Advantages of Bundled Conductors

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Key learnings:
  • Bundled Conductors Definition: Bundled conductors consist of multiple conductors per phase, grouped together by spacers to maintain spacing and enhance parallel connection for electrical transmission.
  • Inductance Reduction: Reducing inductance through conductor bundling increases the line’s power transfer capacity and improves voltage regulation.
  • Corona Discharge Mitigation: Bundled conductors reduce the voltage gradient, decreasing the likelihood and effects of corona discharge, which is crucial in high voltage transmission.
  • Increased Ampacity and Cooling: The design of bundled conductors increases their current carrying capacity and cooling efficiency, boosting overall line performance.
  • Transmission Efficiency: Using bundled conductors leads to less power loss and reduced interference with communication lines, thus enhancing the efficiency of electrical transmission.

What are Bundled Conductors?

In transmission lines, you’ll often find not just one but multiple conductor per phase. These conductors are grouped together by metallic structures known as spacers. Spacers keep the conductors evenly spaced, prevent them from clashing, and ensure they connect in parallel. Phases may include two, three, or four conductors, as demonstrated in the figures below.

bundled conductors
Each conductor joined by the spacer belongs to the same phase, and we will have three such group of conductors in a single circuit transmission or six such groups in double circuit transmission.

This configuration is typically used when transmitting bulk power over long distances at high voltage.
single circuit transmission line with bundled conductors
double circuit transmission line with bundled conductors
Let’s explore the unique advantages of bundled conductors over a single conductor.

Advantages of Bundled Conductors

  1. Bundling of conductors leads to reduction in line inductance.
    We know that inductance of a line is given by

    Where, GMD = Geometric mean distance
    GMR = Geometric mean radius
    For a single conductor of radius r
    GMR = 0.7788r
    For two conductor bundle as shown in figure
    bundle conductor

    For three conductor bundle

    For four conductor bundle

    Hence as we increase the number of conductors the GMR increases and hence L decrease. Now, there are many advantages of reduction in inductance of the line, such as-


    • The maximum power transfer capability of the line increases as


    Where X = wL …reactance of line

    • The voltage regulation of the line is also increased as the reactance of the line is reduced.
  2. On the similar argument for decrease in inductance of line, we can say that the capacitance of the line increases, as capacitance of line to neutral is given by

    Now since we have L decreased and C increased the net SIL of the line also increases automatically, and hence the power transfer capability too. Hence using bundled conductors is an effective way of increasing SIL, i.e. Surge Impedance Loading.
  3. The most important advantage of bundled conductors is its ability to reduce corona discharge. When power is being transferred at very high voltages using a single conductor, the voltage gradient around it is high, and there is a high chance that the corona effect will occur – especially in bad weather conditions. However, using several conductors nearby instead of one conductor, forming a bundled conductor which leads to a reduction of voltage gradient and hence the possibility of corona formation.
    The increase in critical corona voltage depends upon the following-

    • Number of conductors in the group,

    • Clearance between them, and

    • The distance between the groups forming separate phases.


    It has been found out that the optimum spacing between the conductors in a group is of the order of 8-10 times the diameter of each conductor, irrespective of the number of conductors in the bundle.


  4. Reducing corona discharge decreases power loss and enhances the transmission line’s efficiency.
  5. Reduction in communication line interference due to reduction in corona.
  6. The ampacity—or current carrying capacity—of bundled conductors significantly increases compared to a single large conductor, thanks to a reduced skin effect.
  7. As the bundled conductors have more effective surface area exposed to air, it has better and efficient cooling and hence better performance compared to a single conductor.
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