Analysis of AC Transformer Reliability
The reliability of the global power transformer fleet was reviewed again, continuing CIGRE’s long legacy of surveying started forty years ago. As technology and working practices are updated it is important to periodically review reliability and how it is changing. More than 425,000 transformer years of operation collected, there were 1,204 major failures and 1,916 retirements from 66 utilities in 27 different countries. In addition to retirements and major failures, the age distribution was also analysed. As a result of increased emphasis on improving reliability over the life cycle, the failure rate has now fallen by more than half since the last Working Group. For all major failures, the hazard curve was fairly random with a slow increase with age. Failures resulting in the transformer being scrapped showed a clear age-dependency. The hazard rate for scrapped units accelerated after twenty years of age.
Data was sought from new applications of transformers, such as solar and wind farms. However, as they are relatively new there has not been enough operational service-years and failures to make statistically significant conclusions. A recommendation is to continue these surveys to continue to build experience. A thorough discussion has been given on how the industry has improved the reliability of power transformers, with advice how an owner can request a quality design and maintain longevity over the long operating life of this asset class.
Members
Convenor (DE)
S. TENBOHLEN
Secretary (AU & NZ)
D. MARTIN
R. ASANO JR. (BR), M. BUELLESBACH (DE), A. COLLIER (DE), Z. HANIF (DE), J. HERRING (IE), P. MANSKI (PL), P. PACHECO RAMOS (ES), C. PLATH (DE), S. SACCO (IT), K. SELEME (ZA), G. SUPRAMANIAM (MY), S. TEE (UK), E. TENYENHUIS (CA), S. YAMADA (JP)
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.
To read this article subscribe to ELECTRA. Single edition, annual options and CIGRE membership are available. Access to all editions is free for CIGRE members.
Already have an account? Sign in