Single stranded conductors are used in transmission system usually up to 220 KV. But it is not possible to use single-stranded conductor for the voltage above 220 KV systems. For very high voltage system, hollow conductor can be used to optimize the flow of current through it. But erection and maintenance of hollow conductors in the ∑HV system are not economical. The problem can be solved by using bundled conductors instead of hollow conductor in the electrical transmission system above 220 KV voltage level.
What is Bundled Conductor?
We call bundled conductor to those conductors which form from two or more stranded conductors, bundled together to get more current carrying capacity.
Here, we use two or more stranded conductors per phase. Also, to increase the current carrying capacity of the system, a bundle conductor also contributes various facilities to the electrical transmission system. A bundled conductor reduces the reactance of the electric transmission line. It also reduces voltage gradient, corona loss, radio interference, surge impedance of the transmission lines.
By making bundle conductor, the geometric mean radius (GMR) of the conductor increased. As the self GMR of the conductor increases, the inductance of the conductor decreases. Theoretically, there is an optimum sub-conductor spacing in bundle conductor that will give minimum voltage gradient on the surface of bundle conductor. The optimum spacing between sub-conductors for reducing voltage gradient is eight to ten times of the diameter of the conductor.
Since the voltage gradient gets reduced, the radio interference also gets reduced.
As the inductance of the bundled conductor is reduced, the surge impedance of the line is reduced became the formula of surge impedance is
Where L is the inductance per phase per unit length, and C is the capacitance per phase per unit length of the transmission line. As the surge impedance gets reduced due to bundling the conductor, the surge impedance loading, of the conductor gets increased. Increased surge impedance loading makes the transmission capacity of the system more.