Mechanical Design of
Transmission Lines
General Considerations
Electrical Considerations for T.L. Design:
• Low voltage drop
• Minimum power loss for high efficiency of
power transmission.
• The line should have sufficient current
carrying capacity so that the power can be
transmitted without excessive voltage drop
or overheating.
• Conductivity of Conductor:
R = ρ.L/A , or
R = L/Ϭ. A
Where:
L: Conductor length.
A: Conductor cross sectional area.
ρ: resistivity
Ϭ: Conductivity (Ϭ= 1/ρ)
• The conductor conductivity must be very high
to reduce Conductor resistance R and hence
reduce losses
PL= 3 I2 .R
Mechanical Considerations for T.L. Design:
• The conductors and line supports should
have sufficient mechanical strength:
- to withstand conductor weight, Conductor
Tension and weather conditions (wind, ice).
- The Spans between the towers can be long.
- Sag will be small.
- Reducing the number and height of towers
and the number of insulators.
• Heat expansion coefficient must be very small.
Rt = R0. (1 + α0 .t)
αt = α0/(1+ α0.t)
α t is the heat expansion coefficient at t.
TYPES OF CONDUCTORS
MATERIALS
1- All Aluminum Conductors (AAC)
lowest cost – low mechanical strength
Used for small span
2- Aluminum Conductor Steel
Reinforced (ACSR)
1- Steel strands
2- Aluminum strands
ACSR (26/7)
Advantages of ACSR
• High mechanical strength can be utilized by
using spans of larger lengths.
• A reduction in the number of supports also
include reduction in insulators and the risk of
lines outage due to flash over or faults is
reduced.
• losses are reduced due to larger diameter of
conductor.
• High current carrying capacity.
‫‪3- All Aluminum Alloy Conductor‬‬
‫)‪(AAAC‬‬
‫وهى عبارة عن سبيكة من األلمونيوم والماغنسيوم‬
‫والسيليكون المعالجة حراريا‬
‫ له متانة عالية (أكبر نسبة متانة مع الوزن( – وبالتالى يمكن‬‫زيادة المسافة بين االبراج مما يقلل من التكلفة‬
‫ له مقاومة أقل وبالتالى يقلل من الفقد فى القدرة‬‫‪ -‬غير معرض تآكل الجلفنة كما فى النوع السابق‬
‫‪4-Aluminum Conductor Alloy‬‬
‫)‪Reinforced (ACAR‬‬
‫وفيه استبدل القلب المكون من أسالك الصلب بقلب من أسالك‬
‫من سبيكة من االلمونيوم‬
Types of Supports
• Wooden Poles
• Reinforced Concrete Poles
• Steel Poles
• Lattice Structure Steel Towers
Wooden Poles
Reinforced Concrete Poles
Steel Poles
‫‪Lattice Structure Steel Towers‬‬
‫األكثر استخداما فى الجهد العالى‪:‬‬
‫األعلى نسبة متانة‪ /‬الوزن‬
‫األطول عمرا‬
‫سهولة التركيب والتجميع‬
‫تتحمل قوى ميكانيكية عالية‬
‫يعيبها‪:‬‬
‫ وجوب دهانها من وقت آلخر‬‫ تحتاج اساسات خرسانية‬‫– تكاليف نقلها عالية‬
Types of Towers
1- Suspension Tower
2- Tension Tower
3- Angle Tower
4- End Tower
1- Suspension Tower
2- Tension Tower
3- Angle Tower
4- End Tower
This type of towers exists in the beginning and
at the end of the line which exposed to
tension in one side.
SAG AND TENSION
CALCULATIONS
Sag of Transmission Lines
Sag of T.L depends on:
-
Conductor weight.
Span length,
Tension in the conductor, T
Weather conditions (wind , ice).
Temperature.
Minimum Clearance between the
ground and the conductor
kV
0.4
11
33
66
132
220
400
C (m)
5.5
5.5
6.0
6.2
6.2
7.0
8.4
Conductor Spacing
Spacing = (S )0.5 + V/150
Where:
S: Sag in meters.
V: Line voltage in kV.