P37.113: Polymer Bushing Life Management
Objective
Power transformers are among the most critical and capital intensive assets for electrical utilities. The reliability of transformers is directly related to system performance, safety, and utility costs. Experience across the industry has shown that transformer reliability is often limited by the performance of an individual component rather than multiple items failing simultaneously.
High voltage bushings are among the most critical components of a power transformer, providing the electrical interface between the transformer. However, they must function while being constantly subjected to sustained electrical, thermal, mechanical, and environmental stresses. Industry surveys and operating experience have indicated that conventional oil impregnated paper (OIP) bushings can account for a significant share of transformer failures (20% or greater), highlighting an ongoing need to evaluate alternative technologies that may improve reliability and reduce risk.
Polymer (also known as dry type) bushings have gained increasing attention as alternatives to traditional OIP bushings, particularly OIP bushings with porcelain housings. Polymer bushings offer several potential advantages including, but not limited to, reduced fire risk, lower weight, and potentially simplified field maintenance. As a result, interest in different types of polymer bushings has grown among utilities seeking to improve asset safety and performance. At the same time, adoption has been relatively slow, reflecting the industry’s desire for more data regarding long term performance, aging behavior, and reliability under a wide range of service conditions. The limited duration of field experience and the relatively small installed base compared to OIP bushings have constrained the availability of publicly accessible performance data, resulting in uncertainty for utilities considering broader deployment.
This project is intended to address this challenge by accelerating the development of credible, data-driven insights through coordinated, industry relevant research. In turn, the project supports utility can decision making and reduces uncertainty associated with broader adoption of polymer bushing technologies. The work is structured to deliver value to EPRI members through three primary outcomes:
- Development of a technical knowledge base to support specification, application, operation, and maintenance decisions related to polymer bushing technologies.
- Identification of best practices and potential risks through early insights from laboratory testing and field experience, enabling proactive risk management and improved asset reliability.
- Assessment of the applicability and effectiveness of existing monitoring and diagnostic techniques, largely developed for oil filled bushings, when applied to polymer bushing designs.
This project leverages EPRI’s collaborative research model by integrating utility experience, laboratory testing, and ongoing review of emerging technical literature. Information sharing among participating utilities will help expand the collective understanding of polymer bushing performance while avoiding duplication of effort. Depending on topics identified by members as most relevant each year, laboratory testing can be performed to expose polymer bushings to representative service conditions, extended-duration aging, or extreme cases, as well as evaluate different health diagnostic and maintenance approaches.
Together, this work seeks to provide clear, practical answers to questions that matter most to asset owners, including performance under stress, implications of different loading profiles and intensities, suitability of existing diagnostics, operational and maintenance considerations, and the early identification of reliability risks. By strengthening the industry’s collective understanding of polymer bushings, this project aims to support confident, well informed adoption decisions and contribute to improved transformer reliability across the power system.
Research Value
This research program aims to:
- Provide data driven guidance to utilities that strengthens understanding of polymer bushing reliability, reduces transformer failure risk, and supports the delivery of a more reliable electric service.
- Establish a sound technical basis to support utilities in making informed decisions related to the specification, operation, and maintenance of different polymer bushing technologies across the entire asset life cycle.
- Enable utilities to achieve reductions in life cycle risk and total ownership cost by improving understanding of reliability drivers, failure mechanisms, and asset management strategies.
- Provide insights to help utilities deploy polymer-based bushing technologies with greater confidence, supporting safer transformer operation.
- Support effective utility investment and maintenance strategies to reduce long term costs associated with equipment failure and emergency repairs.
- Present findings that provide a better understanding of the efficacy of various monitoring and diagnostic technologies when applied to polymer bushings.
- Support proactive risk assessment and management by delivering early insights derived from controlled laboratory testing and real world field experience with polymer bushings.
Approach
The research approach of P37.113 encompassing information from short, medium and long term research. The data from the different research currently are categorized into four main areas:
Development of specification, application, and maintenance guidelines. This section continues to synthesize and refine lessons learned across the P37.113 research portfolio, combining findings from individual studies with shared operating experience contributed by participating utilities to develop comprehensive, practical guidelines covering application, installation, operation, maintenance, and diagnostic practices for polymer bushings.
Long term evaluation under extreme environmental and operating conditions. Full scale, outdoor testing of dry type polymer bushings is planned to be continued at the EPRI 138 kV Research Substation in Lenox, Massachusetts, enabling long duration exposure to a wide range of ambient temperatures, precipitation conditions, and electrical and thermal stresses. This includes operation at rated voltage and circulating currents up to and beyond rated current, with controlled wet climate simulation using rain spray equipment. Additionally, findings from focused long-duration studies involving polymer bushings subjected to severe conditions are intended to be included.
Targeted testing to address specific utility concerns. To accelerate learning and deliver timely, actionable insights, the program plans to conduct focused laboratory and field tests addressing specific issues identified by participating members, such as sensitivity to overload conditions, elevated operating temperatures, and mechanical stresses, including high cantilever forces that may arise during through fault events. Topics of interest to explore include sensitivity to overload (electrical loading and temperature), as well as bushing reliability under high cantilever forces associated with throughfault conditions.
Analysis of reliability and field performance experience. A broader reliability assessment is planned to be performed through the compilation and analysis of voluntarily contributed utility data and field experience to characterize the reliability, performance trends, and expected life of polymer bushings across a range of applications and operating environments.
Anticipated Deliverables
| Deliverable | Date |
|---|---|
| Performance of Polymer Bushings Under Extreme Environmental Conditions – Technical Update Report documenting the short- and long- term test results of polymer bushings tested in the 138-kV Research Substation, as well as polymer bushings in other long term and/or intense condition tests | 12/31/2027 |
| Guidelines on Specification & Maintenance of Polymer Bushings – Technical Update Report documenting industry guidance and best practices on applications, operation, and diagnostics of polymer bushings, as well as the fundamentals of polymer bushings | 12/31/2027 |
Past EPRI Work on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002032935 | Guidelines on Specification and Maintenance of Polymer Bushings-2025 Update | Updated version of Polymer Bushing Guidelines | December 2025 |
| 3002032936 | Performance of Dry Bushings Under Extreme Environmental Conditions-2025 Update | Testing and monitoring results of polymer bushings tested in the 138-kV yard in Lenox in 2025 and other studies | December 2025 |