TL _ Vol. IV - Tower Erection

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.