NETC’s 400kV Palatana- Silchar-Bongaigaon double circuit corridor in North Eastern part of India is a very important transmission line. This article describes how the line is maintained to ensure100% availability…

NETC is regularly assessing health of its assets through its risk management mechanisms mentioned before. NETC is in process of formulating health index of its assets. Further to manage lifecycle of assets more effectively, getting higher return with the assets and to reduce the total cost of risk, NETC is actively considering certification of ISO 55001.

Asset management

The asset is being managed by a group of highly experienced personnel with a Corporate Office headed by a Chief Executive Officer designated as Managing Director. For convenience of maintenance, the Transmission System is divided into three line sections with intervening power substations and each line section is further divided into a number of sub sections (2/3) with placement of maintenance teams comprising experienced fitters/foremen. The team leaders report to the concerned line in-charges and carry out patrolling as per the advance planning done. In the vulnerable & most vulnerable stretches of the transmission system having history of component failure, the tower top patrolling is being carried out along with ground patrolling almost on regular basis during adverse climatic conditions. The defects identified during patrolling are categorized as of shutdown and non-shutdown nature. The defects of non-shutdown nature are attended during regular patrolling and defects of shutdown nature are attended by obtaining shutdown of the respective transmission line or during opportunity shut down being availed by others depending upon the severity of the defects. Safety drill is a regular feature before starting any maintenance activity.

The entire maintenance activity is suitably aided by different protection mechanisms including disturbance recorders, event loggers, phase measuring units etc., put in place in the connected power sub stations and the grid and well supported by the grid operators.

Availability of transmission line corridor

NETC has achieved availability factor of transmission corridor above 99.89% under severe environmental conditions since last five years. Table 3 exhibits annual availability factor of last five years. As per Central Electricity Regulatory Commission (CERC) regulation [Reference 6], Normative Annual Transmission System Availability Factor (NATAF) is calculated as per following formulae:



AVo (Availability of ‘o’ no. of AC line elements) =


o = Total number of AC lines.

Wi = Weightage factor for ith transmission line i.e.number of sub-conductors x ckt. km for an AC T/L.

Ti = Total hours of availability of ith AC line excluding time not attributable licensee.

Tnai = The non-availability hours attributable to licensee.


NETC has been successful in maintaining availability of transmission corridor by adopting various innovative and sustainable mitigation measures after identifying the constraints. To reduce the down time, NETC is focusing on new methods of aerial patrolling, remote monitoring, use of modern O&M instruments, advance information about cyclones, earthquake & lightning etc. Use of 400 kV TLAs is one of the measures for future depending on its success in Indian Grid coupled with various state-of-the-art techniques for continuous strengthening of foundations & towers. NETC views human resources as the most precious asset of the company and therefore stresses high importance on mandatory and advanced training programs for upgradation of skill and knowledge.



1.North Eastern Regional Power Committee (NERPC) website for Transmission line corridor in NER
2.Average annual rainfall of the states from
3.IEEE-80: Guide for safety in AC Substation Grounding
4.Improvement of grounding properties by using bentonite, Proceedings: XXIX Conference CIGRE, Paris, 1982 Veledar, M,Timic, Z. Skok, S. and First, Z
5.NETC in house document – System Operating Procedure for Operation & maintenance, Internal Document (not for circulation)
6.Central Electricity Regulatory Commission (Terms and Conditions of Tariff) Regulations, 2019.





Satyajit Ganguly (Main Author) is the Managing Director of NETC (North East Transmission Company Ltd.).

Co- writers; Ashwani Kumar Srivastava, D. K. Sarma, Robin Kumar Sarkar and Harshal Radheshyam Malewar; are also from NETC.

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