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Wednesday, 1 October 2014

Live-line maintenance and up-gradation of Transmission lines

What is Live-line Maintenance?

Carrying out the maintenance and up-gradation work on transmission lines while the line is still energized or charged is called Live-line maintenance.
Live-line work can be an economic way to upgrade and maintain High Voltage (H.V) and Extra High Voltage (EHV) transmission system components. Performing the Live-line maintenance work saves the utility several millions Rupees as there is continuity of service and avoids congestion in other lines (in case the work has been carried after supply shut down). Today remote controlled robots, able to monitor the crucial parameters of a transmission line are available. They aid the operator and give them access to the strategic data of the transmission system on which maintenance and other decisions are based.

The live line maintenance and up-gradation works involves inspection of conductor joins, insulator and cross arm replacement, replacement of conductors and towers. All the live line or hot line work are carried out by linemen or line workers specially trained and adapted to work on energized HV / EHV lines.

Different Live-line Techniques:

The different live-line techniques available or adopted has its own merits and limitations and are best suited for a particular job or condition. 

Bare Hand Technique:

The live line “bare hand” technique from helicopters is a fast and efficient method for testing conductors joins (sleeves). In this technique the linemen wear conductive suits, specialized gloves, socks and boots to ensure safety. These conductive suits are made of microscopic stainless steel fibers and Nomex material and provide protection against fire also. Use of helicopters in live line work can significantly reduce the time taken for repair and up-gradation. But there are certain limitations viz. hilly areas, limited clearances and inclement weather can interfere with the free movement of helicopter.  

Hot stick Technique:

“Hot stick” technique for live line work can be used along with “bare-hand” technique if the crew has the required skills and tools. “Hot-sticks” are insulated fiberglass sticks of length 12 feet or so with tools mounted on it. The technique permits to work on hot end without maintaining the required clearances. Insulated ladder or platform can also be used to work on conductors or the pole/ tower itself.

Cranes with insulated boom:

Cranes with insulated boom can also be used to work on live lines and makes the job easier and safer. These cranes with a lengthy reach can be utilized to reach out on hard to access job locations and can lift heavy loads. Although problems are encountered in setting up a crane and the job requires well experienced and certified crane operators.

Utilities around the world are going for live-line up-gradation wherever possible as it is a huge relief to the existing power system. For example in 2013, the American Electric Power re-conductored it’s heavily loaded 345 kV transmission line in South Texas with ACCC conductors. It was a live-line conductor replacement project, the largest in the live-line conductor replacement category. 

Live Transmission line Training in India:

In India the Hot Line Training Centres (HLTC)  at Bangalore and Ganguwal in Punjab are involved in imparting Live-line maintenance training on transmission lines and sub-stations since 1958. These training centres are now part of the National Power Training Institute (NPTI), under the Ministry of Power (MoP), Government of India.

These training centres offer training courses on Live-line maintenance technique using the "Hot-stick" method up to 220 kV level and up to 400 kV level using the "Bare-hand method".  

Live Transmission line Maintenance in India:

Insulator replacements, i.e. replacement of broken disc insulators with composite insulators account for nearly 80% of the live line maintenance work in the country. Replacement of spacers of bundled conductors is another significant live-line maintenance activity.

In 2012, Torrent Power Ltd., re-conductored an existing 132 kV line in Ahmedabad, (India) and this was a live-line re-conductoring project.