TRAINING SESSIONS ON
CONSTRUCTION, PLANNING &
DESIGN OF EHV
TRANSMISSION LINES
BY
S. M. TAKALKAR
PROPRIETOR
POWER CONSULTANTS & AGENCIES
A / 198 VISHVAMITRY TOWNSHIP, OPP: - GUJARAT TRACTORS, VADODARA - 390 011
Phone: 0265 - 2356291, Mobile: 9879599402/9925233951
Email: smtakalkar@yahoo.com
TATA POWER COMPANY LTD
KALIAN
TECHNICAL SESSION – I
Power Consultants & Agencies
Page 1
CONSTRUCTION OF EHV TRANSMISSION LINES
1.0 Introduction
1.1 Construction of EHV Transmission line is a very specific and specialized job. It involves lot of
precision and accuracy. The transmission line is standing for many years in the open terrain and
faces vagaries of nature. The construction practice should therefore ensure that the parameters, on
which the design of transmission line is made, are not exceeded.
1.2 The construction mainly includes the following activities.
• Survey & Alignment
• Foundation Work
• Erection of Super Structure
• Stringing of Shield wire & Conductor
• Testing & Commissioning
1.3 Each of above activity can be further divided into sub‐activities. All the erection activities are based
on the design inputs as well as site situation. For example, the type of tower and foundation to be
adopted will depend upon the profile & site situation, where as the span/deviation angle limitations
will be based on the design factors of the tower. This part deals with the general specifications for
construction of EHV lines.
2.0 Survey & Alignment
2.1 Whenever EHV transmission line is to be constructed between two subs‐stations, the ideal route
length will be the direct topographical distance between the two stations. However, this will not be
possible as number of obstructions in the form of villages, town important civil establishments, big
ponds, rivers etc. will prevent the straight run of the line. The obstruction will result into line
deviations. It will therefore be necessary to carry out survey by various means. The survey will establish
the following:
• The topography of the route of the line.
• The important deviation points of the line.
• The approximate quantity of Towers and extension.
• First hand information regarding the soil strata along the route, leading to approximate
estimation of foundation work quantities.
• The obstructions which may result into line deviations.
• Major River, Railway, Road and Power line crossings and type of structures for the same.
• Information regarding availability of inputs for foundation work (cement, aggregates steel and
water).
• Right of way problems which are likely along the route.
• Cost of transportation of material to various locations.
• Tentative time frame for completing the work.
2.2 It is also usual to make trial pits or carry out soil investigation along the proposed route of the
transmission line at certain fixed interval or at the points where abrupt change in soil strata is
suspected. This exercise results in to the approximate estimation of the foundation types and
Power Consultants & Agencies
Page 2
excavation/concrete volumes and the re‐enforcement for the foundation work. The various stages of
survey works are described in details as under.
2.3 Reconnaissance and Route Alignment Survey
2.3.1 A provisional route of transmission line is initially plotted on survey maps (topo sheets) and
a reconnaissance/ walkover survey is carried out. This is essential to fix up angle tower
positions tentatively, since many of the physical features on the ground may not be clearly
available in the survey map due to developments that might have taken place subsequent to
the preparation of the maps by department of survey of India. The topo sheets are obtained from
the office of The Survey of India Deharadoon by indicating the Longitude & the Lattitude of the
proposed route of the transmission line. In most of the cases more than one Topo sheets are required
to cover the route of the line.
SCHEMATIC ROUTE ALIGNMENT SURVEY
ROUTE MAP
82°10'
82°15'
82°20'
82°25'
82°30'
82°35'
T-05
400KV D/C KASAIPALLI TO BHARARI TRANSMISSION LINE
DILWADIH
BLOCK
L BE
T-05
COA
BAGDEWA
BLOCK
INDIA(N.T.S.)
AR
IN
G
T-05
CK
DAM
16/0
16/1
17/0
17/1
22/4
22/2
22/0
21/5 21/4
20/4
21/1 21/0
L 053
24/2
24/3
20/2
20/3
19/0
19/1
19/2
20/1
18/6
18/5
18/4
18/3
18/2
18/1
15/0
14/1
14/0
10/2
10/1
EX
11/1
IS
NG
TI
40
0
KV
TO
W
EX
IS
6/0
NE
LI
TI
NG
40
0
KV
C
D/
4A/0
3/0
2/3
PROP
OS
COAL
ED
EXTE
NS
AREA ION
31/0
32/0
30/5
30/6
30/3
30/4
33/0
22°20'
33/1
30/2
30/1
30/0
29/0
29/2 29/1
29/4 29/3
27/0
27/1
N
CO
AL
ZO
AR
33/3
PROPOSED
ROUTE OF
SION LINE
TRANSMIS
34/0
34/1
34/2
400kV
MEGHALAYA
PRADES
H
MANIPUR
AND
RKH WEST
JHA
BENGAL
MIZORAM
ORISSA
RA
SHT
ANDHRA
PRADESH
BAY OF BENGAL
SRI
LANKA
INDIAN OCEAN
START POINT
PROPOSED 400 kV
SWITCH YARD
20/0
DESCRIPTION
AL
AR
BE
ING
AR
EA
SYMBOL
Proposed route with AP
SITE FOR DIPKA COLONY
Pond
Forest
Cart-track
Development
Railways broad gauge
Temple, Mosque
Railways other gauge
Hutment
GEVRA
EAST OF
KARTALI
NARAIBODH
SYMBOL
Tree
Wells lined, unlined
Contours with heights
PROPOSED 2x50 MW RATIJA
132 kV POWER STATION
SWITCH YARD
DESCRIPTION
River
Roads metalled/Asphalted road
Roads unmetalled
Stream
EA
KARTALI
BLOCK
TREE
PLANT
33/2
ARA
Canal
NE
27/2
28/0
28/1
28/2
28/3
28/4
MAH
BANKI
BLOCK
12/0
13/0
18/0
CO
NO
SINGHALI
BLOCK
2/1
2/0
BHUTAN
BANGLADESH
LEGEND :-
25/1
26/0
2/2
1/0
GANTRY
25/2
25/3
SARAIPALI
BLOCK
COAL BEARIN
G AREA
MADHYA
6A/0
5/0
NE 4/0
LI
CH
HA
TIS
GAR
H
7/1 7/0
GUJARAT
ER
22°20'
25/0
PROPOSED COAL
EXTENSION AREA
21/3 21/2
ck
22/1
ROAD
22/3
24/0
24/1
Car
t Tra
23/0
23/1
23/2
23/3
23/4
23/5
DUMARKACHHAR
BLOCK
11/0
ADU
7/2
8/1 8/0
9/1
9/2
10/0
10/3
AR
EA
LA
KERA
IN
G
CAR
T TRA
AR
AKA
NAT
KAR
CHAPI WATER SCHEME
BE
SEA
IAN
ARAB
CO
AL
Lahrapara
HAL
NACSH
ARUADE
PR
ASSAM NAGALAND
L
BIHAR
ILN
8/2
9/0
METAL ROAD
Batra
UTTAR
PRADESH
RAJASTHAN
CKBD 2 x 30 MW
EXISTING POWER PLANT
TAM
RC
C
CAR
T TRA
CK
CART TRACK
T-05
22°25'
22°25'
T-05
C
EA
AR
RC
NEPA
DAM
Dhadhipara
Nagrahi
N
N
JAMMU &
KASHMIR
HIM
PR AC
AD HA
ES L
H
PUNJAB A UTTARANCHAL
AN
RY
HA DELHI
l Road
Meta
200
Borewells
Power/Telephone line
Reserved/Protected forest
Scrub
Heights triangulated
R.F. / PF
200
Boundary state
Heights point
Boundary district
Bench-mark
Boundary tahsil
Post office
PO
Towns or Villages
Police station
PS
Industries
Coal Bearing Area
200
Coal Zone Alotment Area
AREA BETWEEN
KARTALI & DIPKA
PONRI
DIPKA
NUNBERA
34/3
RATIJA
34/4
COA
L BEA
RING
34/5
34/6
BHILAI
AREA
34/7
34/8
35/0
35/1
COAL BEARIN
G AREA
36/0
36/1
TOTAL LENGTH STATEMENT
36/2
37/0
Sr.
No.
DESCRIPTION
1
PROPOSED 400kV D/C TRANSMISSION LINE
FROM KASAIPALI TO BHARARI
37/1
37/2
ROUTE
Length
(Km.)
54.867
37/3
40/0
40/1
40/2
39/4 39/3 39/2
39/1 39/0
38/3
38/2
38/1
38/0
40/3
40/4
40/5
40/6
22°15'
40/7
40/8
22°15'
40/9
40/10
40/11
NO
DATE
REVISIONS
BY
CHKD
APPD PROJ.ENGR
42/0
42/1
42/2
44/2
44/1
44/0
43/3
43/2
43/1
41/3 41/2 41/1 41/0
43/0
Project:
46/0
45/2 45/1 45/0
Title:
RECONNAISSANCE SURVEY OF 400 kV D/C
END POINT
PROPOSED BHARARI
SUB POOLING STATION
SURVEYED & PREPARED BY-
POWER CONSULTANTS & AGENCIES, VADODARA
198, VISHWAMITRI TOWN SHIP, OPP. GUJARAT TRACTORS, VADODARA-390 011
www.powerconsultant.info
82°10'
82°15'
82°20'
82°25'
82°30'
SCALE
DRAWING NO.
REV.
1 : 50000
PCA/AC/KBPL/400kV/RECCAY/RM-01
0E
82°35'
2.3.2 The reconnaissance survey helps in collecting the first hand information regarding various
important field data required for transmission line works. The reconnaissance survey is carried out
Power Consultants & Agencies
Page 3
by using GPS (Geographical Positioning System). The general points to be kept in view while
establishing the preliminary route at the time of reconnaissance survey are as under.
a) The route should be as short and as straight as possible.
b) Where ever possible, attempt should be made to lay the line near to or along roadway.
Alternatively, the line should be approachable to the extent possible.
c) The number of angle towers should minimum and within these, the number of heavier angle towers
shall be as less as possible.
d) Cost of securing and clearing right of way (ROW), making access roads and time required for these
works should be minimum.
e) Corridor through which line is taken, should be free from Encumbrances such as non‐Agricultural
land, notified area, Defense establishment, oil & gas establishment, acquired mining areas etc.
f) Care is also required to be taken that the line route avoids any big planned development in the
region such as, Airport, State Industrial Estate, Mega Power Projects etc. If this is not done, shifting of
the line may be required later or objection to the construction may occur.
g) Crossing with permanent objects, such as Railway lines and roads should be made preferably at right
angles.
h) In case of hilly terrain, it is necessary to conduct detailed survey and locate the tower positions
suitable to the topography. Detailed survey is recommended for such terrain.
i) The reconnaissance survey will also establish if we can avoid the following:
• Marshy areas, low lying lands, river beds, earth slip zones etc. involving risk to stability of
foundation & the tower.
• Areas subjected to floods, gushing – culverts during rainy seasons, tanks, ponds, lakes, snow
blizzards.
• Inaccessible areas where approach roads are not possible.
• Areas which will create problems of right of way and way leave.
• Route involving abrupt changes in levels, too many long spans, river or power line crossings or
near parallelism to telecommunication lines.
• Thick forest or areas involving heavy compensatory payments for the ROW.
j) The reconnaissance survey is useful for collecting the first hand information about various important
field data required for transmission line construction, which are as under:
• Major power line crossing details (66 KV and above)
• Railway crossing details.
• Major river crossing details.
• Source of construction materials, viz., metal, sand water etc. along the line.
• Important rail heads for the purpose of receipt of materials.
• Important villages or Railway stations along the route for the purpose of selection of labor
camps.
• Nature of soil strata likely to be encountered along the route and the terrain.
• Availability of skilled, semiskilled and un‐skilled labor, their present rate on daily basis or on
contract basis.
• Names of the major towns for the purpose of selection of site offices.
• Likely local support or hindrance from various section of population along the route of the line.
Power Consultants & Agencies
Page 4
For fixing the final alignment and angle points on the ground as per the reconnaissance survey, route
alignment survey shall be carried out with the help of Theodolite and/or Total Station; survey
chains/measuring tapes etc.
2.4 Detailed Survey
2.4.1 The main objective of carrying out detailed survey is to prepare longitudinal and cross section
profiles on the approved route alignment and to prepare the route plan showing details of deviation
angles, important objects coming within the right of way and show the landmark points/objects along
the route with their distance from the alignment of line. Work of detailed survey is normally done in
two stages:
1. By actual field observation taking level readings and calculating distances, level differences,
deflection angles, offset distances etc.
2. By plotting of profiles on graphed tracing papers of mm x mm size.
2.4.2 The use of Total Station facilitates quick measurement of distance, ground levels and the angles
between the two reference points. The Total Station is located at fixed point and there after the prism
mounted in a stand is moved along the route of the line, preferably at an interval of 20 metres. Each
reading gives the distance and level difference. These readings are stored in the memory of Total
Station (TS). The data is there after transferred to the computer.
2.4.3 Field Observation Recording and Calculations
2.4.3.1 The method of taking level readings for preparation of longitudinal and cross section profile can
be one of the following
• By chain and dumpy level
• By tachometric survey with Theodolite
• By using Total Station and the prism
First method is more useful in plain areas where chaining can be done easily with the help of
semiskilled surveyors. Tachometric method offers a great advantage in hilly regions and such other
inaccessible places where chaining is not possible. This method needs skilled surveyors having good
understanding of the use of Theodolite and basic knowledge of trigonometry. In this method, both
traversing and leveling is done by means of a tachometric Theodolite. The horizontal and vertical
distances are computed with the help of readings of the stadia wires taken on the staff held at the
reading point. The accuracy of the work will depend upon the quality and cost of the equipment.
The range of operation of Theodolite is much higher than the dumpy level. The surveyor and his team
will move on an approved route and take ground levels in the field book at an interval of 20 to 30
meters.
2.4.3.2 As stated in 2.4.2 above, the Total Station is the most modern equipment for surveying. It saves
lot of time and the observations are highly accurate. This equipment is very expensive and needs lot of
precautions in handling. If the length of line is very short, Theodolite can also serve the purpose.
2.5 Plotting of Profiles
2.5.1 From the field book entries route plan and longitudinal profile, commonly referred to as “route
profile” or “survey chart” is prepared in the drawing office. These charts are prepared and plotted on
1mm/5mm/1cm square paper of formed drawing sheets of graphed tracing paper. The scale normally
preferred is 1:200mm‐vertical; 1:2000mm‐horizontal.
2.5.2 The profile shall include the following:
Power Consultants & Agencies
Page 5
•
The longitudinal profiles along the centre‐line of the transmission line route including the
bottom conductor catenaries.
• The cross‐section profile wherever appreciable difference in level exists, with references to
centre‐line level. In such cases the cross‐section levels shall be taken at each 50/100m
intervals.
• Route plan giving details of all objects lying within the right of way and just along the boundary
of right of way.
• Angle of line deviation duly marked left (L) or right (R) as the case may be.
• Objects and their distances along the route within the right of way from centre line, nearby
villages, important pucca roads & or rivers/canals, cart tracks etc. should be marked on the
route profile.
• Crossing details with any other power or telecommunication lines, roads, railway lines, canals
or rivers should be marked as clearly as possible.
• Readings should be taken and charts should show, levels of roads, canal embankments,
maximum water/flood levels, railway rail top levels, heights of supports/lines being crossed, all
trees coming within the clearance zone.
• It is advisable to prepare an independent route profile for Major River crossing section
deploying tall special towers or normal towers on piles in the river crossing section, as the river
crossing is a special task in the construction process which involves special design.
2.6 Tower Spotting
2.6.1 The work of tower spotting is a very precise job as it has an implication on overall cost.
After the tower designs are finalized, the tower spotting chart or structure limitation charts are
prepared. Similarly the drawing of the sag template and its replica is prepared on Acrylic sheet.
Application of Sag Template helps to decide optimum tower position on Survey Chart., which
ultimately helps in finalizing the quantity of each type of tower and their extensions (3 meter & 6
meter etc).
2.7 Preparation of Sag Template
2.7.1 Sag template is a very important tool for the surveyor by the help of which Tower spotting can be
done. Depending upon the maximum specified permissible temperature of the conductor and zero
wind condition the ground clearance is to be maintained by the line. Similarly under the specified
minimum temperature of the conductor surface, with zero wind condition, the tower tensions should
be within the specified limits. The sag template curves are first prepared on tracing paper and the blue
print is taken out from the tracing. Their replicas on Acrylic sheets are prepared with the itching
process. The Acrylic sheets are normally 2.5 to 3 mm thick.
2.7.2 The sag templates have the following curves itched on them.
• ‘Cold or Uplift Curve’‐Showing sag of conductor at specified minimum temperature and zero
wind.
• ‘Hot’ or ‘Maximum Sag Curve’ showing maximum sag of conductor under zero wind and
maximum temperature and sag tolerances are also allowed to take care of stringing error,
conductor creep or snow incidences.
• Ground clearance Curve‐Drawn parallel to hot curve and at a distance equal to specified
minimum ground clearance.
Power Consultants & Agencies
Page 6
•
Tower footing Curve‐For normal tower drawn parallel to hot curve under ground clearance
curve and separated by a distance equal to maximum sag at design span.
2.7.3 In erecting an overhead line all the spans cannot be kept equal to normal design span because of
the profile of the ground and proper ground and object clearance considerations. A constant tension is
calculated which will be uniform throughout the Section (from one tension tower to other tension
tower), however the sags in individual spans will vary according to their respective spans. The ‘Cold
and Hot’ Template Curves are plotted as parabola, to the same scale as the survey chart for the
minimum and maximum sags for the normal span (specified in the tender specifications).
2.8 Application of Sag Template for Tower Spotting
2.8.1 The Sag Template is an important tool for correct spotting of the towers after the detailed survey
work is completed. The following are the steps to be followed for correct application of sag template.
• The acrylic sag template is applied to the ground profile by moving the same
horizontally while always ensuring that the vertical axis is held vertical with reference to
graphed lines of the tracing paper below.
• The structure positions are marked where the tower footing curve just touches the
profile, while the ground clearance curve is just clear and above the profile to the left or
right of the centre line up to a distance equal to maximum cross area spread on either
side.
• Besides normal ground clearance, the clearances between power conductor and
objects like, other power or telecommunication lines, houses, trolley wires, roads,
railway tracks, canal embankments etc., shall be checked.
• Extra clearance can be obtained either by reducing the span or providing extension to
tower body, depending on which alternative is most economical.
• The weight span on either side of a tower can be easily obtained by marking the low
points of sags (Null Point) in two adjacent spans and then reading the distance between
the two.
• On inclined spans, null point may be outside the span.
Power Consultants & Agencies
Page 7
•
This indicates that the total weight of conductor is taken up by the higher tower and the
lower tower is being pulled up by a force equal to the weight of conductor between
lower support and the null point.
• Should the upward pull of the uphill span becomes greater than downward load of the
next adjacent span, actual uplift will be caused and the conductor would tend to wing
clear of the tower upwards.
• For any easy check of whether a tower is under uplift or not, the following method may
be adopted.
• The Template is applied horizontally until the tops of alternate supports coincide with
the Cold Curve.
• If the support is under uplift and has to be extended so as to be above it and in case
requisite standard body extension do not suffice for doing this, tower which is designed
to take uplift will have to be used.
• However, for the stability of the line it is not desirable to place a tower in such a
position where it is always under permanent uplift condition.
• In case it becomes mandatory due to route compulsion, the cross‐arms of the tower
subjected to up lift shall be designed to take the extra upward pull.
• The intermediate spans shall be as near as possible to the normal design span.
• In case an individual span becomes too short on account of undulations in ground
profiles, one or more line supports of the Section may be extended by inserting
standard body extensions.
• Even if the line does not deviate for a long run, sections have to be provided after every
12 to 15 tangent towers. (i.e. 3 to 4 km. length).
• For this purpose a small angle tension tower designed for 15° should only be used.
• This is mandatory to afford better stability of the line against Transverse wind forces
and to facilitate easy stringing.
• Besides 15° angle tension tower is most economical amongst the standard angle tension
towers.
2.9 Use of computer for preparing sag template and the tower spotting
2.9.1 Before taking up the tower design on hand, Sag and Tension charts are required to be prepared.
These charts indicate the values of sag and tension of conductor and the earth wire at Maximum
temperature, minimum temperature and every‐day temperature under 100%,36%(66%) and 0% wind
pressure. Normally, in plain terrain in India the maximum, minimum and every‐day temperatures are
considered as 0 Deg.C 75 Deg. C and 32Deg. C. These values may change in the region experiencing
snow or Sub‐Zero temperatures. If the conductor is required to carry large block of power, the
maximum surface temperature of conductor can be taken up to 95Deg. C. For Earth wires the
maximum temperature is taken as 53Deg. C
2.9.2 Based on the sag tension charts, the sag template curves can be plotted on the computer through
a specific programme. The full scale print out of the curves is then used to prepare the Acrylic Sag
Template by itching process.
2.10 Towers Spotting Data
2.10.1 Since each tower is designed to withstand a definite load only, in each of transverse, vertical
and longitudinal directions, the surveyor must know these limitations for the various types of towers
Power Consultants & Agencies
Page 8
available for use on line so than he can spot an appropriate type of tower structures along the route.
These limits are given in a chart form called ‘Structure Limitation Chart or “Tower Spotting Data” which
is prepared by the design department of the utility /contractor. These charts define the limits for
permissible ruling span, weight span, wind span, individual span and the degree of the deviation
allowed on each of the standard towers. These charts are made for normal towers only.
For all special crossings individual tower checking is essential by the design department. These charts
also indicate the additional angle of deviation which can be allowed in the tower by limiting the spans,
so that the design load limits of the tower are not exceeded.
TOWER SPOTTING
Loc. No- 156
45/0
DB+3
Weight Span (Cold)
L
R
213.66 T 198.16
411.82
Weight Span (Hot)
L
R
212.06 T 201.3
413.36
Wind Span
L
R
211 T 211
422
+9M
Loc. No- 159
46/0
DD+0
Weight Span (Cold)
L
R
202.99 T 000.00
202.99
Weight Span (Hot)
L
R
207.72 T 000.00
207.72
Wind Span
L
R
211 T 000.00
211
Loc. No- 158
45/2
DA+3
Weight Span (Cold)
L
R
204.4 T 219.01
423.41
Weight Span (Hot)
L
R
205.2 T 214.28
419.48
Wind Span
L
R
205.83 T 211
416.83
Loc. No- 157
45/1
DA+6
Weight Span (Cold)
L
R
223.84 T 207.26
431.1
Weight Span (Hot)
L
R
220.7 T 206.46
427.16
Wind Span
L
R
211 T 205.83
416.83
+9M
+9M
+6M
+9M
+6M
+6M
+3M
+3M
+6M
Conductor stringing
point at 22.21 Mtr.
+3M
Conductor stringing
point at 22.21 Mtr.
+3M
Conductor stringing
point at 22.21 Mtr.
Conductor stringing
point at 22.21 Mtr.
422
411.66
422
Cold Curve 0° C
Ground Clearance
at 13.26 Mtr.
Cold Curve 0° C
Cold Curve 0° C
Ground Clearance
at 13.26 Mtr.
Hot Curve 85° C
Ground Clearance
at 13.26 Mtr.
Ground Clearance
at 13.26 Mtr.
Hot Curve 85° C
Hot Curve 85° C
Ground Clearance Curve
Ground Clearance Curve
AP48 - CH:53612.02m
AP49 - CH:54867.67m
Ground Clearance Curve
DATUM 262.0m
CUMULATIVE
CHAINAGES(M)
REDUCED
LEVELS(M)
PROPOSED SUB STATION
CROSSING
& INTERFERENCE
AP-45(14°48'23")R
AP-46(75°43'41")L
DETAILS
CONSULTANT: -
POWER CONSULTANTS & AGENCIES
A / 198 VISHVAMITRY TOWNSHIP, OPP. GUJARAT TRACTORS,
VADODARA - 390 011 Ph.(0265) 2343001 Fax.(0265) 2356291
E-mail: smtakalkar@powerconsultant.info ,
smtakalkarpca@gmail.com
Web: www.powerconsultant.info
Power Consultants & Agencies
Project:
CLIENT -
Title:
TOWER SPOTTING & SAG CURVE OF 400kV D/C TRANSMISSION
LINE
SCALE
H:-1 : 2000
V:-1 : 200
DRAWING NO.
REV.
0A
Page 9
2.11 Preparation of Tower Schedule
2.11.1 In order to decide the tower type for a particular location, following information is required
from the design department:
• Angle of line deviation on tower
• Whether it is to be used as section tower or dead end tower
• Sum of adjacent spans
• Weight span on tower
• Whether an immediate lower size of tower can be used in place of the actual angle tower by
limiting the span.
• Whether a river can be crossed using normal tower with/without extensions or by providing
special tower or by locating towers in mid stream by providing the pile foundations.
• Whether a hill side extension will be required.
2.12 Check Survey
2.12.1 Check survey is carried out for the following.
•
To reconfirm the work carried out during detailed survey.
•
To locate and peg mark the tower position on ground, corresponding to the route profiles.
•
To give direction pegs.
2.13 Checking and Line Alignment
2.13.1 In this operation, traversing is done from the known fixed angle point (the starting point or any
other obligatory point fixed by the purchaser) in the direction of given line deviation and up to a
distance equal to the section length between the starting point and the next angle point. If next angle
point is firmly marked in field by means of a permanent peg mark (concrete burjee) then the closing
error is noted both in longitudinal and transverse directions. If the error is within 1% of the total
section length it can be ignored and the permanent mark made during detailed survey is taken as
correct and necessary correction in the line deviation angle at the starting point is made and noted in
the survey chart.
2.13.2 If the second angle point reached is not marked in field by the detailed survey gang (or the mark
is missing), the angle point is tentatively fixed at the place reached as per deviation angle at starting
point and first sectional length and line alignment is carried to the next deviation angle and next
section length as per survey chart. This process is continued till an angle point is reached which is fixed
in field either by a permanent burjee (pillar) or by means of identification marks given in survey charts.
Intermediate checks can also be made by measuring offsets from the line to well defined objects are
shown in survey charts very accurately (but much reliance cannot be given for correct alignment based
on offset distance).
2.13.3 These objects only guide the surveyor in moving as closely on the correct alignment as possible.
If the time span between the detailed survey and the check survey is too long, care is required to keep
the proper track of the original profile bench mark and offset distances. Once the known angle point is
reached, then closing error is judiciously distributed in all the previous temporary sections and all angle
points are finally marked on ground by means of concrete pillars. Once the angle points are marked,
correct angle of deviation and section length are measured and noted on survey charts.
2.14 Spotting and Peg Marking of Tower Locations
2.14.1 Once each angle is fixed in field by the help of permanent concrete burjees and exact section
length is known, the surveyor proceeds to mark all intermediate tower positions on the straight line
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joining the two angle points spaced at distance equal to individual span length as given on survey chart
and after the same is duly adjusted for the closing error.
• In order to achieve correct alignment of all the intermediate towers between two angle points,
a number of alignment pegs are driven at the time of exact distance measurement of the
section.
• The more the number of alignment pegs the better it will be for the readings; as instrument
errors are less if similar distances are measured in one reading.
• These pegs are also very useful when main tower marking burjees are found missing at a later
date (due to mischief of local people or negligence of excavation marking gang or any other
reason).
3.0 Foundation Work
3.1 After the survey work is over, the activity of foundation is taken on hand. The foundation work
mainly includes Pit marking, Excavation, Stub setting, Concreting, Back filling and Curing. They are
described in brief as under.
3.2 Directional Peg Marking for Excavation Pit Marking
3.2.1 Before the activity of excavation is taken up, it essential to accurately mark the centre point of
the tower, centre point of each leg of the tower and the periphery of pit to be excavated for each leg
foundation. This is described in brief as under.
• Directional pegs are essential for correct alignment of tower centre line along longitudinal and
transverse directions.
• On suspension tower, pegs are set along the centre line of route alignment and perpendicular
to it.
• On angle towers these are rotated by an angle equal to half the angle of line deviation and then
the perpendiculars are marked.
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3.3 Preparation/Study of Excavation Plan Suitable For the Proposed Type of Foundation
3.3.1 Trial Pit
At the location of the tower, a trial pit shall be made within the base of the proposed tower width. This
shall be generally 1 x 1 x 3 m size.
3.3.2 Examination of trial pit
The soil strata will be examined by EIC or an expert nominated by him who has expertise in the matter
of soil classification. The detailed examination report of the trial pit will be made then.
3.3.3 Decision for type of foundation
The EIC or the authorized engineer of the purchaser and the engineer of the contractor shall then
decide upon the type of foundation to be adopted for that particular location. Normally, the design
department/ contractor is equipped with the set of foundation design and the excavation plan for
standard type of soils / rocks and their combinations, including sub‐ soil water bound strata. Any one of
the readily available foundation design for the particular type of tower which fits in to the classification
of soil/rock should be adopted. If the strata are too strange, special type of foundation has to be
adopted with the approval of Design department of the purchaser. There are many types of tower
foundation which are in vogue these days. They also relate to various types of soil classification such as
normal soil, clayey soil, hard rock, soft rock, deformated soil, etc. The pile type & well type foundations
are generally used in river crossing and crossing sections of the line. Plate type and grill type
foundations are not being used these days as their reliability is low. The type foundations can be used
for smaller towers.
3.4 Excavation
3.4.1 Pit marketing shall be carried out according to pit marking chart. The pit size in the case of open
cast foundations shall be determined after allowing a margin of 150mm round. No margin is necessary
in the case of undercut foundations. The depth of the excavation at the pit enter shall be measured
with reference to the tower center level. The design office will furnish the survey gang with an
‘Excavation pit Marking Chart’ or ‘Excavation Plan’ which gives distance of pit centers, sides and
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corners with reference to center point of the tower. These distances are measured and each pit
boundary is marked in the field by means of chalk spade or pick axe along the side of the pits. While
excavating, care should be taken that earth is cut vertically/tapered/in steps as per the site
requirement to avoid any mishap during the course of excavation and foundation work.
3.4.2 Actual excavation
Before commencement of the excavation work, corrected and applicable excavation plan in
accordance with the soil/rock classification should be obtained by the construction crew members. The
excavation wall shall be vertical and the pit dimensions shall be strictly as per the excavation plan and
foundation drawing. All excavation shall be protected so as to maintain a clean surface, until the
footing is placed. In case of collapsible soil, precaution should be taken by providing shuttering and
supports for the safety of the crew members.
Various types of foundations used for tower are shown here under.
TYPES & SHAPES OF FOUNDATION
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3.5 Classification of Soil
3.5.1 Normal Soil:
Soil which can be removed by an ordinary pick axe, spade and shovel easily.
3.5.2 Wet Soil (Submerged Soil):
Where the subsoil water table is encountered within the range of foundation depth or/and where
pumping or bailing out of water is required due to presence of surface water will be treated as wet
soil/submerged soil.
3.5.3 Rocky Soil (Strata):
3.5.3.1 Fissured Rock/Soft Rock
Lime stone, laterite, hard conglomerate or other soft or fissured rock which can be quarried or split
with crow bars wedges or pickaxes will be classified as fissured rock/soft rock. However, if required,
light blasting may be resorted to for loosening the material and hasten the excavation activity.
However, this will not in any way entitle the material to be classified as hard rock.
3.5.3.2 Hard Rock
Any rock excavation other than specified under fissured rock/soft rock above, for which blasting,
drilling, chiseling are required.
Where the soil is of composite nature, classification of foundation will be according to the type of soil
which is predominant in the footing. The decision of the Engineer‐in‐charge shall be final and binding
with reference to classification of soil and foundation to be adopted at that particular location.
The adoption of footing depends upon the type of Soil and the tower loadings. The foundation to be
adopted therefore depends upon the type of soil, quantum of tower loading and preference for
structural arrangements of footing.
3.6 Hard Rock Excavation
Where rock is encountered, the holes for tower footings shall preferably be drilled, but where blasting
is to be resorted to as an economy measure, it shall be done with the utmost care to minimize the use
of concrete for filling up the blasted area. All necessary precautions for handling and use of blasting
materials shall be taken. If inadvertently large quantities are excavated / blasted, the full volume
excavated/blasted shall be filled with the structural concrete. If this is not adhered to, there are
chances of reduction of reliability of foundation against upward loads. In case where drilling is done,
the stubs may be shortened suitably with the approval of the owner or his authorized representatives.
The excavation shall be carried out strictly as per the excavation plan approved by the owner/customer
for the particular type of structure with/without extension and the particular type of Soil Rock.
However, while re‐working, the C/C distance between the two pits will be with reference to the
junction of reduced chimney and footing.
3.7 Blasting Material
The Contractor shall procure requisite blasting material and be responsible for the purpose of the
storage and use of this material. Necessary permission/approvals from the concerned Government
department may be obtained by the contractor.
3.8 Shoring and Shuttering
If pits excavated in sandy soil or water bearing strata and particularly black cotton soil where there is
every likelihood of pit collapse, shoring and shuttering, made out of timber planks of 30‐35mm
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thickness or steel frames of adequate strength to suit the requirement, will be provided. Sand
bedding/stone bedding will be provided in foundation of marshy and wet black cotton foundations
which will work as a sub‐grade.
3.9 Dewatering
Dewatering shall be carried out manually or by mechanical means or power driven pumps to facilitate
excavation and casting of foundation. The pumps shall be suitable for handling muddy water.
Dewatering is not necessary in case of bored foundations extending below water table. The size of the
mechanical/electrical pump will depend upon the quantum of water required to be handled per hour.
In areas where sub‐soil water recoupment is heavy and where water cannot be controlled even by use
of power driven pumps, well point system is used for controlling water. In this system a grid of pipes
are laid around the area where the pits are excavated and the system is very effective in pumping
water particularly in sandy soils. After commencing pumping operation the pit can be excavated
avoiding risk of collapse of earth.
3.10 Setting of Stubs
The stubs shall be set correctly in accordance with approved method at the exact location and
alignment and precisely at correct levels with the help of stub setting templates and leveling
instrument. Stubs shall be set in the Presence of Owner’s representative available at site where
required. The stubs are set in such a manner that the distance between the Stubs, the alignment and
slope are as per the approved misfit and design so as to permit assembling of the superstructure
without undue pre‐stress, strain or distortion in any part of the structure. There are three methods by
which this is generally accomplished:
• Use of combined Stub‐setting Template for all the four stubs of the tower including extension
portions.
• Use of individual Leg Template for each stub.
• Use as a Template the lowermost tower section or extension, where Stub‐setting Template is
not available.
The first method is the most commonly used.
• The Stub‐setting Template comprises a light rigid square framework which holds the four stubs
at the correct alignment and slope in four corners.
• The Stub‐setting Template generally of adjustable type which can suit the standard tower as
well as towers with standard extensions of 3 meter & 6 meter height.
• The Template is centered and leveled by sighting through transit.
• The anchors or stubs are bolted to this Template one at each corner of the Template, and are
held in their proper position until the concrete is poured and gets hardened.
The second method is adopted for casting the foundation locations having individual leg extensions or
locations having broad base of Tower.
• In such case, it is not possible to use the four legged stub setting template for various reasons
related to design and construction.
• The answer to this problem is individual leg stub‐setting template.
• The individual Leg Template comprises a steel channel or joist having a length more than the
size of the pit, by about 2 to 3 meters.
• A chamfered cleat is welded in centre of the channel/joist to provide the slope to the stub.
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•
The stub is bolted to the cleat of the Template with holes as required for the slop of the stub is
provided.
• The individual Leg Templates are initially set on each pit approximately to the required position
with reference to the centre point of the tower and with the help of a Theodolite (or Total
Station), Dumpy level and a measuring tape, before fixing form boxes and pouring concrete.
• The other version of individual leg extension is cut corner sections of conventional stub‐setting
template.
• This is easy to fabricate and deploy at site.
• This type of Template are very useful for casting the foundations of individual leg extensions in
which the foundation pits are staggered and use of either a normal Stub‐setting Template or
the first section of the tower is not feasible.
In the third method, lower section of the tower or extension is used for setting stub.
• In this method two opposite sides of the lower section of the tower are assembled horizontally
on the ground, and the stubs are bolted to the same with correct slope and alignment.
• Each assembled side is then lifted clear of the ground with a gin pole and is lowered into the
four pits excavated at four corners of the tower to their proper size and depth.
• The assembly is lifted in such a manner that stubs are not damaged.
• One side is held in place with props while the other side is being erected.
• The two opposite sides are then laced together with cross members and diagonals.
• Then the assembled section is lined up, made square with line and level after the proper
elevation and leveling have been done, the bolts are tightened to make the frame as rigid as is
reasonably possible.
• Thereafter the form boxes for foundations are built and the concrete is poured.
• For heavy towers use of this method is not recommended.
• For heavy towers use of Stub‐setting Template is recommended, as propping, jacking, leveling
etc. will be very difficult.
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3.11 Mixing, Placing and Compacting Of Concrete
It is normal practice to use coarse and fine aggregates available along the line route and/of nearest
locations to the route so as to have economy and better progress. Ordinary plain or reinforced cement
concrete given in IS: 456‐1978 shall be used in overhead line foundations. For main foundation, M15 or
1:2:4 mix cement concrete shall be used. For lean concrete, sub basis or pads, M 10 or 1:3:6 mix
cement concrete may be used. The properties of concrete and mix proportions shall be as given in IS:
456‐1978. It shall be permissible to proportionate the concrete as follows.
Prepare a wooden measuring box of 35 lit capacity (i.e. equal to 1 bag of 50 kg of cement)
with
inside dimensions of 30 cm. x 30cm x 39cm alternatively a cylinder of 34 cm diameter and 39 cm
height shall be made ready for the proportioning.
•
The mix quantities according to the measuring box shall be as follows
M20 (1:1.5:3)
M15 (1:2:4 mix)
M10 (1:3:6 mix)
• Cement
1.0
1 Bag
1 Bag
• Sand
1.5
2 Boxes
3 Boxes
• Metal
3.0
4 Boxes
6 Boxes
The required quantity of water shall be used for concrete mix. The water should be free from oil/acid
and any other impurities. Saline water or sea water should not be used for the concrete work. The
concrete shall be mixed in the mechanical mixer only. However, in case of difficult terrain hand mixing
may be permitted at the discretion of Engineer In charge. Mixing shall be continued until there is
uniform distribution of material and the mix is uniform in color and consistency, but in no case the
mixing be done for less than two minutes.
Normally mixing shall be done close to the foundation, but in case it is not possible, the concrete may
be mixed at the nearest convenient place. The concrete shall be transported from the place of mixing
to the place of final deposit as rapidly as practicable by methods which shall prevent the segregation or
loss of any ingredient or setting. The concrete shall be placed and compacted before setting
commences. Mechanical/pneumatic vibrator shall be used for obtaining homogenous concrete work
and for better finish as well as avoiding honey combing.
3.12 Specification For From Box
3.12.1 The general requirements of form box are as under:
• The form work shall conform to the shape, lines and dimensions as shown on the approval
foundation design drawings, and be as constructed as to the rigid during the lacing and
compacting of concrete, and shall be sufficiently tight to prevent loss of liquid from concrete.
• It shall be of right design, easily removable without distortions and shall be of steel or suitable
materials.
• The inner surface coming in contact with concrete shall be smooth and free from projections.
• Window on one face shall be provided for pyramid forms to facilitate concreting in the lower
parts which shall be fixed after concrete in the bottom part is placed.
• The form work for slabs and pyramids shall be made symmetrical about the base of the
chimney to ensure interchangeable faces.
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3.12.2 Clearing and Treatment of Forms
• All rubbish, particularly chippings, sawdust and traces of residual concrete, if any,shall be
removed from the interior of the forms before the concrete is placed.
• The surface in contact with the concrete shall be wetted and spread with the fine sand or
treated with an approved compositions such as black or waste oil etc., before use, every time.
• The concrete shall be poured in 150mm layers and consolidated well, so that the cement cream
works up to the top and no honey‐combing is left in the concrete.
• The mechanical vibrator shall be employed for compaction of the concrete.
• However, in case of difficult terrain, manual compaction may be permitted at the discretion of
site Engineer.
• After concreting the chimney portion to the required height, the top surface should be finished
smooth with a slight slope towards the outer edge, to drain off any rain water falling on the
coping.
3.12.3 Wet Location
• In wet locations, the site must be kept completely dewatered, both during the placing of the
concrete and for 24 hours thereafter.
• There should be no disturbance to concrete by water during this period.
3.12.4 Removal of From Box
After the form work has been removed, if the concrete surface is found to be defective, the damage
shall be repaired with rich cement and sand mortar to the satisfaction of the Owner’s representatives,
before the foundation pits are backfilled.
3.13 Back Filling and Removal of Stub Template
3.13.1 Process of bake filling
The back filling work is very important for the stability of the foundation. Following is recommended.
• Backfilling shall normally be done with the excavated soil, if the excavated material includes
large boulders/stones, the boulders shall be broken to a maximum size of 80mm.
• At such locations where borrowed earth is required for backfilling, this shall be done by the
Contractor as per the rates, terms and conditions laid down in the contract.
• If the foundation cast is rocky type, backfilling with the borrowed earth may not serve the
purpose.
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•
In such a case backfilling with chipped stones mixed with the cement slurry would be a better
option.
• However, this would be done as per the instructions of the engineers in change.
3.13.2 Material for bake filling
The following is required to be noted for the back filling material.
• The backfilling materials should be clean and free from organic or other foreign materials.
• The earth shall be deposited in maximum 200mm layers, leveled and wetted and tampered
properly before another layer is deposited.
• Care shall be taken that the backfilling is started from the foundation ends of the pits, towards
the outer ends.
• After the pits have been backfilled to full depth, the stub template may be removed.
• In case of urgency, the template can be removed even after 50% of backfilling of the soil.
• The backfilling and grading shall be carried to an elevation of about 75mm above the finished
ground level to drain out water.
• After backfilling, 50mm high earthen embankment (bandh) will be made along the sides of
excavation pits and sufficient water will be poured in the backfilled earth for at least 24 hours.
3.13.3 Curing
The strength of concrete work depends upon the curing provided to it. Following requires to be noted.
• The concrete after setting for 24 hours shall be cured by keeping the concrete wet continuously
for a period 10 days after lying.
• The curing will be done from the top of the pit within the embankment area.
• No saltish or brackish water shall be utilized for curing.
3.13.4 Earthing
Earthing of tower is very important for the performance of insulators and conductor of the
transmission line. Each tower shall be earthed after the foundation has been cast. For this purpose,
earth strip shall be fixed to the stub during concreting of the chimney and taken out horizontally below
the ground level. In normal circumstances, the earth strip shall be provided on No.1 stub leg as given in
the structural drawings. Normally, the tower leg whish has the step bolt, is provided with the earthing
strip. Following may be noted.
• The footing resistance of all towers shall be measured by the Contractor in dry weather after
the erection of superstructure but before the stringing of earth wire.
• In no case the tower footing resistance shall exceed 10 ohms.
• In case the resistance exceeds the specified values, multiple pipe earthing or counterpoise
earthing shall be adopted in accordance with the following procedure, but without interfering
with the foundation concrete even though the earth strip/counterpoise lead remains exposed
at the tower end.
• The connections in such case shall be made with the existing lattice member holes on the leg
just above the chimney top.
Pipe type earthing and counterpoise type earthing, wherever required, shall be done in accordance
with the stipulations made in IS:3043‐1966 and IS:5613 (Part II/Section 2) 1976.
• Pipe type earthing
The installation of the pipe type earthing shall be in accordance with IS: 5613‐ 1985 (part
II/section 2). A typical example of pipe type of earthing is given.
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•
Counter poise type earthing
Counterpoise type earthing consists of four lengths of galvanized steel stranded wires, each
fitted with a plug for connection to the tower leg at one end. The wires are connected to each
of the legs and taken radially away from the tower and embedded horizontally 450mm below
ground level. The length of each wire is normally limited to 15 m but may be increased if the
resistance requirements are not met (i.e. 10 ohms or less). Galvanized steel stranded wire
preferably of the same size of the overhead ground wire may be used for this purpose. Such
type of earthing is provided for hilly terrain locations where earth pit excavation to a depth of
about 2.5 to 3 m is not feasible and the resistivity of the earth is very high.
4.0 Erection of Super Structure and Fixing Of Tower Accessories
4.1 The towers shall be erected on the foundations only after 10 days of pouring of concrete or till such
time that the concrete has acquired sufficient strength. The towers are erected as per the erection
drawings furnished by the manufacturers to facilitate erection. For the convenience of assembling the
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tower parts during erection operations, each member is marked in the factory to correspond with a
number shown in the erection drawing. Any damage to the steel and injuring of galvanizing shall be
avoided while the stringing work is in progress. No member shall be subjected to any undue over
stress, during erection.
4.2 Method of Erection
There are four main methods of erection of steel transmission towers which are described below:
• Build‐up method or piecemeal method
• Section method
• Ground assembly method
• Helicopter method
4.3 Build up Method
This method is most commonly used in this country for the erection of 66KV, 132KV, 220KV and 400KV
transmission line towers due to the following advantages:
• Tower materials can be supplied to site in knocked down condition which facilitates easier and
cheaper transportation, loading and unloading.
• It does not require any heavy machinery such as cranes etc.
• Tower erection activity can be done in any kind of terrain and mostly throughout the year (save
difficult time of heavy rain).
• Availability of workmen at reasonable rates.
• In this method, the tower is erected member by member.
• The tower members are kept on ground serially according to erection sequence.
• The erection progresses from the bottom upwards.
• The four main corner leg members of the first section of the tower are first erected and guyed
off.
• Sometimes more than one continuous leg sections of each corner leg are bolted together at the
ground and erected.
• The cross braces of the first section, which are already assembled on the ground, are raised one
by one as a unit and bolted to the already erected corner leg angles.
• First section of the tower thus built and horizontal struts (belt members) if any, are bolted in
position.
• For assembling the second section of the tower, two gin poles are placed one each on the top
of diagonally opposite corner legs.
• These two poles are used, for raising parts of second section.
• The leg members and bracings of this section are then hoisted and assembled.
• The gin poles are then shifted to the corner leg members on the top of second section to raise
the parts of third section of the tower in position for assembly.
• Gin poles are thus moved up as the tower grows. This process is continued till the complete
tower is erected.
• Cross‐arm members are assembled on the ground and raised up and fixed to the main body of
the Cross‐arm members.
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For heavier towers, a small boom is rigged on one gin pole is used instead of two gin poles. In order to
maintain speed and efficiency, a small assembly party goes ahead of the main erection gang and its
purpose is to sort out the tower members, keeping the members in correct position on the ground and
assembling the panels on the ground which can be erected as a complete unit.
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4.4 Section Method
• In the section method, major sections of the tower are assembled on the ground and the same
are erected as units.
• Either a mobile crane or a gin pole is used.
• The gin pole used is approximately 10 m long and is held in place by means of guys by the side
of the tower to be erected.
• The two opposite sides of the section of the tower are assembled on the ground.
• Each assembled side is then lifted clear of the ground with the gin or derrick and is lowered into
position on bolts to stubs or anchor bolts.
• One side is held in place with props while the other side is being erected.
• The two opposite sides are then laced together with cross members and diagonals; and the
assembled section is lined up, made square to the line.
• After completing the first section, gin pole is set on the top of the first section.
• The gin rests on a strut of the tower immediately below the leg joint.
• The gin pole then has to be properly guyed into position.
• The first face of the second section is raised.
• To raise the second face of this section it is necessary to slide the foot of the gin on the strut of
the opposite face of the tower
• After the two opposite faces are raised, the lacing on the other two sides is bolted up.
• The last lift raises the top of the towers.
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•
After the tower top is placed and all side lacings have been bolted up, all the guyes are thrown
off except one which is used to lower the gin pole.
• Sometimes whole one face of the tower is assembled on the ground, hoisted and supported in
position.
• The opposite face is similarly assembled and hoisted and then the bracing angles connecting
these two faces are fitted.
4.5 Ground Assembly Method
• The complete tower is assembled in a horizontal position on an even ground.
• The tower is assembled along the direction of the line to allow the cross arms to be fitted.
• On slopping ground, however elaborate packing of the low side is essential before assembly
commences. After the assembly is complete, the tower is picked up from the ground with the
help of a crane and carried to its location and set on its foundation.
• For this method of erection, a level piece of ground close to footing is chosen from the tower
assembly.
• This method is not useful when the towers are large and heavy and the foundations are located
in arable land where building and erecting complete towers would cause damage to large areas
or in hilly terrain where the assembly of complete tower on sloping ground may not be possible
and it may be difficult to get crane into position to raise the complete tower.
• In India, this method is not popular because of prohibitive cost of mobile crane, and non
availability of good approach roads to tower locations.
4.6 Tightening Of Nuts & Punching of Threads and Tack Welding of Nuts
4.6.1 Following are the requirements for tightening of nuts and bolts.
• All nuts shall be tightened properly using correct sized spanners.
• Before tightening, it is ensured that filler washers and plates are placed in relevant gaps
between members, bolts of proper size and length are inserted and one spring washer is
inserted under each nut.
• In case of step bolts, spring washer shall be placed under the outer nut.
• The tightening shall be carried on progressively from the top downwards, care being taken that
all bolts at every level are tightened simultaneously.
• It may be better to employ four personnel (fitters), each covering one leg and the face to his
right.
• The threads of bolts shall be projected outside the nuts by one to two threads and shall be
punched at three positions on the top inner periphery of the nut and bolt to ensure that the
nuts are not loosened in course of time due to the effect of the vibration.
• If during tightening process, a nut is found to be slipping or running over the bolt threads, the
bolt together with the nut shall be changed outright.
• To prevent the pilferage of the tower members it is a common practice these days to tack weld
the nut with the bolt in threaded portion.
• The welding is generally done for lowermost two sections of the tower.
• The galvanization of nuts and bolts is lost due to welding.
• This has to be made good by the application of zinc rich paint.
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4.6.2 Painting of Joints
For galvanized tower in coastal or highly polluted areas, the joints shall be painted with zinc rich paint
on all contact surfaces during the course of erection.
4.6.3 Checking the Verticality of Erected Towers
The finally erected tower shall be truly vertical and no straining is permitted to bring it in alignment.
Tolerance limit for vertical shall be one in 360 of the tower height.
4.7 Tower Testing and Protomodel
4.7.1 Introduction
Transmission line towers are highly indeterminate structures. In the analysis of design of these
structures and their detailing a number of theoretical assumptions are made. The structures are mass
produced and the quality of materials, fabrication and the assembly require checking. It is desirable
that the Designers and Users both are convinced that the tower can stand and most critical loads for
which it is designed and are therefore subjected to full scale prototype test. For a Prototype test, the
material used shall be made to the same standards, as those that will apply to all towers during mass
production.
4.7.2 Testing Requirements
This full scale testing of tower is generally termed as Prototype Test and for conducting Prototype
tests, a tower testing station is required where it is possible to measure the applied loads and
deflections and observe the behavior of the tower on application of the external design loads.
4.7.3 Description of a Tower Testing Station
A tower Testing Station shall consist of:
(i) A Test Bed to withstand maximum possible compression and uplift loads and shear resulting from
the external loads on a prototype tower with the highest voltage and no.ofr circuits, which has to be
subjected to testing at the Testing Station.
(ii) Permanent Anchors of adequate capacity to take the Transverse, Longitudinal and Vertical Pulls
applied to the tower of maximum expected with, height and strength proposed to be tested on a test
bed. Longitudinal Mast(P) is a structure of adequate dimension and height, constructed at a sufficient
distance from the tower bed and equipped with all Riging arrangements for applying longitudinal
loads. The Transverse loads are applied through pulleys positioned on the Transverse Mast (B). Vertical
loads are applied by means of dead weight or through anchors on the test bead.
(iii) The arrangements for applying the combination of given loads at a specified rate of increase, if
required with the help of a Multi Sheave Pulley, to take mechanical advantage and reduce load on the
winch.
(iv) Electrical Winches operated by remote control from a Central Control Room used for applying
loads at the different points of tower structure, as far as possible simultaneously.
Instruments used for recording the load applied are either Mechanical Spring Gauges or
Electrical/Electronic
Transducers/Dynamometers.
The
dials
of
the
respective
Dynamometers/Transducers indicate the load in the particular wire. Transverse & longitudinal
deflection readings are taken by Theodolities on scales fitted at appropriate positions on the tower.
(v) Remote control of loading mechanisms.
(vi) Remote and precise reading of measuring instruments, like Mechanic.al Spring Gauges or
Electrical/Electronic Transducers/Dynamometers.
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(vii) Arrangement for calibration of the measuring instruments. From Control Room, the winches and
the dynamometers are operated / controlled. Control room shall have the facility to have the complete
view of transverse and longitudinal testing arrangements of the test tower. All the electrically operated
machines and instruments shall be connected to and controlled from the Control Room.
4.7.4 Calibration
In order to ensure the correctness and reliability of all measuring instruments and in turn the validity of
the tests the calibration of all instruments before the test is conducted. Calibration of the load cells is
done with the use of UTM, the UTM shall be periodically (once in every six months) calibrated by an
external third party.
4.7.5 Assembly of Prototype Tower
The prototype tower, fabricated as per structural drawings approved by the Purchaser shall be
assembled and erected on a fixed base. Fitment of any member shall be easy, natural and shall not be
a forced one. The Bolts should be tightened simultaneously on all four faces.
4.7.6 Rigging Arrangements And Location of The Load cells
To enable application of the external loads in the most representative manner and to simulate tower
design conditions, the tower structure is rigged suitably, impact of any variance in inclination of rigging
wires with respect to the directions accounted for in designs is considered while preparing Rigging
Chart. Loads are applied as per these approved rigging charts. The load cells shall be attached to the
tower through the rigging wires, positioned as close as possible to the test tower so that frictional
losses do not cause impact on the load cells.
4.7.7 Test Procedure
The Prototype Tower is erected on the test bed and all the rigging arrangements are completed. The
Tower is examined carefully to see that all the bolts and nuts are tightened properly. The tower is
made truly plumb and square. All its members are checked for freedom from any visible defect. Two
graduated metallic scales are fixed at Peak and Top Cross arm level on the transverse face. Readings on
these scales with reference to the plumb line are taken by Theodolite.
4.7.8 Testing of Prototype Tower
4.7.8.1 Bolt‐Slip Test
In order to eliminate as far as possible, the play between the bolts and the holes throughout the
structure. Bolt take‐up test is done in the beginning. Under this test all the transverse and vertical
loads are increased simultaneously as far as possible to 50% of the ultimate normal condition
(Reliability Condition) loads. The loads on the tower are held for 1 minute. Transverse deflection
readings are taken for NO LOAD and LOADED conditions. The loads on the tower are then reduced to
zero or to as low a value as possible. The deflection reading is once again taken for this Zero loading.
The differences between the two zero readings are the permanent deflections on tower. For
subsequent test purposes, the readings with zero loads taken after the Bolt Slip Test taken are
considered as the initial readings.
4.7.8.2 Sequence of Test Loading Cases
Sequence of test loading cases shall be pre‐determined. The choice of the test sequence shall largely
depend upon simplification of the operations necessary for carrying out the test programme.
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4.7.8.3 Details of Tests
Test 1: (Broken wire Condition) Security and Safety Conditions as well as Anti‐cascade conditions.
Under this condition (all conditions involving longitudinal loads in addition to the transverse and
vertical loads) all the transverse and vertical loads are first increased to about 100%. Longitudinal loads
are then increased in steps of 50%‐75%‐90%‐95% of the ultimate loads. At all stages of loading it shall
be ensured that the transverse and vertical loads are not less than the values for corresponding step of
the longitudinal load. At each step the loads are maintained for one minute and the deflections are
noted. All loads are then increased to 100%. At this final 100% loading stage, towe3r is observed for 2
minutes and deflections are noted. The tower is required to withstand these loads without showing
any failure. After every test the loads are brought down and deflection readings are taken for no load
condition.
Test 2: (Normal Condition) Reliability Condition:
These loads are applied as far as possible simultaneously at all points in steps of 50‐75‐90 & 95%. The
waiting period of one minute shall be maintained at each step. The waiting period at the final 100%
loading stage shall be 2 minutes. Throughout the process of loading under all tests, the tower shall be
closely observed for any visual sign of deformation. Whenever such deformation is observed the loads
shall be brought down and remedial measures shall be taken. It is pointed out here that the tendency
of bowing in bracings shall not be considered as a sign of failure even though it is during the final
waiting period.
Test 3: Destruction Test:
If no Destruction Test is required by the Purchaser the loads on tower after 100% under Test‐2 above,
shall be gradually brought down to zero. If desired by the Purchaser, in continuation to test 2, after the
final waiting period, the transverse loads only are increased in steps of 5% till the failure occurs. The
Destruction test, however, ca be discontinued beyond a certain limit on mutual agreement between
the Purchaser, Design & Testing Station Authority. The point of failure is detected from the sudden
drop of load indication in the instrument dials in the Control Room.
4.7.8 Special Requirements
• The test tower shall be black or galvanized tower as desired by Purchaser.
• The tower which has been tested shall not be part of supply and is not to be used online.
• Test tower shall be provided with unbraced portion of stub equivalent to distance of chimney
top to the point of connection of bracing with leg.
• During the process of tower test, when a number of tests have been completed satisfactorily
and a failure occurs as a subsequent test, the design will be reviewed and tower will be
reinforced, if required. The reinforced tower will be put to test again and subjected to balance
tests, unless the failure is of major nature, which will require all the tests to be repeated, or as
mutually agreed between the Purchaser and the Supplier.
• Application of Loads on Test‐Tower
As considered in design:
Transverse longitudinal and vertical loads.
At peak and respective cross‐arm points.
(i) Wind load from top at peak and respective cross‐arm points upto bottom cross‐arm will be
simulated suitably at ground‐wire. Top Cross‐arm, Middle cross‐arm and Bottom cross‐arm
levels.
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(ii) Wind loads on tower below bottom cross‐arm will be simulated to act at bottom cross‐arm
point and test will be carried out accordingly.
(iii) For tower with extension, wind load on extension will be simulated on Top of Extension.
4.7.9 Acceptance of Test Results
Test is considered as passed, if tower is able to withstand the specified ultimate loads (100% step) with
no visible sign of deformation for the specified waiting period. A detailed report incorporating test data
and the results of complete tests along with photographs of the tower shall be prepared by the test‐
authority, in quadruplicate.
4.7.10 Presentation of Test Results
5.0 Conductor & Conductor Accessories
5.1 Conductors:
The different types of conductors are used on the transmission line, depending upon the voltage class
and amount of current to be handled, In India, it is a standard practice to use following conductors for
different voltages.
1. 66kV
‐ACSR “Dog” conductor
2. 66, 132kV
‐ACSR “Panther” conductor
3. 220kV
‐ACSR “Zebra” Conductor
4. 400kV
‐ACSR Twin Bundle “Moose “Conductor.
TABLE ‐1
Size &
Normal
Over
Current
operating
Name of
Unit
Sr.
UTS
all
carrying
stranding
voltage
weight
No Conductor
Kg.
dia.
capacity at
Alu.
Steel
kV
Kg/Mtr.
cm.
75ºC (Amp)
No/mm No/mm
1
ACSR
33/66
6/4.72
7/1.57
300
1.2
3299
0.394
Dog
2
ACSR
66/132
30/3.0
7/3.0
480
2.10
9177
0.976
Panther
3
ACSR
220
54/3.18 7/3.18
735
2.86
13316
1.62
Zebra
4
ACSR
220/400 54/3.53 7/3.53
800
3.18
16250
2.02
Moose
For special industrial connections at EHV, the conductor size shall be worked out on the basis of
maximum system current. The insulation is provided in accordance with the voltage.
5.2 Insulators:
5.2.1 The standard type of conductor if used has also an advantage that the current carrying capacity,
voltage, loading limit and impedances are also standardized and well defined. Thus there is an easy
access for a system analyzing engineer for evaluation and assessment of power flow and optimum line
loading. Thus the current loading limit and power transfer capability of various transmission lines are
given in Table‐2. They are based on the allowable voltage regulation on EHV/UHV lines.
Sr.No.
Line Voltage
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Power Transfer capability per 3‐phase Circuit
(MW)
50kM
100kM
200kM
300kM
Page 28
1
2
3
4
66kV
132kV
220kV
400kV
22
120
400
1500
11
60
200
750
5.5
30
100
375
3.6
20
67
250
5.2.2 In case of transmission line having a concentrated load and low voltage, it may become
mandatory to use higher size of conductor e.g. system having 33kv line voltage with two loads of 10
and 30MW at end of 4 to 5kM long feeder may require “Zebra” conductor to be strung on it. Since with
reduction in voltage the current to be carried becomes very high and use of lower size of conductor
may be hazardous. Similarly a lightly loaded 132kV lines can also be strung with ACSR “Dog” conductor.
The thermal loading limits of the conductor are increasing day by day. Of‐late it has been customary to
consider 75ºC as a maximum surface temperature of the conductor. Operating lines at high thermal
limits is not advisable due to two reasons.
i) Line losses increase with increase in temperature.
ii) Sag may increase bringing down the statutory clearance below the conductor to
non acceptable level.
With this in view, the conductors used in the substation buses are one size up in diameter or in bundle
configuration. Thus the 220kV side bus of 400kV substations may have quadruple “Moose” conductor
and 66kV bus of 220kV substation may have a Twin “Zebra” or Twin “Moose” conductor (Bus).
5.3 Choice of Insulators:
The glazed disc type porcelain insulators have been a standard material in use for last 50 years in this
country. The insulator string consist of No. of disc unit in optimum width at about 13.5kV per disc up to
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a voltage of 220kV. For 400kV class of line the insulator size and creep age distances are higher, and
thus No. of insulators to be used are 23 for suspension and 24 for tension tower. The important
parameters for disc insulator string used in various voltage of transmission line are given in Table‐3.
Table‐3
Length
of
Weight of
Size of
No.of
Electro
insulator
each
Line
insulators Insulator
Sr.
‐mech.
string
String
No Voltage insulator disc Strength per string
Single
Single
Single
.
Kg
(D x H)
Double
Double
Double
mm x mm
mm
mm
Kg
No
No Kg
1 66kV
1300
1000
150
75
10
5
7000
Suspensio 255 x 146
1280
1140
170
85
12
6
8180
255 x 146
n
Tension
2
132kV
1716
1600
240
120
18
9
8180
Suspensio 255 x 146
2190
1790
260
130
20
10
11500
255 x 146
n
Tension
3
220kV
Suspensio 255 x 146
8180
14
28
130
260
2340
2640
n
255 x 146
11500
15
30
140
280
2850
3200
Tension
4
400kV
4400
4200
550
275
46
23
11500
Suspensio 255 x 146
6200
5900
1280
640
48
24
16500
255 x 146
n
Tension
5.3.1 Other insulator types in vogue these days are a solid core insulator stack and high density
polymer insulator. Even though the polymer long rod insulators are simpler and low weight, they are
yet to be popular in this country because of very high cost.
5.3.2 The design of insulators does not only depend upon the creep age `distances but they have
many intricacies such as the type of material used in the insulators, capacitance grading, thermal
capability, back flash over etc.
5.3.3 The insulators used on the line are also governed by the basic insulation level selected in power
system.
5.3.4 The choice of disc insulators to be used depend upon the terrain & the pollution level through
which the transmission line has to pass and thus fog type and antifog type disc insulator are in use for
different applications. The antifog type insulators are in use for different applications. The anti‐fog type
insulators are found most suitable in the polluted atmosphere.
5.4 Conductor Accessories
5.4.1 Mid span Joint – It is used to provide joint in the conductor. For AC Conductor, the joint
comprises one small steel tube and the other bigger Aluminum tube. The steel tube is compressed
(crimped) against the two ends of Steel which are exposed by peeling of the Aluminum Strands for half
the length of steel tube strands of ACSR & the Aluminum strands. Hydraulic equipments are used for
crimping. For AAAC or AAC conductor only Aluminum tube is used which is also crimped after steel
tube is crimped after sliding over the crimped steel tube.
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5.4.2 Repair Sleeve – It is used when one or two strands of the outer Aluminum strands are broken.
The sleeve is manufactured in two parts longitudinally and circumferentially major part is 70% on
diameter and minor part is 30% on diameter. The length of both the parts is the same. After sliding
both the parts on the conductor, the sleeve is crimped on the affected part.
5.4.3 Pre‐formed Armor rods – This is a set of twelve helical right hand, ball ended Aluminum rods of
appropriate length. The set is wound on the conductor at suspension tower location and then the
entire assembly along with the conductor is clamped in the suspension clamp. The PA rods prevents
damage and reduces fatigue on the conductor due to the relative movement of the clamp and the
conductor and also helps in reducing the effect of conductor vibration on clamp & the tower cross‐
arm.
5.4.4 Vibration Dampers –They are used to damp the Aeolian vibrations on the conductor. The
dampers are clamped to the conductor near the cross arm point on both the sides at a distance of 3 to
5Mtr. The vibration damper comprises a clamp, a messenger cable, and dead weight. The dampers can
be solenoid type or 4R type.
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5.4.5 Spacer cum Dampers‐ They is used for bundle conductor spacing and for damping the vibrations.
They comprise two arms with clamping device and a spacing yoke having a spring action. They are
made of Aluminum.
5.4.6 Cushioned (Armour grip) spacers‐ They are used as spacers for bundle conductor with amour
grip. They comprise an aluminum rod, two neoprene rubber jaws and two sets of armour rods (each
having six rods). Rigid spacers are used for twin bundle conductor jumpers.
5.4.7 Earthwire – The earth wire is used for protecting the conductor in the mid span. It is provided at
such a height which affords an angle of shield not more than 30º with Top conductor. The common size
of earth wire used is 7/3.15 and 7/3.66. In case of 400kV and above, two earth wires are used for
better protection.
Earth wire Accessories includes the following:
5.4.7.1 Suspension Clamp ‐ This is used for suspending the earth wire through the earth wire peak of
the transmission tower. The earth wire passes through the suspension clamp.
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5.4.7.2 Tension Clamp ‐ This is used on tension locations of tower and provided in tension position on
both the sides of the tension tower.
5.4.7.3 Copper Earth bond‐ This is used for providing direct passage to the lightning surge to the
tower. The copper bond is made out of stranded copper mesh with two lugs on the ends and is about
500mm long. One end of this is connected to the suspension/tension clamp of earth wire and the other
end is connected to the tower body.
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5.4.7.4 Cross bye clips (sister wire clamps) – This is used for providing better continuity to the earth
wire. They are nothing but a sort of parallel groove clamp. They are provided in set of three from either
side of the tower.
5.4.7.5 Mid Span Joint ‐ This is used to connect the cut ends of the earth wire. This is nothing but a
steel tube which is crimped on the ends of the earth wire.
5.4.8 The Insulators are connected in series or in series –parallel to form a single or double string on
the tower. Suitable hardware is required for securing the insulators to the tower. The insulator
hardware commonly used is as follows:‐
5.4.8.1 Single Suspension hardware – This is used on suspension locations of the tower line falling in
the rural areas and also falling in the agricultural field. The hardware has a hook on the tower side and
socket on the conductor side.
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5.4.8.2 Double Suspension hardware—this is used on suspension tower locations which require a road
crossing or a railway crossing & river crossing. They have anchor and a yoke on the tower side and yoke
& sockets on line side. They also have a Suspension clamp on the line side.
5.4.8.3 Single Tension hardware— This is used on tension tower locations. This hardware has a
shackle on the line side and a dead end clamp on the line side.
5.4.8.4 Double Tension hardware— This is used on tension tower location having a major road
crossing, river crossing, power line crossing, railway crossing etc. They have D‐shackle, yoke on tower
side and yoke, dead end clamps on the line side.
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5.5 Relation of Conductor With Transmission Line Components:
5.5.1 The Transmission line components described above has relation with the conductor. Some salient
points are described below‐
The earth wire provided on the tower provides a cover to the conductor against lightning surges, if the
conductor is placed within an umbrella of 30º degrees. If earth wire is not provided or is missing, the
conductor will be loaded by lightning and stray discharges. The conductor will carry this along the line
and insulators may get damaged. The earth wire accessories help in supporting the function of earth
wire.
The transmission tower provides full support to the conductor with two extremities –
a) To allow sufficient ground clearance and object clearance to the conductor under maximum
temperature & still air.
b) Absorb the maximum tension of the conductor under 0ºC temperature with certain percentage of
wind pressure. Any deficiency in the tower design will lead to a catastrophe.
5.5.2 The insulators keep the conductor in position on suspension and tension locations & also insulate
the conductor from the tower body. Any damage to insulator will cause a short circuit on the
conductor and may also lead to the break down.
5.5.3 The hardware part of the insulator string is very important for the performance of the conductor.
Any loose end will result into damage to the conductor. The hardware permits the conductor to swing
to some extent and also restrains the conductor from over swing.
5.5.4 The earthing system provides a safe passage to the fault current & lightning /switching surges. If
earthing system is poor, the life of conductor and insulator will be reduced.
5.5.5 The long span of River & Creek Crossing imposes differential stresses due to variation in wind
pressure and temperature along the long span. The length of the catenary is very long & therefore the
conductor swing is also very big. The variation in wind velocity over tall tower also steps up the
vibration level.
6.0 Stringing of Conductor and Ground Wire
6.1 Stringing is the last major item of construction activity. The stringing activities are most important
and time consuming activities in transmission line construction. This requires much skill and technical
know‐how. The stinging crew shall include skilled laborers, experienced fitters and supervisor. The
stinging tools and tackles should be of good quality and in good working condition.
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6.2 The stringing activities are mainly consisting of the following:
• Hoisting of insulators
• Paying of conductor/ground wire
• Rough sagging of conductor
• Final sagging of conductor/ground wire
• Clipping/clamping of conductor and jumpering.
6.3 Hoisting of Insulators
Following may be noted for hoisting of insulators.
• The insulators used on transmission lines are 11KV antifog type Disc insulators having capacity
as 70KN, 90KN, 120KN and 160KN.
• The suspension insulator strings shall be used on all suspension locations (tangent towers) and
tension insulator strings on all tension locations (angle towers having15/30/60deg Deviation
and Dead end towers).
• The insulator strings shall be assembled on ground.
• All the insulators shall be cleaned and examined for hair cracks or any damage.
• The strings are then hoisted and fixed to the tower cross‐arm along with hardware and Arial
rollers.
• The security clips (R pin/W pin) should be properly placed before hoisting.
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6.4 Paying out of Conductor/Ground wire
Following may be noted for paying of conductor.
• Before commencing of string works, copies of sag tension charts (supplied by the design
department) showing initial and final sag should be made available at site to EIC.
• Normally ground wire drums are mounted on turntable near tension location.
• The ground wire is pulled manually or by tractor along the line. The ground wire running blocks
are hoisted on the towers prior to taking up this operation.
• The ground wire drums should be opened and laid carefully in such a way to avoid
cracks/damages.
• It should be ensured that no joint in ground wire is within 30m from the suspension/tension
clamp.
• Sufficient number of aluminum snatch blocks shall be used for paying out of conductor.
• Precautions should be taken to avoid conductor rubbing on the ground by providing adequate
number of ground rollers.
• Additional rollers shall be provided for crossing thorny hedges, fencing and other obstructions
which are likely to cause damage to the conductor.
• No joints of conductor shall be allowed within 30m from suspension/tension hardware .
• In case of railway/road crossing spans, no joints shall be permitted. Further not more then one
joint in a span of each conductor shall be permitted.
• Prior to taking up of conductor paying activity, the areal rollers are fitted to the towers along
with suspension strings.
• The conductor drums should be handled carefully at site to avoid any damage to the outer
aluminum layer.
• The mid span joints and tension hardware are compressed by using hydraulic compression
machine.
• All the compression joints shall be carefully made and a record of initial and final lengths of the
joints signed by the contractor’s and purchaser’s representative should be maintained.
6.5 Rough Sagging of Conductor
• On completion of conductor paying work between two tension locations (i.e. is line section),
the conductors of all the phases shall be anchored near the tension location.
• During the rough sagging, the conductor will be lifted above the ground by about 3 meters.
• Thus the tension on the wire will minimum.
6.6 Final Sagging of Conductor/Ground wire
Following may be noted for final sagging of conductor / ground wire.
• The conductor and ground wire shall be made to sag correctly as per the approved stringing
charts.
• All conductors shall be stressed to their maximum working tension at the time of stringing
according to the sag tension charts.
• Dynamometers shall be used in tensioning of conductors, check for sag should also be made at
intervals corresponding to the ambient temperature shown by the thermometer placed at site.
• Extra sag of 150mm should be allowed at all important tension locations of railway crossing /
major road crossing/ river crossing spans.
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•
It should be ensured that the conductor/ ground wire after being pulled shall not be kept on
stringing sheaves for more than 72 hours before being pulled to the specified sag.
• During the time when conductor/ground wire is on the stringing sheave (before final sagging) it
shall be ensured no damage of conductor/ground wire occurs due to wind, vibrations, vehicles
or any other reasons.
• The conductor shall be pulled up to desired sag (final sag) and left in aerial stringing sheaves for
at least one hour. After which the sag shall be rechecked and adjusted if required, before
clipping work is taken on hand.
• During final sagging of conductor, the sag at intermediate spans should be verified with the
help of sag board provided at suitable distances (as per the approved stringing chart and the
corresponding site temperature) on the tower body of intermediate locations.
• The stringing of bundle conductor (two or more conductor) shall be carried out by using tension
stringing equipment.
• Using this method, the conductors are kept under tension during the stringing process to keep
conductor clear of the ground and obstacles which may cause conductor surface damage as
well as clear of the energized circuits.
• This method is applicable where it is desired to keep the conductor off the ground to minimize
surface damaged or in areas where frequent crossings are encountered.
• The equipments involved in this method are reel stands, tensioner, pullers, reel winder, pilot
line winder, splicing cart and pulling vehicle.
• One more important reason to use the tension stringing equipment for stringing of bundle
conductor is to release, payout, rough sag and final tensioning of all the sub‐conductors of the
bundle under equal physical tension.
• This will ensures equal sags of each sub‐conductor in a span and sub‐span.
6.7 Clipping/Clamping of Conductor and Jumpering
The clipping/clamping work includes fixing of suspension hard wares, providing of preformed armour
rods, removal of aerial sheaves, etc. Following required for clipping / clamping:
• Conductor shall be clamped within 24 hours of final sagging.
• The sag, before clamping, should be checked in the first and last span of the section having
eight spans.
• The check should be provided at intermediate span also, if the section is having more than eight
spans.
• At all the suspension locations, the preformed armour rods shall be wrapped keeping the
centre of the preformed armour rods at the centre point of the stringing sheaves.
• Care should be taken to see that all the strands of the rods are fixed on the surface of the
conductor without any void.
• The suspension clamps of the suspension hardware should be fixed (bolted) at the centre of the
preformed armour rods.
• The vibration dampers should be fitted on tension locations at an appropriate distance from
the tension hardware (specified by the design department) during the rough/ final sagging of
conductors.
• The vibration dampers on suspension locations shall be fitted at an appropriate distance on
either side of the suspension hardware as specified.
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Page 39
•
The jumpering work of conductor includes cutting of proper length of jumper providing of
jumper cones on both the ends of jumper, fixing of the jumper to the tension hardware on
either side of the tension location etc. Care should be taken to compress the jumper cones
with hydraulic compressor machine so as to have firm grip with the conductor.
• The tightening of bolts/nuts should be proper, over tightening should be avoided.
• The clearance with the tower body, after providing jumpers, shall be checked as per the
approved tower drawing.
• The ground wire jumpers are also prepared using appropriate length of ground wire having
compressed jumper cones on either side.
• The prepared jumpers shall be then fitted to the tension clamps on either side of the tension
locations.
• An additional ground wire piece called sister wire is fitted on the newly strung ground wire at
the top of all the locations using 2 to 3 numbers of cross by clips, also known as sister wire
clamps, on either side of the locations.
• The bolts and nuts of cross by clips should be properly tightened.
• The vibration dampers for ground wires shall be provided at appropriate distance on either side
of the location as specified.
• The earth wire stringing is normally done before the stringing of conductor.
• The rough sagging and final sagging is done exactly as per the procedure described for
conductor.
• The approved stringing charts are used for stringing of earth wire.
• After final tensioning of the earth wire, the suspension clamps are provided on the suspension
locations and compression type dead end clamps are provided on the tension locations.
• Jumpering work is done on the earth wire tension tower.
• Sister wires and clamps are provided on each tower making an additional loop on the top of the
earth wire point which also ensures better conductivity & continuity.
• The earth wire suspension and tension clamps are connected to the main tower body using
braided copper earth band.
• This earth bond gives direct path to the lightning discharges traveling on the earth wire to the
mother earth through towers and safe guards the conductors.
• Vibration dampers are also provided on the earth wire to damp the Aeolian vibrations. The
clamps are required to be properly tightened to ensure proper connectivity and trouble free
service.
6.8 Fixing of Tower Accessories
After the stringing work is done it is necessary to fix the tower accessories such as phase plate, Number
plate, Danger plate, Circuit identification plate, Anti climbing devices etc as per their respective
position shown on the structural drawings.
6.9 Protection of Towers
• In the hilly terrain, the foundations of the tower are susceptible to the damage due to the
erosion of soil covering it.
• This happens because of gushing water from upstream. Sometimes the tower is spotted on the
ravines or river banks and one or more of the four tower legs are subjected to soil erosion.
• In both the above cases it is usual to provide retaining wall and or revetment.
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Whenever the Transmission line is passing through a corridor having major road on both the
sides or the tower line is passing very near to the major road it is necessary to provide a steel
barrier around the tower up to height of 3 meters.
This barrier has to be sufficiently strong and made out of girders and channels.
The barriers have to be well founded to take the impact of the dashing vehicles.
7.0 Details of Manpower Tools, Tackles Equipment, Vehicles and Infrastructure
Required For the Construction of The EHV Transmission Line
7.1 The details of man power tool, tackles, equipments and vehicles required for the construction of
EHV line of various voltage classes such as 66 KV, 132 KV, 220 KV and 400 KV etc. are given here after.
The erection activities are spread over a long period and are mostly carried out in the rural areas and
therefore appropriate infrastructure is required. The activities are labor oriented and besides there are
restrictions on the use of automatic machineries due to the constraint of cost and the constraint of
movements in the rural and in‐accessible tower and line locations.
The transmission line construction activity generally includes:‐
• Survey and alignment
• Foundation work
• Erection of super structure
• Stringing of shield wire and conductor
• Testing and Commissioning
Each of the above activity need different types of tools, tackles, man power etc. The details given here
under give a broad view of the tools, tackles, equipments, man power and other infra structure
required in the construction of EHV transmission lines.
7.2 Infrastructure for Survey
• This is the first and foremost activity in the transmission construction.
• Expert surveyor assisted by helpers and suitable vehicles to carry instruments is the basic need.
• This survey work is different from the survey work required to be done for civil establishments.
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The surveyor must have the knowledge of preparing profiles and also various methods to carry
out the correct survey.
The surveyor should also have in‐depth knowledge of tower spotting.
The infra structure required for carrying out survey work is listed below.
Average output per month per gang consisting of about 10 crew members will be :
(i) Alignment survey
15 km
(ii) Detailed Survey
20 km
(iii) Check Survey
20 km
Wherever topographical survey is to be carried out the output will be less and will depend on
the quantum of work and terrain.
The output in hilly terrain may be substantially low.
Tools required for Survey Gang
Theodolite(or Total Station) with stand
1 NO
Dumpy level with stand
1 NO
Ranging rod
5 NO
Leveling Staff
2 NO
Engineers chain
‐30 m
1 NO
Engineers chain
‐20 m
1 NO
Steel Tape
‐30 m
1 NO
Steel Tape
‐20 m
1 NO
Survey umbrella
1 NO
Chain pins
30 NO
Spades, knives and exes for clearing the bushes and trees
As per requirement
Tents, buckets, water drums camping cots, tables, chairs, petromax etc. As per requirement
Transport required for Survey Gang Jeep with trailers
7.3
1 NO
Foundation activity
• This activity has to be carried out from location to location spread over a distance which is
sometimes as large as 400 meters. Excavation has to be carried out in various types of soils and
rocks.
• The excavation plan will change accordingly. Sometimes, in hilly locations we may have to blast
the rock. In case sub soil water is encountered during excavations, dewatering has to be
resorted to. In case soil collapse shoring and shuttering are required. The foundation depth may
vary from 1m to 5m depending upon the soil/rock and decision regarding the type of
foundation has to be adopted.
The infra structure required for this activity is as below.
Average output per gang consisting of about 85 people per month will be:
Excavation
60 m³ Soft rock
150 m³ soft rock
400 ‐500 m³
Normal soil
+180 m³ normal
soil
Output of hard rock will depend on situation
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Stub‐setting & Concreting
Tools and Plants required for Excavation, Stub‐setting and
Concreting Gang
Stub‐setting Templates
Stub‐setting Jacks
Form boxes/Chimneys
Mixture Machine ‐Diesel engine driven
Mixture Machine ‐ Hand driven
Needle vibrator
Dewatering pump
Air compressor for drilling holes in rock
High carbon drilling rods for drilling holes in rock
Exploder
Water tanker trailor
Theodolite with stand
Ranging rod
Dumpy level with stand (or Total Station with Prism)
Leveling staff
Survey umbrella
Concrete cube mould (for testing the concrete)
Wooden shuttering & poles
Mixing Sheets
Measuring Box
Metal screen (for course aggregate) ‐ 40 mm mesh
Metal screen (for course aggregate) ‐ 20 mm mesh
Metal screen (for course aggregate) ‐ 12.5 mm mesh
Sand screen
‐ 4.75 mm mesh
Empty barrel (200 liters capacity)
Steel/Aluminum/Wooden ladder (3.5m length)
30 m metallic tape
30 m steel tape
Engineers’ spirit level
Steel piano wire/thread
Crow bar
Pick axe
Spade
Shovel
Gamelas
Buckets
Iron rammer (4.5 Kg)
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60 – 70 m³
As per
requirement
‐do‐
‐do‐
1 NO
2 NO
1 NO
2 NO
1 NO
As per
requirement
1 NO
1 NO
1 NO
3 NO
1 NO
1 NO
1 NO
6 NO
As per
requirement
12 NO
6 NO
1 NO
1 NO
1 NO
1 NO
6 NO
5 NO
1 NO
1 NO
2 NO
50 m
20 NO
12 NO
25 NO
8 NO
30 NO
12 NO
5 NO
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Masonry trowel
Manila rope ‐ 38 mm dia.
Manila rope ‐ 12 mm dia.
Poking rod (16 mm dia) ‐ 3 m length
Poking rod (16 mm dia) ‐ 1.5 m length
Blasting materials, binding wire
6 NO
150 m
30 m
2 NO
2 NO
As per
requirement
Hammer, Tommy bar, plumb bob (0.45 Kg), Hook (12 mm dia),
spanners (both ring and flat) etc.
As per
requirement
Tents, buckets, water drums, camping cots, Tables and chairs
petromax etc.
Transport required for Stub‐setting & Concreting Gang Truck (For
transportation of metal and sand from Source, cement,
reinforcement steel and Other materials from site stores)
Tractor with trailer
Motor cycle
As per
requirement
1 NO
1 NO
1 NO
7.4 Tower Erection
• Tower erection requires lot of precision. Besides the material has to be lifted from the ground
level to various heights, depending upon the type of tower. While erecting it is necessary that
equilibrium is maintained and damage to the tower material and accidents are avoided.
The infrastructure required for this activity is given under
• Average output per gang considering of about 50 crew members per month will be ‐ 80 M.T.
• Tools required for Tower Erection Gang
Ginpole / Derric Pole ‐ 75/100 mm dia & 8.5 – 9 m length
2 NO
Polypropylene rope ‐ 25 mm dia
700 m
Polypropylene rope ‐ 19 mm dia
1000 m
Single sheave pulley ‐ closed type
8 NO
Single sheave pulley ‐ Open type
4 NO
Crow bars (25 mm dia & 1.8 m length)
16 NO
Spanners (both ring and flat), Hammers, Slings (16 mm dia & 1 m
As per
length), Hooks (12 mm dia) ‘D’ shackle, tommy bars
requirement
Tents, buckets, water drums, camping Cots, tables, chairs,
As per
petromax etc
requirement
Transport required for Tower Erection Gang
1. Truck
1 / 2 NO
2. Tractor with trailer
1 NO
3. Motor Cycle
1 NO
7.5 Stringing
Stringing work is almost the last activity, save commissioning, in the overall construction
activities in the EHV transmission lines. This is really a very precise and hazardous activity.
While stringing operations are on, load balance and rigging arrangement has to be full –
proof.The man power deployed has to be proportional to the actual physical tension
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required to be given to the earth wires and conductors. Excess man power may result into
over tension and less man power may result into improper stringing and accidents.
The infrastructure required for stringing operations is given under
Average output per gang consisting of about 200 persons per month with Tension Stringing
– Machine stringing method.
For 400 KV single circuit
15 km
For 400 KV double circuit
8 km
For +/‐ 500 HVDC multi circuit
5 km
Requirement of man power and average output per gang for carrying out various types
transmission lines by manual method is furnished here under :
Description of line
Man power (NO)
Average output / month (km)
66 KV single circuit
75
30
66 KV double circuit
75
15
132 KV single circuit
100
30
132 KV double circuit
100
15
220 KV single circuit
125
30
220 KV double circuit
125
15
400 KV single circuit
225
15
400 KV double circuit
225
8
Tools and plants required for stringing Gang for Tension/Manual Stringing
TSE sets (Tensioner and Puller of 8/10 T capacity)
Running block for conductor
Running block for earth wire
Head Board
Pilot wire each of 800 m length
Pilot wire joint
Ground roller for Tension/Manual Stringing
Wire mesh pulling grip (one end open) of required dia for
conductor
Wire mesh pulling grip (one end open) of required dia for earth
wire
Wire mesh pulling grip (double end open) of required dia for
earth wire
Articulated joint – Heavy duty (20T)
Articulated joint – Medium duty (10T)
Articulated joint – light duty (5T)
Drum mounting jack for conductor drum of 10T capacity
Turn table (5T capacity)
Anchor plate (1.5 m x 1.0 x 8 mm) with 15 Nos. anchor pins (45
mm dia & 850 mm long)
Hydraulic compressor machine 100 T capacity with die sets
Traveling ground
Dynamometer ‐ 10T
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1 SET
100 NO
60 NO
2 NO
10 NO
12 NO
30/100 NO
6 NO
2 NO
4 NO
10 NO
10 NO
5 NO
4 SETS
2 NO
8 NO
12 SETS
4 NO
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Dynamometer ‐ 2 T
Pilot wire reel stand
Four Sheave pulley with 12 mm dia 300 m length wire rope
Four sheave pulley with 9 mm dia 300 m length wire rope
Four sheave pulley with 12 m dia 150 m length wire rope
Equalizer pulley (10 T) capacity
Conductor lifting tackle
Winch – motorized/ manual – 10 T capacity
Come along clamp for conductor (bolted type / automatic)
Come along clamp for earth wire (bolted type / automatic)
Tirfor (5 T capacity)
Aerial chair (For conductor)
Aerial Trolley
Turn Buckle ‐ 10T
Turn Buckle ‐ 3 T
Tension/Sag plate (for tensioning purpose)
Sag Board
Marking roller
Mismatch roller
Joint protector
Walkie talkie set
Theodolite with stand (or Total Station with Prism)
Thermometer
Survey umbrella
Hydraulic wire cutter
Binocular
Flag (red and green)
Crow bar (1.8 m length)
Nail puller
Wire rope
‐ 19 mm dia
Wire rope
‐ 16 mm dia
Wire rope
‐ 14 mm dia
Polypropylene rope ‐ 25 mm dia
Polypropylene rope ‐ 19 mm dia
‘D’ – Shackle ‐ 190 mm long
‘D’ – Shackle ‐ 150 mm long
Bulldog clamp
‐ 100 mm long
Bulldog clamp
‐ 100 mm long
Hammers, spanners (both flat and ring), round files, flat files,
screw drivers, cutting pliers, steel and metallic tapes, hacksaw
frame and blades, scaffolding, slings etc.
Tents, buckets, water drums, camping cots, table, chair,
petromax, etc.
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2 NO
4 NO
6 SETS
2 SETS
4 SETS
16 NO
4 SETS
4 NO
50/20 NO
15/10 NO
6 NO
6 NO
4 NO
16 NO
6 NO
6 NO
8 NO
4 NO
2 NO
6 NO
4 NO
1 NO
3 NO
1 NO
2 NO
3 NO
30 NO
10 NO
6 NO
1000 m
150 m
900 m
500 m
500 m
40 NO
125 NO
125 NO
35 NO
As per
requirement
As per
requirement
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7.6 Transport Required for Stringing
Truck
75 h.p. tractor
35 h.p./45 h.p. Tractor and trailors
Jeep
Motor Cycle
Tension Stringing
Manual Stringing
4 NO
2 NO
5 NO
2 NO
4 NO
1 NO
6 NO
2 NO
1 NO
1 NO
8.0 Conclusion
8.1 Construction of EHV transmission line is a very precise and skillful job. Proper construction practice
ensures high reliability and long life of the transmission line
8.2 The main activities of foundation, tower erection & stringing are completely diverse from each
other and require different type of skill workers as well as tools tackles and equipment.
**********
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