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 , orR = L/Ϭ. A

Where:L: Conductor length.A: Conductor cross sectional area.ρ: resistivityϬ: Conductivity (Ϭ= 1/ρ)

• The conductor conductivity must be very highto 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 strands2- 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)

األلمونيوم من سبيكة عن عبارة وهىحراريا المعالجة والسيليكون والماغنسيوم

- – ) الوزن ) مع متانة نسبة أكبر عالية متانة لهمما االبراج بين الم*سافة زيادة يمكن وبالتالى*

التكلفة من يقللفى - الفقد من يقلل وبالتالى أقل مقاومة له

القدرةالسابق - النوع فى كما الجلفنة تآكل معرض غير

4-Aluminum Conductor Alloy Reinforced (ACAR)

الصلب أسالك من المكون القلب استبدل وفيهااللمونيوم من سبيكة من أسالك من بقلب

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

العالى الجهد فى استخداما :األكثر / الوزن متانة نسبة األعلى

عمرا األطولوالتجميع التركيب سهولة

عالية ميكانيكية قوى تتحمل

:يعيبهاآلخر - وقت من دهانها وجوب

خرسانية - اساسات تحتاجعالية – نقلها تكاليف

Types of Towers1- 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 C (m)0.4 5.511 5.533 6.066 6.2

132 6.2220 7.0400 8.4

Conductor Spacing

Spacing = (S )0.5 + V/150Where:S: Sag in meters.V: Line voltage in kV.