What is the Benefits of Bundle conductor for EHV (Extra High Voltage) Transmission Lines?

Generally, 230kV or higher system overhead transmission line uses single-stranded conductors; above this voltage system multi-stranded like two, three, or four strands with bundle conductor spacers is required.

As per the nature of current flowing on conductive materials, maximum electrons tend to flow through the surface of the conductor rather than the inner. Considering this property hollow conductor is more suitable to optimize the current flow for higher capacity power transmission in an extra-high-voltage (EHV) system.

Theoretically, the hollow conductor may be viable, but practical conductors are not economical for maintenance and erection. So, the concept of a bundle conductor is the best solution to instate a hollow conductor.

Advantages of Using bundle conductors in EHV overhead transmission system

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A bundle conductor in a transmission line is used to get the following advantages:

1.    Bundle conductor of transmission line reduces the reactance of the electric transmission line;

2.    Bundle conductor in power system also reduces corona loss, which improves the transmission efficiency as loss due to corona effect;

3.    Bundle conductor in EHV transmission system provide the higher capacitance to neutral when compared to single lines. This results in higher charging currents which helps in improving the power factor;

4.    In bundled conductor lines, as the effective GMR (geometric mean radius)  of the bundled conductor increases the conductor diameter, virtually acts like a larger diameter hollow conductor, and  the inductance per phase of the conductor decreases;

5.    The bundle conductor spacers give optimum spacing (8 to 10 times the diameter of the conductor) between sub conductors in bundled conductors that gives a minimum voltage gradient on the surface of bundle conductors;

6.    As the advantage of bundled conductors in transmission lines by reducing voltage gradient, the radio interference is also reduced or minimized;

7.    With the decrease in inductance of bundled conductors, the surge impedance of the line is also reduced, L=(u0/2π)* ln(Mutual GMD)/(Self GMD)) H/m/phase;

8.    Due to bundling the conductor uses the surge impedance reduction, so more SIL-surge impedance loading (Z=(L/C)^1/2)) of the conductor increases which increases the transmission capacity of the system.

The remarkable phenomenon of the overhead transmission system is the “Corona effect” that can be observed when the air medium present between the phases is charged up and start to ionize and acts as a conducting medium.

Primarily bundle conductor concept is employed to reduce the corona loss and radio interference of transmission lines. Especially EHV at around 400 kV or higher corona losses are very high that can reduce using bundled conductors.

To know more details about Corona Effect and Radio interference, read-

Mysterious Corona Effects in Transmission Lines

How Power Cable Interfere with Instrumentation and Communication Cable

Bundle Conductor Formation

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Usually following three types of bundle conductor formation used in power transmission systems:

1.    Duplex formation;

2.    Triplex formation;&

3.    Quadruplex.

Bundle Conductor in Overhead Line

Usually Used Bundle Conductor Formation

The geometric mean radius of a bundled conductor for a two-conductor (duplex), a three-conductor (triplex), and a four-conductor (quadruplex) arrangement is shown in Figs.

In conclusion, we can say bundle conductors are used for transmission purpose as it helps in obtaining better voltage regulation and efficiency by reducing the inductance and skin effect that are present in the power lines.