAL APPLICATION OF THE METHODOLOGY The methodology discussed here links the conductor properties with the properties defining the OHL structure in a way Fig. 6. Flowchart for choosing the appropriate technique for uprating the thermal limit of an aerial power system. that enables investigating the benefits afforded by uprating techniques, such as re-tensioning and reconductoring, as illustrated in the flowchart in Fig. 6. It can also be used to evaluate the improvement in performance that different conductor sizes and/or types may result in, and compares this with different conductors and system operating conditions on a prespecified OHL system (Fig. 6). Hence, it enables the overall performance evaluation of lighter conductor technologies on a specified system, rather than comparing only their sag performances. The methodology can then be used to compare the electrical and mechanical performance of different conductors for the same OHL structure and identify the one that allows more electrical power to be transferred through the specified structure and evaluate the losses. Changes in the OHL structure cause changes in the system and, thus, the performance of the same conductor would be different. Weather changes (e.g., ambient temperature, maximum wind speed, etc.) also influence the performance of the overall system. KOPSIDAS et al.: HOLISTIC METHOD FOR CONDUCTOR AMPACITY AND SAG COMPUTATION This methodology can be used to identify the effect of increase in operating temperature as well as the impact of vibration dampers on the conductor or the effect of increases in ambient temperature (due to global warming) [45]. Furthermore, it can be used to identify the effect of changes on the OHL design (i.e., increasing the height of the conductor attaching points or their maximum tensile strength). It can also compute the additional creep effect caused by the initial overtension applied to negate the conductor’s plastic deformation. The electrical computation section addresses all of the bimetallic conductors and with small modifications in the spiraling factors, skin effect, and magnetization factor, it can also be used for composite core conductors with or without conductive cores (i.e., the conductors in [40] and [14]). Consequently, it increases the flexibility of the calculations at any temperature for any conductor technology and design (even for those for which the properties are known but still not fully developed), and allows the direct comparison of the performance of different conductor sizes and technologies on the same OHL structure. For example, modeling the performance of the different nonexisting ACCC/TW core to aluminum ratio conductors can be performed to find the optimal fit for a particular OHL system at a given location. This methodology has already been used to show how different conductor technologies behave in standard U.K. OHL structures [45]–[49], highlighting the potential of reconductoring with novel HTLS conductors. VI. CONCLUSION The current rating and sagging performance of a conductor erected on an OHL structure are influenced by the weather, the conductor, and its installation method, the OHL structure, and operational conditions. The methodology presented in this paper links all of these parameters together in order to evaluate the actual performance of a conductor on a prespecified structure. It enables performance comparison of different conductor types and sizes on the same structure. This is important since, in some cases, the structure limits the conductor’s performance. 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Spec., no. 3, 2004. [45] K. Kopsidas and S. M. Rowland, “A performance analysis of reconductoring an overhead line structure,” IEEE Trans. Power Del., vol. 24, no. 4, pp. 2248–2256, Oct. 2009. [46] K. Kopsidas, S. M. Rowland, M. N. R. Baharom, and I. Cotton, “Power transfer capacity improvements of existing overhead line systems,” in Proc. IEEE Int. Symp. Elect. Insul., 2010, pp. 1–5. [47] K. Kopsidas and S. M. Rowland, “Evaluating opportunities for increasing power capacity of existing overhead line systems,” Inst. Eng. Technol. Gen., Transm. Distrib., vol. 5, pp. 1–10, 2011. [48] K. Kopsidas and S. M. Rowland, “Investigating the potential of re-conductoring a lattice tower overhead line structure,” in Proc. IEEE Power Eng. Soc. Transm. Distrib. Conf. Expo., 2010, pp. 1–8. IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012 [49] K. Kopsidas, I. Cotton, and S. M. Rowland, “Towards a holistic perspective of the existing overhead line power network to facilitate its flexible expansion,” in Proc. IEEE/Power Energy Soc. Power Syst. Conf. Expo., 2011, pp. 1–7. Konstantinos Kopsidas (M’06) was born in Lefkas, Greece. He received the B.Eng. degree in electrical and electronic engineering from The University of Manchester Institute of Science and Technology (UMIST), Manchester, U.K., in 2004, and the M.Sc. (Hons.) degree in electrical power system engineering, and the Ph.D. degree in electrical power engineering from The University of Manchester, Manchester, U.K., in 2005 and 2009, respectively. He was a Research Assistant/Associate with the SuperGen V (AMPerES) and is now a Lecturer with the School of Electrical and Electronic Engineering, The University of Manchester, also collaborating with Arago Technology Ltd., Manchester, U.K. Dr. Kopsidas received the Scottish Power “Power Learning Award” and the UMIST course prize twice. Simon M. Rowland (SM’07) was born in London, U.K. He received the B.Sc. degree in physics from the University of East Anglia and the Ph.D. degree from London University, London, U.K. He has worked for many years on dielectrics and their applications. He has also been Operations and Technical Director within multinational manufacturing companies. He joined The School of Electrical and Electronic Engineering, The University of Manchester, Manchester, U.K., as a Senior Lecturer in 2003. He was appointed Professor of Electrical Materials in 2009. Dr. Rowland received the IEE Duddell Premium Award in 1994 and became a Fellow of the Institute of Electrical Engineers in 2000. Currently, he is President of the IEEE Dielectric and Electrical Insulation Society. Boud Boumecid received the M.Sc. degree in civil engineering from the University of Salford, Manchester, U.K., in 1994. He previously worked with consultants and contractors, where he was involved in the civil and structural design of power stations, substations, and overhead lines. He is a Design Engineer (Overhead Lines) with the Electricity Network Investment Department—Asset Policy, National Grid, U.K. Mr. Boumecid is an active member of CIGRE Study Committee SC B2 (Working Group 23 on Foundations) and of the BSI-PEL/011 Committee.

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