Analysis of AC Transformer Reliability

Introduction and Scope

The last CIGRE international survey for transformer reliability was published in 2015 (CIGRE WG A2.37, 2015). However, it was not possible to compare failure rates because the age distribution of the investigated transformer population was not known. Consequently, a new survey of failures and retirements of power transformers and reactors operating at 100 kV and above was performed, which includes detailed information about the individual age distributions.

Key Country Updates since 2015

Reasons why reliability has improved were also explored. Power transformer reliability and maintenance strategies have evolved across various regions since the last comprehensive update in 2015. Updates gathered from ASEAN, Australia, New Zealand, North America, South Africa, and Spain show the diverse approaches and advancements made to quantify reliability and ensure the resilience and longevity of transformer fleets. In ASEAN, a shift towards proactive maintenance regimes, adoption of advanced monitoring technologies, and strategic specification improvements reflect a concerted effort to mitigate risks and enhance asset performance, particularly in the face of challenging environmental conditions. Similarly, utilities in Australia and New Zealand have made strides in data collection and analysis, leveraging collaborative efforts to gain valuable insights into failure trends and lifecycle management strategies. The emphasis on statistical calculations and comprehensive reporting underscores a commitment to informed decision-making and regulatory compliance. In North America, a steady improvement in transformer reliability over the past decade is attributed to a multifaceted approach encompassing improved maintenance practices, planned interventions, and reduced false trips. The downward trend in transformer failures underscores the effectiveness of these measures in enhancing grid resilience and operational efficiency. South Africa's experience highlights the impact of targeted modifications, such as the transition to resin-impregnated bushings, in mitigating catastrophic failures and informing future asset management strategies. In Spain, a focus on technical specification updates and maintenance enhancements underscores a proactive approach to optimising transformer performance and longevity. The integration of fibre optic temperature sensors, variable frequency power factor measurements, and advanced monitoring equipment underscores a commitment to leveraging cutting-edge technologies for real-time asset management and risk mitigation.

Collectively, these insights underscore the importance of continuous innovation, collaboration, and data-driven decision-making in ensuring the reliability, resilience, and longevity of power transformer fleets in an ever-evolving energy landscape. As utilities navigate emerging challenges and opportunities, the exchange of best practices and lessons learned will remain critical in driving ongoing improvements and advancements in transformer reliability and maintenance strategies.

Measures to Increase Reliability

Technical specifications play a crucial role in defining various aspects, including industry standards, characteristics, manufacturing requirements, and testing protocols. These specifications significantly influence transformer reliability and performance. Key areas covered include performance and service conditions, insulation levels, dielectric tests, thermal performance, and ageing considerations. Emphasis is placed on managing insulation material condition through measures like controlling moisture ingress and specifying breathing systems. By adhering to international standards and leveraging resources like the CIGRE Technical Brochure 528, stakeholders can formulate robust technical specifications tailored to their needs, ensuring transformer integrity and longevity.