Longitudinal Loading: Fact Versus Myth by Ed Niedospial

Utilities have been moving more and more towards compact line designs for tangent structures. These typically use polymeric line post and braced post insulators due to the demand for lower project costs as well as growing limitations on land and right of way corridors. Line post and braced post insulators have been used for over 25 years and have performed well in this regard. Moreover, application of braced posts has now accelerated rapidly with new applications, such as at 345 kV, and this means that mechanical limitations are being extended to new levels. The key to meeting the requirements of these new applications is the need to better understand possible limitations as well as to establish safe working loads for each braced post design. This is typically accomplished using load curves, or interaction diagrams, to determine when an insulator is mechanically sound or when its limitations have been exceeded. Moreover, nothing complicates the design process more than longitudinal loads. This presentation aims to explore the ‘Facts’ and the ‘Myths’ pertaining to longitudinal loads.