What is Transmission Line ?
Transmission line should transmit the power over the required distance economically and satisfy the electrical and mechanical requirements prescribed in particular cases.
Design of Transmission Line
- Electrical Design Consideration
- Mechanical Design Consideration
- Other Design Consideration
Electrical Design Consideration
Conductor Material and Conductor Size
The conductor should be selected from stand point of the permisible corona loss in addition to other considerations like required operatin g characteristics and economy.
Spacing Between Conductors
Voltage Regulation and Transmission Voltage
Difference in voltage at receiving end of transmission line between the condition of no load condition and full load condition is called the voltage regulation.
Transmission Efficiency
Ration of receiving end power to the sending end power of the transmission line is known as transmission efficiency
Transmission Line Constants
Inductance, Capacitance, Resistance
Skin Effect
Tendency of alternating current to the outer surface of the conductor is known as skin effect.
Mechanical Design Consideration
String Efficiency
The voltage across the whole string to the product of number of discs and the voltage across disc nearest to the conductor is known as string efficiency.
To Improve String Efficieny
- By Longer Cross Arm
- By Grading the Insulators
- By Using a Guard Ring
Sag Effect
The Difference in the overhead transmission line level between two points of supports and the lowest point on the conductor is called the sag.
Corona Effect
The phenomenon of violet glow, hissing noise and production of ozone gas in overhead transmission line at critical dissurptive voltage is known as the corona effect.
Critical Dissurptive Voltage : It is minimum phase to neutral voltage at which corona occurs.
Visual Critical Voltage : It is minimum phase to neutral voltage at which corona glow appears along the conductors.
Factors Affecting Corona
- Atmosphere
- Conductor Size
- Spacing Between Conductors
- Line Voltage
To Reduce Corona Effect
Conductor Size Incerement, Spacing Between Conductor Increment
Other Design Consideration
Line Supports
- Wooden Poles
- Steel Towers
- RCC Poles
- Steel Towers
Insulators
- Pin Type Insulators
- Suspension Type Insulators
- Strain Type Insulators
- Shackle Type Insulators
Bundled Conductors
When there are two or more than two conductors for any one of the phase for transmission line the conductor is known as the bundled conductor.
