In transmission lines, a large amount of power is transmitted over a long distance. So, voltage regulation is not important because in some lines, 40% regulation is considered satisfactory. In such cases, only the economy is important. The cost of the conductor is the main part which decides the total cost of the transmission line. Hence, the selection of the proper size of the conductor for a particular line is most important.
The most economical area of the conductor is that for which the total annual cost of the transmission line is minimum. This is known as Kelvin’s law and was given by Lord Kelvin in the year 1881.
It states that the most economical cross-section of a conductor is the value at which the annual cost of the electric energy wasted in the conductor, and annual cost of the interest and depreciation on the capital cost of the conductor are equal. Thus, the total annual charge on an overhead transmission line can be expressed as :
Total annual charge =P1 + P2α or Variable part of the energy charge = Annual cost of energy wasted.
P1 and P2 are constants
α is the area of the X-section of the conductor.
In the given circuit if R = 0 then the circuit becomes purely inductive. So the phase angle between v(t) and i(t) is 90°.
According to the Norton theorem, to find the Norton current, first remove the load resistance RL from the network terminals AB. Short circuit the terminals AB as shown in Figure calculate the current ISc or IN through the short circuit.
Now resistance of 150Ω will not show any effect in the circuit. So only resistance of 30Ω will be effective.
Norton current IN = 360/30
IN = 12 A
Susceptance is symbolized by the capital letter B. It is the reciprocal of AC reactance. Susceptance, like reactance, can be either capacitive or inductive. In the case of a magnetic field, the susceptance is inductive. In the case of an electric field, the susceptance is capacitive. Capacitive susceptance is symbolized BC and inductive susceptance is symbolized BL. In the case of a magnetic field, the susceptance is inductive. In the case of an electric field, the susceptance is capacitive. Inductive susceptance is assigned negative imaginary number values, and capacitive susceptance is assigned positive imaginary number values.
The formula for inductive susceptance is
The unit of Inductive susceptance is Siemen or Mho.