Prioritization procedure for transmission network assets revitalization D. Bajs, G. Majstrovic Transmission and Distribution Department Energy Institute Hrvoje Pozar Zagreb, Croatia dbajs@eihp.hr I. Medic Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture University of Split Split, Croatia Abstract - Important issue for Transmission System Operators is how to deal with older transmission assets. To ensure system reliability and security over long time frame, Transmission System Operators have to develop appropriate methodology and procedure for transmis- sion assets/facilities revitalization or replacements. This paper describes one possible way to prioritize transmis- sion facilities for revitalization. Example of this proce- dure is also given in the paper. Keywords: System reliability and security, Transmis- sion assets, Revitalization, Replacements, Transmission network development. 1. INTRODUCTION Transmission assets ageing process has significant im- pact on system operation and planning. Unreliable and older facilities may jeopardize overall system reliability and security, while increasing transmission system opera- tional costs. Important issue for Transmission System Operators is to choose an optimal moment for assets revitalization or replacement, in order to ensure satisfac- tory level of system reliability and security. At the same time, revitalization or replacement costs should be reduced and economically justified. Transmission facilities and equipment (overhead lines, cables, transformer stations, protection devices, measuring, telecommunication devices etc.) are getting older during their operation. Each transmission facility and equipment has its expected lifetime. Transmission facilities are expected to operate under declared characteristics during their lifetime, without significant number of failures or problems. For the same group of transmission facilities, lifetime may vary under quite wide range because different influential factors like climate, operational or construc- tional ones. During aging process equipment slowly losses its characteristics so number and duration of failures increase. With satisfactory and periodical maintenance activities transmission facilities may operate reliable under declared characteristic, until this is not possible any more due to their obsoleteness. Transmission facilities and equipment were revitalized or replaced in the past mostly because their characteristics didn’t match technical operational requests any more due to constant load increase. Today, in the age of slower load increase and competitiveness in the electricity business, revitalization activities are mostly initiated by technical (system reliability and security) and economical requests. Transmission system operators are responsible for reliable and secure network operation in an open electricity market environment, while operating a network in an economi- cally reasonable way at the same time. Moreover, large number of transmission equipment constructed during last century will exceed their lifetime soon. One possible way to prioritize transmission facilities for revitalization or replacement will be described in this paper. The prioritization is based on three main criteria: - transmission facilities real condition, - transmission facilities importance in the system, and - expected costs which are caused by particular transmission facilities. Each criterion is evaluated using points (marks) from 0 to 5. Transmission facilities revitalization list includes only facilities appraised with certain number of points. The candidates for revitalization or replacement are chosen among transmission facilities when following requests are fulfilled: - facility oldness is larger than its expected lifetime, - facility average last five-years unavailability is lar- ger than average five-years unavailability of the group of the same facilities (overhead lines, cables, transformers etc.), - facility average last five-years outages number is larger than average five-years outages number of the group of the same facilities, - facilities that not fulfill established technical crite- ria, - facility book value is zero. Transmission facility real condition is determined ac- cording to past and present performance indicators like: last five-years average forced and planned unavailability and the number of outages, maintenance record, opera- tional conditions in the past, visual examination and laboratory tests. Transmission facility importance evaluation is based on the probabilistic simulations of transmission system operation. Probabilistic simulations are based on Monte- Carlo method, DC power flows and linear programming. Simulations are performed for one year period taking into account different parts of annual load duration curve. Expected undelivered electricity costs and re-dispatching costs caused by particular transmission facility with different values of its unavailability are calculated.