Bundle conductors in transmission line

By: Chandna kumar

What is Transmission Line

Transmission Line cont.……• Electric-power transmission is the bulk transfer of

electrical energy, from generating power plants to electrical substations located near demand centers.

• Historically, transmission and distribution lines were owned by the same company, but starting in the 1990s, many countries have liberalized the regulation of the electricity market in ways that have led to the separation of the electricity transmission business from the distribution business.

• Transmission lines, when interconnected with each other, become transmission networks. The combined transmission and distribution network is known as the "power grid"

Problem In Transmission Line• Electricity is transmitted at high voltages (120 kV or above) to

reduce the energy losses in long-distance transmission.

• One of the key concerns in the transmission of electricity is the power loss in transmission lines, dissipated as heat due to the resistance of the conductors.

•High-voltage transmission lines are used to transmit electric power over long distances. Normally, high voltage (HV) transmission power lines are made of high voltage (between 138 and 765 kilovolts) conducting lines of copper and/or aluminum.

Bundle Conductors• Bundled Conductors are used in transmission

lines where the voltage exceeds 230 kV.

• At such high voltages, ordinary conductors will result in excessive corona and noise which may affect communication lines. 

• The increased corona will result in significant power loss.  Bundle conductors consist of three or four conductors for each phase.

• The conductors are separated from each other by means of spacers at regular intervals.  Thus, they do not touch each other.

How Bundle Conductor Work.for extra high voltage lines corona causes a large problem if the conductor has only one conductor per phase. Corona occurs when the surface potential gradient of a conductor exceeds the dielectric strength of the surrounding air.

This causes ionization of the area near the conductor. Corona produces power loss. It also causes interference with communication channels. Corona manifests itself with a hissing sound and ozone discharge. Since most long distance power lines in India are either 220 kV or 400 kV, avoidance of the occurrence of corona is desirable.

• The high voltage surface gradient is reduced considerably by having two or more conductors per phase in close proximity. This is called conductor bundling .

• The conductors are bundled in groups of two, three or four . The conductors of a bundle are separated at regular intervals with spacer dampers that prevent clashing of the conductors and prevent them from swaying in the wind. They also connect the conductors in parallel.

Advantage Of Bundle Conductor

• Bundled conductors are primarily employed to reduce the corona loss and radio interference. However they have several advantages:

• Bundled conductors per phase reduces the voltage gradient in the vicinity of the line. Thus reduces the possibility of the corona discharge. (Corona effect will be observed when the air medium present between the phases charged up and start to ionize and acts as a conducting medium. This is avoided by employing bundled conductors)

• Improvement in the transmission efficiency as loss due to corona effect is countered.

Advantage Cont..• Bundled conductor lines will have higher capacitance to neutral

in comparison with single lines. Thus they will have higher charging currents which helps in improving the power factor.

• Bundled conductor lines will have higher capacitance and lower inductance than ordinary lines they will have higher Surge Impedance Loading  (Z=(L/C)1/2). Higher Surge Impedance Loading (SIL) will have higher maximum power transfer ability. 

• With increase in self GMD or GMR inductance per phase will be reduced compared to single conductor line. This results in lesser reactance per phase compared to ordinary single line. Hence lesser loss due to reactance drop. 

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