18-12-2012, 03:04 PM
Inductance of three-phase line with unsymmetrical spacing with transposed:
Inductance of three-phase.rtf (Size: 4.56 MB / Downloads: 42)
Introduction
Consider a three phase line having three conductors but not spaced equilaterally. The problem of finding the inductance in this case is difficult. The flux linkage and the corresponding inductance will not be same in each phase. Due to this different inductance per phase there is unbalance in the circuit through the currents in each phases are balanced.The drops in the three phases due to these inductance are observed to be different. Thus at the receiving end we will not get the same voltage.In order to achieve balance under this case, transposition of transmission line is preferred after a certain fixed distance. This is shown in the Fig. 1.
The positions of the conductors are exchanged at regular interval along the line so that each conductor occupies the original position of every other conductor over an equal distance. This exchange of conductor positions is called transposition. Thus balance in the three phase is restored.The Fig. 2 shows complete transposition cycle. The conductors in the individual phases are denoted by x, y and z where the positions are given by 1, 2, and 3. The same average inductance over the complete cycle is obtained due to the transposition.
Capacitance of Single Phase Line:
Capacitance between the two conductors of a two wire line is the charge on the conductor per unit of potential difference between them. Capacitance of the line per unit length is given by,
C = q/v F/m
The capacitance of single phase line is obtained by substituting in above equation v in terms of q.
Consider a single phase overhead transmission line consisting of two conductors 'a' and 'b' which are separated by a distance of D in air as shown in the Fig. 1. The charges on each conductors are respectively +q and -q coulombs per meter length.