Why are Bundle Conductors used in Transmission Line?

Bundle conductors are used in transmission line for achieving better regulation and transmission efficiency. The bundle conductors have two or more sub-conductors and they form one phase conductor. The bundle conductors are generally used for a voltage of more than 220 kV.

Bundle conductors improve voltage regulation and transmission efficiency by reducing the inductance and skin effect in the transmission line.

bundle conductors

There are numerous advantages of bundled conductors in transmission lines. Now, we will discuss the advantages of the use of bundle conductors.

Advantages of Bundle Conductors

We can achieve the following advantages with the use of bundle conductors.

  • Reduced Inductance
  • Reduced Corona loss
  • Reduced Surge Impedance

Reduced Inductance

A bundled conductor reduces the reactance of the transmission line. When we make bundle conductors, the conductor’s geometric mean radius (GMR) increases. The formula for the inductance of the transmission line is;

reduced inductance with bundle conductors

GMR (Geometric mean radius)  is proportional to the distance between the conductor’s bundles. Therefore, GMR increases with more bundles. With an increase in GMR, the inductance of the transmission line reduces. The reduction in inductance causes a reduction in the reactance(XL) of the line.

The voltage drop in the transmission line depends on the reactance of the line. The decreased reactance by conductor bundling causes less voltage drop in the line and, thus bundling improves the voltage regulation of the transmission line.

Reduced Corona loss

Bundled conductors per phase cause a reduction in voltage gradient in the vicinity of the line. Thus there is less possibility of corona discharge. As a result of bundling, there is reduced corona loss.

Reduced Surge Impedance

The surge impedance of the transmission line depends on the inductance and capacitance of the transmission line. The surge impedance of the line is;

surge impedance of transmission line

By bundling, the capacitance increases, and inductance decreases. Therefore, the surge impedance of the transmission line increase. The increased surge loading means the line can now deliver more power. Thus, the maximum power transfer capacity of the transmission line increases by bundling of conductors.

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