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1. Transmission Line Categorized by
Voltage Class
-132 kV / 220 kV / 400 kV / 500 kV / 800 kV
Number of Circuits
-Single / Double / Multi Circuit
AC or DC
-EHV AC / UHV AC / HVDC

2. MAJOR COMPONENTS OF A
TRANSMISSION LINE
Conductor
Towers (and Foundations)
Earthwire
Insulators ] Insulator
Hardware Fittings] strings
Accessories

3. 765 kV S/C Transmission Line
-Suspension, Tension Towers

4. 500 kV HVDC Transmission Line

5. 400 kV D/C Transmission Line

6. 220 kV D/C Transmission Line

7. BASIC DESIGN ASPECTS
Electrical Design Aspects
-Power Flow / Line Loadability
-Electrical Clearances (Operational, safety)
-Corona & Interference
-Insulation Requirements
Mechanical Design Aspects
-External (Dynamic) loads due to wind, ice etc.
-Self Weight of components
-Temperature conditions, Climatological factors
-Vibrations

8. LOADABILITY OF TRANSMISSION LINES
Stabilitylimit:Determinedbysystemconfiguration.
Thermallimit:Determinedbyconductorsize&its
permissibletemp.
Indianpracticesformax.conductortempforACSR:
-65degCin1970’s.
-Increasedto75degreesin1980’s.
LineLoadabilitygenerallyrestrictedbystabilitylimit.
Thermallimitsarenotfullyexploitedforlongerlines.
FACTs,Seriescompensationetc.,improvestabilitylimits&
enableloadingclosetothermallimits.
Maxm.Permissibletemperaturelimitsincreasedto85degC
ingeneralbyPOWERGRIDandupto95degConcaseto
casebasis

9. SELECTION OF CLEARANCES
Tower Clearance (Strike Distance) for different swing
angles
Phase to Phase Spacing (Vertical, Horizontal)
Ground Clearance
Mid Span Clearance and Shielding Angle

10. MAXM. SAG=12.87 M
GROUND CLEARANCE = 8.84 M
TYPICAL 400KV S/C TOWER: CLEARANCES
PHASE TO PHASE
CLEARANCE =
8.0M (MIN)
MID SPAN CLEARANCE = 9.0 M (MIN)
A
B
A= CLEARNCE AT 0 DEG
SWING (FOR
SWITCHING / LIGHTNIG
OVERVOLTAGE)
B= CLEARNCE AT MAX
SWING (FOR POWER
FREQ.OVERVOLTAGE)

11. SELECTION OF CLEARANCES: TYPES OF
OVER VOLTAGES
Power Frequency Over voltage
-Line to ground faults (Typically 1.4p.u to
1.7p.u)
Switching Over voltages
-Energizing or High speed Reclosings
Lightning Over voltages

12. SELECTION OF CLEARANCES
Strike distance (Live metal clearances): Clearance
requirements are to be based on two assumptions;
-Instillairorunderverymoderatewinds,the
clearanceshouldbewideenoughtowithstandthe
lightningorswitchingimpulsevoltages.
-Underhighwindtheclearancemayberelatedto
thepowerfrequencyvoltage.

Swing from vertical of
sus. Insulator (degree)
Minimum Clearance in
mm


400 kV
Nil
22
44
Max Swing
3050
3050
1860
1200

13. SELECTION OF CLEARANCES
(CONTD.)
Phase to Phase Clearances: Dictated by live metal
clearances for standard tower configurations adopted
in India
Ground Clearances: Min clearance Based on I.E rules
and interference criteria (Electric field, surface
gradient, AN, RIV)
Mid Span Clearance: Between earthwire and
conductor: Based on voltage level, span etc.

14. BUNDLE CONDUCTOR SELECTION AND
OPTIMISATION
Size, Type and Configuration of Conductor influences
-Tower and its geometry
-Foundations
-Optimum spans
-Rating and configuration of Insulator string
-Insulator swings
-Ground clearance
-Line interferences like electric field at ground,
corona, radio & TV interference, audible noise etc

15. CAPITAL COST OF 400kV D/C TRANS.
LINE VS. DESIGN SPAN (Indicative)
0
10
20
30
40
50
60
70
80
250300350400450500550
Design Span (M)
Capital Cost (Rs/km)

16. CONDUCTOR TYPES
ACSR
AAAC
ACAR
AAC
New Technology Conductors
-Trapezoidal
-ACSS
-INVAR
-Self Damping
-Vibration Resistant

17. DESIGN OF TOWERS
Transmission Line Towers are designed as per
IS:802:1995 considering wind zones as per
IS:875:1987
SALIENT DESIGN CONDITIONS CLIMATIC LOADS
RELIABILITY REQUIREMENTS UNDER
NORMAL CONDITION
SECURITY REQUIREMENTS FAILURE CONTAINMENT
LOADS UNDER BROKEN
WIRE CONDITION
SAFETY REQUIREMENTS LOADS DURING CONSTRUC -
TION AND MAINTENANCE
LOAD.

18. DESIGN OF TOWERS
The reliability of transmission line towers
depends on the appropriate selection of
design criteria/parameters.
Climatic conditions play an important role
in determining the reliability of
transmission line tower.
A significant number of transmission line
failures can be the result of wind speed
exceeding design limits due to deficiencies
in selection of design parameters/criteria.

19. TOWER DESIGN
1.TOWER TYPES
2. CLASSIFICATION OF TOWER
3.TOWER CONFIGURATION
4.LOADING OF TOWER
5.ANALYSIS AND DESIGN

20. Type of Towers
a). Tangent towers with suspension string
(0°to 2 °)
b). Small angle towers with tension
strings (2°to 15 °)
c). Medium angle towers with tension
strings (15 °to 30 °)
d). Large angle (30 °to 60 °) and dead
end towers with tension strings.

21. CLASSIFICATION OF TOWERS
ACCORDING TO CONSTRUCTIONAL FEATURE:
-Self Supporting Towers.
-Conventional Guyed Towers.
-Chainette Guyed Towers.
ACCORDING TO NO OF CIRCUITS THEY CARRY:
-Single Circuit Towers.
-Double Circuit Towers.
-Multi Circuit Towers.
ACCORDING TO TOWER SHAPES:
-Horizontal Towers.
-Vertical towers.

22. TOWER CONFIGURATION
A TOWER IS CONSTITUTED OF FOLLOWING:
-PEAK
-CROSS ARM
-BOOM
-CAGE
-TOWER BODY
-BODY EXTENSION
-LEG EXTENSION
-STUB/ANCHOR BOLT & BASE PLATE
ASSEMBLY.

23. Wind Zones and Basic Wind
Speeds
Wind Basic Wind Speed
Zone (Vb) m/sec
1 33
2 39
3 44
4 47
5 50
6 55

24. Reliability Levels
RELIABILITYRETURN SUGGESTED FOR
LEVEL PERIOD
1 50 FOR EHV TRANS LINES UPTO 400KV
CLASS
2 150 FOR TRANS LINES ABOVE 400KV CLASS
AND TRIPLE & QUAD CIRCUIT TRANS LINE
UPTO 400KV.
3 500 FOR TALL RIVER CROSSING TOWERS AND
SPECIAL TOWERS.

25. Loads Due To Conductor &
Earthwire
i).Transverse Load
a). Due to Conductor & Earthwire.
Pd . Cdc. L . Gc. d
b). Due to insulator string. Where,
Cdi. Pd. Ai . Gi Pd = Design wind pressure
c). Deviation loads Cdc, Cdi = Drag co-officients
2T. Sin(D/2) L = Wind span
Gc, Gi = Gust response factors
ii). Vertical Load d= Dia of cable
T = Design tension
iii). Longitudinal Load D = Deviation angle

26. Tower Loads
i).Transverse Load
Pd. Cdt. Ae. Gt
ii). Self Weight
Load Combinations
Reliability Conditions
Security Conditions
Safety Conditions

27. NAME, VOLTAGE, CLASS,
WIND ZONE & BASIC DESIGN
PARAMETERS ( FROM
APPROVED FR OR SEF
GROUP)
GEOLOGICAL CONSTRAINTS
DETAILS OF ROUTE & BILL
OF QUANTITIES (FROM SITE)
DESIGN PHILOSPHY (FROM
IS / IEC/ STANDARDISATION
COMMITTEE REPORTS)
REVIEW
INPUTS
CONFOIGURATION & TYPE OF TOWERS
TOWER LOADINGS & CONDITIONS
REVIEW
STURUCTIRAL ANALYSIS
-BY COMPUTER
-BY MANUAL VERIFICATION
REVIEW
FINAL DESIGN (THEORITICAL)
STRUCTURAL DRAWINGS
PROTO MANUFACTURE/ FABRICATION
PROTO TESTING (FULL SCALE)
MODIFY DESIGN
REVIEW
FAILED
DESIGN FINALISED
SUCCESSFUL
DESIGN
STAGES
TESTING &
FINALISATION
FLOW CHART FOR TOWER DESIGN

28. MAXIMUM/ CRITICAL TOWER LOADINGS FROM TOWER DESIGN/ PREVIOUS SIMILAR FDN
DESIGN
, TOWER DIMENSIONS & SLOPE FROM TOWER DESIGN
FOUNDATION LOADINGS
LARGE VARIATION WRT
PREVIOUS SIMILAR DESIGN/ NIT
ESTIMATE ?
END
START
FOUNDATION DESIGN BY COMPUTER /MANUALLY
FOUNDATION DRAWINGS
DESIGN FINALISED
TYPE OF FDN FROM BOQ (SITE INPUT), SOIL
PROPERTIES FROM SPECN/ SOIL INV.
REPORT & CONCRETE PROPERTIES FROM
SPECN
DESIGN PHILOSPHY (FROM IS/ CBIP /
(STANDARDISATION COMMITTEE
REPORTS)
YES YES
INPUTS
FINALISATION
REVIEW
REVIEW
REVIEW
REVIEW
REVIEW
FLOW CHART FOR FOUNDATION DESIGN

29. INSULATION CO-ORDINATION
•Insulationco-ordinationaimsatselectingproperinsulation
levelforvariousvoltagestressesinarationalmanner.The
objectiveistoassurethatinsulationhasenoughstrengthto
meetthestressonit.
Over Voltage Probability Density
Insulation Flashover Probability
Voltage-kV
Stress
Strength
How many
Flashovers?

30. CAP & PIN DISC INSULATOR

31. DISC INSULATOR

32. PORCELAIN LONG ROD INSULATOR STRING

33. PORCELAIN LONG ROD INSULATOR STRING

34. INSULATOR AND INSULATOR STRING DESIGN
Electrical design considerations
•Insulation design depends on
-Pollution withstand Capability
Min. nominal creepage dist. = Min nominal specific
creepage dist X highest system voltage phase to phase
of the system
Creepage Distanceof insulator string required for different pollution
levels
Pollution
Level
Equiv.SaltDepositDensity
(mg/cm
2)
Min
m
nominalspecific
creepagedist(mm/Kv)
Light 0.03to0.06 16
Medium 0.10to0.20 20
Heavy 0.20to0.60 25
VeryHeavy >0.60 31
-Switching/ Lightning Over voltage

35. INSULATOR AND INSULATOR STRING DESIGN
Mechanical design considerations
•a)EverydayLoadingCondition
Everydayload20to25%ofinsulatorratedstrength.
•b)UltimateLoadingCondition
Ultimateloadoninsulatortonotexceed70%ofits
rating.Thislimitcorrespondsroughlytopseudo-elastic
limit.
•c)Inaddition,capacityoftensioninsulatorstringsatleast
10%morethanratedtensilestrengthoftheline
conductors.

36. Earthwire
Function
To protect conductor against lightning flashovers
To provide a path for fault current

37. LIGHTNING FLASHOVERS
Direct Flashover
Occurs due to shielding failure with lightning on the conductor ,
flashover taking place across the insulator string from
conductor to ground.
Back Flashover
Occurs due to high tower footing resistance with a high voltage
at the grounded tower cross arm compared to conductor,
resulting in a flashover across the insulator string from ground
to conductor.

38. HARDWARE FITTINGS
•For attachment of insulator string to tower
–D-Shackles,Ball clevis, Yoke plate, Chain link
•For attachment of insulator string to the conductor
–Suspension & tension assembly
–Fittings like D-Shackles, Socket clevis, chain link
•For protection of insulator string from power follow
current
–Arcing Horn
•For making electric field uniform and to limit the electric
field at the live end
–Corona Control Ring/ Grading Ring
•For fine adjustment of conductor sag
–Sag Adjustment Plate, Turn Buckle

39. HARDWARE FITTINGS
•Arcing Horn
–The air gap is maintained for satisfactory performance under
actual field conditions.
–For power follow current
•Yoke Plate
–To withstand mechanical loads-Thickness & shear edge
maintained
–To maintain sub conductor spacing
•Corona Control Ring/ Grading Ring
–To cover atleast one live end insulator disc
–To cover hardware fittings susceptible for Corona/RIV

40. HARDWARE FITTINGS
•Suspension Assembly
–Shaped to prevent hammering between clamp & conductor
–To minimize static & dynamic stress in conductor under various
loading conditions
–Minimum level of corona/RIV performance
–For slipping of conductor under prescribed unbalanced conditions
between adjacent conductor spans
•Tension Assembly
–To withstand loads of atleast 95% of conductor UTS
–To have conductivity more than that of conductor
•Sag Adjustment Plate/ Turn Buckle
–To adjust sag upto 150mm in steps of 6mm

41. ACCESSORIES FOR CONDUCTOR &
EARTHWIRE
•For joining two lengths of conductor/earthwire
–Mid Span Compression joint for Conductor/ earthwire
•For repairing damaged conductor
–Repair Sleeve
•For damping out Aeolian vibrations
–Vibration Damper for conductor & earthwire
•For maintaining sub conductor spacing along the span
–Spacers
•For damping out Aeolian vibrations, sub span oscillation and to
maintain sub conductor spacing
–Spacer Damper

42. ACCESSORIES FOR CONDUCTOR &
EARTHWIRE
•Mid Span Compression joint for Conductor/ earthwire &
Repair Sleeve
–To withstand at least loads equivalent to 95% of the
conductor UTS
–To have conductivity better than equivalent length of
conductor (99.5% Aluminium)

43. TYPE OF WIND INDUCED VIBRATIONS
AEOLIAN VIBRATIONS
High frequency, low amplitude vibrations induced by
low, steady & laminar wind
WAKE INDUCED VIBRATIONS
Low frequency, medium amplitude vibrations induced
by high velocity steady winds on bundle conductors
GALLOPING
Very low frequency, high amplitude vibrations induced
by high velocity steady winds on conductors with
asymmetrical ice deposit

44. FACTORS INFLUENCING VIBRATION
PERFORMANCE
TYPE , STRANDING & DIA OF CONDUCTOR,
EARTHWIRE
CONDUCTOR/EARTHWIRE TENSION
SUB-CONDUCTOR SPACING IN BUNDLE
CONDUCTORS
BUNDLE CONFIGURATION

45. VIBRATION CONTROL DEVICES
VIBRATION DAMPERS
Commonly used for vibration control of single
conductor systems as well as bundle conductors
alongwith spacers
SPACER DAMPERS
Used for vibration control of bundle conductors
(instead of combination of vibration dampers &
spacers)
DETUNING PENDULUMS
Used for control of galloping

46. VIBRATION DAMPER

47. SPACER-DAMPER