Project Overview

Objective

The reliability of a utility’s power transformers highly depends on the condition and performance of its components such as bushings. Today, it has been estimated than more than 20% of transformer failures could be related to bushing issues. Dry-type, polymer bushings offer an attractive alternative to traditional oil-impregnated paper bushings with porcelain exteriors for several reasons. However, there is not a significant body of experience with these newer bushing technologies to provide a measure of if and how beneficial they could be. In particular, the longevity and reliability of dry-type bushings are significant unknowns. A portion of the work proposed under this effort aims to understand some of the unknown information surrounding the application of polymer bushings through long-term testing under simulated field conditions and climate extremes. Any concerns identified in this long-term testing can then be studied with more targeted research.

This project (P37.113) aims to produce guidelines on selection, application, operation, and diagnostics for these new technologies based on research to date and the aggregate shared experience of funding members.

The research is structured to specific uncertainties surrounding polymer bushings by performing a mix of medium- and long-term laboratory experiments. Brief experiments and data collection will also be performed to obtain insights in the short term:

• How do polymer bushings perform under extreme environmental conditions and operating stresses {electrical, thermal, and mechanical}?
• How would the polymer bushings be affected by overloading, and does this require different specification and/or operating practices?
• Are present monitoring and diagnostic test methods sufficiently effective for assessing the condition of polymer bushings?
• Are there unique operating or maintenance concerns with polymer bushings?
• Can we identify prevalent failure modes or emerging reliability issues earlier to mitigate concerns with widespread adoption?

Research Value

The core value that this research aims to provide includes:

• Greater confidence in the adoption of polymer bushings
• A sound technical basis for decisions when specifying, operating, and maintaining new polymer bushing technologies
• Lower life-cycle risks and costs to improve reliability and affordability
• Help in assessing and managing risks through early insights gleaned from laboratory testing and field experience
• Better understanding of the efficacy of various monitor and diagnostic test technologies applied to polymer bushings

Planned 2025 Research

• Performance evaluation of polymer bushings under extreme environmental conditions and operating stresses: In a full-scale setting, EPRI intends to continue conducting long-term testing of polymer bushings under a range of environmental and operating stresses. The 138-kV research substation in Lenox, Massachusetts affords the opportunity for convenient outdoor testing under a wide range of ambient temperatures and precipitation types. In addition, rain spray equipment is available to simulate wet climates. The bushings can be simultaneously energized to rated voltage while circulating currents up to, and in excess of, rated current. This is a continuation of a test program that commenced in 2019 and is ongoing.

• Guidelines on specification and maintenance of polymer bushings: Work will continue to incorporate the distilled learnings and insights developed through this research and through the combined operating experience of participating utilities into a series of guidelines on application, installation, operation, maintenance, and diagnostics of polymer bushings.

• Targeted testing of specific concerns: The full-scale testing in the 138-kV research substation is necessarily a long-term task. To accelerate learnings, and to provide actionable information on specific areas of concern, -such as sensitivity to overloading or exposure to high mechanical stresses, -EPRI intends to perform specific, targeted tests to address concerns identified by participating members.

• Analysis of the reliability and performance experience of polymer bushings: This task will provide the results of a broader statistical study to classify the reliability, performance, and life expectancy of polymer bushings utilizing voluntary contributions of data and field experience from interested members.