Inductance of Bundled Conductor Lines

Inductance of Bundled Conductor Lines

The bundled conductor lines consist of two, three or four conductors. A two conductor bundle has its subconductors placed in a horizontal plane with certain spacing between them. A three conductor bundle has its subconductors placed on the vertices of an equilateral triangle. Similarly a four conductor bundle has its subconductors placed at the comers of a square. The arrangement of bundled conductor configurations is shown in the Fig. 1.23.1.

If the subconductors in a bundle are untransposed then division of current and charge between subconductors is unequal. Practically for finding the inductance, it may be assumed that division of current is assumed to be uniform.

Let r be the radius of each subconductor in a bundle and r' is GMR, of any one of the subconductors.

r' = 0.7788 r

Consider the bundle of two subconductors

Let d be the spacing between two conductors in a bundle.

Here x is number of subconductors in each bundle.

In case of two conductor bundle, x = 2 

Consider the bundle of three subconductors situated at vertices of an equilateral triangle.

Let d be side of an equilateral triangle.

Now, let us consider the bundled conductor with 4 subconductors arranged on the comers of square of side d. (See Fig. 1.23.3).

Let D_m be the mutual GMD between conductors of one bundle and those of another.

Let us consider the case of three conductor bundle of a 3 phase line as shown in the Fig. 1.23.4.

Let D_AB, D_BC and D_CA be the distances between the centres of the bundles of the phases A, B and C.

Thus the inductance of a bundled conductor is given by,

Review Question

1. What is the effect of using bundled conductors on line inductance ?