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 strand with bundle conductor spacers is required.

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

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

Advantages of Using bundle conductors in EHV overhead transmission system

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Bundle conductor in transmission line is uses 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 bundled conductor increases the conductor diameter, virtually act like a larger diameter hollow conductor and  the inductance per phase of the conductor decreases;

5.    The bundle conductor spacers gives optimum spacing (8 to 10 times of the diameter of 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 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 reducing, so more SIL-surge impedance loading (Z=(L/C)^1/2)) of the conductor increases which increase the transmission capacity of the system.

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

Primarily bundle conductor concept 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-

Bundle Conductor Formation

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Usually following three types of bundle conductor formation use in power transmission system:
1.    Duplex formation;
2.    Triplex formation;&
3.    Quadruplex.

bundle conductors in overhead transmission system
Bundle Conductor in Overhead Line



bundle conductor configuration
Usually Used Bundle Conductor Formation


The geometric mean radius of a bundled conductor for a two- conductor (duplex), a three-conductor (triplex) and four conductor (quadruplex) arrangements 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 present in the power lines.

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