Transmission Line: Ravi Shankar Singh (E6S304)
Transmission Line: Ravi Shankar Singh (E6S304)
Transmission Line: Ravi Shankar Singh (E6S304)
1
Component of Transmission Line
o Conductor
o Earth wire
o Insulator
o Transmission Tower
hardware(Clamp, Spacer,
Vibration dampers,
connectors etc.
2
Design Methodology
Gather preliminary line design data and available climatic data
Select reliability level in terms of return period of design
Calculate climatic loading on components
Calculate loads corresponding to security requirements (failure containment)
Calculate loads related to safety during construction and maintenance
Select appropriate correction factors, if applicable, to the design components
such as use factor, strength factors related to numbers of components,
strength coordination, quality control, and the characteristic strength.
Design the components for the above loads and strength.
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Reliability Levels
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Selection of Transmission Voltage
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Economic Voltage of Transmission of Power –
L KVA
E 5.5
1.6 150 E = Transmission voltage (KV) (L-L).
L = Distance of transmission line in KM
KVA=Power to be transferred
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Types of Towers
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Different Types of Towers
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Selection of Tower Structure
Single circuit Tower/ double circuit Tower
Length of the insulator assembly
Minimum clearances to be maintained between ground conductors, and
between conductors and tower
Location of ground wire/wires with respect to the outermost conductor
Mid-span clearance required from considerations of the dynamic
behavior of conductors and lightning protection of the line
Minimum clearance of the lowest conductor above ground level
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Tower Design
Tower height
Base width
Top damper width
Cross arms length
H h1 h 2 h3 h 4
h2=Maximum sag
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Determination of Base Width
The base width(at the concrete level) is the distance between the centre of
gravity at one corner leg and the centre of gravity of the adjacent corner
leg.
A particular base width which gives the minimum total cost of the tower and
foundations.
Ryle
Formula
The ratio of base width to total tower height for most towers is generally
about one-fifth to one-tenth.
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Spacing and Clearances
Ground Clearances
CL 5 . 182 0 . 305 * K
V 33
Where- K
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1) Mecomb's formula
D
Spacing(cm) 0.3048* V 4.010 S
W
Where-
V= Voltage of system in KV
D= Diameter of Conductor in cm
S= Sag in cm
NESC formula
L
Spacing(cm) 0.762 *V 3.681 S
2
Where-
V= Voltage of system in KV
S= Sag in cm
L= Length of insulator string in cm
18
Swedish formula
Where-
E= Line Voltage in KV
S= Sag in cm
French formula
E
Spacing (cm) 8.0 S L
1.5
Where-
E= Line Voltage in KV
S= Sag in cm
L= length of insulating string(cm)
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Offset of conductors (under ice-loading conditions)
Sleet Jump:
The jump of the conductor, resulting from ice dropping off one
span of an ice-covered line, has been the cause of many serious outages
on long-span lines where conductors are arranged in the same vertical
plane.
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Clearances b/n Conductors
SYSTEM TYPE OF Vertical spacing Horizontal spacing
VOLTAG TOWER b/n b/n
E conductors(mm) conductors(mm)
SINGLE A(0-2°) 1080 4040
CIRCUIT
B(2-30°) 1080 4270
C(30-60°) 1220 4880
66 kV
DOUBLE A(0-2°) 2170 4270
CIRCUIT
B(2-30°) 2060 4880
C(30-60°) 2440 6000
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SINGLE A(0-2°) 5200 8500
CIRCUIT
B(2-15°) 5250 10500
220 kV C(15-30°) 6700 12600
D(30-60°) 7800 14000
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Sag and Tension Calculation
Span ≤300 m Sag & Tension Span >300 m
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Types of Conductors
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Selection of Conductor Size
Mechanical Requirement
Electrical Requirement
Mechanical Requirement
Tensile Strength(For Tension)
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Electrical Requirement
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Continuous Current Rating.
t 2 * R1
I 2 I1*
t 1 * R 2
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Short Time Rating
A 7.58 * IF * t
Where A=area of conductor(mm2)
IF= fault current(KA)
t= fault duration(1 sec.)
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Corona
Visual corona voltage in fair weather condition is given by-
r (1 0.3) D
V 0 21.1 m log n r
r
V0= corona starting voltage, KV(rms)
r= radius of conductor in cm
D= GMD equivalent spacing b/n conductors in cm
m= roughness factor
= 1.0 for clean smooth conductor
=0.85 for stranded conductor
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Voltage gradient at the surface of conductor at operating voltage-
V
3
g 0
D
(rms kv/cm)
Log n
r
Corona discharge form at the surface of conductor if g 0≥ corona
starting gradient i.e.
(1 0.3)
g 0 21.1 m r r
A= Annual fixed charge on capital in Rs./ Rupees of capital cost (interest 14%+depreciation 5%+ operation and maintenance cost 1-3%)
V= Line voltage(KV)
R= Resistance of conductor/Km/phase
Cosø=Power factor
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J
12 M LF 2
8760 L H
1000
Pm V cos
C A 1/ 2
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Some Others Consideration in
Conductor Selection
AL/St Area (For longer span & less sag with economic consider)
Weight/ Dia (Less Weight/Dia ratio conductor swing more hence require longer
cross arms witch increase torsional load. Consider optimum value W/d in design.)
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INSULATOR
Insulator are required to support the line conductor and provide
clearance from ground and structure.
Insulator material-
High grade Electrical Porcelain
Toughened Glass
Fiber Glass
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Type of Insulator-
Disc Type
Strut Type
Disc type Insulator
It consist of central suitable shaped porcelain/ glass body like a disc with
an metal clamp on one side and metal ball pin on other side
Cap is made of malleable cost iron and the ball pins is of forged steel.
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Strut Type Insulator
It consist of several insulator disc cemented altogether without
any link.
It is rigid and can take both tension and compression load.
These are used for holding the conductor out of way of
structure.
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INSULATOR STRING
Disc insulator are joint by their ball pins and
socket in their caps to form string.
or tension.
o Reduces voltage stress across the insulating strings during lightning strokes
Design criterion:
Shield angle
25°-30° up to 220 KV
20° for 400 KV and above
Earth wire should be adequate to carry very short duration lightning
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A 5 I t
A= Area(in mm2) of cu conductor
I =current in KA
t = Time insecond
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Mid span clearance:
Direct distance b/n earth wire and top power conductor.
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Tower Grounding
Tower footing resistance will be 10Ω and should not be more than
20 Ω under any condition throughout the year.
Earth resistance depend upon soil resistivity(general 100 Ω-m)
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Method of Tower Grounding
Buried Conductor
One or more conductor are connected to tower lags and buried in back filled
of tower foundation.
o Used where soil resistivity is low
Counterpoise Wire
A length of wire/ Strip of 50 m is buried horizontally at depth of 0.5 m bellow
ground. This wire is connected to tower lags.
o Used when earth resistance is very high and soil conductivity is mostly
confined to upper layer)
Rod Pipe
Pipe/Rod of 3 to 4 m is driven into ground near the tower and top of rod is
connected to tower by suitable wire/strip
o Used where ground conductivity increase with depth
Treated Earth Pits
Pipe/Rod of 3 to 4 m are buried in treated earth pits and top of rod is
connected to tower by suitable wire/strip.
o Used in very high resistivity near tower
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Reference Standards
43 IE Rules,
1956
Thank You….
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