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 coe cients 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 coe cient of thermal expansion to be verified. However, there are other factors that also a ect it. This paper analyzes the e ect of some of the uncertainty sources in the testing of the coe cient 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 e ect on the CTE testing are quantified.This research was funded by the MINISTERIO DE ECONOMÍA, INDUSTRIA Y COMPETITIVIDAD, Spain, DPI2016-77215-R (AEI/FEDER, UE)

Sag-tension evaluation of high-temperature gap-type conductor in operation

[EN] Low-sag conductors are characterised by their ability to operate above the "knee-point temperature" (KPT). Sag-tension performance must be calculated while designing a new overhead line. The ampacity limit of the conductor is influenced by the sag and the temperature of the conductor. The maximum sag must be limited to a certain value to ensure a safe clearance between the conductor and ground. In this study, a gap-type conductor in operation was monitored to evaluate the actual KPT. The KPT in low-sag conductors is a crucial factor since it affects the sag of the conductor, which must be limited for safety reasons. The KPT was detected based on the change in the coefficient of thermal expansion value of the conductor. To perform this detection, the conductor tension and temperature were monitored. This study proposes a procedure to estimate the coefficient of thermal expansion (CTE) value. The results showed a gradual displacement in CTE. This procedure was used to perform measurements in a pilot line.This work is financially supported by the Ministerio deEconomía, Industria y Competitividad, under the project DPI2016-77215-R (AEI/FEDER, UE) and by the Universityof the Basque Country UPV/EHU (ELEKTRIKER researchgroup GIU20/034)

Improvement of safety operating conditions in overhead conductors based on ampacity modeling using artificial neural networks

Thermal ratings are usually considered for planning the operating conditions for overhead lines and are usually obtained with static parameters. These conditions can be improved using dynamic ratings based on the region weather forecasts, and this improvement can be ever higher when a local prediction is performed at the point where the line is located. In this work, a model based on artificial neural networks techniques is applied to predict the ampacity property of a transmission overhead line, in order to adjust and optimize the operation point of the grid under safety conditions. These predictions are calculated for a time horizon of 24 hours and are validated with actual conditions of a real overhead line monitored by sensors. With the conclusion that applying the selected model, the operational security of the conductor can be improved, passing from a 17.82% of overheating conditions to only a 3.91%.This work is financially supported by the Ministerio de Economía, Industria y Competitividad, Spain, under the project DPI2016-77215-R (AEI/FEDER, UE)

Overhead line ampacity forecasting and a methodology for assessing risk and line capacity utilization

This paper proposes a methodology for overhead line ampacity forecasting that enables empirical probabilistic forecasts to be made up to one day ahead, which is useful for grid scheduling and operation. The proposed method is based on the statistical adaptation of weather forecasts to the line-span scale and aims to produce reliable forecasts that allow the selection of a low risk of overheating overhead conductors by TSOs and DSOs. Moreover, a methodology for the evaluation of probabilistic forecasts and line capacity utilization is also proposed.This work was supported by the Ministerio de Economia, Industria y Competitividad, under the Project DPI2016-77215-R(AEI/FEDER, UE), and by the University of the Basque Country UPV/EHU (ELEKTRIKER research group GIU20/034)

Adaptive Static Line Rating for Systems with HTLS Conductors

Operation and planning of a power system are constrained by the rating of power lines. Usually, the static line rating is used for system operation and planning. The static line rating defined for an electric grid uses the same conservative weather assumptions for the whole grid regardless of the location of each line or its maximum-allowable conductor temperature. A separate analysis of the weather magnitudes measured in a pilot line shows how favorable air temperature and solar heating compensate for unfavorable wind speed. However, this compensation is limited for high maximum-allowable conductor temperatures. As a result, the risk of the static line rating exceeding this maximum temperature is higher for HTLS conductors. An adaptive static line rating is proposed to control the assumed risk. The wind speed assumption for the static rating is reduced for higher maximum-allowable conductor temperature.This study is financially supported by the Ministerio de Economía, Industria y Competitividad, under the project DPI2016-77215-R (AEI/FEDER, UE), and by the University of the Basque Country UPV/EHU under the project EHU16/19

Review of dynamic line rating systems for wind power integration

When a wind power system is connected to a network point there is a limit of power generation based on the characteristics of the network and the loads connected to it. Traditionally, transmission line limits are estimated conservatively assuming unfavourable weather conditions (high ambient temperature, full sun and low wind speed). However, the transmission capacity of an overhead line increases when wind speed is high, due to the cooling caused by wind in the distribution lines. Dynamic line rating (DLR) systems allow monitoring real weather conditions and calculating the real capacity of lines. Thus, when planning wind power integration, if dynamic line limits are considered instead of the conservative and static limits, estimated capacity increases. This article reviews all technologies developed for real-time monitoring during the last thirty years, as well as some case studies around the world, and brings out the benefits and technical limitations of employing dynamic line rating on overhead lines. Further, the use of these DLR systems in wind integration is reviewed.This work is financially supported by the Ministerio de Economía y Competitividad under the project DPI2013-44502-R and the Eusko Jaurlaritza under the project SAI12/103

System for ampacity monitoring and low sag overhead conductor evaluation

MELECON 2012 - 2012 16th IEEE Mediterranean Electrotechnical Conference, 25 Mar - 28 Mar 2012, TúnezAmong the different alternatives to achieve the uprating and better use of existing overhead power lines are the use of high temperature low sag conductors and the use of real time monitoring systems for knowing the ampacity of the lines. So far, the uprating of a power line through both alternatives have been considered separately. However, it is possible to combine both solutions and obtain greater benefit in terms of achievable uprating, and a better control of the reliability of the conductor. This paper presents a system for monitoring the ampacity and for the evaluation of the low sag behavior of the overhead power lines. This system allows knowing the power flow of the lines in order to optimize their use and evaluating the conductor monitored in order to validate their behavior in operating condition.This work is financially supported by the Ministerio de Ciencia e Innovación under the project DPI2009-08454, the University of the Basque Country UPV/EHU under the project EHU09/18 and the financial assistance UFI 11/28, and the Eusko Jaurlaritzako Hezkuntza, Unibertsitate eta Ikerketa Saila (Euskal unibertsitate-sistemako ikerketa-taldeak Ref. IT532-10)

Field validation of gap-type overhead conductor creep

Gap-type overhead conductor sag-tension calculations based on experimental conductor creep tests are based on stress-strain and metallurgical creep tests. Although for bi-metallic conductors, these tests are carried out for both the core and the full conductor, for gap-type overhead conductors the aluminum metallurgical creep is usually neglected and the full conductor metallurgical creep is not carried out. The purpose of the presented study is the validation of these calculation methods. For this purpose, field measurements have been obtained in a pilot line in operation. The gap-type conductor installation process has been measured and the conductor creep has been monitored during three years of line operation. In order to model relevant events such as the pre-sagging and sagging steps during the installation, and ice and wind events during the operation, a flexible sag-tension calculation method has been used. Besides, the widely used graphical sag-tension method has also been evaluated, obtaining similar results as the flexible method. The tension-decrease is used as the indicator of the creep. The calculated and measured tension-decrease values are close. Therefore, it is concluded that the sag-tension calculations based on experimental conductor creep tests are valid to represent the actual creep of the conductor in operation.This work was supported by the Ministerio de Economía, Industria y Competitividad, Spain, [DPI2013-44502-R and DPI2016-77215-R (AEI/FEDER, UE)]; and by the University of the Basque Country UPV/EHU [EHU16/19]

Energia Elektrikoaren Sorkuntza

Helburuak: Sektore elektrikoan gaur egun energia elektrikoa sortzeko erabiltzen diren teknologiei buruzko oinarrizko ezagutza bat lortzea. Norentzat: Energia elektrikoaren sorkuntza ikasgai bezala duten ikasleentzatEdukia: 1. Eskariari erantzuna ematea 2. Sistemaren kudeaketa ekonomikoa. Merkatu elektrikoa 3. Sorkuntza konbentzionala 4. Energia berriztagarriak eta baterako sorkuntza 5. Sorkuntzaren sare-konexioa 6. Sorgailu trifasikoak 7. Sorgailu elektrikoen egonkortasuna 8. Zentralen kontrola 9. Zentralen babesaLiburu honek UPV/EHUko Euskararen Arloko Errektoreordetzaren dirulaguntza jaso d