FOR INTERNAL CIRCULATION ONLY
user’s manual of Construction (part one)
Transmission Lines Volume-4 Tower Erection
Construction Management
Power Grid Corporation of India Limited (A Government of India Enterprise)
DOCUMENT CODE NO. : CM/TL/TOWER ERECTION/96 1996
JUNE,
FROM THE DESK OF DIRECTOR (PERSONNEL)
Four “M’s” viz. men, material, machine & money are vital to run an organization. However the key to success of the organization lies the way our employees structure and manage the construction, operation and maintenance activities of transmission system. Construction activitiy in transmission system is an important aspect and time, quality and cost are it’s critical parameters.
Experience, no doubt, is a great teacher and a valuable asset. However, the knowledge of underlined principles of sound working is also equally important. Preparation of these user’s manuals is the work of our experienced senior field staff and I find these to be very useful to our site personnel. These manuals for transmission lines (Vol. 1 2 & 4) alongwith SFQP (Vol. 1) will be of immense help to our line staff to manage their resources in a more efficient and systematic way to achieve high quality and reduced time. I find sincere efforts have gone into preparation of these manuals for which I congratulate Construction Management team and I am sure the authors will continue their efforts to bring out more and more such manuals.
(R.P. SINGH)
CONTENTS CHAPTER-I TOWER CONFIGURATION 1.1
PURPOSE OF TRANSMISSION TOWER
1.2
FACTORS GOVERNING TOWER CONFIGURATION
1.3
TOWER HEIGHT
1.4
ROLE OF WIND PRESSURE
1.5
MAXIMUM & MI8NIMUM TEMPERATURE
1.6
LOADING OF TOWER
CHAPTER-2 TYPES OF TOWERS 2.1
CLASSIFICATION ACCORDING TO NUMBER OF CIRCUITS
2.2
CLASSIFICATION ACCORDING TO USE
2.3
400KV SINGLE CIRCUIT TOWERS
2.4
400KV DOUBLE CIRCUIT TOWERS
2.5
RIVER CROSSING TOWERS
2.6
RAILWAY CROSSING TOWERS
2.7
HIGH WAY CROSSING TOWERS
2.8
TRANSPOSITION TOWERS
2.9
MULTI CIRCUIT TOWERS
2.10
TOWER EXTENSIONS
2.11
LEG EXTENSIONS
2.12
TRUNCATED TOWERS
2.13
WEIGHT OF DIFFERENT TYPES OF TOWERS
CHAPTER-3 TOWER FABRICATION
3.1
GENERAL
3.2
BOLTING
3.3
WASHERS
3.4
LAP AND BUTT JOINTS
3.5
GUSSET PLATES
3.6
BRACING TO LEG CONNECTIONS
3.7
CONNECTION TO REDUNDANT MEMBERS
3.8
CROSS-ARM CONNECTIONS
3.9
STEP-BOLTS AND LADDERS
3.10
ANTI-CLIMBING DEVICES
3.11
DANGER AND NUMBER PLATES
3.12
PHASE AND CIRCUIT PLATES
3.13
BIRD GUARD
3.14
AVIATION REQUIREMENT
3.15
PACKING, TRANSPORTATION AND STORAGE OF TOWER PARTS
CHAPTER-4 METHODS OF ERECTION 4.1
GENERAL
4.1.1
BUILT UP METHOD
4.1.2
SECTION METHOD
4.1.3
GROUND ASSEMBLY
4.1.4
HELICOPTER METHOD
4.2
EARTHING
4.3
TRACK WELDING
4.4
PERMISSIBLE TOLERANCES IN TOWER ERECTION
ANNEXURE-E/1
-
TOOLS & PLANTS REQUIRED FOR TOWER ERECTION GANG
ANNEXURE-E/2
-
MANPOWER REQUIREMENT FOR TOWER ERECTION GANG
CHAPTER-5 GUIDE LINES FOR SUPERVISION GL-1
PRE-ERECTION CHECKS
GL-2
CHECKS DURING TOWER ERECTION
GL-3
TIGHTENING AND PUNCHING
GL-4
FIXING OF TOWER ACCESSORIES
GL-5
EARTHING
GL-6
PRE-STRINGING TOWER CHECKS
CHAPTER-6 STANDARDISATION OF TOWER DESIGN
6.1
INTRODUCTION
6.2
STANDARDISATION IN POWERGRID
CHAPTER-7 FORMAT OF TOWER ERECTION CHECKING
Chapter-1 Tower Configuration
___________________________________________________________________________ CHAPTER
ONE _________________________________________________________
TOWER CONFIGURATION
1.1
Purpose of transmission tower Back to contents page The structures of overhead transmission lines, comprising essentially the supports and foundations, have the role of keeping the conductors at the necessary distance form one another and form earth, with the specified factor of safety to facilitate the flow of power through conductor form one point to another with reliability, security and safety.
1.2
Factors governing tower configuration Back to contents page
1.2.1
Depending upon the requirements of transmission system, various line configurations have to be considered ranging from single circuit horizontal to double circuit vertical structures with single or V-strings in all phase, as well as any combination of these.
1.2.2
The configuration of a transmission line tower depends on:
1.3
(a)
The length of the insulator assembly.
(b)
The minimum clearances to be maintained between conductors and between conductor and tower.
(c)
The location of ground wire or wires with respect to the outermost conductor.
(d)
The mid span clearance required from considerations of the dynamic behavior of conductors and lightning protection of the line.
(e)
The minimum clearance of the lower conductor above ground level.
Tower height
Back to contents page The factors governing the height of a tower are: (a)
Minimum permissible ground clearance (H1)
(b)
Maximum sag (H2).
(c)
Vertical spacing between conductors (H3).
(d)
Vertical clearance between ground wire and top conductor (H4).
Thus the total height of the tower is given by H = H1 + H2 + H3 + H4 in the case of a double circuit tower with vertical configuration of conductors as shown in Fig. 1.1. 1.3.1
Minimum permissible ground clearance From safety considerations, power conductors along the route of the transmission line should maintain clearances to ground in open country, national highway, rivers, railway tracks, tele-communication lines, other power lines etc. as laid down in the Indian Electricity Rule or standards or code of practice in vogue.
1.3.2
Maximum sag of Lowermost Conductor The size and type of conductor, wind and climatic Conditions of the region and span length determine the conductor sag and tensions. Span length is fixed from economic considerations. The maximum sag for conductor span occurs at the maximum temperature and still wind conditions. This maximum value of sag is taken into consideration in fixing the overall height of the steel structures. In snow regions, the maximum sag may occur even at 0OC with conductors loaded with ice in still wind conditions. While working out tension in arriving at the maximum sag, the following stipulations laid down, in I.E. Rules (1956) are to be satisfied. (i)
The minimum factor of safety for conductors shall be based on their ultimate tensile strength.
(ii)
The conductor tension at 32OC (90OF) without external load shall not exceed the following percentages of the ultimate tensile strength of the conductor. Initial unloaded tension percent
.
.
35
Final Unloaded tension Percent
.
.
25
In accordance with this stipulation, the maximum working tension under stringent loading conditions shall not exceed 50 percent of the ultimate tensile strength or conductor. Sag-Tension computations made for final stringing of the conductors, therefore, must ensure that factor of safety of 2 and 4 are obtainable under maximum loading condition and every day loading condition, respectively.
1.3.3
Spacing of conductors The spacing of conductors is determined by considerations which are partly electrical and partly mechanical. The material and diameter of the conductors should also be considered when deciding the spacing, because a smaller conductor especially if made of aluminum, having a small weight in relation to the area presented to a cross wind, will swing synchronously (in phase) with the wind, but with long spans and small wires, there is always the possibility of the conductor swinging nonsynchronously, and the size of the conductor and the maximum sag at the centre of span are factors which should be taken into account in determining distance apart at which they should be strung.
1.3.4
Vertical clearance between ground wire and top conductor. This is governed by the angle of shielding i.e. the angle which the line joining the ground wire and the outermost conductor makes with the vertical, required for the interruption of direct lightning strokes at the ground and the minimum mid span clearance between the ground wire and the top power conductor. The shield angle varies from about 20 degrees 30 degrees, depending on the configuration of conductors and the number of ground wires (one or two) provided.
1.4 Role of wind pressure Back to contents page The wind load constitutes an important and major component of the total loading on towers and so a basic understanding of the computation of wind pressures is useful. In choosing the appropriate wind velocity for the purpose of determining the basic wind pressure, due consideration should be given to the degree of exposure appropriate to the location and also to the local meteorological data. The country has been divided inot six wind zones of different wind speeds. The basic wind speeds for the six wind zones are: Wind Zone
Basic wind speed-m/s
1
33
2
39
3
44
4
47
5
50
6
55
Fig. 1.2 shows basic wind speed map of India as applicable at 10m height above mean ground level for the six wind zones. In case the line traverses on the border of different wind zones, the higher wind speed may be considered.
1.4.1
Variation of wind speed with height At ground level, the wind intensity is lower and air flow is turbulent because of friction with the rough surfaces of the ground. After a certain height, the frictional influence of the ground becomes negligible and wind velocity increases with height.
1.4.2
Wind force on structure The overall load exerted by wind pressure, on structures can be expressed by the resultant vector of all aerodynamic forces acting on the exposed surfaces. The direction of this resultant can be different from the direction of wind. The resultant force acting on the structure is divided into three components as shown in Figure 1.3. These are : (a)
A horizontal component in the direction of wind called drag force FD.
(b)
A horizontal component normal to the direction of wind called horizontal lift force FL H.
(c)
A vertical component normal to the direction of wind called the vertical lift force FLV.
1.5 Maximum & minimum temperature :Back to contents page A knowledge of the maximum and the minimum temperature of the area traversed by transmission line is necessary for calculating sag and tensions of conductors and ground wires, thereby deciding the appropriate tower design. The maximum and minimum temperature normally vary for different localities under different diurnal and seasonal conditions. The absolute maximum and minimum temperature which may be expected in different localities in the country are indicated in the map of India in Fig.1.4 and 1.5 respectively. The temperature indicated n these maps are the air temperatures in shade. The absolute maximum temperature values are increased suitably to allow for the sun’s radiation, heating effect of current, etc. in the conductor. The tower may be designed to suit the conductor temperature of 75 degree C (max) for ACSR and 85 degree C (max) for aluminum alloy conductor. The maximum temperature of ground wore exposed to sun may be taken as 53 degree C.
1.6
Loading of transmission line towers Back to contents page
1.6.1
As per revision o IS;802 regarding materials, loads and permissible stresses in transmission line owes, concept o reliability, security and safety have been introduced. (a)
Reliability The Reliability that a transmission system performs a given task, under a set of conditions, during a specified time. Reliability is thus a measure of the success of a system in accomplishing task. The complement to reliability is the probability of failure or unreliability. In simple terms, the reliability may be defined as the probability that a given item will indeed survive a given service environment and loading for a prescribed period of item.
(b)
Security:The ability of a system to be protected from a major collapse such as cascading effect, if a failure is triggered in a given component. Security is a deterministic concept as opposed to reliability which is a probabilistic concept.
(c)
Safety:The ability of a system not to cause human injuries or loss of lives. It relates mainly to protection of workers during construction and maintenance operation. The safety of public and environment in general is covered by National regulations.
1.6.2
Nature of loads on Transmission Tower Transmission lines are subjected to various loads during their life time. These are classified into three distinct categories, namely: (a)
Climatic loads:Which relates to reliability requirements.
(b)
Failure containment loads:Which relates to security requirements.
(c)
Construction & maintenance loads:Which relates to safety requirements.
1.6.3
Computation of various loads on towers
The loads on of various loads on towers consist of three mutually perpendicular systems of loads acting vertical, normal to the direction of the line, and parallel to the direction of the line. It has been found convenient in practice to standardise the method of listing and dealing with loads as under: Transverse load Longitudinal load Vertical load Torsional shear Weight of structure Each of the above loads is dealt with separately below: (a)
Transverse load due to wind on conductors and ground wire The conductor and ground wire support point loads are made up of the following components: (i)
Wind on the bare (or ice-covered) conductor / ground wire over the wind span and wind on insulator string.
(ii)
Angular component of line tension due to an angle in the line (Figure 1.7). The wind span is the sum of the two half spans adjacent to the support under consideration. The governing direction of wind on conductors for an angle conditions is assumed to be parallel to the longitudinal axis of the cross-arms (Fig.1.8). Since the wind is blowing on reduced front, it could be argued that this reduced span should be used for the wind span. In practice, however, since the reduction in load would be relatively small, it is usual to employ the full span.
(b)
Transverse load due to line deviation The load due to an angle of deviation in the line is computed by finding the resultant force produced by the conductor tensions (Fig. 1.7) in the two adjacent spans. It is clear from the figure that the total transverse load = 2T Sin Ø/2 where Ø is the angle of deviation and T is the conductor tension.
(c)
Wind load on tower In order to determine the wind load on tower, the tower is divided into different panels having a height ‘h’. These panels should normally be taken between the intersections of the legs and bracings.
1.6.3.2
Longitudinal load (a)
Longitudinal load acts on the tower in a direction parallel to the line (Fig. 1.6B) and is caused by unequal conductor tensions acting on the tower. This unequal tension in the conductors may be due to deadending of the tower, broken conductors, unequal spans, etc. and its effect on the tower is to subject the tower to an overturning moment, torsion, or a combination of both. In the case of dead-end tower or a tower with tension strings with a
broken wire, the full tension in the conductor will act as a longitudinal load, whereas in the case of a tower with suspensions strings, the tension in the conductor is reduced to a certain extent under broken-wire conditions as the string swings away from the broken span and this results in a reduced tension in the conductor and correspondingly a reduced longitudinal load on the tower. (b)
Torsional load: The longitudinal pull caused by the broken wire condition imposes a torsional movement, T, on the tower which is equal to the product of unbalanced horizontal pull, P and its distance, from the centre of tower in addition to the direct pull being transferred as equivalent longitudinal shear, P as shown in Fig.1.9. The shear P and the torsional movement T = Pe gets transferred to tower members in the plane ABCD.
1.6.3.3
Vertical Load Vertical load is applied to the ends of the cross-arms and on the found wire peak (Fig.1.6C) and consists of the following vertical downward components: (i)
Weight of bare or ice-covered conductor, as specified, over the governing weight span.
(ii)
Weight of insulators, hardware etc., covered with ice, if applicable.
(iii)
Arbitrary load to provide for the weight of a man with tools.
1.6.3.4
Weight of structure
The weight of the structure like the wind on the structure, is an unknown quantity until the actual design is complete. However in the design of towers, an assumption has to be made regarding the dead weight of towers. The weight will no doubt depend on the bracing arrangement to be adopted, the strut formula used and the quality or qualities of steel used, whether the design is a composite one comprising both mild steel and high tensile steel or make use of mild steel only. However, as a rough approximation, it is possible to estimate the probable tower weight from knowledge of the positions of conductors and ground wire above ground level and the overturning moment. Having arrived at an estimate of the total weight of the tower, the estimated tower weight is approximately distributed between the panels. Upon completion of the design and estimation of the tower weight, the assumed weight used in the load calculation should be reviewed Particular attention should be paid to the footing reactions, since an estimated weight which is too high will make the uplift footing reaction too low. 1.6.3.5
Various loads as mentioned above shall be computed for required reliability, security and safety.
Chapter-2 Types of Towers
-------------------------------------------------------------------------CHAPTER
TWO --------------------------------------------------------------------------
TYPES OF TOWERS
2.1
Classification according to number of circuits Back to contents page The
majority
transmission
of
lines
high
voltage
employ
vertical configuration
a
double
vertical
circuit
or
nearly
of conductors and single
circuit transmission lines a triangular arrangement of
conductor, single circuit lines, particularly
at 400 KV and above, generally employ horizontal arrangement
of
conductors.
The
conductor and ground wires in
arrangement
of
these configurations
is given at Figure No. 2.1 to Figure No. 2.5. The number of ground wires used on the line depends on the isoceraunic level (number of thunderstorm days/hours
per
year) of the area, importance
the
and
the
line,
Single
circuit
angle
of
lines
using
configuration generally employ due to the comparative whereas
lines
coverage
desired. horizontal
two ground wires,
width of the configuration;
using
vertical
and
offset
arrangements more often utilise one ground except
on
above, where string
two
of
higher voltage lines of 400 KV
wire and
it is usually found advantageous to ground
wires,
as
the
phase
to
phase
spacing of conductors would require an excessively high positioning of ground coverage.
Details
of
wire to give adequate
different
types
of
400
KV
single circuit and 400 KV double circuit towers are given at Clause No. 2.3 and 2.4.
2.2. Classification according to use Back to contents page Towers
are
independent
classified
of
the
according
number
of
to
their
conductors
use they
support. A tower has to withstand the loadings ranging from straight runs up to varying angles and dead ends. To
simplify
economy
in
the
designs
first
cost
and and
ensure
an
maintenance,
overall tower
designs are generally confined to a few standard types as follows. 2.2.1 Tangent suspension tower Suspension towers are used primarily on tangents but often line
are designed to withstand angles in the
up to two degrees or higher in addition to
the wind,
ice, and
transmission
line
broken-conductor loads. If the traverses
relatively
flat,
featureless terrain, 90 percent of the line may be composed of this type of tower. Thus the design of tangent
tower
provides
for the structural
the
engineer
greatest
opportunity
to minimise the total
weight of steel required.
2.2.2 Angle towers Angle towers, sometimes called semi-anchor towers, are used where the lines makes a horizontal angle
greater than two degrees (Figure 2.6). As they must resist a transverse load from the components of the line tension induced by this angle, in addition to the they
usual are
wind,
ice
and
necessarily
broken
heavier
conductor than
loads,
suspension
towers. Unless restricted by site conditions, or influenced
by
conductor
tensions,
angle
towers
should be located so that the axis of the crossarms bisects the angle formed by the conductors. Theoretically, different
towers,
different
line
but
economy
for
angles
require
there
is
a
limiting number of different towers which should be used. This number is a function of all the factors which make the total erected cost of a tower line. However, experience has shown that the following angle towers are generally suitable for most of the lines : 1. Light angle
- 2 to 150 line deviation
2. Medium angle
- 15 to 300 line deviation
3. Heavy angle
- 30 to 600 line deviation (and dead end)
While the angles of line deviation are for the normal span, the span may be increased up to an optimum
limit
by
reducing
the
angle
of
line
deviation and vice versa. IS:802 (Part I) - 1977 also recommends the above
classification.
The loadings on a tower in the case of a 60 degree angle condition and dead-end condition are almost the same. As the number of locations at which 60 degree
angle
towers
and
dead-end
towers
are
required are comparatively few, it is economical to design
the
heavy
degree
angle
angle
condition
towers and
both
dead-end
for
the
60
condition,
whichever is more
stringent
for each individual
structural member. For each type of tower, the upper limit of the angle range
is designed for the same basic span as
the tangent tower, so that a decreased angle can be accommodated with an increased span or vice versa. It would be uneconomical to use 30 degree angle towers in locations where angles higher than
2
degree and smaller than 30 degree are encountered. There are limitations to the use of 2 degree angle towers at higher angles with reduced spans and the use of 30 degree angle towers with smaller angles and
increased
spans.
The
introduction
of
a
15
degree tower would bring about sizable economics. Pilot suspension insulator string - This shall be used if found necessary to restrict the jumper swings to design value at both middle and outer phases. Unequal cross arms -
Another method to get over the difficulty of
higher swing of Jumper is to have unequal cross arms. 2.3
400 kv single circuit towers Back to contents page The bundled conductors are kept in horizontal configuration phase
with a minimum clearance of 11 mtrs.
to phase.
The
latticed
parts
are
fully
galvanised.
Galvanised hexagonal round head bolts and nuts are used for fastening with necessary spring or plate washers. Normally 4 types of single circuit towers are used as detailed below :a) "A" type towers : These
towers
are
used
as
tangent
towers
for
straight run of the transmission line. These are called suspension or tangent towers. These towers can carry only vertical loads and are designed for carrying the weight of the conductor, insulators and
other
accessories.
These
designed for a deviation upto
towers
are
also
2 degrees.
b)" B" type towers : These towers can be used as sectionalising towers without angle and angle towers from 2 degrees up to 15 degrees deviation. c) " C" type towers These towers can be used for deviations ranging from 15 degrees up to 30 degrees. They are also being
used
as
transposition
towers
without
any
angle. d) "D" type towers : These towers can be used as Dead End or anchor towers without any angle on the tower.
Also these
towers can be used for deviations ranging from 30
degree
-
60 degree.
These towers are usually provided as terminal towers near gantry with slack span on one side or as
anchoring
tower
before
major
river
crossing,
power line crossing, railway crossings etc. Fig. 2.8 shows two types of tower configuration for 400 KV single circuit towers. A section of 400 kv single circuit towers is shown in Fig.2.9.
2.4
400 KV Double circuit towers Back to contents page These towers are designed to carry two circuits consisting
of
3
conductors.
Here,
phases the
each,
circuits
having are
bundled
placed
in
a
vertical configuration. A minimum phase to phase clearance
of
8
clearance
of
11
mtrs. mtrs.
is is
maintained. maintained
A
minimum from
one
circuit to another. Two earthwires are placed above each circuit in such a way to provide the required shielding angle.
Like single circuit towers, these towers are also galvanised, lattice steel type structures designed to carry the tension and weight of the conductor alongwith
the
insulators,
earthwire
and
its
accessories. Normally these towers are identified as P (D/C suspension towers), Q, R & S (D/C tension towers) or as
DA, DB, DC and DD respectively.
As in the single circuit towers, DA/P towers are used as suspension towers from O degrees-2
degrees
deviations. DB/Q,DC/R and DD/S towers are used as tension
towers
with
angle
of
deviation
from
2
degrees-15 degrees, 15 degrees-30 degrees and 30 degrees - 60 degrees respectively. DB towers are also used as sectionalising towers without angle. DC tower is also used as transposition tower without any angle. The Double Circuit towers are used while crossing reserved
forest,
corridors
near
major
river
switchyards
crossings,
etc.
so
as
narrow to
make
provision for future transmission lines since the approval from various at
one
time
(for
authorities can be obtained
example,
from
forest,
aviation
authorities etc.) and to minimise expenditure in laying foundations in rivers. Fig.2.8 shows two types of tower configuration for
400 kv double circuit towers. 2.5
River-crossing tower Back to contents page The
height
considerably
`unbroken'
governing
weight
depending
clearance above of
and
of
on
water, ice
the
towers
span,
vary
minimum
and wind loads, number
conductors,
specification
the
etc.
requires
Usually that
the
towers
employed for crossing of navigable water ways be designed for heavy loading conditions and utilise larger minimum size members than the remainder of the
line.
In
addition
to
these
structural
requirements, it is often necessary to limit the height
of
tall
crossing
towers
because
of
the
hazard they present to aircraft. Fig.2.10 shows a view of 400 kv double circuit River crossing tower. 2.6
Railway crossing tower Back to contents page Angle or dead end towers (Type B,C or D) with suitable
extensions
and
with
double
tension
insulator strings are employed for railway crossing in conformity with the relevant specification of Railway Authorities. 2.7
High way crossing tower Back to contents page Angle
towers
(Type
B,C
or
D)
with
suitable
extension employed
and for
with high
double way
tension
crossing.angle
strings
are
towers
are
used for National High way crossing to make the crossing
span
as
a
single
section
so
facilitate independent and prompt striginig.
as
to
2.8
Transposition tower Back to contents page
2.8.1 Power transmission lines are transposed primarily to
eliminate
or
reduce
disturbances
in
the
neighboring communication circuits produced by the geometric imbalance of power lines. An incidental effect of transposing power line section is the geometric
balancing
of
such
terminals which assumes every point of the Improvements
and
communications
and
circuits
between
balanced conditions at
power
transmission system.
developments
in
power
have,
fields
both
the
however,
greatly reduced the need for transposition of high voltage lines at close India,
the
central
intervals. In fact, in standing
committee
for
coordination of power and telecommunication system has ruled that "the
power supply authorities need
not provide
transposition
coordination
with
on power
lines
for
telecommunication lines".
2.8.2 However, when transposition are eliminated, there are
the
effects
of
geometric
imbalance
of
the
conductor arrangements on the power system itself, and the residual imbalance asymmetry
of of
current
the
three
conductor
to be considered. phase
voltages
arrangement
due is
The to not
considered serious in view of the equalizing effect
of
the
three
synchronous
phase
transformer
machinery at various
bank
points
on
and the
system. The remaining consideration viz. residual currents due to the elimination of transposition, might be important from the point of view of relay settings to
prevent
causing undesirable
tripping
of ground current relays. Operating experience has shown that many disturbance on high voltage line occur
on
records
transposition
indicate
outages
is
that
towers
at
least
physically
and one
statistical of
associated
the with
four a
transposition. 2.8.3 A good practice would be to adopt about 200 KM as the permissible length of the line without taking recourse
to
special
transposition
transposition being confined
structures,
to substation
and
switching station only, provided they are located at suitable intervals. 2.8.4 Tower type C under O degree deviation limit and with
suitable
modification
shall
be
used
for
transposition for line maintaining all the required clearances
and
shielding.
Arrangement
of
transposition is shown at Figure 2.7. A view of 400 kv single circuit transposition tower is also shown in Fig.2.11. 2.9
Multi circuit towers. Back to contents page
To transmit bulk power at a economical rate, Multi circuit towers are used. It may be mentioned here that
a
double
circuit
line
is
cheaper
than
two
independent single circuit lines and four circuit line
cheaper
than
two
double
circuit
lines.
However, the capital outlays involved become heavy and it is not easy to visualise the manner in which the loads build up and the powerflow takes place in the
longterm
prospective.
Further,
reliability
considerations become very important at extra voltages. between
A
balance
has
therefore
the two somewhat opposing
to
be
high struck
considerations.
2.10
Tower extensions Back to contents page All towers are designed in such a way that they can be provided with standard tower extensions. Extensions are designed as +3, +6 +9 and + 25 in Mtrs.
These
extensions
can
be
used
alongwith
standard towers to provide sufficient clearance over ground or while crossing power lines, Railway lines, highways, undulated, uneven ground etc. A view of 400 kv single circuit towers crossing anoth er 400 kv single circuit line is shown at Fig. 2.12 2.11
Leg extensions Back to contents page Leg extensions are designed to provide extension to
tower
ground
legs
which
are
located
at
uneven
where different legs of the tower are at
different levels.
Standard designs can be made for 1.5, 2.5 and 3.5 M leg extensions. These leg extensions can be utilised where towers are located on hill slopes, undulated ground etc. By
providing
areas,
leg
heavy
avoided
extensions,
cost
of
specially
in
benching/revetment
hilly
can
be
completely or reduced substantially.
2.12 Truncated towers
(Tower reductions) Back to contents page
Similar to extension towers, truncated towers can also be used for getting the sufficient electrical clearance while crossing below the existing
Extra
High
Mtrs.
Voltage
lines.
For
instance,a
DD-6.9
truncated tower has been used in 220 KV RSEB S/Stn. at Heerapura (Jaipur). In this particular case 2 nos. of 400 KV S/C lines are already crossing over the 220 KV D/C Kota-Jaipur RSEB feeders with A+25 Mtrs. extension type of towers. While constructing another D/C 220 KV line from Anta to Jaipur which was
also
to
be
terminated
in
the
same
sub-stn.
either to under cross these 400 KV S/C lines by using gantry system or to make use of
the existing
A+25 Mtrs. extension towers. But with the existing A+25
Mtrs
extension
tower,
required
clearance
between the earth wire of the 220 KV line and hot Conductor
of
permissible
400 limit.
KV So
lines for
were
not
getting
within
the
the
required
electrical clearance either to remove the earthwire of 220 KV line or to use truncated tower. So to avoid
the
removal
of
earth
wire
a
`DD'
type
truncated tower (-6.9 Mtrs.) has been used in order to cross these lines safely and with the required permissible electrical clearances. The truncated tower is similar to normal tower except 6.9 has
Mtrs
of bottom section of normal tower
been removed, the other section of the tower
parts
remain un-changed.
This is a ideal crossing in an area where one line has already crossed over the existing lines
with
Special extension tower and we have to accommodate another line in the existing crossing span. 2.13
Weight of different types of towers Back to contents page The weight of various types of towers used on transmission lines, 66 KV to 400 KV, together with the
spans and
sizes of conductor and ground wire
used in lines are given in Table 2.1. Assuming that 80
percent
towers towers,
and and
are 5
tangent
towers,
percent
600
allowing
15
15
towers percent
percent and
300
dead-end
extra
for
extensions and stubs, the weights of towers for a 10 kms. line are also given in the Table 2.1. Table 2.1 Weights of towers used on various voltage categories in India
(Metric tones) 400 kV
220 kV
220 kV
132 kV
132 kV
66 kV
66 kV
Single
Double
Single
Double
Single
Double
Single
Circuit 400 Moose
Circuit 320 Zebra
Circuit 320 Zebra
Circuit 320 Panther
Circuit 320 Panther
circuit 245 Dog 6/4.72
Circuit 245 Dog 6/4.72
54/3.53 mm
54/3.18 mm
54/3.18
30/3 mm
30/3 mm
mm Al. +
Al. +
al. + 3.53
Al +
mm Al. +
Al. +
Al.+7/3
7/1.57 mm
7/1.57 mm
mm Steel
7/3.18 mm
7/3.18
7/3 mm
mm Steel
Steel
Steel
7/4 mm 110
Steel 7/3.15 mm
mm Steel 7/3.15
Steel 7/3.15
7/3.15
7/2.5 mm
7/2.5 110
Kgf/mm2
110
mm 110
mm 110
mm 110
110
Kgf/mm2
quality
Kgf/mm2
Kgf/mm2
Kgf/mm2
Kgf/mm2
Kgf/mm2
quality
Tangent Tower 30 Deg. Tower 60 Deg. And Dead-end
7.7 15.8 23.16
quality 4.5 9.3 13.4
quality 3.0 6.2 9.2
quality 2.8 5.9 8.3
quality 1.7 3.5 4.9
quality 1.2 2.3 3.2
0.8 1.5 2.0
Tower Weight of towers for
279
202
135
126
76
2
48
20%
reduction
Span (m) Conductor
Groundwire
a 10-km line
Note:
Recent
weights.
designs
have
shown
10
to
in
-------------------------------------------------------------------------CHAPTER
THREE
Chapter-3
--------------------------------------------------------------------------
Tower Fabrication 3.1
TOWER FABRICATION
General Back to contents page After
completing
assembly details
drawing of
the is
joints,
tower
design,
a
prepared.
This
gives
member
sizes,
bolt
structural complete
gauge
lines,
sizes and lengths of bolts, washers, first and slope
dimensions,
etc.
From
this
drawing,
second a
more
detailed drawing is prepared for all the individual members. This is called a shop drawing or fabrication drawing. Since all parts of the tower are fabricated in accordance with the shop drawing, the latter should be drawn to a suitable scale, clearly indicating all the details required to facilitate correct and smooth fabrication. Towers used are of bolted lattice type. In no case welding
is
allowed.
fittings are
All
members,
galvanised. Spring
bolts,
nuts
washers are
and
electro
galvanised. Fabrication of towers are done in accordance with IS codes which is ensured by visit to the fabrication workshops
and
undertaking
specified
tests,
in
the
presence of POWERGRID quality engineers. The following may be ensured during fabrication of the towers.
i)
Butts, splices should be used and thickness of inside
cleat
should
not
be
less
than
that
of
heavier member connected. Lap splices are used to connect unequal sizes. ii)
While designing, joints are to be made so that eccentricity is avoided.
iii) Filler should be avoided as far as practicable. iv)
The dia of hole = dia of bolt
+ 1.5 mm
v)
Drain holes are to be provided where pockets of depression are likely to hold water.
vi)
All similar
parts should
be interchangeable
to
facilitate repairs. vii) There should be no rough edges. viii) Punched holes should be square with plates and must have their walls parallel. ix)
It
should
drilling completely.
be or
checked
that
punching Drilling
or
all
burrs
should
be
reaming
to
left
by
removed enlarge
defective holes is not allowed. 3.2
Bolting Back to contents page
3.2.1 The minimum diameter of bolts used for the erection of transmission line towers is 12 mm. Other sizes commonly used are 16 mm and 20 mm. 3.2.2 The length of the bolt should be such that the threaded portion does not lie in the plane of contact of members.
Figure 3.1 shows the wrong uses and the correct uses of bolt threads. 3.2.3 Table 3.1 gives the minimum cover to free edge and bolt spacing as per IS:802 (Part II)-1978 Code of Practice for Use of Structural Steel in Overhead Transmission line Towers. The bolts used with minimum angle sizes restrict the edge distances as given in Table 3.2 for the bolt sizes of 12 mm, 16 mm and 20 mm used on 40 x6 mm, 45x6 mm and 60x 8 mm angle sizes respectively.
Table 3.1 Spacing of bolts and edge distances (mm) ------------------------------------------------------------Bolt Hole Bolt spacing Edge distance(min) Dia dia min. Hole Hole centre centre to rolled to edge sheared edge ------------------------------------------------------------12 13.5 32 16 20 16 17.5 40 20 23 20 21.5 48 25 28 ------------------------------------------------------------(See next page)
Table 3.2 Maximum edge distance possible with minimum angle size (mm) --------------------------------------------------------Size of bolted Maximum edge Bolt dia. leg of angle distance that section and its can be thickness actually obtained -------------------------------------------------------12 40x6 17 16 45x6 18 20 60x8 25 --------------------------------------------------------
3.2.4 The bolts may be specified to have Whitworth or other approved standard threads to take the full depth
of
the
nut,
enough to permit
with
the
threading
done
far
firm gripping of the members but
no farther, and with the threaded portion of each bolt projecting through the nut by at least one thread.
It
may
also
be
specified
that
the
nuts
should fit hand-tight to the bolts, and that there should be no appreciable fillet at the point where the
shank
Emphasis
of
the
should
bolt be
connects
laid
on
to
the
head.
achieving
and
maintaining proper clamp load control in threaded fastners.
If
a
threaded
fastener
is
torqued
too
high, there is a danger of failure on installation by stripping the threads or breaking the bolt or making the fasteners yield excessively. If the bolt is torqued too low, a low preload will be induced in the fastener assembly, possibly inviting fatigue or vibration failure. For every bolt system, there
is an optimum preload objective which is obtained by proper torquing of the bolt and nut combination. The three techniques for obtaining the required pretension are the calibration wrench method, the turn-of-the-nut
method
and
the
direct
tension
indication method. The calibrated wrench method includes the use of manual torque wrenches and power wrenches adjusted to stall at a specified torque value. Variations in bolt tension, produced by a given torque, have been found to be plus minus 10 percent. The turn-of-the-nut method has been developed where the pretensioning force in the bolt is obtained by specified
rotation
of
the
nut
from
an
initially
snug tight position by an impact wrench or the full effort
of
a
method
is
man
using
found
to
an
be
ordinary
reliable,
wrench. cheapest
This and
preferred. The
third
establishing indicator.
and
bolt There
washers,
where
assessed
by
the
most
tension
is
recent by
method
direct
tension
are
patented
correct
bolt
tension
the
deformation.
observing
load
for
indicating could
be Upon
tightening the bolt, the washers are flattened and the gap is reduced. The bolt tension is determined by measuring the remaining gap. 3.2.5 Most of the transmission line specifications do
not specify the maximum permissible group length of bolts. It is a good practice to ensure that no bolt connects aggregate thickness more than three times the
diameter of the bolt. Further more, the grip
strength developed by a bolt depends not only upon the thickness of the members but also on the number of members to be connected. This is due to the fact that
the
surface
of
the
members
may
not
be
perfectly smooth and plain and, therefore, if the number of members to be connected is too many, the full grip strength would not be developed. In the tower construction, the need for connecting more than three members by a single bolt rarely arises, it would be reasonable to limit
the number of the
members to be connected by a single The
limitation
regarding
the
bolt to three.
thickness
of
the
members and the number of members to be connected is necessary not only from the point of view of developing maximum grip strength but also from the point of view of reducing the bending stresses on the bolt to a minimum. 3.2.6 The threaded portion of the bolt should protrude not less the 3.3
than
3 mm and not more than 8 mm
over
nut after it is fully tightened.
Washers Back to contents page At present, both flat and spring steel washers are
being
used
in
line
towers
the
in
construction
India.
The
of
transmission
advantage
of
spring
washers over flat washers is that the former, in addition to developing the full bearing area of the bolt,
also
serve
to
lock
the
nuts.
The
disadvantages, however, are that it is extremely difficult to get the correct quality of steel for spring washers, and also that they are too brittle and
consequently
break
when
the
nuts
are
fully
tightened. Furthermore, the spring washers, unlike flat
washers
tend
to
cut
into
and
destroy
the
galvanising. When spring washers are used, their thicknesses should be as recommended in IS:802 (Part II)-1978 and given in Table. 3.3 Table 3.3: Thicknesses of spring washers (mm) -----------------------------------------------------------Bolt dia. Thickness of spring washer -----------------------------------------------------------12 2.5 16 3.5 20 4.0 -----------------------------------------------------------With general
regard practice
to is
the to
locking lock
the
arrangement, nuts
by
the
centre
punching of the bolts or punching the threads. In special cases such as tall river-crossing towers which
are
subjected
to
unusual
vibrations,
the
bolts are secured from slacking back by the use of
lock nuts, by spring washers, or by cross-cutting of the thread. A
minimum
thickness
of
3mm
for
washers
is
generally specified. In our transmission lines, we are using spring
3.4
washers
under
all
nuts
of
tower.
washers
are electro-galvanised.
These
spring
Lap and butt joint (figure 3.2 and 3.3) Back to contents page Lap splices are normally preferred for leg members as
these
joints
economical
are
compared
generally to
the
simpler
heavier
and
butt
more
joints
which are employed only if structural requirements warrant their use. In lap splices, the back(heel) of the inside should
be
ground
to
clear
the
fillet
angle of
the
outside angle. 3.5
Gusset plates Back to contents page In the case of suspension towers, the stresses in the web system are usually small enough to keep the use
of gusset plates to the minimum. On heavier
structures, however, the web stresses may be very large and it
may not
be
possible to accommodate
the number of bolts required for the leg connection in
the
space
available
on
the
members,
thus
necessitating the use of gusset plates. Plates may also be required to reduce the secondary stresses introduced due to eccentricity to a minimum. The bracing members should preferably meet at a common point
within
the width of the tower leg in
order to limit the bending stresses induced in the main members due to eccentricity in the joints. To satisfy
this
condition,
it
may
necessary to use gusset plates.
sometimes
become
3.6
Bracing to leg connections Back to contents page Typical connections of diagonals and struts to a leg member are shown in Figure 3.4. The number of bolts required in these simple connections load and bearing.
is
derived
directly
from
the
member
the capacity per bolt either in shear or Diagonal
members
which
are
clipped
or
coped for clearance purposes must be checked for capacity
of
the
reduced
net
section.
Note
that
gusset plates are not used at leg connections, but eccentricity is kept to a minimum by maintaining a clearance of 9.5mm to 16mm between members. If the leg does not provide enough gauge lines to accommodate
the
required
bolts
in
a
diagonal
connection, a gusset plate as shown in Figure
3.5
may be employed. The thickness of gusset plate must be
sufficient
to
develop
the
required
load
per
bolt. Typical gusset plate connection at waist lines on the normal face for a wasp-waist tower is shown in Figure 3.6.
3.7
Connection of redundant members Back to contents page Redundant sub-members usually require only one
bolt connection to transfer their nominal loads. Thus,
gusset
clipping
and
plates coping
can
easily
are
be
used
avoided
to
if
advantage.
Typical connections, shown in Figures 3.7, 3.8 and 3.9 indicate the methods of clipping or turning members in or out to keep the number of bolts to a minimum. Figure 3.7 illustrates the use of a small plate rather than connecting five members on one bolt, as it has been found that erection of more than
four
thicknesses
per
bolt
is
particularly
awkward. 3.8
Cross-arm connections Back to contents page The cross-arm to leg connection (Figure 3.10) must be considered as one of the most important joints on
a tower
since all loads originating from the
conductors are
transferred
to
shaft
the
tower
by
through the cross-arms means
of
these
bolts.
Because of its importance, a minimum of two bolts is often specified for this connection.
An example of a hanger-to-arm-angle connection on `Vee' cross-arm is shown in Figure 3.11, Both vertical and horizontal eccentricities may become excessive if the detail of this joint is not carefully worked out. Suspension towers are provided with holes at the
ends
3.10,
of
for
string
the
cross-arms,
U-Bolts
clamps.
which
Strain
as
shown
receive
towers,
in
the
Figure
insulator
however,
must
be
supplied with strain plates (Figure 3.12) which are not
only
capable
of
resisting
the
tension, but also shock and fatigue
full
line
loads as well
as wear. 3.9
step bolts and ladders Back to contents page The step bolts usually adopted are of 16mm diameter and 175mm length. They are spaced 450mm apart and extend from about 3.5 metres above the ground level to the top of the tower. The bolts are provided with
two
securely
nuts to
on
the
one
tower,
end
to
and
fasten
button
the
heads
bolts at
the
other end to prevent the foot from slipping away. The step bolts should be capable of withstanding a vertical load of not less than 1.5 KN. Step bolts are provided from 3.5 m to 30 m height of the superstructure. For special structures, where the height
of
the
superstructure
exceeds
50
metres,
ladders along with protection rings are provided
(in
continuation
longitudinal above
of
face
ground
of
level
the the
to
step
bolts
tower)
the
from
top
of
on 30
the
the
metres special
structure. A platform, using 6mm thick chequered plates, from
along with a suitable
step
ladder
railing
bolts to the ladder
to
each
cross-arm,
and
for access
and the
from
the
ground
wire
support is also provided. 3.10
Anti-climbing devices Back to contents page All towers are provided with anti-climbing devices at
about
details
3.5
of
metres
above
anti-climbing
ground
devices
level.
are
The
shown
in
Figure 3.13. 3.11
Danger and number plates Back to contents page Provision is made on the transverse face of the tower for fixing the danger and number plates while developing accessories
the are
fabrication generally
fixed
drawing. at
about
These 4.5mm
above the ground level. Fig. 3.18 and Fig.3.16 show the
details
of
danger
and
number
plates
respectively. The letters, figures and the conventional skull and bones of the danger plates should conform to IS:2551-1982 Specification for Danger Notice Plates and
they are
to
be painted in signal red on the
front
of
the plate.
3.12
Phase and circuit plates Back to contents page Each tension tower shall be provided with a set of phase plates. The transposition towers should have the provisions of fixing phase plates on both the transverse faces. The details of phase plate are given in Fig. 3.15. All the double circuit towers shall be provided with
circuit
details
of
plate
fixed
circuit
near
plates
are
the
legs.
The
indicated
in
Fig.3.17. These plates shall also be fixed at about 4.5m above ground level. 3.13
Bird guard Back to contents page Perching of Birds on tower cross arms results in spoiling of insulator discs of suspension strings which leads to tripping of line. To overcome this problem,
bird
guards
are
fixed
over
suspension
insulator string. The details are given at Figure No. 3.14. Bird guards shall be used for type-I string only.
3.14
Aviation requirements :Back to contents page
3.14.1 The river crossing towers and any other towers in
the vicinity of an airport shall be painted and the crossing caution
span
shall
be
provided
with
markers
to
the low flying air craft.
3.14.2 The full length of the towers shall be painted over of
the
galvanised surface in contrasting bands
orange or
red
and
white. The bands shall be
horizontal. Fig.2.10 shows the river crossing tower with aviation paints.
3.15
Packing, transportation and storage of tower parts. Back to contents page
3.15.1
Packing : a)
Angle section shall be wire bundled. Cleat angles,
gusset
plates,
hangers
plates,
brackets,
fillet
and similar loose pieces
shall be bolted together to multiples or securely wired together through holes. b)
Bolts, nuts, washers and other attachments shall
be
packed
in
double
gunny
bags
accurately tagged in accordance with the contents. c)
The
packing
shall
be
properly
done
avoid losses/damages during transit.
to
Each
bundle or package shall be appropriately marked. 3.15.2
Transportation. The transport of steel towers from the works to the nearest railway station presents no special difficulty. The towers are delivered in trucks having one or two towers per truck according to the weight involved. A station having a loading bay
is
highly
desirable,
as
this
greatly
facilitates handling. The lorries can be backed against the bay and the ease of then
offset
any
slight
handling
increase
in
will
haulage
costs from a station less well equipped. The parts of each tower should be kept separate so that they can be delivered from the bay direct to the tower site. Tower sets are made up in sections,
since
it
is
impracticable
for
the
corner angles to be in one length. Each section is
carefully
section
marked
at
the
works.
In
each
there are generally one or more panels
and these are marked to facilitate erection. The tower sets should be carefully checked when unloaded
from
the trucks and then placed in a
suitable position on the bay where they can be picked up easily as
a
complete unit. If the
steelwork is delivered in bundles, the checking is even more important and there are two methods
of
laying
doing the
this.
steelwork
Some out
Engineers in
members
prefer while
others prefer it laid out in towers and in our opinion
the
advantages.
latter Shortages
method are
has easily
many spotted
and scheduled and the tower can be loaded and taken to its particular position. All bolts, washers, nuts and small parts should be in bags and labelled with the number of the tower they are intended for. A word of warning
re-garding
the handling of the long corner angles be
should
clearly displayed. These must be carefully
transported or they may get bent and it is a very difficult job to straighten them without damaging
the
transport
shall
suitable
for
effects
of
galvanising. be
the any
All
undertaken
purpose
and
chemical
material
in
vehicles
free
from
substances.
the
Tower
members shall be loaded and transported in such a manner that these are not bent in transit and sharp-bent
members
are
not
opened
up
or
location
of
a
important
as
the
damaged. 3.15.3
Storage. A.
The
selection
construction
of
store
is
movement of construction materials is time consuming process and it requires detailed planning
and
Managerial
attention.
The
selection of location is generally based on the following criteria. a.
Close
proximity
to
rail
heads,
National
Highways. b.
Proximity to urbanisation and towns.
c.
Availability
of
water
and
electrical
power. d.
Distance
from
the
land.
(The
proposed
line
and
approach. e.
Type
of
store
should
not
be
located on marshy or wet lands. Also, the
low lying and water stagnant areas) f.
Availability of land in sufficient area.
g.
Communication facilities.
h.
Availability of labour for the work in the stores.
B.
Once
land
is
selected,
it
is
better
to
identify the space for towers, insulators, conductors, plants
hardware
of
selection
and
erection of
place
the
tools
contractor. for
each
type
& The of
material should be very judicious and in such
a
movement through other
way of
that one
inward item
the stacking item.
Proper
or
should
outward not
be
of the materials of board
markings
pointers may be kept for each
item
and for
easy identification. C.
Tower parts should not be kept directly on
the ground
above stones of
and it should be placed proper size or sleepers
to avoid contact with mud. D.
It is always preferable to stack the tower parts in
a neat and systematic fashion in
tower wise order. On request of erection gang,
store-keeper
should
be
able
to
provide him one full set of tower without any difficulty and delay.
E.
The following points may be ensured in the stores. a.
Complete fencing of the store yard.
b.
24 hours vigilant security.
c.
Proper lighting.
d.
Fire protection equipments.
Chapter-4 Methods of Erection
-------------------------------------------------------------------------CHAPTER
FOUR --------------------------------------------------------------------------
METHODS OF ERECTION
4.1
GENERAL Back to contents page There are four main methods of erection of steel transmission towers which are described as below i.
Built-up method or Piecemeal method.
ii.
Section method
iii. Ground assembly method. iv. 4.1.1
Helicopter method
Built up method Back to contents page This method is most commonly used in this country for the erection of 66 KV, 132 KV, 220 KV and 400 KV Transmission
Line
Towers
due
to
the
following
advantages. i.
Tower
materials
can
be
supplied
to
knocked down condition which facilitate and ii.
site
in
easier
cheaper transportation.
It does not require any heavy machinery such as cranes etc.
iii. Tower erection activity can be done in any kind of terrain and mostly through out the year.
iv. Availability of workmen at cheap rates. This method consists of erecting the towers, member by member. The tower members are kept on ground serially according to erection sequence to
avoid
search
or
time
loss.
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 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
(bet
members) if any, are bolted in position. For assembling the second section of the towers, two gin poles are placed one each on the top of the
diagonally opposite corner legs. These two
poles
are
used
for
raising
parts
of
second
section. The leg members and braces 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. The gin pole is 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 tower.
For
heavier
towers,
a
small
boom
is
rigged on one of the tower legs for hoisting purposes.
The
members/sections
Are
hoisted
either manually or by winch machines operated from
the
ground.
For
smaller
base
towers/vertical configuration towers, 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, position
keeping on
the
the ground
members and
in
correct
assembling
the
panels on the ground which can be erected as a complete unit. Sketches indicating different steps of erection by built up method are shown at Figure 4.1 to Figure 4.7. List of Tools and Plants and Manpower for Tower Erection is given at Annexure E/1 and E/2. Guying arrangement - Guying arrangements are to be done at waiste level/bottom cross-arm level as well as in the girder level/top cross-arm level depending on SC/DC towers and it is to be
installed at 450 from vertical. The deadments for
guying
arrangements
is
to
be
properly
made. A sample of deadments drawing is enclosed at Figure 4.8 for reference. Guying should be steel upon
wire
or
polypropylene
requirements.
Nominal
rope
tension
depending is
to
be
given in guying wire/rope for holding the tower in position. 4.1.2
Section method Back to contents page 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 lower 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 diagonals; and the assembled section is
lined
up,
made
square
with
the
line,
and
levelled. 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 section is raised. To raise the second face of this section it is necessary to slide
the
foot
of
the
gin
on
the
strut
to
the
opposite 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. After the tower top is placed and all side of the lacings have been bolted up, all the guys 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 bracing angles connecting these two faces are fitted.
4.1.3
Ground assembly method Back to contents page This
method
ground,
consists
and
of
erecting
assembling
as
a
the
complete
tower unit.
on The
complete tower is assembled in a horizontal position on even ground, at some distance from tower footing. The tower is assembled in a linewise position to allow
the
cross-arms
to
be
fitted.
On
sloping
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 the footing
is
chosen
for
the
tower
assembly.
This
method is not useful when the towers are large and heavy
and
land
where
would
the
building
cause
terrain
foundations
damage
where
the
and to
are
located
erecting large
assembly
of
in
arable
complete
towers
areas
or
in
complete
hilly
tower
on
slopping 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
generally
adopted
because of prohibitive cost of mobile crane, and non-availability
of
good
approach
roads
to
the
location. 4.1.4
Helicopter method Back to contents page n the helicopter method, the transmission tower is erected in sections. For example bottom section is first lifted on to the stubs and then upper section is lifted and bolted to the first section and the process
is
erected.
repeated
Sometimes
till
a
the
complete
tower
is
complete
assembled
tower
is
raised with the help of a helicopter. Helicopters are also used forlifting completely assembled towers with guys from the marshalling yards, where these are fabricated and then transported one by one to line location. The helicopter hovers over the line location
while
the
tower
is
securely
ground crew men connect and tighten
guyed.
The
the tower guyed
and as soon as the tie lines are bolted
tight, the
helicopter disengages and return to the marshalling yards
for
another
particularly
when
tower. the
This
method
approach
is
is
adopted
extremely
difficult. 4.2
Earthing Back to contents page Once
the
geometry
of
the
tower
and
the
line
insulation level are fixed, the one factor which affects the lightning performance of a line that can be controlled during the construction phase of the
line,
is
the
Tower-footing
resistance.
Consequently, this should be measured during this phase of the work and, if necessary, extra earthing provided. The measured resistance alters if the soil conditions change due to seasonal variations. When the footing resistance exceeds a desired value from the lightning protection point of view, the towers are earthed generally with pipe type and, in special cases, with counterpoise type earthing.
In
the former case, a 25mm diameter galvanised iron pipe,
3,050mm
long,
is
holes drilled at 150mm
used
with
6.5mm
diameter
apart to facilitate ingress
of moisture, and is surrounded by a layer of finely broken coke of 25mm granular size and salt. The earthing should be done in accordance with the stipulations made in IS:3043-1972 and IS:5613 (Part II/Section 1)-1976. The general earthing arrangement is shown in Figures 4.9
and
4.10.
Where
the
tower
stands
on
rock,
efforts should be made to obtain a good ground by carrying a length of galvanised steel tape from the tower leg to the
pipe driven in soil, at as short a
distance from the tower as possible. The connecting tape is burried in a groove cut in the rock surface and 4.2.1
adequately protected from damage.
Measurement of Tower Footing Resistance The megger can be used in two ways to measure the
resistivity of the soil, namely, the three point method
and
the
four-point
method.
The
method is simpler and more accurate and
four-point is
briefly
described below. a)
Soil Resistivity Four
similar
electrodes
are
burried
in
the
earth to a depth B at equal distances A from one
another
in
a
straight
line.
The
megger
connections are shown in Figure 4.11. If the crank of the instrument is then rotated at the stipulated resistance resistance
speed R, of
as
(usually read
the
on
earth
100 the
rpm),
scale,
between
is
the the
the
two
equipotential surfaces with which P1 and P2
are
in contact. If the depth of the electrode in soil B (in cm)
is
small
resistivity
of
in the
comparison soil
is
with
A,
the
given
by
the
following expression. 2x22 x AxR ----------7
P = Where
P = earth resistivity in ohms/cm3 A = spacing between the electrodes in cm, and R = resistance in ohms as read on the megger. For all practical purposes, A should be at least twenty times that of B.
b)
Tower Footing Resistance For
measuring
tower
footing
resistance,
Terminal C-1 of megger shall be connected with tower leg instead of electrode C-1. The value of
resistance
read
on
the
megger
multiplied
with multiplying factor gives the tower footing resistance in ohms.
4.3
Tack welding :Back to contents page All bolts/nuts below waist level in single circuit tower or bottom cross arm in Double circuit tower, shall
be
tackwelded
to
prevent
theft
of
tower
members. Two 10mm thick welding tacks should be done on each bolt & nut in the diagonally opposite direction by suitably selecting welding electrods of size 1.6mm to 2.5mm equivalent to over cord-S, code AWS-E6013 (Advani-Oerlikon). welding,
zinc
After
rich
removing
(90%
zinc
slag
over
content)
tack cold
galvanising paint equivalent to epilux-4 of Berger Paint shall be applied on the welding. 4.4
Permissible tolerances in tower erection Back to contents page As per IS;5613 (Part 3/Sec.2) :1989, the following tolerances in tower erection are permitted:
4.4.1
No member of a tower shall be out of straightness by
more
than
one
in
1000.
Members
failing
the
requirements shall be straightened before erection in a manner that shall not damage their properties or the protective finish. 4.4.2
The tower shall not be out of vertical by more than 1 in 360 before stringing is carried out.
Annexure - E/1 Back to contents page POWER GRID CORPORATION OF INDIA LIMITED (CONSTRUCTION MANAGEMENT) LINE CONSTRUCTION ERECTION ACTIVITY Tools & plants reqd. for Tower erection gang
1.
2.
Ginpole/Derric Pole 75/100mm dia. and of length 8.5-9m.
2nos.
Polypropylene rope
25mm dia. 700 m. 19mm dia.1000 m.
3.
Single sheave pulley
4.
Crow Bars(25mm dia and 1.8m length)
5.
Closed type
16 nos.
Spanners,(both Ring and Flat) Hammers,Slings,(16mm dia.and 1m length), hooks (12mm dia) D shackle,Tommy Bars.
6.
As per reqt.
Tents,Buckets,Water drums, camping, cots, tables, chairs, and petromax
7.
8.
etc.
As per reqt.
D Shackle 7.6 cm (3 in.)
6 nos.
Hexagonal box spanner with fixed liver and end of the liver pointed to use
Reqd. sizes
8 nos.
hole bar. 9.
Each size 6 nos.
Safety equipments : i. ii.
Safety helmets
40 nos.
Safety belts
10 nos.
iii. Safety shoes
50 nos.
iv.
Welding Goggles
2 nos.
v.
First Aid Box
1 no.
Note :
The quantity of safety equipments may be changed as
per manpower engaged.
Annexure - E/2 Back to contents page POWER GRID CORPORATION OF INDIA LIMITED (CONSTRUCTION MANAGEMENT) CONSTRUCTION ACTIVITY MANPOWER REQUIREMENT FOR TOWER ERECTION GANG
One Engineer shall be earmarked exclusively for the work of Tower Erection being carried out by different gangs. Following manpower is required for each Tower Erection gang. 1)
Supervisor
1 No.
2)
Fitter
8 Nos.
3)
Skilled workers
12 Nos.
4)
Unskilled workers
20 Nos.
Note: Average output per gang per month will be approximately 80
MT.
The
requirements
man
power
may
be
regulated
depending
upon
Chapter-5 Guide Lines
-------------------------------------------------------------------------CHAPTER
FIVE --------------------------------------------------------------------------
GUIDELINES GL-1 PRE-ERECTION CHECKS Back to contents page NAME OF LINE___________________
LOCATION NO. _____________
NAME OF CONTRACTOR_____________
TYPE OF TOWER ____________
Before taking up tower erection works, following preparations need to be made. 1.1
Foundation checks
1.1.1
Tower erection work shall be taken up only after concreting
is
cured
and
set
for
14
days
as
per
technical specifications. This is essential so that concrete
gains
various
forces
sufficient acting
strength
during
and
to
withstand after
tower
erection. 1.1.2
The
stubs
shall
be
set
such
that
the
distance
between the stubs and their alignment and slop is in accordance
with
the
approved
drawings
so
as
to
permit assembling of superstructures without undue strain or To
ensure
distortion in any part of the structure. above
following
checks
are
necessary
before tower erection. (a)
Level of all the four stubs shall be on one horizontal and
plane
in order to ensure
correct
smooth tower erection. The level of top of
the stubs shall be checked to ensure that these are on one horizontal plane. (b)
Distance
between
the
approved
drawing
so
tower
erection
stubs that
is
shall
correct
achieved.
be
as
and
Hence
per
smooth
distance
(diagonals) between the stubs are measured and verified for its correctness. 1.1.3
Revetment/Benching
wherever
required
shall
be
completed so that there is no danger to foundation during and after tower erection. However, if it is felt
that, non-completion
of Revetment/Benching is
not going to harm foundation during and after tower erection, the same may be programmed and executed on later date. 1.2
Tower materials
1.2.1
It
shall
be
ensured
that
approved
structural
drawings and Bill of Material with latest revision are available at
site to facilitate tower erection.
Preferably one set of structural drawings properly laminated and Bill of Material in Bound Book shall be available at site with each gang.
1.2.2
All tower Members shall be available at site as per approved
Bill
of
Material
and
shall
be
serially
placed on ground in order of erection requirement. 1.2.3
It shall be checked that no tower Member, Nut/Bolt, accessories are rusted, bent or damaged.
1.2.4
All
required
sizes
of
Bolts/Nuts,
spring/packing
washers in required quantity are available at site. 1.2.5
If
any
defects
in
protective
surface
finish
are
found in case of hot dip galvanised members, the damage shall be repaired by applying two coats of zinc-rich
paint
having
atleast
90%
zinc
contents
conforming to I.S. code. 1.2.6
Members bent in transit shall be straightened such that the protective surface finish is not damaged.
1.3
Tools & plants
1.3.1
All
the
tools
efficient
and
tower
plants
erection
required shall
site.A list of necessary tools at 1.3.2
for
be
safe
available
and at
and plants is given
Annexure-E/1.
All the tools and plants shall be tested as per approved
safety
norms
certificates shall above,
be
periodic testing
be carried
out
and
relevant
available.
test
In addition to
of tools and plants shall
and its safe working capacity shall
be worked out. 1.4
Personal protective equipments
1.4.1
All the persons working on tower shall wear safety helmet, safety belt and safety shoes,.Similarly all the
persons
working
on
ground
shall
wear
safety
helmet and safety shoes. List of personal protective equipments is given at Annexure-E/1. 1.4.2
Safety
equipments
shall
be
tested
as
per
safety
norms
and
necessary
test
certificate
shall
be
available. Also, a periodic check shall be carried out to ensure requisite strength. 1.5
Manpower
1.5.1
Manpower engaged for the purpose of tower erection shall
be
skilled
and
competent
enough
to
ensure
safe, smooth and efficient tower erection activity. 1.5.2
A
list
of
necessary
manpower
required
for
tower
erection is given at Annexure-E/2. 1.6
Miscellaneous
1.6.1
If there is any LT/HT power line near the vicinity of tower
erection, necessary shutdown of the
power
line shall be obtained in writing from the concerned Agency in order to avoid electrical hazards caused by accidental touching of stay/Guy ropes with power line. 1.6.2
In order to develop and maintain cordial relations with
field
owners,
it
is
desired
that
crop/tree
compensation of foundation is paid to the owners before taking up tower erection works.
GUIDELINES GL- 2. CHECKS DURING TOWER ERECTION Back to contents page NAME OF LINE _________
LOCATION NO._______________
NAME OF CONTRACTOR __________
TYPE OF TOWER ______________
2.1
Safety precautions Safety
shall
be
given
utmost
importance
during
tower erection. The following need to be ensured. 2.1.1
Safe working conditions shall be provided at the erec-tion site.
2.1.2
All the persons on tower shall wear safety helmet, safety belt and safety shoes and all the persons on ground shall wear safety helmet and safety shoes.
2.1.3
Immediate Medical care shall be provided to workmen met with accident. First Aid Box shall be available at erection site.
2.1.4
First section of tower shall be completely braced and
all
plane
diagonals
shall
be fixed
avoid
any mishappening.
relevant
to
the
section
before assembly of upper section to
Some times erection crew members tend to neglect providing
bracing
for the simple reason
that
the
same retard the pace of erection. Since wind load is one
of
the
main
governing
factors,
therefore,
neglecting the bracing at the erection stage may prove
hazardous,
should
there
be
a
gusty
wind
following the erection arm
level,
the
of superstructure upto cross
possibility
of
failure
cannot
be
ruled out. 2.1.5
It shall be ensured that all bolts/ nuts as per approved drawing are provided and tightened for the erected
portion
bolts/nuts
may
of
tower.
lead
to
Fixing
shearing
of of
insufficient the
provided
bolts and subsequent failure of structure. 2.1.6
Subsequent
sections
shall
be
erected
only
after
complete erection and bracing of previous section to ensure safety. 2.1.7
One of the prime aspects during tower erection is to counter balance all the erection forces to avoid any
undue
stresses
in
tower
members.
It
may
be
mentioned here that all the members in tower are designed Under
the
for
tensile
or/and
circumstances,
the
compression members
forces.
cannot
be
subjected to bending or torsion. If during erection, if such forces are imposed upon the tower member, they may fail. Guying of tower shall be done as per requirement. Crow bars used for terminating stay ropes shall be fixed
on
Firm
ground
to
withstand
requisite
anchoring force. 2.2
Checking erection process
2.2.1
All the approved drawings and Bill of Materials as mentioned in para 1.2.1 shall be referred to.
It
shall be verified that tower erection is carried out strictly
as
per
approved
drawings
and
Bill
of
Material. 2.2.2
All
Bolts/Nuts,
flat/spring
washers
shall
be
provided in accordance with approved drawings and Bill of 2.2.3
Material.
All Bolts shall have their nuts facing outside the tower
for
horizontal
connection
and
or
nearly
downwards
horizontal
bolt
vertical
bolt
for
connections. 2.2.4
Spring washers shall be provided under outer nut of step bolt.
2.2.5
Straining
of
members
shall
not
be
permitted
for
bringing them into position. 2.2.6
No bending or damage of member shall be observed during erection.
2.2.7
No filing of holes or cutting of member to match the
fixing
shall
be
permitted.
Also
it
may
be
checked that no extra tolerance in holes is given during fabrication. A properly erected tower shall be symmetrical with respect to the central vertical axis. A check with an erected tower, with regard to the
length
uncover
the
and
shape
of
fabrication
its error.
members, A
well
will
help
fabricated
member will not pose any problems during erection. 2.2.8
No heavy hammering of bolt causing damage to its threads, shall be permitted.
2.3
In
order
to
ensure
safe,
correct
and
efficient
erection works and to take timely remedial measures if needed, the first of every type of towers A,B,C and D shall officer not
be supervised below
closely by a senior
the rank of Manager.
GUIDELINES GL- 3. TIGHTENING AND PUNCHING Back to contents page NAME OF LINE_________
LOCATION NO._______________
NAME OF CONTRACTOR__________
TYPE OF TOWER______________
3.1
Tightening
3.1.1
All
the
members
shall
be
fitted
with
requisite
quantity of Nuts/Bolts, flat/spring washers as per approved drawings and Bill of Material as at 3.1.2
(a)
mentioned
Para 1.2.1. Tightening shall be done progressively from top to bottom, while care being taken that all the bolts at every
horizontal level are
tightened
simultaneously. Tightening shall be done with correct size spanners. (b)
Improper
tightening
clamping
force
of
at
bolt
the
causes
joint
unequal
and
load
redistribution in tower member. If the bolt/nut is
torqued
too
high,
there
is
a
danger
of
failure by stripping the threads or breaking the bolt or making the bolts yeild excessively. If the bolt is torqued too low, a low preload will
be
induced
in
the
bolt/nut
assembly
possibly inviting fatigue or vibration failure. (c)
A torque wrench may be used on a few bolts/ nuts at random to ensure
optimum tightening.
3.1.3
Spring washers shall be provided under outer nut of step bolt.
3.1.4
Slipping/running over Nut/Bolt shall be replaced by new ones.
3.1.5
All left over holes shall be fitted with correct size of bolt/nut.
3.1.6
Threaded position
of bolt projected outside of nut
shall not be less than 3 mm. 3.2
Punching
3.2.1
The
threads
of
bolts
projected
outside
of
nuts
shall be punched at three position on diameter to ensure that nuts are not loosened in course of time. 3.3
Verticality
3.3.1
Tower shall be checked for vertically with the help of theodolite
both in longitudinal and transverse
direction. 3.3.2
Tower shall not be out of vertical by more than 1 in 360.
3.4
Earthing
3.4.1
Tower shall be earthed in accordance with Guide line GL-5.
3.4.2
Tower footing resistance shall be measured before and after earthing in dry season.
3.4.3
The permissible value of Tower footing resistance is 10 Ohm.
GUIDELINES GL- 4. FIXING OF TOWER ACCESSORIES Back to contents page
NAME OF LINE_________
LOCATION NO. _____________
NAME OF CONTRACTOR__________ 4.1
Tower accessories
4.1.1
All
the
approved
TYPE OF TOWER______________
drawings
properly
laminated
and
Bill of Material in bound book with latest revisions shall be
available at site to facilitate fixing of
various tower accessories. 4.1.2
Number plate indicating location no. of tower shall be fixed on Transverse face no. 1 as shown in Figure No. 5.1 as per technical specification.
4.1.3(a)
Phase
plates
for
indicating
phases
of
different
conductors shall be fixed on Transverse face No.1 on all
(b)
the tension towers as shown in Figure No.
5.1
as per technical specification.
In
case
of
transposition
tower,
since
phase
sequence is changed, the phase plates shall be fixed on both of Transverse faces No. 1 and 3 as shown in Figure No. 5.1 as per technical specification.
4.1.4(a)
Danger plate having details of voltage level and word
"Danger"
English/Hindi
is
written
in
fixed
tower
on
local as
language, a
statutory
requirement to ward off unauthorised persons from climbing the tower. (b)
Danger plate shall also be fitted on Transverse face NO. 1 on all the towers as shown in Figure No. 5.1 as per technical specification.
4.1.5
Anticlimbing devices and barbed wire shall be fixed on
all
the
technical
tower
as
per
specifications
approved
to
drawings
prevent
and
unauthorised
persons from climbing the tower. This is a statutory requirement. 4.1.6(a)
Aviation technical
paints/signals
shall
specifications
of Aviation
in
be
line
provided with
as
per
requirement
Authority. These aviation signals are
required to caution the low flying air craft to keep off the tower. (b)
The full length of towers shall be painted over the galvanised surface in contrasting bands of red and white colours. The bands shall be horizontal having height between 1.5 to 3.0 meters.
4.2
Tack welding
4.2.1
All the Bolts/Nuts shall be tackwelded below waist level
(S/C tower) and bottom cross arm (D/C tower)
to prevent theft of tower member. 4.2.2
The
threads
of
bolts
projected
outside
the
nuts
shall be tackwelded at two diametrically opposite places having a length of 10 mm each. 4.2.3
It shall be ensured that there shall be no overburning
of
Nut/Bolt
during
tackwelding.
For
this
purpose, correct current range shall be used for welding
as
per
recommendation
of
electrode
manufacturer. 4.2.4
Standard
quality
of
welding
rods
conforming
to
Indian standards shall be used. 4.2.5
Slag or carbon layer over welding shall be chipped and cleaned with wire brush before application of paint.
4.2.6
Atleast
two
coats
of
cold
galvanised
zinc
rich
paint having 90% zinc contents shall be applied on the
welding to avoid rusting.
GUIDELINES GL- 5.
EARTHING Back to contents page
NAME OF LINE_________
LOCATION NO.________________
NAME OF CONTRACTOR__________
TYPE OF TOWER _______________
5.1
General All
the
provide
towers
are
protection
required of
to
transmission
be
earthed line
to
against
lightening and other overvoltages. The tower footing resistance after earthing shall not be more than 10 Ohm. 5.1.2
There are basically two types of earthing provided on transmission towers. a)
These are :
Pipe type Earthing This shall be adopted where location of tower is situated on normal cohesive or non-cohesive soil where excavation 4 m below ground level is possible by auguring.
b)
Counter Poise Earthing This shall be provided where location of tower is situated
on rocky areas where excavation to
the depth of 4 m below ground level is not feasible. 5.1.3
Tower footing resistance before earthing shall be measured and recorded.
5.1.4
All
the
shall be
approved
drawings
and
Bill
of
Material
available at site to facilitate earthing
of different types. 5.2
Pipe type earthing
5.2.1
All the materials as per approved drawings and Bill of
Materials
shall
be
available
at
site.
The
material required for each tower earthing is given as under :a)
G.S. Pipe 25 mm dia and 3060 mm length - 1 No.
b)
G.S. flat - section 50x6 mm and length 3325 mm - 1
5.2.2
No.
c)
Nuts/Bolts/Washers as per approved drawing.
d)
Coke-150 Kgs.
e)
Salt-15 Kgs.
Earthing shall be provided on leg. `A' as shown in Figure 5.1 i.e. the leg with step bolts.
5.2.3
In case of Railway crossing towers, two earthings per tower shall be provided as per requirement of Railway Authorities. For this purpose, earthing on leg. A and leg. C shall be provided.
5.2.4
Excavation for placing of G.S. Pipe and flat shall be carried out in accordance with approved
drawings
and technical specification. 5.2.5
G.S. Pipe and flat are placed and tightened firmly with Nuts/Bolts as per approved drawings. It shall be ensured that there is no sharp bent in G.S. Flat
or G.S. strip connected with stub. 5.2.6
Finely broken coke/charcoal having maximum granular size 25 mm and salt in ratio 10:1 shall be filled in the excavated bore hole as per approved drawing. Backfilling
shall
be
carried
out
with
proper
compaction as per technical specification. 5.3
Counter poise earthing
5.3.1
All the materials as per approved drawings and Bill of
Material
shall
be
available
at
site.
The
material required for each tower is given as under:a)
One set of G.S. wire of 10.97 mm dia comprising of 4 nos. of G.S. wires with G.S. lugs forged at one end. The minimum length of each wire shall be 15 m.
b) 5.3.2
Nuts/Bolts/Washers as per drawings.
Excavation upto minimum depth of 1 m and minimum length
of
15
m
shall
be
done
in
four
radial
directions as per approved drawings. 5.3.3
G.S.
wire
shall
be
placed
and
lugs
tightened
firmly with Nut/Bolt as per approved drawings.
The
backfilling shall be done with proper compaction as per technical specification. 5.3.4
The length of G.S. wire may be increased beyond 15 m, if the tower footing resistance is more than 10 ohm.
5.4
The tower footing resistance after earthing shall be measured in dry season and recorded. The permissible
limit is 10 Ohm.
GUIDELINES GL- 6 PRE-STRINGING TOWER CHECKS Back to contents page
NAME OF LINE_________
LOCATION NO_______________
NAME OF CONTRACTOR__________
TYPE OF TOWER______________
Before taking up stringing works, the tower shall be checked thoroughly. The following procedure shall be followed. 6.1
The
tower
starting
shall
be
checked
simultaneously
from
by the
two
supervisors
bottom
of
the
tower at two diagonally opposite legs. The checking shall be carried out towards the top of the tower and the supervisors will come down checking through the 6.2
other
opposite diagonal legs.
It shall be ensured that correct size of bolts/nuts are used and fully tightened.
6.3
It shall also be ensured that all bolts/ nuts have been provided with spring washers.
6.4
A torque wrench may be used at random to ensure sufficient tightness.
6.5
Any missing members shall be provided with correct size member.
Chapter-6 Standardisation of Tower Design
-------------------------------------------------------------------------CHAPTER
SIX --------------------------------------------------------------------------
STANDARDISATION OF TOWER DESIGN
6.1
Introduction : Back to contents page India is divided into six wind zones of basic wind speed of 33 m/s, 39 m/s, 44 m/s, 47 m/s, 50 m/s and 55 m/s, the maximum temperature isopleths traversing the country vary from 37.5 degree C to 50 degree C in steps of 2.5 degree and the minimum temperature from -7.5 degree C to 17.5 degree C in steps of 2.5 degree. Accordingly, the power supply utilities in different,
parts
of
the
country
design
their
transmission lines on the basis of the wind pressure and temperature relavent to them. However, if a standardisation could be undertaken covering
these
possible
by
various way
of
parameters, materials,
the
savings
money,
time,
engineering and other organisational effort would be considerable.
Also
standard
towers
can
be
inter-
changed among different transmission lines. It means that if construction of line is lagging because of shortage of tower material, the same can be diverted from other line to match the completion schedule. Also if some of the towers have collapsed during operation
stage,
the
replacement
can
be
arranged
from any suitable store. In addition to this, the quantity of spare towers to be
kept
reduced considerably thus saving in
shall also cost
be
of spare
towers, storage, handling etc. Similarly number of angle sizes used in tower should be restricted to optimum level. In minimising the number of sizes, the emphasis has been not so much on the economy of the support as such but on easier fabrication, different
lack
of
confusion
in
handling
sizes, transportation, storage etc.
A project for standardisation of towers on these lines deserves to be undertaken at the level
in
consultants, 6.2
association
with
the
National utilities,
fabricators and erectors.
Standardisation in POWERGRID Back to contents page POWERGRID is taking a lead in standardisation of towers of transmission lines in India. In view of overall economy and time, the standardisation shall be finalised for wind zones of 44 m/s and 50 m/s for all type of towers. The standard towers for wind zone of 44 m/s shall also be utilised for wind zone of 33 m/s and 39 m/s. Similarly the standard towers for wind zone of 50
m/s shall
also be adopted, for
wind zone of 47 m/s. At present no standardisation is required for wind zone of 55 m/s, since this wind zone is confined to negligible area of the country. A list of standard tower designs for wind zone of 39
m/s, 44 m/s and 50 m/s for 400kV single circuit and double circuit transmission lines is given in Table 6.1. Also the names of the transmission lines, where these standard tower designs have been adopted, has also been given in Table 6.1. It has been decided that in future, the aforesaid standard tower design shall
be
adopted
for
all
future
non-IDA
funded
transmission lines. It may be mentioned here that World Bank is not accepting standardisation of towers by POWERGRID in respect of World Bank funded project. However, the matter is again being taken up with World Bank to resolve this problem.
TABLE 6.1 – LIST OF STANDARD DESIGN TOWERS Sl.
Type
of
Standard
No. 1.
towers 400 kV Single Ckt. Suspension
Medium
2.
‘A’ type tower 400 kV Single
M/Sec. As per IS : 802-1977 -do-
400 kV S/C Chatta-Ballabgarh TC (BY TSL) 400 kV S/C Dadri-Panipat Line (Only D
3.
Tower type B.C. and D/DE 400 kV Double Ckt. Suspension
-do-
type tower used by M/s Dodsal) a) 400 kV D/C Jamshedpur-Rourkela TL
-do-
b) a)
400 kV D/C Misa-Balipara TL 400 kV D/C Jamshedpur-Rourkela TL
b)
400 kV D/C Misa-Balipara TL
c) a)
400 kV D/C Kaiga-Sirsi TL 400 kV D/C Talcher-Tourkela TL
b)
400 kV D/C Talcher-Rengali TL
c)
400 kV D/C Jaypore-Gazuwaka TL
d) a)
400 kV D/C Ranganadi-Balipara TL 400 kV D/C Talcher-Rourkela TL
b)
400 kV D/C Talcher-Rangali TL
c)
400 kV D/C Jeypore-Gazuwaka TL
d)
400 kV D/C Gandhar-Dehegoan TL
e)
400 kV D/C Ranganadi-Balipara TL
Ckt.
Design
Tension
Design Wind Zone wind
zone
Name of the Adopted Trans. Lines tower
45
400 kV S/C Agra-Chatta TL (By Dodsal)
‘DA’ type tower 4.
400
kV
Double
Ckt.
Tension
tower type DB, DC and DD/DDE
5.
6.
400 kV Double Ckt. Suspension
As per draft IS : 802 wind
tower DA
zone 50 M/Sec.
400
kV
Double
Ckt.
Tension
-do-
towers type DB, DC and DD/DDE
7.
8.
400 kV Single Ckt. Suspension
As per draft IS : 802 wind
a)
400 kV S/C Gandhar-Padghe TL
tower type ‘A’ type
zone 44 M/Sec. b) a)
400 kV S/C Kishenpur-Chamera TL 400 kV S/C Gandhar-Padghe TL
-do-
b) a)
400 kV S/C Kishenpur-Chamera TL 400 kV D/C Gandhar-Dehegoan TL
400 kV Double Ckt. Suspension
As per draft IS : 802 wind
b) a)
400 kV D/C Kaiga-Sirsi TL 400 kV D/C Uri-Wagoora TL
tower type DA (With 15 mm ice
zone 39 M/Sec.
zone) 400 kV
-do-
a)
400 kV D/C Uri-Wagoora TL
400
kV
Single
Ckt.
Tension
tower type B, C and D/DE 9.
400 kV Double Ckt. Suspension
As per draft IS : 802 wind zone 44 M/sec.
tower DA 10.
11.
Double
Ckt.
Tension
tower type DB, DC and DD/DDE (With 15 mm ice zone) Notes : 1.
Standardisation of tower design presently done on the highest wind velocity basis by clubbing 33.39 and 44 m/sec. Similarly, wind velocity of 47 m/sec. And 50 m/sec. Have been clubbed to 50 m/sec.
2.
The basis wind speed at 10 M height for some important Cities/Towns of India as given below.
City/Town Agra Ahmadabad Ajmer Almora Amritsar Asansol Aurangabad Bahraich Bangalore Barauni Bareilly Bhatinda Bhilai Bhubaneshwar Bhuj Bikaner Bokaro Bombay Calcutta Calicut Chandigarh Coimbatore Cuttack Darbhanga Darjeeling Dehra Dun Delhi Durgapur Gangtok Gauhati Gaya Gorakhpur Hyderabad Imphal Jabalpur Jaipur Jamshedpur
Basic Wind Speed (m/s) 47 39 47 47 47 47 39 47 33 47 47 47 39 50 50 47 47 44 50 39 47 39 50 55 47 47 47 47 47 50 39 47 44 47 47 47 47
City/Town Jhansi Jodhpur Kanpur Kohima Kurnool Lakshadweep Lucknow Ludhiana Madras Madurai Mandi Mangalore Moradabad Nagpur Nainital Nasik Nellore Panjim Patiala Patna Nellore Port Blair Puna Raipur Rajkot Ranchi Roorkee Rourkela Simla Srinagar Surat Tiruchchirrapalli Trivandrum Udaipur Vadodara Varanasi Vijaywada Visakhapatnam
Basic Wind Speed (m/s) 47 47 47 44 39 39 47 47 50 39 39 39 47 44 47 39 50 39 47 47 50 44 39 39 39 39 39 39 39 39 44 47 39 47 44 47 50 50
Chapter-7 Check Format
-------------------------------------------------------------------------CHAPTER
SEVEN --------------------------------------------------------------------------
Check Format Back to contents page
POWER GRID CORPORATION OF INDIA LIMITED (CONSTRUCTION MANAGEMENT) LINE CONSTRUCTION Check Format
NAME OF LINE_________________
LOCATION NO. ___________
NAME OF CONTRACTOR____________
TYPE OF TOWER __________
-------------------------------------------------------------ITEM CHECKED RESULT OBSERVATION -------------------------------------------------------------1)
Setting period of foundation is allowed for atleast 14 days as per specn. Back filling is O.K.
2)
Yes/No
All tested tools and plants and safety equipments in working conditions are available at site.
3)
Yes/No
All tower members, Nuts/Bolts are available at site without any damage, bent or rusting.
4)
Yes/No
Benching/Revetment,if any, completed. If not, then programme of completion.
5)
Yes/No
Shutdown of powerline, if required, is arranged.
Yes/No
6)
Reqd. no. of safety helmets, safety belts & safety shoes are being used.
7)
Yes/No
First section is completely braced and all plane diagonals are placed in proper position.
8)
Yes/No
Guying of tower provided as per approved drawings and norms. Guying to be terminated on firm ground.
9)
Yes/No
All Nuts/Bolts, flat/spring washers are provided as per approved drawings.
10)
Yes/No
All horizontal Bolt heads are facing inside and vertical Bolt head facing upwards.
11)
Yes/No
Subsequent section are erected only after complete erection and bracing of previous section.
12)
Yes/No
Any undue stress, bending or damage of member during erection noticed.
13)
Yes/No
Any filing of holes or cutting of members during erection observed.
14)
Yes/No
Any heavy hammering of bolt causing damage of threads noticed.
15)
Any substitute of tower member erected. If yes, member nos.
16)
Yes/No
Tightening is done progressively from top to bottom.
17)
Yes/No
All bolts at the same level are
Yes/No
tightned simultaneously. 18)
Slipping/running over nut/bolts are replaced by new ones.
19)
Yes/No
Yes/No
Threaded portion of bolts projected outside of nut is not less than 3mm.
20)
Yes/No
Punching of threads projected outside is done at three positions on dia.
21)
All left over holes are filled with correct size of bolt/nut.
22)
Yes/No
Yes/No
Verticality of tower is checked with help of the odolite for both longitudinal & transverse direction. This is with in specified limits.
23)
Details of missing members, nut, bolts etc.
24)
Yes/No
Yes/No
Tower Accessories All the following tower accessories are fixed as per specn/ apprd. drg. a)
Number plate.
Yes/No
b)
Danger plate.
Yes/No
c)
Phase plate.
Yes/No
d)
Anti-climbing devices/ barbed wires.
e)
Aviation signals/paints as per requirement/specn.
25)
Yes/No
Yes/No
Tack welding is done as per specn. using standard quality of welding rods.
Yes/No
26)
Zinc Rich (90%) cold galvanising paint applied over tack welding.
27)
A.
Yes/No
Earthing i.
Tower footing resistance
Ohm
ii.
Type of earthing
Pipe Type/
approved
Counter Poise
Pipe Type Earthing i.
Earthing provided on Leg `A'
ii.
G.S. Pipe, flat tightened
Yes/No
with Nut & Bolt and placed as per apprd. drg.
Yes/No
iii. There is no sharp bent/ damage in earthing strips/ flat. iv.
Yes/No
Finely broken coke (max. size 25mm) and salt in Ratio
v. (B)
10:1 filled in bore holes.
Yes/No
Backfilling done, properly.
Yes/No
Counter Poise Earthing i.
Excavation done upto reqd. depth (min. 1m) and length (min. 15m) in four radial direction.
ii.
Yes/No
G.S. Wire placed in excavation and lugs firmly tightened with Nut and Bolt.
iii. Backfilling done as per
Yes/No Yes/No
specn. (C)
Value of tower footing resistance after earthing in dry season (permissible limit - 10 ohm).
..Ohm
Certificate : Tower erection is complete in all respects and footing resistance is within permissible limit.
For CONTRACTOR
For POWERGRID
SIGNATURE
SIGNATURE
NAME
NAME
DESIGNATION
DESIGNATION : E1/E2/E3
DATE
DATE
VERIFIED & APPROVED
SIGNATURE
NAME
DESIGN.: Line Inch./ Grp.Head
DATE
__________________________________________________________________________ _ RESUMES 1.
Sh. V.C. Agarwal, AGM, is B.E. (Civil) and M.E. (Hons.) in ‘Soil Mech. and Fndns. Engg.’ From Univ. of Roorkee, Roorkee. He has 27 yrs. of vast experience in Construction, Planning and Monitoring of large Transmission Projects.
2.
Sh. D.K. Valecha, Sr. Manager, is B.Sc. Engg. (Electrical) from Reg. Engg. College, Kurukshetra. He has 17 yrs. of varied experience in Planning & Monitoring, Construction, Operation & Maintenance of Transmission Lines and Substations.
3.
Sh. J.K. Parihar, Manager, is B.E. Elect. (Hons.) from Univ. of Jodhpur, Jodhpur. He has 13 yrs. of varied experience in Planning & Monitoring, Construction, Operation & Maintenance of Transmission Lines and Substations.
4.
Sh. R. Nagpal, Manager, is B.E. Elect. (Hons.) from Punjab Engg. College, Chandigarh and MBA from Indira Gandhi National Open Univ., New Delhi.
5.
Sh. B.K. Jana, Dy. Manager, is B.E. (Civil) from Regional Engineering College Durgapur and M. Tech. In Applied Mechanics from I.I.T. Delhi. He has 13 yrs. of varied experience in Design, Planning & Coordination of Substation works, TL Fndns., Pile Fndns. & other special heavy Foundations.
