A comparative review of transformer reliability on a individual and population scale and an assessment of reliability methodologies

Power transformers are considered to be one of the most critical components of a power system. Due to ageing the majority of transformer populations are at or approaching their anticipated design lives, causing growing concerns over possible consequential impacts to system reliability. It is essential for utilities to maintain high levels of system reliability and ensure the continued cost-effectiveness of the power system through forward planning. Accurate transformer lifetime modelling is essential to achieving these goals and can be used to determine short, medium and long term replacement volumes. However transformer reliability can be considered on an individual and a population basis and different reliability methodologies also exist. In this paper a comparison of different reliability methodologies is made and the relationship between individual and population reliability is investigated. Further to this a new approach of modelling the reliability of transformers paper insulation is proposed based on tensile strength reduction.