Quasi-coaxial Feeder

Author: Edmund A. Laport

Quasi-coaxial Feeder with Tubular Inner Conductor of Large Diameter and Eight Grounded Wires Enclosing It, the Latter Equally Spaced on a Concentric Circle. For very low impedance lines of very high power transmission capacity, this type of line (Fig. 4.9) has certain mechanical advantages over a full-concentric line. It has the mechanical simplicity and reliability of an open-wire system while giving the electrical characteristics ordinarily desired when a concentric feeder is specified. Its cost of construction is lower than for a full-concentric type, as can be judged immediately by reference to Fig. 4.10.

Fig. 4.9

When h » a

When h >>>a, k ->1.0 and Z₀ - > 138 log₁₀(a/ ρ). With ρ₁ and ρ₂ in inches,

An idea of the electrical possibilities is shown by the following values:

Fig. 4.10: COnstruction for type VIII feeder

In regions devoid of ice, the inner conductor may be made of a circle of parallel wires, using a sufficient number closely to approximate, electrically, a continuous tubular conductor. This may allow the cost of the line to be reduced further, both in respect to weight of copper and perhaps also in respect to fewer supports.