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Effect of End Fitting Design on Controlling Corona

EPRI Research Results after 20,000 Hours of Aging

Based on the study of hundreds of in-service polymer insulators and decades of insulator research, EPRI understands the importance of controlling the electric field (E-field) around the end fitting which in turn controls the presence of corona. The insulator end fitting shape and size are a factor in that control. Direct contact with corona discharges is one of the leading causes of brittle fracture failure and flashunders.

This report describes EPRI’s effort to develop a small scale short term test to assess how the design of the polymer insulator end fitting controls the position and direction of end fitting corona and its effect on the longevity of the insulators. Small scale tests such as described in this report can help utilities specify uniform performance criteria for polymer insulators in their specification documents.

This test was designed using easy to manufacture parts and off the shelf components making the test lower cost than the large counterparts.

The latest version of the test has the insulators energized in a 90+ relative humidity chamber which has resulted in accelerated degradation of the hydrophobicity. With the rubber becoming hydrophilic, the stress on the insulator shifted away from the end fitting towards the grounded cage.

In 2020, a new test with new insulators is planned with revised test parameters to improve the representativeness of aging of the end fitting seal region.

Available on EPRI’s Research >>







DayCor® cameras identify end fitting issues and pinpoint their location, as seen in these pictures that were taken by UVollé, Superb and Luminar HD cameras.

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