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Abstract(s)
A capacidade de transporte de uma linha eléctrica aérea depende de factores relacionados com as características próprias do condutor tais como o material que o compõe, a resistência eléctrica, o diâmetro, a elasticidade mecânica, a emissividade e absortividade.
Além das características físicas do condutor, existem factores externos que afectam a sua capacidade de transporte. De entre esses, contam-se os factores meteorológicos, como a temperatura ambiente, a chuva, a neve, a velocidade e a direcção do vento, a intensidade de radiação solar e a densidade do ar.
No projecto de uma linha é estipulada uma temperatura máxima do condutor à qual essa linha pode ser explorada em condições de segurança. Essa temperatura é denominada temperatura de projecto.
A cada dia, o operador de rede português informa o MIBEL - Mercado Ibérico de Electricidade da capacidade de interligação para o dia seguinte, entre Portugal e Espanha. Além disso, procede informaticamente à validação do perfil de geração do MIBEL, recorrendo a uma ferramenta denominada VTP – Verificação Técnica do Programa de Exploração.
Por outro lado, o operador de rede fornece, para a ENTSO-E - European Network of Transmission System Operators for Electricity, um ficheiro DACF – Day Ahead Congestion Forecast para cada hora do dia, que contém toda a informação relevante sobre a redeeléctrica nacional para as 24 horas seguintes. Nesse ficheiro inclui-se a informação sobre os limites decapacidade de transporte das linhas e topologia darede.
Tradicionalmente, os operadores utilizam métodos determinísticos, baseados em indicadores meteorológicos nacionais, sobre os quais são estabelecidos valores de referência. O cálculo da capacidade de transporte das linhas é feito com recurso a equações empíricas e em função da hora do dia e do ano.
A abordagem determinística pode ser considerada conservadora, pois os valores de referência de temperatura ambiente, velocidade do vento e radiação solar visam minimizar o risco. Porém, o recurso aeste tipo de abordagem pode ter como consequência onão aproveitamento das linhas na sua plenitude.
Neste contexto, com esta dissertação pretende-se estudar e apresentar uma metodologia para previsão dacapacidade de transporte das linhas para o mercado diário do MIBEL do dia seguinte e comprovar que a sua aplicação permite prever, com um grau de segurança aceitável, uma capacidade de transporte superior, na maior parte do tempo, àquela que é calculada actualmente pelo operador.
Pretende-se também comprovar que a metodologia permite aproximar a capacidade de transporte prevista daquela que pode ser calculada, em tempo real, no dia seguinte. A aplicação desta metodologia deverá resultar num risco menor de market splitting e de distorção do perfil de geração.
Neste trabalho, são criadas várias combinações de parâmetros meteorológicos, com valores de referênciae com valores previsionais. São usados dois modelosde cálculo, numa metodologia unificada, onde um dos modelos, denominado de Kuipers & Brown, é o actualmente usado por grande parte dos operadores da rede de transporte e o outro, mais detalhado principalmente no que diz respeito à modelação do arrefecimento por efeito de convecção, foi desenvolvido por grupos de trabalho na CIGRÉ - Conseil International des Grands Réseaux Électriques.
Na presente dissertação não se pretende estudar a utilização de medições meteorológicas em tempo real,para realizar o chamado ratingdinâmico nem usar métodos estatísticos para fazer previsão. Pretende-se apresentar uma alternativa ao ratingdos operadores e criar uma metodologia que possa ser usada em conjunto com um modelo Mesoescala de previsão meteorológica, para gerar previsões de capacidade de transporte das linhas eléctricas para o dia seguinte.
É feita uma comparação entre os resultados da metodologia proposta, usando dados meteorológicos reais,aplicada a uma linha da RNT - Rede Nacional de Transportee o cálculo em tempo real da capacidade de transporte da mesma linha, confirmando-se a adequabilidade da metodologia e sua aplicabilidade.
O objectivo da dissertação cumpre-se com a apresentação e análise de previsões diárias e resultados anuais de capacidade de transporte das linhas, usando a metodologia proposta e com a comparação dos resultados quer com a metodologia actualmente em uso pelo operador, quer com o cálculo em tempo real do operador referente ao ano de 2015.
No final, são apresentadas algumas considerações e sugestões para melhoramento da metodologia, com vista a desenvolvimento futuro.
Abstract: The ampacity of an overhead power line depends on factors related with the conductor’s physical characteristics, such as the material from which it’s made of, it’s electrical resistance, mechanical elasticity, diameter, emissivity and absorptivity. The external factors that influence the conductor’sampacity are mainly the meteorological factors such as air temperature, rain, snow, wind speed and direction, solar radiation and air density. During the design stage of a power line, a maximum operating temperature, called design temperature, is defined for that line. The design temperature is the maximum temperature allowed for the line conductors. Each day, the Portuguese network operator informs MIBEL - Iberian Electricity Market about the interconnection capacity between Portugal and Spain for the day ahead. Furthermore, the operator validates the MIBEL’s generation profile, with a tool called VTP – Verificação Técnica do Programa de Exploração. On the other hand, the network operator delivers to ENTSO-E - European Network of Transmission System Operators for Electricitya DACF – Day Ahead Congestion Forecastfile for each hour, which contains all the relevant information concerning the grid for the next 24 hours. Information about line ampacity and grid topology is included in the DACF file. Traditionally, network operators use deterministic methods, based on meteorological historical information, to establish reference values. Ampacity calculations are performed with empirical equations and considering the season of the year and the timeof the day. This can be regarded as a conservative approach since the reference values, such as air temperature, wind speed and solar radiation, are aimed at lowering the risk. A possible consequence of this type of approach is that the power lines are frequently underexplored. In such a context, this dissertation carries out the study and presentation of a methodology to forecast a power line’s ampacity for the day ahead market of the MIBEL. The goals are to prove that it is possible to obtain, whilst maintaining an acceptable safety level, forecasts with greater line ratings, and to prove that the rating forecast is very similar to the real time rating. The implementation of the methodology should result in decreased risk of market splittingand generation profile distortion. In this work, various combinations of meteorological parameters are used, both with reference and forecast values. Two mathematical models are used in a unified methodology. The Kuipers & Brown model, currently used by many transmission network operators, is used. The second model is more detailed in terms of convection cooling and has been developed by CIGRÉ - Conseil International des Grands Réseaux Électriques workgroups. This dissertation is not about studying the use of real time weather parameters measurement to performdynamic rating nor about using statistical methods to forecast ampacity. The goal is to present an alternative to the operator’s rating method and to propose a methodology witch can be used with a Mesoscale weather forecast model, to generate powerline ampacity forecasts for the next day. In this work, a comparison is made between the results obtained with recorded weather parameters and the proposed methodology and the operator’s real time rating, confirming the suitability of the methodology for this purpose. The goal of the dissertation is attained by presenting and analyzing daily forecasts and yearly results, obtained using the proposed methodology and by comparing the obtained results with the operator’s current rating method and with the operator’s real time rating, based on 2015 weather measurements. Some considerations and suggestions are presented at the end, with the goal of improving the methodology for future development.
Abstract: The ampacity of an overhead power line depends on factors related with the conductor’s physical characteristics, such as the material from which it’s made of, it’s electrical resistance, mechanical elasticity, diameter, emissivity and absorptivity. The external factors that influence the conductor’sampacity are mainly the meteorological factors such as air temperature, rain, snow, wind speed and direction, solar radiation and air density. During the design stage of a power line, a maximum operating temperature, called design temperature, is defined for that line. The design temperature is the maximum temperature allowed for the line conductors. Each day, the Portuguese network operator informs MIBEL - Iberian Electricity Market about the interconnection capacity between Portugal and Spain for the day ahead. Furthermore, the operator validates the MIBEL’s generation profile, with a tool called VTP – Verificação Técnica do Programa de Exploração. On the other hand, the network operator delivers to ENTSO-E - European Network of Transmission System Operators for Electricitya DACF – Day Ahead Congestion Forecastfile for each hour, which contains all the relevant information concerning the grid for the next 24 hours. Information about line ampacity and grid topology is included in the DACF file. Traditionally, network operators use deterministic methods, based on meteorological historical information, to establish reference values. Ampacity calculations are performed with empirical equations and considering the season of the year and the timeof the day. This can be regarded as a conservative approach since the reference values, such as air temperature, wind speed and solar radiation, are aimed at lowering the risk. A possible consequence of this type of approach is that the power lines are frequently underexplored. In such a context, this dissertation carries out the study and presentation of a methodology to forecast a power line’s ampacity for the day ahead market of the MIBEL. The goals are to prove that it is possible to obtain, whilst maintaining an acceptable safety level, forecasts with greater line ratings, and to prove that the rating forecast is very similar to the real time rating. The implementation of the methodology should result in decreased risk of market splittingand generation profile distortion. In this work, various combinations of meteorological parameters are used, both with reference and forecast values. Two mathematical models are used in a unified methodology. The Kuipers & Brown model, currently used by many transmission network operators, is used. The second model is more detailed in terms of convection cooling and has been developed by CIGRÉ - Conseil International des Grands Réseaux Électriques workgroups. This dissertation is not about studying the use of real time weather parameters measurement to performdynamic rating nor about using statistical methods to forecast ampacity. The goal is to present an alternative to the operator’s rating method and to propose a methodology witch can be used with a Mesoscale weather forecast model, to generate powerline ampacity forecasts for the next day. In this work, a comparison is made between the results obtained with recorded weather parameters and the proposed methodology and the operator’s real time rating, confirming the suitability of the methodology for this purpose. The goal of the dissertation is attained by presenting and analyzing daily forecasts and yearly results, obtained using the proposed methodology and by comparing the obtained results with the operator’s current rating method and with the operator’s real time rating, based on 2015 weather measurements. Some considerations and suggestions are presented at the end, with the goal of improving the methodology for future development.
Description
Dissertação para obtenção do grau de mestre em Engenharia Electrotécnica
Keywords
Linhas eléctricas aéreas Overhead power lines Previsão de capacidade de transporte de energia Line rating Comportamento térmico de condutores aéreos Thermal balance of overhead conductors Kuipers& Brown
Citation
SILVA, Marco André Timóteo da - Previsão da capacidade de transporte das linhas aéreas para o mercado diário do MIBEL. Lisboa: Instituto Superior de Engenharia de Lisboa, 2016. Dissertação de mestrado.
Publisher
Instituto Superior de Engenharia de Lisboa