# Transmission Line Parameters - What are they?

Generally, the electrical power is generated far away from the load centres. In order to transmit this generated power to the load centres transmission lines are used. The transmission line consists of conductors having a uniform cross-section throughout the line. These conductors are supported on towers and are spaced at a distance from each other. The air between the conductors acts as the insulating medium.

But when the electrical power is transmitted through the transmission lines, the receiving end wave of voltage and current is not similar to the sending end. This is due to the presents of electrical parameters or constants know as transmission line parameters.

## Transmission Line Parameters or Constants :

The transmission lines are the electrical circuits having parameters or constants like resistance, inductance, capacitance and shunt conductance, which are distributed along the entire length of the line as shown below.

Resistance and inductance are the series parameters whereas capacitance and shunt conductance are the shunt parameters. Let us see briefly about various transmission line parameters.

### Resistance :

The presence of resistance is due to the fact that every electric conductor offers some opposition to the flow of electric current through it. The resistance is the major cause of the power losses in the transmission line. In general, the presence of resistance in the transmission line is due to the fact that every electric conductor offers some opposition to the flow of electric current through it. The resistance of the line is given by,

R = ρl/A

#### ρ = Resistivity of the materiall = Length of the conductorA = Area of the cross-section of the conductor.

So, the resistance increases with the length of the line and decreases with an increase in diameter (since the area of cross-section, a diameter) and it is independent of the distance between conductors. The presence of resistance in the transmission line causes power loss (I2R loss) in the transmission line. The value of resistance of an overhead line conductor can be calculated based upon the following factors,

### Inductance :

When alternating current flows in the transmission lines, the conductors produce alternating magnetic flux. Due to this, there will be a change in the number of flux linkages with the conductor and hence causes to induce an emf according to Faraday’s Law. This induced emf is nothing but inductance to be present in the line.

The inductance of a conductor is the ratio of total magnetic flux linkages to the current flowing through it or flux linkages per ampere.

L = ψ/I

The inductance of the line increases with the length of the line and also the distance between conductors and decreases with an increase in the diameter of the conductor. This inductance is distributed along the length of the line and limits the power transfer capability of the line.

### Capacitance :

We know that capacitance is formed by two conducting plates separated by an insulating medium. In the same manner, there exists a capacitance between two conductors of a transmission line or between a conductor and earth. Here, the air present between acts as an insulating medium thus forming capacitance.

The capacitance of the line causes a charging current to flow or charging of conductors and affects voltage regulation, efficiency and power factor of the line. It constitutes the shunt parameter of the transmission line and is distributed along the length of the line. It is expressed as the ratio of charge to the potential difference or charge per potential difference.