Risk Assessment for Operations in the Portuguese Transmission System The Key Issues for the Probability of Contingencies
The increasing competitiveness of the power systems’ environment has created new challenges to the power system security assessment, demanding the development of new methodologies. Important aspects of this evolution are the unbundling of generation, transmission and distribution, caused by regulatory changes and creating a more competitive environment, the increased environmental concerns making it more difficult to build new assets, and the strong incentives to the generation from renewable energy sources. These factors contribute to the increasing stress on operating conditions and, consequently, cause more vulnerable networks. In recent years, the daily routine of transmission system operators has become more complex. The interconnected network is no longer just for mutual support; nowadays it has become the base platform for trading electricity allowing the shifting of increasing volumes of power across the system. Despite all the benefits that doubtless are many, from the operations perspective, the free electricity market presents more unpredictable and less stable power flows, a market-dependent generation pattern, also more unpredictable and less controllable. In addition to the latter, the significant amount of generation from renewable energy sources also contributes to place the system closer to its security limits. Therefore, and despite the bigger complexity and increased quality of service requirements, the energy supply and the optimization of resources remain a permanent goal, fulfilling all the security principles used for system operation. Incidents are naturally unpredictable and after the large disturbances which occurred in recent years (such as the blackouts on 9th May of 2000 in Portugal, on August 14th 2003 in the United States of America, on September 28th 2003 in Italy and in the European UCTE Network on November 4th 2006), the awareness of the risk of unpredictable disturbances has increased, and it has become essential for the decision-making process to have security indices that allow the operator to react in advance and to be aware of inherent risks, preventing harmful situations. The use of methodologies that take advantage of the actual real-time conditions in combination with past knowledge is extremely interesting in the system operation environment, because it gives a more accurate overview to the control room operators. Since long, the deterministic security assessment has been used to guarantee a high level security in system operations of Transmission Systems, being known as N-1 criterion. It tends to provide a conservative security region for protecting the system against severe contingencies. In the deterministic approach only the consequences of contingencies are assessed, but it does not consider likelihood, or better it does consider likelihood equal to one for all contingencies, therefore it cannot address increased or decreased uncertainty in operating conditions, such as adverse meteorological conditions or risk of forest fires. The advantages of probabilistic methods in comparison with deterministic ones are further developed in 1, 2. Hence, the probabilistic assessment has become an important topic for researchers and engineers, because by combining consequences and probability it is possible to evaluate risk of contingencies, as in (1): Riskcontingencyi = probabilitycontingencyi × severitycontingencyi (1) Through the historical data, it is possible to affirm that most incidents originate from overhead lines (OHL). From 2001 until the end of 2008, OHL represent on average 91％ of the incidents with origin in the Portuguese transmission system. Overhead lines, due to their dispersion over a wide geographic area and because of the many different ground characteristics where they are deployed, are more exposed to the action of external factors which cause most of the grid incidents. An accurate characterization of each incident’s cause, an analysis of their occurrence and of the intrinsic characteristics of the Portuguese territory is presented in reference 3, including geographical and meteorological data, which are a crucial part of the inputs for the risk assessment methodology. This paper aims to describe the key issues of the calculation of the circuit-part of overhead lines contingencies probability, as part of the risk assessment methodology (figure 1), which is being developed and has as main purpose to support control room operators in their continuous task.
Incidents Probability of Occurrence Operation Transmission System Risk
Susana A.B.De Almeida Rui Pestana F.P.Maciel Barbosa
Rede Eléctrica Nacional, S.A. Faculdade de Engenharia da Universidade do Porto Portugal Rede Eléctrica Nacional, S.A. Faculdade de Engenharia da Universidade do Porto Portugal
国际会议
桂林
英文
1-6
2009-10-28（万方平台首次上网日期，不代表论文的发表时间）