B2-00. SPECIAL REPORT FOR SC B2 (Overhead Lines) V. NAIDOO J. IGLESIAS S. ANSORGE. Special Reporters

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1 CIGRE 2016 B2-00 SPECIAL REPORT FOR SC B2 (Overhead Lines) V. NAIDOO J. IGLESIAS S. ANSORGE Special Reporters Introduction Study Committee B2 covers the design, construction and operation of overhead lines. This includes the mechanical and electrical design and experimental validation of new line components (conductors, ground wires, insulators, accessories, structures and their foundations), the study of in-service line performance and assessment of aged line components, line maintenance, the refurbishment and life extension as well as upgrading and uprating of existing overhead lines. SC B2 comprises members from 22 countries plus observers from 15 countries. Seven Advisory Groups help to coordinate 21 working groups and two joint working groups with a total 534 members from 41 countries. SC B2 has selected three preferential subjects for the CIGRE Session They are listed below: PS 1 Overhead Lines for high power transfer capacity Design for AC and DC Lines including dedicated metallic return Climatic and environmental considerations Influence of operational aspects on reliability and line security PS 2 Project management, construction and maintenance New methods for construction, replacement and refurbishment Experience with contracting and financing models Reliability evaluation of installed components and their change with time PS 3 Application of new materials and technologies Conductors, insulators, fittings and structures Experience and trends Specification and test requirements for line components Naidovi@eskom.co.za jiglesias@ree.es ansorge@gmx.ch 1

2 PS1 : Overhead Lines for high power transfer capacity Special Reporter: Vivendra Naidoo (South Africa), Naidovi@eskom.co.za Growing economies and increasing world population manifests itself in the need for electricity. Transmission lines are vital to the electrical networks, however opposition to new transmission lines had resulted in utilities and designers to look into innovative ways of maximising the utilisation of assets. So sparks the interest in high power transfer capacity overhead lines and UHVAC and HVDC transmission. The first preferential subject has a large number of papers out of which 15 papers have been selected. These papers have been divided into the following three groups: 1.1 Design for AC and DC Lines including dedicated metallic return 1.2 Climatic and environmental considerations 1.3 Influence of operational aspects on reliability and line security 1.1 Design for AC and DC Lines including dedicated metallic return Paper B2-101 describes the studies and basic design of two 800kV HVDC transmission lines in Brazil totalling 4600 km, in particular environmental data gathering, conductor selection process, insulation co-ordination and tower top clearances right of way determination. Paper B2-113 describes the design of a 525kV HVDC line in Norway that runs parallel to two AC lines for a short section and covers the optimum location of the positive pole to cause least audible noise, corona testing of hardware strings, tower design, pollution monitoring and dimensioning of the insulator strings. Paper B2-103 describes the conversion of a 345kV AC line to DC with the aim of transmitting 2300MW. The studies established that the allowable DC voltage is limited by the ground field effects and suggests that the industry needs to improve its methods for field effect limit assessment. Paper B2-107 describes research that was conducted pertaining to the conversion of a 500kV HVAC line to HVDC by increasing of structure heights, changing insulation and use of HTLS conductors. It was established that the conversion of 1 of the 4 AC lines to DC could result in a 1.8 times increase in the load transfer capability for the corridor. Paper B2-111 describes the typical design, properties of equipment and the operational experience of 3168 km of 1000kV UHVAC in China. New Silicone rubber insulators were designed with the maximum electric field on the surface being limited to 7kV/cm. The paper concludes that based on 10 years of commercial operational experience, UHV AC can considered a viable option. Question 1.1: What processes are used elsewhere for conductor selection for HVDC lines especially with respect to the tolerable I 2 R losses which impact on the line life cycle cost. Question 1.2: What are the design criteria for: EMF and audible noise in the optimisation process for HVDC and UHVAC lines and how these are influenced by parallel lines (HVAC or HVDC). Insulation co-ordination for UHVAC lines The effects of space charge on clearances in the presence of live line tools Quantifying the effect of space charge on shield wires when designing for corona free performance Experts are invited to comment on the needs for standards pertaining to UHVAC lines. 3

3 Question 1.3: What are the experiences in other countries on the: conversion of AC lines to DC lines with focus on the electrical aspects of the design operation of hybrid lines with respect to clearances, complexities and methods used for live line maintenance 1.2 Climatic and environmental considerations Paper B2-102 describes the increase of a transmission lines capacity by linking it to generation at the wind farm to which it connects. The thermal rating for the line was allowed to vary with measured wind speed rather than maintaining a fixed rating value based on deterministic weather data. Paper B2-105 describes the use of existing distribution infrastructure fitted with real time monitoring (RTM ) in order to integrate wind farms located far from load centres. The RTM system was verified according to CIGRE WG22.12 and now TB 601 has been in operation since The increase in transmission capacity was due to the high winds experienced during electricity generation. Question 1.4: Country experts are invited to comment on their experiences with RTM systems and its integration with the network operating and control centre? Paper B2-104 describes a feasibility study using HTLS conductor on a 115kV line in Mexico with the aim on increasing the transfer capacity of the corridor. The lines under investigation experienced voltage problems at the receiving end due to the high voltage drop on the lines and as such the HTLS conductor was found to provide minimal benefit in the uprating study. Paper B2-115 describes the use of FACTS devices to achieve compaction of AC lines while increasing power transfer capabilities. The paper states that the use of FACTS devices can result in a times increase in capacity without changing the voltage class and can result in a 50% reduction in land space required. Paper B2-106 describes the use of insulated cross-arms for compaction of a structure and to reduce the ROW and increase the transfer capacity in the corridor. Both static and dynamic assessments of the structure loadings were performed and a failure mechanism was built into the structure to help reduce longitudinal loads when the design capacity was exceeded. Paper B2-110 describes the design of a 220kV AC steel monopole structure. The tapered poles have been designed to improve aesthetics using flanged plates with hidden connections. The design criteria, methods for hiding connections and maintenance aspects are discussed. Question 1.5: The authors of paper 110 are invited to comment on the increase in power transfer achieved in the corridor and at what cost? (USD/MVA). Experts are invited to present their designs on compact transmission structures and high power transfer capacity transmission lines. Question 1.6: What are the experiences in other countries with the use of FACTS devices in overhead line design? Paper B2-108 provides test results for thermal rating verification of HTLS conductors and compares this to the results obtained through calculation methods provided in CIGRE brochure TB 601 & TB 207. The results show that using TB 601 for calculation of conductor surface temperature at 1800A leads to a 12 degree overestimation of the temperature. 4

4 Question 1.7: Are there other experts that have performed verification tests on the thermal rating calculations for HTLS conductors and if so, how do the results compare with the calculated values using TB 601? 1.3 Influence of operational aspects on reliability and line security Paper B2-112 compares the results of sag and tension from currently built transmission lines to address uncertainties caused by use of the ruling span approximation when designing lines. It was established that when span lengths vary drastically in a strain/tension section and/or when the line is expected to operate in areas of high mechanical loads e.g. ice loading, the finite element analysis of the strain/tension sections is essential to correctly predict the sag and corresponding tensions. Paper B2-114 describes the use and validation of an advanced local scale meteorological model to estimate ice loads using a test line. The tests showed that the rotational stiffness and smaller area of a single conductor resulted in less ice accretion than twin bundle and that sudden dropping of ice due to external environmental factors contributed significantly to the reduction in ice loads. Paper B2-109 describes the modelling techniques to establish the electrical parameters and environmental conditions that are responsible for triggering an arc between an HV line and vegetation. Question 1.8: Experts are invited to discuss other models, software and/or techniques used to predict severe environmental mechanical loading conditions. Question 1.9: Experts are invited to provide information on research pertaining to flashovers to vegetation and/or crops and its subsequent impact on the line designs. Preferential subject 2: Project management, construction and maintenance Special Reporter: Javier Iglesias (Spain), jiglesias@ree.es In many systems, large investments for new transmission facilities and major renewals or upgrades are needed, so efficient management models and innovative construction techniques become essential tools to afford them at a reasonable cost. And at the same time, in order to take the right decisions for investments or maintenance, the focus of grid owners is turning to the methods for evaluating existing components, given the increasing requirements of network availability and reliability. A total of 12 papers have been selected to cover this preferential subject. These papers are grouped in the following subsections: 2.1 New methods for construction, replacement and refurbishment 2.2 Experience with contracting and financing models 2.3 Reliability evaluation of installed components and their change with time 2.1 New methods for construction, replacement and refurbishment In order to keep electrical supply at maximum levels, it is necessary not only to ensure that the equipment and materials are well maintained and in full working order, but also to carefully plan the repair schedules, minimizing the outage periods, the costs and, what is more important, maintaining the safety levels. In many mature transmission networks, most of the overhead lines are reaching or overpassing their nominated life, and cost-effective refurbishment or maintenance solutions are needed. This is the case explained in Paper B2-203, where three examples are presented to illustrate how to integrate the many changes and improvements available today with the old philosophies and practices used when those lines where built. 5

5 Question 2.1: Experts are invited to present their experiences of adopting specific design standards and methods to permit continued use of aged components, designed and constructed with obsolete philosophies. Paper B2-209 proposes the introduction of several improvements to the conductor stringing process, allowing a reduction of work time and manual operations. A particular example of conductor replacement is explained with detail in Paper B Due to corrosion problems in a strait-crossing section of a 500 kv line, it was decided to reconductor the section with a new developed type of conductor, providing a high tensile strength and improved corrosion characteristics. Question 2.2: Experts and stringing machine suppliers are invited to present similar proposals for conductor stringing or replacement methods. Authors of Paper B2-202 are invited to provide details of the new developed conductor and ground wires (creep considerations, sag-tension performance ), and their comparison with other types of conductor. Tower replacement is also a delicate issue for transmission assets owners. The use of land and services surrounding the towers often collide with the requirements of electrical clearances and a safe operation of the line. Paper B2-207 proposes a standardized method to substitute lattice towers at the same location to gain height, minimizing the outages and electrical hazards. Question 2.3: Experts are invited to present efficient solutions for tower replacement and height increase. 2.2 Experience with contracting and financing models The desire to rapidly develop transmission facilities force utilities to consider different models and methods to improve developing, constructing and operating transmission lines while reducing costs. For example, paper B2-205 describes the Public-Private Partnership model (PPP) to introduce competition, share risks and improve the management of the system. It also compares different models in other jurisdictions around the world, where important investments are required. In addition the rapid growth of the demand in certain mega-cities makes the augmentation of the existing transmission infrastructure a big challenge. Paper B2-204 highlights some examples of this challenge. Question 2.4: Experts are invited to present their experiences. 2.3 Reliability evaluation of installed components and their change with time A key factor for an effective line maintenance, refurbishment and upgrade is evaluation of the installed components, so several improvements and new methods are arising at lower costs while maintaining the reliability and availability of the service. Paper B2-211 presents a global management system aiming to monitor and control many parameters of the transmission grid in real time such as conductor temperature and tension, weather parameters, hoar/frost detector, anti-vandalism system, etc.. On the other hand Paper B2-208 presents detailed studies and intensive laboratory tests have in order to analyse the process of outages caused by bird dropping over polymeric insulators, which is one of the main causes of unexplained outages in a transmission grid. 6

6 Question 2.5: Experts are invited to propose solutions to the problem of unexplained outages as described in Paper B2-208 (monitors, V-strings, insulator covers ) Overhead line connectors are identified as one of the most critical components of overhead lines due to its catastrophic consequences in case of failure. Paper B2-212 presents and describes a new diagnostic technique ("the pulse current method") to assess the condition of the connector. Similarly, broken wires due to Aeolian vibration of aged lines are a big concern. Paper B2-206 presents a portable X-ray system for in situ detection of broken ACSR strands at suspension clamps. Question 2.6: Can experts comment on solutions like tele-operated robots for accessing the joint? What are the experiences in other countries for live-line inspections? One of the parameters that have been identified as most critical in transmission lines is the maximum conductor sag. Paper B2-201 summarizes the methods available to determine the sag, focusing on typical cases where existing ACSR conductors are to be operated at higher temperatures. Alternatively, Paper B2-210 describes a novel thermo-mechanical model to calculate the sag of bimetallic conductors operating at high temperatures. Question 2.7: Model in Paper B2-210 includes the knee-point temperature of the conductor, but can the authors explain how the model considers the plastic elongation and creep of aluminum layers, as described in paper B2-201 and also in Cigre TB324? Is it possible also to include the compression and residual stresses in the aluminum? All experts are invited to present how to consider both radial and axial temperature differences in the sag-tension calculation models. Preferential Subject 3: Application of new materials and technologies Special Reporter: Samuel Ansorge (Switzerland), ansorge@gmx.ch For the third preferential subject 12 papers have been chosen coming from 11 different countries. Based on new requirements of today s overhead lines like compactness (reduced height, reduced right of way, reduced floor space) and the reduction in visual impact - all of that increasing the public acceptance - several new materials and technologies were presented. But also in conventional lines issues with severe environmental conditions, insufficient transmission capacity, high cost of full-scale tower tests and quality of insulators have to be addressed which again ask for improved materials and better test procedures. The papers have been divided into the following five sub-topics: 3.1. Compact Lines (3 papers) 3.2. Conductors (3 papers) 3.3. Towers (3 papers) 3.4. Insulators (2 paper) 3.5. Fittings (1 paper) Each sub-topic will be dealt with separately in the following. 3.1 Compact Lines In Paper B2-301 the possibility to increase the capacity of an existing overhead line by uprating the voltage level from 220 kv to 380 kv is presented. An insulated cross arm in horizontal Vee configuration is used instead of the existing steel lattice ones to obtain the necessary clearance. New conductors were used to reduce the corona noise having increased diameter and a hydrophilic coating. Another compact line project is presented in Paper B2-307 with the aim to significantly reduce the height of the towers and as well the required right of way. The key elements are the addition of a 7

7 highly tensioned steel rope in addition to the phase conductor bundle resulting in a much smaller sag. Additionally, a communication concept including the visualization has been provided and an acceptance study has been performed. A first pilot project is planned to be commissioned in Paper B2-308 presents a new design of overhead lines loaded with 90 kv AC as an alternative to underground solutions. The line uses poles made out of composite material, which are 50 % smaller than conventional ones. The right of way and the footprint of the pole are strongly reduced as well. The line has no shield wire, but will be equipped with surge arresters. Questions 3.1 How are the service experiences with compact lines for HV and EHV transmission in general and particularly with respect to the maintenance, public acceptance and environmental issues especially with birds? 3.2 Conductors Paper B2-303 deals with corrosion issues to ACSR conductors caused by sea salt. A corrosion resistant material was developed to reduce this problem. Further an estimation method was created, which takes the environmental conditions like humidity and salinity concentration into account, to estimate the deterioration rate of ACSR conductors in existing transmission lines. Paper B3-310 deals with the development of a new conductor having a cross section of 1250 mm 2 based on ACSR and ACAR conductors. This is needed to increase transmission capacity, reduce losses and reduce the surface electrical field for UHV DC transmission lines. Paper B2-313 investigates the use of hydrophilic conductors to reduce the audible noise. On site measurements on a twin-bundle 400KV double circuit line and laboratory experiments were conducted and compared with two different calculation methods. Question 3.2 For critical environmental conditions in terms of corrosion by salt and industrial pollution, can conductors with composite core be a long-durable alternative (so-named ACCC Aluminium Conductor Composite Core) despite being developed as HTLS solution? Question 3.3 What is the practical experience with the large conductor diameters under AC and DC in terms of corona and audible noise? Is a surface treatment of the conductor required or advantageous at all? 3.3 Towers The actual behaviour of bolted lattice towers is hard to predict by using numerical methods only. Therefore costly full-scale tests are often performed. Paper B2-302 describes the possible application of the hybrid testing method for bolted steel-lattice towers. Paper B2-304 presents an experimental investigation about the properties of concrete poles envisaged for the Wintrack bi-pole configuration as an alternative to steel ones. In Paper B2-309 the design, testing and installation of new tower is presented inspired by trees. A first line section using this kind of towers is installed since Question 3.4 How is the cost comparison (based on TCO) of new tower designs compared to conventional steel lattice towers? Question 3.5 8

8 In B2-309 the post insulator function is provided by porcelain insulators. In other compact lines and when applying shock loads in testing, the porcelain posts typically failed, while the composite posts were not damaged due to their flexibility. How is the general experience with the use of composite insulators compared to porcelain ones for the use as post insulators on transmission lines? 3.4 Insulators Paper B2-306 deals with the quantification of hydrophobicity and describes an appropriate test procedure. It further reviews different polymeric materials particularly silicone rubber. It shows that the Inclined Plane philosophy can be applied for this purpose. Paper B2-311 presents an intensified test program to verify the quality of glass cap and pin insulators. Although the technology is well proven and mature, some issues in service have shown a large variance in manufacturing quality. Based in a test matrix presented in Cigré in the year 2014 experience was gathered by performing these tests on randomly chosen samples from ordered goods. It could be shown that this intensified test procedure is representative, repeatable, reproducible and cost-effective and will be considered as a basis for the possible update of IEC Question 3.6 How is the experience in other laboratories with the quantification of the hydrophobic properties? Question 3.7 Are there other examples, where the current IEC standards are not sufficient to ensure an appropriate quality of insulators? 3.5 Fittings A study is presented in Paper B2-305, where the temperature profile in a AAAC conductor in and near tension clamps are analysed as elevated stresses occur in the conductor at these locations. The result of this study should lead to a lifetime prediction of exiting lines. Question 3.8 How are the experiences with using dynamic ratings of overhead lines? Are similar investigations for compression dead end clamps available? Main session and preview meeting The main session of Study Committee B2 will be held on Wednesday, August 24th, in the Grande Amphitheatre 08:45h 18:00h. Authors of the session papers and other delegates wishing to present contributions to the questions raised by the Special Reporters are requested to send in advance and not later than Friday, August 5th, their intended contributions to the respective Special Reporter and SC Chairman Konstantin O. Papailiou (konstantin@papailiou.ch) and Secretary Herbert Lugschitz (herbert.lugschitz@apg.at). The related documents, i.e. guide, template and sample page, can be found under and have to be strictly observed. B2 Study Committee Chairman and Secretary together with the Special Reporters will meet with the contributors on Tuesday, August 23rd, from 9:30h 16:00h in room 361, in order to discuss their proposals and to allocate the period of time for their presentation. 9