And so far you have looked where? We wouldn't want to waste your time giving you information you've probably already obtained doing basic Google searches, etc.
I'm not sure of references but some maintenance practices are:
1. Wood pole testing for rot
2. Testing of steel tower grounding
3. Visual and infrared inspections by helicopter
4. Right of Way vegetation control
Ive been too in transmission maintenance. Annually we do it. Here are some of our things to do:
1. Terminal hotspot test - using thermal scanning, this must be done prior to the maintenace period and if possible with the highest load posible during testing time. Upon learning where the hotspots are probably loose contact are present,etc.
2. Cleaning of dust of insulators - dust are electrical conductors, it produces a hizzing sound if there are so many of it already. Clean the insulators with soft cloth and with water or something that has low conductivity.
3. Vegetation - Trimming of trees and other aliens that may come in close contact to the lines.
4. Most Important - DC power supplies of the SF6 breakers. These are the ones that are forgotten. It may have not tripped for quite sometimes due to no fault. But when time comes the cause of breaker bot tripping is the absence of DC power supply, hehehehe.
5. Others - mentioned and are in the sites u read.
