Affordable Cable System Reliability and Life Extension Strategy
Today, there is increased pressure for electric distribution cooperatives to maintain system reliability without increasing membership costs. This challenge is further compounded by the need to maximize existing legacy infrastructure. While membership reliability is a key consideration, a static economy, a commitment to a lower carbon footprint and the need for rate stability are also key factors that translate into increased operating costs. Many consider age to be the silent killer of America's critical infrastructure. The large fleets of equipment deployed by electric utilities and limited real-time monitoring makes it nearly impossible to know the duty each specific piece of equipment has experienced, thus age alone is used as the main determinant of remaining life. The economic and staffing requirements to replace these aged fleets based solely on in-service life is untenable. The need to find a lean approach to better address this challenge has lead to new technologies that provide detailed information about the equipment's true health or condition to allow the right measure of asset rehabilitation, replacement or extended deployment using actual condition assessment. There are millions of miles underground power distribution systems in service today that are operating beyond the original accounting defined depreciation life and failing at an ever increasing rate. Until recently, management of these underground assets was particularly challenging because once put into service, their concealment prevents visible inspection. A new cable life extension process is revolutionizing the industry by providing a means to field assess, rehabilitate and then certify cable systems to like new status. The proven assessment technology has certified more than 90,000 underground cable systems around the world and has shown that over 75% of aged assets still perform as well or better today as they did when they were first installed, decades ago. The Federal Energy Regulatory Commission's ("FERC") decision to allow capitalization of this new cable life extension technology is prompting many utilities and electric cooperatives coast to coast to reduce cable replacement budgets and make a positive impact on membership costs. These forward looking utilities have experienced extended capital reach, lowered operating and maintenance (O&M) expenditures, efficient resource utilization, minimal property intrusion and a dramatic real-time improvement in cable system reliability.
Técnicas para Diagnóstico e Estimativa de Vida Útil de Cabos Subterrâneos: Discussão sobre Alternativas, Aplicações e Potencialidades
The great challenge for the industries and electric power companies that operate with underground power cables is to identify the ones that are in good operating conditions, those that require maintenance and the units that will need to be replaced soon, so that an appropriate operation planning be developed to optimize the use of the company human and financial resources. Researchers around the world have been focusing their efforts to find a methodology able to identify the insulation status of these cables and provide an estimation of the remaining useful life, so that a safe and reliable operation can be established. However, so far, no single technique was able to provide an ultimate answer for this question. In this context, this paper presents an extensive literature review of different techniques that are used to diagnose aged underground cables, estimate the the failure rate and predict the remaining lifetime. It is also presented case studies of the application of these techniques and the results obtained. The discussion is established around the sufficiency of the results obtained in the application of each methodology for the effective elaboration of preventive maintenance programs, for planning the replacement problematic cable stretches and for guidance in making long-term budgetary decisions. Resumo: O grande desafio para empresas e concessionárias que possuem redes elétricas subterrâneas é identificar os cabos que estão em boas condições de operação, os que demandam manutenção e aqueles que precisarão ser substituídos em um curto intervalo de tempo, para que se torne possível realizar um planejamento adequado dos investimentos e das intervenções de manutenção, otimizando a utilização de seus recursos. Pesquisadores ao redor do mundo há tempos vêm direcionando esforços para conceber uma metodologia capaz de avaliar o estado da isolação destes cabos de modo a fornecer uma estimativa da vida útil restante, assegurando uma operação segura e confiável, com elevada disponibilidade do mesmo. Entretanto, até então nenhuma das técnicas utilizadas isoladamente foi capaz de atender, em definitivo, esta necessidade. Neste contexto, o presente trabalho apresenta uma extensa revisão bibliográfica de diferentes técnicas que são utilizadas para realizar o diagnóstico dos cabos subterrâneos envelhecidos, estimar a taxa de falhas da rede e prever o tempo de vida restante para estes cabos. Estudos de caso de aplicação destas técnicas, assim como os resultados obtidos, reportados na literatura por diferentes empresas, foram compilados e também apresentados neste artigo. A discussão é estabelecida em torno da suficiência dos resultados obtidos na aplicação de cada metodologia para a elaboração dos programas de manutenção preventiva, de planejamento para substituições dos trechos de cabos problemáticos e para orientação na tomada de decisões orçamentárias a longo prazo.
Mechanism for impulse conversion of water trees to electrical trees in XLPE
A lightning impulse causes substantial capacitive current in a water tree channel which, as a result of its small cross section, has relatively low conductance. Transient, nonlinear finite element computations with coupled thermal and electric fields for the geometry of a 15 kV XLPE dielectric cable indicate that an 80 kV lightning impulse can cause the water within a water tree channel to boil over a range of four orders of magnitude in water conductivity, from 10/sup -2/ S/m to 10/sup 2/ S/m. Boiling of the water in a water tree channel reduces substantially the yield stress of the XLPE, raises the pressure within the water tree channel, and is likely to leave a cavity which can support partial discharge resulting in electrical tree initiation.