P35.011: Polymer and Composite Overhead Transmission Line Insulators

Perform Multi-Stress Aging Tests: This task intends to help utilities understand the degradation mechanisms of different polymer insulators under the same stress that represents the real-world service conditions. The objective is to identify what mitigation options are effective at reducing degradation rates. This test applies multiple accelerate aging stresses to polymer insulators designed to simulate the in-service environment and document the condition of the insulators twice per year. EPRI plans to periodically add new insulator designs that reflect industry trends.

Perform Small-Scale Degradation Test: This task intends to understand how different end fitting designs affect corona related degradation of the polymer insulator housings. Using this knowledge, utilities can make informed design decisions around the use of corona rings. This test evaluates the water drop corona performance of polymer insulators in a small-scale test. EPRI intends to continue monitoring the aging of samples, refine the test methodology, and report on the findings.

Update the Insulator E-Field Modeling Software, Insulator Calculation Engine (ICE): Recognizing the critical role of electric fields in the service life of polymer insulators, this software calculates the electric field on new or existing insulator designs, helping utilities determine the need for corona rings. EPRI works with user feedback to keep this tool user-friendly and relevant.

Refine Polymer Insulator Impulse Testing Methodology: The standardized method of performing steep impulse testing of polymer insulators requires adjustment of the impulse steepness due to the varying height of the electrodes. This dependence affects the efficiency and repeatability as reconfiguration is needed to achieve the target steepness. Steep impulse tests of polymer insulators are a useful method for evaluating their electrical integrity and quality of the housing interface. This task intends to refine the steep impulse testing method to improve efficiency and repeatability when applied to polymer insulators.

Update the Insulator Reference Book (The Violet Book): This comprehensive guide provides state-of-the-art information on insulator selection, inspection, and maintenance to help utilities better specify, install, and manage transmission line insulators. Revisions to the book intend to include mechanical considerations when selecting insulator for different configurations.

Improve the Nondestructive Weathershed Bonding Assessment Method: Poor bonding between the weathershed housing and core of a polymer insulator can lead to internal tracking and partial discharges that ultimately result in insulator failure. Current methods are destructive resulting in loss of product and sampling can be ineffective at finding poor bonding. This task evaluates the use of ultrasound technology and nondestructive stress application to more effectively detect poor weathershed bonding in polymer insulators without destroying them. EPRI intends to proof test the methodology across field aged samples and develop an active feedback technique to reduce effort and time.

Track Insulator Failures: This task collects information about polymer insulator failures from utilities, records it in a database, and performs trending analyses. The results provide utilities with insight into failure modes, rates, and emerging risks within their existing insulator populations. Utilities can use this information to assess fleet‑level risk, support asset management decisions, and justify acceptable service life assumptions for polymer insulators.

Allowable Compression in V-String Insulators: While V-strings assemblies offer a stable support point for suspended assemblies under most wind loads, few V- strings can accommodate extreme wind loads without one leg going into compression. Fundamental research and experimentation intends to be performed in 2027 to explore safe bending limits on composite long rod insulators and as well as ceramic captain pin insulators. This initiative will be performed as a shared deliverable in conjunction with project 35.007.

Provide Tools and Resources on The Transmission Resource Center: The following calculators, tools, result summaries, and references are planned to be available on the Polymer Insulator Transmission Resource Center: