Aerial Bunched Cable is always twisted because of Transposition.\\Transposition of transmission lines refers to a specific arrangement or configuration of conductors in a multi-phase transmission line. Transposition is done to reduce the mutual inductance between adjacent phases of the transmission line and to balance the capacitance between the conductors. This helps in achieving better electrical performance and reducing electromagnetic interference in high-voltage power transmission systems.
In a typical overhead transmission line, conductors for each phase (usually three phases in AC power transmission) are arranged side by side on a set of transmission towers or poles. When these conductors are arranged in a straight line without any twisting or transposition, there can be undesirable electromagnetic coupling between the phases. This can result in power losses and unwanted electromagnetic interference, especially at higher voltages and frequencies.
To mitigate these issues, the conductors are often transposed, meaning they are intentionally twisted or arranged in a specific pattern along the length of the transmission line. The goal of transposition is to ensure that each conductor spends an equal amount of time in close proximity to the other phases over the entire length of the line. This equalizes the capacitance and reduces the mutual inductance between the phases, resulting in better line performance.
Transposition can be achieved in various ways, including:
- Simple Helical Transposition: In this method, the conductors are twisted together in a helical pattern, with each conductor taking turns being in the center and on the outside of the helix.
- Longitudinal Transposition: Conductors are shifted longitudinally along the transmission line, periodically reversing their positions.
- Short-Interval Transposition: This involves more frequent and shorter twists or changes in the positions of the conductors.
Transposition is especially important in high-voltage transmission lines, where minimizing losses and optimizing the line’s electrical characteristics are critical. It helps ensure that the transmission line operates efficiently and effectively while maintaining a balanced distribution of electrical energy between the phases.