Power Transmission Line Conductors Overview

Power Transmission Line Conductors

• Different conductor types are used in power transmission lines, including:
  • All Aluminium Conductor (AAC)
  • All Aluminium Alloy Conductor (AAAC)
  • Aluminium Conductor, Steel Reinforced (ACSR)
  • Aluminium Conductor, Alloy Reinforced (ACAR)
• Conductor selection is a compromise balancing several factors:
  • High tensile strength is needed to withstand high breaking loads and long spans between towers.
  • Low resistivity to reduce power losses and voltage drop.
  • Low cost for installation and maintenance and a long life.
  • Low corrosion resistance.
  • Low skin effect and corona losses to minimize any extra losses.

Conductor Materials (Copper, Aluminum, Steel)

• Copper:
  • High conductivity, making it suitable for high current density.
  • Strongest compared to other metals, making it ideal for withstanding wind pressure and sag.
  • Homogeneous with consistent properties throughout.
  • Durable.
• Aluminum:
  • Second highest conductivity, but at a lower price.
  • Lighter in weight, which reduces sag and the need for stronger supports.
  • Lower tensile strength than copper, needing reinforcement
  • More prone to damage from short circuits or corrosion.
• Steel and Steel-Cored Aluminum:
  • High tensile strength, suitable for reinforcing conductors that carry high tension.
  • Lowest conductivity, used primarily for supporting conductors to increase overall tensile strength, not for carrying current directly.
  • Prone to rust and reduce efficiency when exposed to damp atmospheres.

Types of Conductors in Power Transmission

• AAC: All Aluminum Conductor. Mostly used for short spans in LV distribution systems. Relatively poor strength.
• AAAC: All Aluminum Alloy Conductor. Higher strength and conductivity used for distribution lines.
• ACSR: Aluminum Conductor, Steel Reinforced. Commonly used high-voltage transmission lines, balancing strength and weight. Stronger than AAC.
• ACAR: Aluminum Conductor, Alloy Reinforced. Higher strength than ACSR, often used in certain applications.

Bundling of Conductors

• Bundling conductors, especially in high-voltage, high-capacity lines, is used for several reasons:
  • Increases heat dissipation because of larger surface area.
  • Reduces wind loading.
  • Reduces inductance.
  • Increases current-carrying capacity due to reduced skin effect.

Inductance of a Transmission Line

• The inductance of a transmission line depends on spacing and conductor size.
  • Greater spacing means greater inductance.
  • Greater conductor radius means lower inductance.

Capacitance of a transmission Line

• The capacitance of a transmission line depends on spacing and conductor size.

  • Greater spacing means lower capacitance.
  • Greater conductor radius means higher capacitance.

• Calculating total capacitance and inductance is crucial when designing a power transmission system.

Inductive Reactance of A Line

• The inductive reactance of a line is directly proportional to the frequency and length of the line.
• The greater the frequency or length of the line, the greater the inductive reactance.

Example Calculations

• Example calculations are provided, demonstrating how to calculate series resistance, inductance, capacitance, impedance, and admittance.