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.
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| 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 four conductor
(quadruplex) arrangements shown in Figs.
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