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Three-wire Unbalanced Feeder

Author: Edmund A. Laport

This configuration (Fig. 4.5) is an improvement over that of type IV because a smaller proportion of current returns in the earth. The design is simple and inexpensive to build and can be applied to many low- and medium-frequency situations where short- to medium-distance runs are required.

This is a one-insulator type, where the insulator supports the high-potential wire. No insulators are needed for the grounded wires in low-power applications, but in high-power applications the convergence of the electric-flux lines at the grounded wires can produce large gradients near them, causing dielectric loss in any poor insulating material near the grounded wires. The grounded wires should then be insulated.
Fig. 4.5:

Possible constructions for this type of line are shown in Fig. 4.6. Only a very small difference results from having the ground wires slightly below the level of the central wire. When h » a,


When ρ1 = ρ2


Some typical electrical values are:

ρ (inches) h (inches) a (inches) k Z0 (ohms)
0.064 120 5 -0.678 336
0.064 120 10 -0.592 380
0.064 120 15 -0.537 413
FIG. 4.6. Constructions for type V feeder.

Last Update: 2011-03-19