Cantilever hold the assembly of contact wire , catenary and dropper assembly. It transfers all vertical load, lateral forces and bending moment load through insulator to Mast. It is an insulated swiveling type structural member and keeps the overhead catenary system in a position assisting smooth current collection by the pantograph at the designed speed. It is flexible with all joints having swiveling arrangement permitting movement in all direction.
Portal structures are used to accommodate OHE of many lines (2 to 8 tracks) where it is not possible to erect independent mast due to restriction of track center.
There are three types of portal namely N, O and R type. Clear span (distance between inner face) in N type- 10- 20M (4 tracks), O type – 20-30M (upto 6 tracks), R type – 30-40M (upto 8 tracks).
Different types of steel mast which are used in railway are BFB (broad flanged beam), RSJ (rolled steel joist) and K-type, B-type fabricated mast.
Selection of Mast
General guidelines for use of different design of mast is as follows:
Normal location and OHE on tangent Track :BFB Mast
Normal Location on curves : RSJ Mast
Structures with multiple OHE with anchorage:K150, 175
Turn-out location with higher torsion stress: K200, 250
This is an alternative where it is not possible to manage with mast as well as portal.