The advantages of braced line post (BLP) assemblies have led to their rising use in transmission line design. Moreover, as line designers push for greater efficiency, these assemblies are seeing application at increasing voltages as well as with higher mechanical ratings. However, present standards do not yet well define proper test techniques to determine their electrical and mechanical ratings. Moreover, the complexity of such assemblies, which combine a post insulator and a braced suspension insulator, makes it a challenge to properly test and rate them. As such, more work is needed to drive standardization. It is also important that present non-standardized test methods be well understood by end users so that they can better consider the impact these might have on results as well as on BLP assembly ratings.  

 A strut or line post insulator is designed to withstand combined tension and compressive loads. Depending on material and base, this insulator can also withstand bending loads.

The strut insulator is typically mounted to a structure horizontally (e.g. typically ≤ 15° from horizontal) with various types of line end mounting attachments based on anticipated loading. To make up the rest of the braced insulator assembly, the line end of the line post (strut) insulator is restrained by a suspension insulator which is also attached to the structure at a defined distance above the strut, thus forming an interior angle between insulators.

Braced insulator assemblies are generally categorized into two types:

(1) assemblies with the line post (strut) insulator rigidly attached to the support structure and therefore unable to rotate about the attachment point in response to unbalanced longitudinal conductor loads; and

(2) assemblies where the line post insulator is attached in a non-rigid manner to the support structure by means of an articulated fitting that can provide rotation about the attachment point.

Common terms for assemblies of the first type are 'braced posts' or 'rigid/fixed base horizontal vees'. Assemblies of the second type can also be referred to as a 'pivoting horizontal vee'. In this discussion, the general term for both assemblies with be a Braced Line Post or 'BLP' and further distinction between the two types will be noted as necessary.

Reference: www.inmr.com advancing-the-testing-of-braced-line-post-assemblies