TRANSMISSION LINE PATROLLING PROTOCOL/GUIDELINES FOR
NORTHERN REGION
1. Background
Hon'ble Commission in its Order on Petition No. 146/MP/2013 with IA 36/2013 dated
20.02.2014 had pointed out that there were instances of Grid disturbance due to nonclearance of bushing/jungle clearance or non-trimming of tree branches within the RoW to
transmission lines periodically.
2. Transmission Line Patrolling Protocol/Guidelines for NR-NRPC
Regular and Periodic maintenance of transmission system is of utmost importance for its
uninterrupted operation. All the Power Utilities have their own set procedure. State-of-theArt Operation and Maintenance Practices that includes state of art condition monitoring
techniques, Live Line monitoring and maintenance, Disaster Management System etc. need
to be initiated.
Trees and power lines are not a good mix. One tree limb may cause a "blackout" that cut
power to million people in the country. Patrolling and tree trimming/removal or jungle
clearance shall always be part of maintenance of Transmission Licensee to eliminate
potential hazards. The patrols, which could be done by helicopter or "foot" patrols, will
include trimming and removal of trees within the power line right-of-way. This effort will
ensure a reliable electric system while protecting the public safety for customers throughout
the Region. By maintaining an appropriate clearance in the power line right-of-way, we can
reduce tree-related power outages. Trees and limbs falling on power lines cause power
outages and disruptions of electric system. Trees too close to power lines can provide a
path for electricity to reach the ground, which can result in property damage or serious
injury to anyone touching the tree. Therefore in order to avoid any unforeseen, it is
necessary to have transmission line patrolling protocol/guidelines which shall also take into
account the terrain, forest cover and reach in that area and ensure regular monitoring as
per requirement in that area to ensure efficient operation.
Proper maintenance of transmission lines help to reduce scheduled outages and increase
the stability and reliability of power system. Systematic and regular maintenance works is a
pre-requisite for a healthy power system.
3. Patrolling Guidelines to be followed A detailed schedule of patrolling is to be chalked
out for each line by various levels (From Work man to Executive). The person carrying out
patrolling has to check various items as per the standard check list and indicate the same in
the format. These checks, the next level person verifies, when he goes for patrolling.
3.1 Categorization: Transmission lines shall be patrolled at periodicity depending upon the
terrain and different patrolling schedules shall be implemented by the transmission
licensees for normal sections, vulnerable sections/terrains and most vulnerable
sections/terrain.
Most Vulnerable Section/Terrain:
Transmission lines
i.
passing through coastal, forest, high/fast tree growth areas
ii.
Passing through areas prone to flux/soil erosion/hilly tracts/ level crossings
iii.
Passing through areas change of river course/ critical due to flood/ critical land sliding
iv.
Very heavy polluted areas
Vulnerable Section/Terrain:
Transmission lines
i.
emanating from generating stations
ii.
of 765 kV, 400 kV and 220/230 kV(Critical lines)
iii.
of Multiple circuit lines
iv.
prone to theft
v.
Heavy/medium polluted areas
Normal Sections:
Transmission line sections not prone to frequent defects and not covered under above
vulnerable and most vulnerable sections
Each transmission utility would categorize each of the line with the above criteria and
furnish the details to NRPC/NRLDC. Some lines could be categorized under different
category however location details, Ckm under different category would be furnished. New
elements details would be furnished as and when they are commissioned.
3.2 Frequency of Patrolling
SL.
No.
Section/Terrain
Frequency and by whom
1
Normal
Quarterly by
Junior Staff
Six monthly by Yearly by
Senior
Executive
Engineer
2
Vulnerable
Bi-Monthly
(Once in two
months) by
Junior Staff
Once in four
months by
Senior
Engineer
Half Yearly by
Executive
3
Most Vulnerable
Monthly by
Junior Staff
Quarterly by
Senior
Engineer
Half Yearly by
Executive
3.2.1 The patrolling schedules for ground inspection of live lines and tower top inspection
of de-energized lines shall be separately issued by the licensees. Patrolling and condition
monitoring of the lines shall be done both by inspection from ground using visual and
thermal instruments as well as tower top inspections.
3.2.2 Tower top patrolling shall be done for the transmission lines categorized under Most
Vulnerable Section/terrain under live condition or during shut down.
3.2.3 The important lines shall be inspected by senior engineers after patrolling by junior
staff and maintenance works such as tree cutting and replacement of damaged insulators
shall be carried out immediately after patrolling, wherever required.
3.2.4 Patrolling would be ensured up to switch yard of generating stations/switch yards of
other transmission utilities wherever applicable. Necessary cooperation would be ensured
by respective utilities.
3.3 Patrolling Check list
Patrolling check list would cover at least the following points. However, the transmission
utility would add additional check points as per requirement.
A. Clearance of Trees, Shrubs etc:
•
Check adequacy of clearance of trees, shrubs, bushes, etc., from line conductor
•
Cut all trees, bushes, shrubs which infringe on clearance
•
Check grass growth on boundary wall of farms, which can grow to a height to infringe
clearance
B. Towers:
•
•
•
•
•
•
•
•
•
•
Check the back filling/soil removal of foundation of Tower.
Check the concrete of chimney for cracks.
For tower location, provided with revetment ensure that retaining wall is neither broken
nor in danger of falling.
Check earthing of tower.
Check all tower members are intact, in place and not damaged.
Check galvanizing / painting of tower members are in proper condition.
Check there is no corrosion of any part of tower/ hardware.
Check anti climbing devices and barbed wiring are fixed and are in place.
Check the number plate, danger board, phase plate and circuit plate.
Clear all bird nests on tower / cross arms.
C.
Insulator and Hardware:
•
Check flash over / chipped insulators.
•
Test insulators by Hot line method once in a year for healthiness of insulators.
•
Replace failed insulators.
•
Check arcing horns for loose connections.
•
Check vibration dampers
•
Check jumpers connections by thermo vision camera by hot line staff.
•
Check armour rods of suspension clamps.
•
Check jumper connections at tension point, suspension clamps.
•
Check earth bond provided on suspension and tension hardware of earth wire.
D. Conductor and Earth Wire
•
•
Check for visible damages like cut strands, deposits, burn marks.
Check midspan joint of conductor / ground wire damage of conductor and ground
wire strands.
3.4 Patrolling reporting/ record
Each transmission utility would furnish the annual schedule of patrolling to NRPC/NRLDC along with
annual outage data by October each year. Compliance report of the patrolling/maintenance carried
out during previous month with respect to schedule would be furnished to NRPC/NRLDC in the OCC
meeting
4. Maintenance
4.1 Each line would be maintained as per the following schedule.
Area
Frequency
Forest/ High growth
/Very heavy
polluted
Once every four (4) months. It would be
ensured in the months of May/June
before monsoon
Heavy / Medium
polluted
Once in every four (4) months. It would
be ensured in month of November just
before winter
Coastal
Once in every four (4) months. It would be
ensured in month of February just before
summer
Light polluted
Once in six months. It would be ensured
in month of November just before winter
Lines emanating
from Generating
Stations
Once in six months
Balance(not covered
above)
Once in a year
4.2
Maintenance and cleaning of various equipment fittings, accessories, primary
instruments and sensors shall be carried out when they are de-energized during the shutdown of main equipment so as to minimize shutdown time.
4.3
Where defects are observed through condition monitoring or during patrolling and
inspection, the maintenance work/attending works on various items of equipment may be
advanced depending on the condition of the equipment.
4.4
Pruning of tree branches and clearing of vegetation within the Right of Way and up
to 10m away from Right of Way and sectioning of vegetation around the tower footing shall
be carried out frequently in a continuous manner.
4.5
The maintenance responsibility would be clearly spelt out for the lines terminating at
switch yards of generating stations/other transmission utilities. Maintenance would be
ensured as per the above schedule.
4.6
Maintenance records:
The records of all maintenance carried out for each transmission line shall be kept in the
table formats in electronic form and hard copy and the next due date for maintenance of
each item of work shall be clearly marked in such tables and formats.
4.7
Duration of Outages:
All the planned maintenance would be completed within 8 hours in day. All the transmission
utilities would arrange for additional man power to meet the requirement. Only in extreme
contingency planned maintenance would be permitted for two days or more after the
approval from the OCC forum.
4.8
Maintenance of Tools and Equipment
The maintenance staff shall be made aware of the list of tools, devices and equipment for
various maintenance and rectification works on transmission lines and the tools shall be
made readily available and certified for usage.
4.9 Inventory control and spare part management-
The required spare parts shall be kept in stock, to ensure speedy the maintenance of the
equipment. Computerized materials management system shall be developed by the Entities
to optimize inventory.
4.10
Identified defects during patrolling would be closed by maintenance as per the line
schedule / requirement and it would be recorded. During next visit by senior staff/executive,
he would ensure all patrolling points have been cleared.
5. Maintenance/Patrolling Audit
a) An internal committee may be established by the Entities to verify whether actual
maintenance/patrolling works are carried out for the over head transmission line in
compliance of the RPC Guidelines and procedures/policy of the transmission company.
b) The observations of the Committee shall be put up to the management of the Entity for
perusal and taking corrective action, if any.
6. Disaster management.
a) The maintenance staff shall be trained in disaster management and a detailed procedure for the
same shall be developed by the Entity and displayed prominently
b) This detailed procedure shall be reviewed periodically and also based on mock exercises
carried out by the Entity.
c) The maintenance staff shall be trained in emergency restoration procedures for
managing major failures and breakdowns.
d) The equipment including vehicles, diesel generating sets and firefighting equipment and
Emergency Restoration System for transmission lines shall be kept available at sub-station
or at appropriate location for disaster management.
7. Failure analysis
a) All failures of equipment and tower collapse shall be analyzed by the Entity to avoid
recurrence and a copy of the report shall be submitted to the Regional Power Committee
(RPC) and Central Electricity Authority (CEA).
b) CEA may appoint a group of experts for investigation and analysis and the
representatives of manufacturers may be invited to participate in such analysis.
c) All relevant data which may help the group of experts in analyzing the failures shall be
furnished by the respective Entities.
d) The recommendations of the group of experts shall be submitted to the CEA and the
recommendations accepted by the CEA shall be implemented and circulated to all within
the organization and to other concerned organizations to prevent recurrence of similar
failures.
8. Training.
a) Every person involved in operation and maintenance of transmission lines shall be
trained at the induction level and at least once in a year.
b) The maintenance personnel of every entity shall be trained in preventive and breakdown
maintenance of various equipment and the personnel shall be trained in various detailed
maintenance procedures.
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