In the first power generating plants were only able to serve their local areas electricity didn’t have to travel between where it was created and where it was using then things have changed the most of us get our electricity from the grid use interconnected areas of the power producers and users as power plants grow larger and further away from populated area the need for ways to efficiently move electricity over long distance has become more and more important stringing power lines across the landscape to connect cities to power plant may seem as simple as connecting an extension cord to an outlet birthday engineering behind this electric super highways is more complicated trade and fascinating.
Parameters of transmission line
The performance of transmission line depends on the parameters of the line. The transmission line has mainly four parameters resistance, inductance, capacitance and shunt conductance. These parameters are uniformly distributed along the line. Hence, it is also called the distributed parameter of the transmission line.
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Transmission-line-model
The inductance and resistance form series impedance whereas the capacitance and conductance form the shunt admittance. Some critical parameters of transmission line are explained below in detail.
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Line inductance
The current flow in the transmission line induces the magnetic flux. When the current in the transmission line changes, the magnetic flux also varies due to which emf induces in the circuit. The magnitude of inducing emf depends on the rate of change of flux. Emf produces in the transmission line resist the flow of current in the conductor, and this parameter is known as the inductance of the line.
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Line capacitance
In the transmission lines, air acts as a dielectric medium. This dielectric medium constitutes the capacitor between the conductors, which store the electrical energy, or increase the capacitance of the line. The capacitance of the conductor is defined as the present of charge per unit of potential difference.
Capacitance is negligible in short transmission lines whereas in long transmission; it is the most important parameter. It affects the efficiency, voltage regulation, power factor and stability of the system.
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Shunt conductance
Air act as a dielectric medium between the conductors. When the alternating voltage applies in a conductor, some current flow in the dielectric medium because of dielectric imperfections. Such current is called leakage current. Leakage current depends on the atmospheric condition and pollution like moisture and surface deposits.
Shunt conductance is defined as the flow of leakage current between the conductors. It is distributed uniformly along the whole length of the line. The symbol Y represented it, and it is measured in Siemens.
Performance of transmission lines
The term performance includes the calculation of sending end voltage, sending end current, sending end power factor, power loss in the lines, efficiency of transmission, regulation and limits of power flows during steady state and transient conditions. Performance calculations are helpful in system planning.
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Voltage regulation
Voltage regulation is defined as the change in the magnitude of the voltage between the sending and receiving ends of the transmission line. And the voltage-regulation efficiency of the transmission lines is defined as the ratio of the input power to the output power.